T h e C l e a r C h o i c e ™

3rd quarter 2004

The Radio Frequency Systems BulletinThe Radio Frequency Systems Bulletin

T h e C l e a r C h o i c e ™

Shared and sculpted: LA broadcast ing in the l imel ightConnections, corrugations and costsAlberta SuperNet—broadband for the future Minimizing microwave antenna interference

Shared and sculpted: LA broadcast ing in the l imel ightConnections, corrugations and costsAlberta SuperNet—broadband for the future Minimizing microwave antenna interference

Normalised radiation [dB]

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has been carefully engineered to combat

RF interference—one of the greatest

challenges of network optimization and a

primary key to ensuring QoS. Complemented

by a remote antenna tilt system, the RF

control afforded by the Optimizer range will

ensure operators can offer premium QoS

both now and in the future.

But many factors come into play—in

particular, a focus on total system solutions.

Carefully engineered for optimum

performance at a component level, the

RFS range of high-performance cellular

antennas, low-attenuation transmission

line and RF conditioning components also

combine to provide fully integrated base

station solutions that meet the most

stringent demands of operators. Ongoing

QoS objectives are achieved through

precise RF control and tuning flexibility;

while the broadband functionality and

built-in future-proofing streamline the path

to network expansion and migration to

new technologies. In other words, RFS

offers both expansion capability and quality

of service in the one solution set.

The dilemma is unlikely to go away; the

choice between network expansion and

enhancing network performance has been

the ‘lot’ of wireless operators since the

inception of mobile services. In fact,

operators will face even more of a juggling

act as they deploy next-generation

technologies such as push-to-talk, WiFi and

mobile video.

RFS is committed to these next-generation

technologies. Our focus is on providing

optimal RF solutions in order for them to be

realized. Both network expansion and

quality of service are important and, with

the right technology, the choice of how to

act can be made easier. It’s all about striking

the right balance.

It is a well-known industry maxim that it

costs four times as much to attract a new

customer than to retain an existing one.

With this very real cost of churn in mind, it

makes business sense for mobile operators

to maintain a tight focus on customer

satisfaction. If, as LogicaCMG points out,

many mobile operators are focusing on

business expansion at the expense of

improving quality of service, they are clearly

shooting themselves in the feet.

This choice between network expansion

and enhancing network performance is not

a new dilemma. Network optimization is an

ongoing challenge for operators the world

over--a constant balancing act between

coverage, capacity and quality of service

(QoS). To-date, these have often been

regarded as mutually exclusive; one to be

prioritized at the expense of the others. But

this doesn’t have to be the case.

Radio Frequency Systems has developed a

comprehensive suite of RF products that

allow operators to consider more than one

goal at a time. This suite permits operators

to achieve both immediate and long-term

expansion objectives, plus fulfil immediate

and long-term goals for improvements in

QoS—not to mention a generous dose of

future-proofing.

Our Optimizer range of high-performance

cellular base station antennas is an ideal

case-in-point. Featuring a host of advanced

features such as reduced side lobes and an

extended tilt range, the Optimizer series

A recent report by global wireless

consultancy, LogicaCMG, raises some

interesting points about the threat of

subscriber churn for mobile operators.

Based on a survey of UK mobile phone

users, the report states that operators risk

losing a full third of their customers due to

poor quality of service. It even goes so far

as to put a figure on what this might

cost the UK telecoms industry in 2004—an

estimated _3 billion.

And the rate of subscriber churn in the

telecommunications industry remains

significant. In May this year, the global

average across fixed and mobile sectors

was estimated by communications research

group, Chorleywood, to be at 22 per cent.

Yet of perhaps greater concern to mobile

operators is what might happen to their

bottom line if LogicaCMG’s predictions

come to pass and the rate of churn increases.

TNS Asia Telecoms Index has also revealed

that, compared with a year ago, 33 per

cent more Asian mobile users are indicating

they’d like to change networks within the

next six months.

What is causing this rising dissatisfaction

with mobile services? The attraction of

more competitive pricing has long been a

factor, but new issues related to the service

itself are coming to the fore. Surveys have

cited problems with coverage, reception,

customer service, billing and roaming as

strong and legitimate reasons for

customers to seek alternative providers. If

the service is not up to scratch, then the

fight over how much to pay for it becomes

somewhat moot.

3

Expansion vs QoS:str ik ing the balance

E D I T O R I A L

3 EditorialExpansion vs QoS: striking the balance

4 What’s NewBDA/duplexer series supports in-building 3G

Broadband Optimizers complete 90-degree range

Ultra-compact manifold combiner

Dual function DAB Band III filter family

6 Cover StoryShared and sculpted: LA broadcasting in the limelight

8 Feeder SystemsConnections, corrugations and costs—the feeder cable debate

11 MicrowaveAlberta SuperNet—broadband for the future

14Technology FocusMicrowave antenna options for minimizing interference

18In Touch3G focus for Chinese expo

RFS shines the DTT light in Hungary

IBC 2004: RFS to display digital solutions

Kerrang! rocks with FM solution

PREVIEW: Base station technology—anRF interface evolution

Dr Klaus-Dieter MischerikowRadio Frequency Systems President

Klaus-Dieter Mischerikow

IMPR

INTRadio Frequency Systems

WorldWideWeb: http://www.rfsworld.com

Publisher: Jörg SpringerExecutive Editor/Editor Asia Pacific:Peter WaltersEditor EMAI: Regine SulingEditor Americas: Ann PolanskiManaging Editor: Dr Ellen GregoryProduction Editor: Christian MichatschArt Director: Marilu Krallmann

Authors: Allan Alderson, Dr Ellen Gregory, Anita Talberg

Photos: RFS archives, Alcatel Canada, CMS Wireless, inform archives, GettyTechnical illustrations: Pamela Seaman

Cover images: RFS archivesCover art: Marilu Krallmann

Print: Print Design, Minden

Layout and Graphics:inform Advertising, Hannover

Editorial Services:Relate Technical Communications, Melbourne

Trademarks: CELLFLEX®, BDA®, FLEXWELL®, MicroTenna™, Optimizer®, RADIAFLEX®, Radio Frequency Systems®, RFS®, RFS CompactLine®,SlimLine® and The Clear Choice™ are trademarks,service marks or registered trademarks of Radio Frequency Systems.

On the cover:Dual RFS broadband panel arrays provide sculpteddigital/analogue signals for four Los Angeles television broadcasters at Mount Wilson in California.

Alberta SuperNet—broadband for the futureFrom Alberta’s Rocky Mountains to its northernice lakes, RFS microwave antenna solutionsplay an important role in realizing province-widebroadband connectivity.

Microwave antenna options for minimizing interferenceWith microwave network density on the rise,the potential for signal interference is alsoincreasing. RFS looks at ways of minimizinginterference-causing distortion of radiofrequency signals.

BDA/duplexer series supports in-building 3GA new series of bi-directional amplifiers (BDA)and duplexers offers a convenient andinexpensive means of overlaying UMTS onexisting 2G in-building RF distribution systems.

Shared and sculpted: LA broadcasting inthe limelightAn innovative, shared broadcast system atopMount Wilson provides four LA broadcasterswith high performance—and highly sculpted—digital and analogue television coverage.

Connections, corrugations and costs—the feeder cable debateTo make sense of base station feeder cabletechnology, start where it all begins and ends:at the base station site with the site crews andnetwork development teams.

146

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8

I N D E X

In support of global digital audio broadcasting (DAB) deployments, Radio Frequency Systems

is launching a new family of DAB Band III coaxial filters. Tuneable over the entire VHF Band III,

the new filters offer a compact and flexible solution for both transmitter mask filtering and

digital RF channel combining.

The DAB filter range is founded on RFS’s world-leading RF combining technology and utilizes

a similar platform of components to the company’s VHF Band III digital television combiners.

Six and eight-pole versions of the coaxial filters will be available in three cavity sizes

(100 mm, 180 mm and 270 mm), accommodating transmitter powers of 500 W, 1500 W

and 2500 W respectively. The nominal bandwidth is 1.54 MHz, as specified by the global

‘Eureka 147’ DAB standard.

The eight-pole DAB filters can be incorporated within transmitters to provide critical mask

filtering of the digital RF signal, in keeping with global DAB standards. When used as the key

components of a balanced DAB combiner, the eight-pole filters can achieve both critical

transmitter masking and adjacent channel combining simultaneously, eliminating the need

for additional filters within the transmitter.

Exhibiting low losses for these cavity sizes, the RFS DAB Band III filters are of compact design,

with the 100-mm models able to be installed within a standard 19-inch rack.

“The 90-degree aperture cellular antenna is

proving to be a vital complement to

conventional 65-degree aperture

antennas,” said Patrick Nobileau, RFS Vice

President Base Station Antenna Systems.

“In some cases, 65-degree proves the best

choice, as it results in a minimal bit error

rate. In other cases, a 90-degree aperture is

optimal, as in a tri-sector configuration it

provides coverage that is closer to a perfect

5

Three new broadband 90-degree

beamwidth cellular antennas have joined

Radio Frequency Systems’ high-performance

Optimizer family. The new additions—the

variable electrical tilt APXV18-20914 and

APXV18-20915, and the fixed tilt

APX86-909014L—complete the Optimizer

90-degree aperture series, making it one of

the most comprehensive of its kind

available today.

4 W H A T ’ S N E W

BDA/duplexer ser iessupports in-bui ld ing 3G

circle. RFS now offers complete antenna

solutions in both 65- and 90-degree

beamwidths, ensuring network planners

greater network optimization flexibility.”

Importantly, all three antennas are

broadband, with the APXV18-20914 and

APXV18-20915 supporting frequencies in

the 1710 to 2170 MHz band, while the

APX86-90914L accommodates frequencies

in the 806 to 960 MHz band. As a result,

Ultra-compact manifold combinerThe latest addition to the leading UHF

combiner range of Radio Frequency Systems

is an ultra-compact manifold combiner

ideal for low-power digital television (DTV)

broadcast sites. Designed for combining

digital channels up to 250 W, the UHF

manifold combiner offers an economical

and space-efficient alternative to balanced

modules.

“The manifold combiner has been developed

in direct response to requests from broad-

casters for an ultra-compact solution,”

said RFS Area Product Manager

Broadcast, Graham Broad.

“It’s a fully integrated unit,

and contains less

than half the

components

used within

our balanced

combiner

modules. For

instance, the manifold

configuration has just one

50E filter instead of two, and the whole unit

is therefore less than half the weight, has

half the footprint, and is lower in cost.”

Displaying similar performance characteristics

to RFS’s low-power integrated balanced

combiner, the manifold model is also

tuneable over the entire UHF band (470 to

860 MHz) for 6, 7 or 8 MHz bandwidths,

A new series of bi-directional amplifiers

(BDA) and duplexers from Radio Frequency

Systems offers a convenient and inexpensive

means of overlaying universal mobile

telecommunication services (UMTS) on

existing second-generation (2G) in-building

RF distribution systems.

“RFS has had the foresight to build in

future-proofing in its 2G in-building RF

coverage solutions—as a result, these are

sufficiently broadband to support the

simple overlay of new third-generation (3G)

UMTS services,” said Peter Raabe, RFS

Global Product Manager for Wireless

Distributed Communications Systems. “In

many cases though, the UMTS RF power

levels may prove inadequate, due to the

higher insertion losses of the 2G network

cabling. The new RFS I-BDA2100 and

I-DUX2G/3G combination is one of the

first on the market to offer a cost-effective

and simple means of overcoming

this situation.”

The series comprises two band-specific

UMTS bi-directional amplifiers (I-BDA2100-1

and I-BDA2100-2), plus a broadband

duplexer (I-DUX2G/3G-1). The new BDAs

supply 35 dB nominal gain in RF downlink

and uplink, and are provided in two output

power ratings, 18 dBm and 9 dBm. Used in

combination with the new duplexer, the

bi-directional amplifiers may be used to

support a ‘3G on 2G’ overlay on an existing

broadband in-building system.

Both I-BDA2100 models support the full

UMTS band, and provide automatic gain

control in accordance with the Third

Generation Partnership Project’s (3GPP)

specified UMTS requirements. Manual gain

control is also provided for final system

levelling. The unit’s 10-30Vdc power

Broadband Optimizers complete 90-degree range

Dual function DAB Band III filter family

features double temperature compensation,

and exhibits low losses for its given filter

sizes. According to Broad, a key differentiator

is the availability of coaxial filters of up to

7-poles, offering semi-adjacent channel

combining and transmitter DTV masking.

Although the manifold configuration can

only combine channels down to semi-adjacent

spacings, it can be used with balanced

modules in a hybrid system to realize adjacent

channel combining. “Essentially, the semi-

adjacent combined channels

exiting the manifold

system can be fed into

the wideband input

of a balanced combiner

system, and adjacent

channels inserted,” said

Broad. “This means that

multiple adjacent channels can be

combined using half-balanced and

half-manifold units, resulting in a highly

compact and low-cost system.”

Designed for wall mounting or installation

within a standard 19-inch rack, the manifold

combiner units alone can be used to combine

up to six semi-adjacent channels, with a

combined maximum output power of 750 W.

This equates to 6 x 125 W or 3 x 250 W of

potential input powers into the combiner,

providing superior flexibility for broadcasters

operating low power sites.

requirements can be realized ‘locally’ via the

unit’s power port, or ‘remotely’ via the RF

coaxial feeds, permitting the units to be

cascaded in a wide range of combinations.

The I-DUX2G/3G-1 duplexer is uniquely

broadband, with its 2G port supporting

frequencies between 800 and 1880 MHz.

It provides particularly low insertion loss at

both the 2G and 3G ports, and comes

complete with two separate on-board

dc power input ports, allowing even

greater flexibility in system power

configuration.

The new series of bi-directional amplifiers(BDA) and duplexers from RFS is used for overlaying UMTS on existing 2G in-building RF distribution systems.

I-DUX2G/3G-1IBDA2100-1 IBDA2100-2

the APX86-90914L supports ‘cellular’

850 MHz, trunking/specialized mobile radio

(SMR) 800 MHz, and global system for

mobile communications (GSM) 900 MHz

services. The APXV18-20914/15 antennas

support GSM 1800 MHz, personal

communication services (PCS) 1900 MHz

and universal mobile telecommunications

system (UMTS) 2100 MHz services. As

operators and OEMs worldwide

roll-out multiple and often co-located

wireless platforms, the broadband nature

of the optimizer 90-degree antennas

provides them with a powerful means

of rationalizing and reducing antenna

inventories.

All three antennas exhibit the superior

performance characteristics common

to all members of the RFS Optimizer

antenna family. This includes side lobe

suppression typically better than 20 dB

across the entire frequency and tilt range,

significantly increased gain, and superior

front-to-back ratio.

RFS 90-degree beamwidth Optimizer antennas

Type Model No. Bandwidth Tilt Length Gain

Low band fixed tilt APX86-90914L-T0 and T6 824 - 940 MHz Fixed 0 and 6 degrees 2 metres 15.5 dBi

Low band variable tilt APXV86-90914 824 - 940 MHz Variable 0-10 degrees 2 metres 15 dBi

High band fixed tilt APX18-209014-T2 and T5 1710 - 2170 MHz Fixed 2 and 5 degrees 1.3 metres 15.8 dBi

High band fixed tilt APX18-209015-T2 and T5 1710 - 2170 MHz Fixed 2 and 5 degrees 1.8 metres 17.5 dBi

High band variable tilt APXV18-20914 1710 - 2170 MHz Variable 0-10 degrees 1.3 metres 16.5 dBi

High band variable tilt APXV18-20915 1710 - 2170 MHz Variable 0-10 degrees 1.8 metres 17.5 dBi

Crucial combiningA crucial component of the system is the

pair of parallel RFS directional waveguide

combiner chains, which support the dual

broadband arrays. The channel combiner

sub-systems each comprise five directional

waveguide filters and one blank section to

allow for the introduction of additional

channels. The total system is also designed

to accommodate future channel reallocation,

and its compact nature means that space is

available in the building for two additional

combiner systems, if required for future

expansion.

In order to accommodate the high

transmitted powers of analogue services

on channels 50 and 56, a new ‘full-

wavelength’ directional waveguide combiner

was developed. This incorporates resonators

a full wavelength in height (instead of half

wavelength), providing twice as much

surface area to dissipate the greater heat

generated by losses in the high-power,

higher-frequency channels. This means that

forced air cooling is not required to ensure

that the operating combiner will not exceed

the design temperature rise.

Complementing the combiner system is a

network of rigid transmission lines linking

the transmitters, mask filters, combiners,

and flexible coaxial feeders, which are each

in different locations owing to the crowded

nature of the site. Care was taken during

the design phase to minimize the reflections

that might otherwise have occurred due to

the number of components in the rigid feed

system; this involved the development of

high-performance, broadband ‘elbows’,

which were tuned to optimize system

performance. In addition, a total of eight

5-inch RFS HELIFLEX flexible coaxial

transmission lines were installed to feed the

panel array—four for each sub-array.

The net performance result of the

transmission line system was reflected

power so low across all channels that

several transmitters’ reflected power

indicators did not even move when the

transmitters were energized.

Structural challengesOwing to both the congested nature and

potential seismic activity of the Mount

Wilson site, installation of the combiner

system proved an interesting challenge. A

newly constructed combiner room was

built as a bridge suspended over an existing

building; and the entire combiner and

separate digital mask filter systems were

bolted onto several steel frameworks, also

suspended from groups of four vertical

steel members. Seismic horizontal ties,

connecting the steel frameworks to the

building structure itself, prevent the frame-

works from excessive swinging during

seismic activity.

This was not the only structural innovation.

The internal cavity of the antenna column

needed to be expanded in order maintain

human access, as well as contain a large

volume of equipment—including the eight

flexible feeders and the branch feeders and

power dividers used for pattern sculpting.

The result was an asymmetrical cross-

section, which led to issues with the

antenna/tower interface. This was solved

in collaboration with the tower designer

through the fast-track development

of a unique multi-dimensional antenna

clamping mechanism.

An additional design consideration was the

minimization of tower harmonics due to

wind-induced vibrations. To provide

dynamic stability to the antenna

structure—which comprises the two RFS

panel arrays plus a third antenna mounted

on top of these—a tuned, liquid damper

was introduced at the top of the 20-level

panel antenna column. This comprises

stainless steel tanks filled with a specifically

calculated volume of ethylene glycol, which

moves against the modes of vibration,

potentially increasing the damping

characteristic from around 0.0025 to 0.05

(that is, reducing the magnitude of

oscillations by a factor of 20).

Team effortConceived and designed over a period of

more than four years, the final RFS combiner/

antenna system at Mount Wilson has the

capacity to accommodate a total of 12 digital

or analogue services from channel 32 to 56.

The combiner chains were installed in the

first half of 2003, followed by the raising

of the two stacked panel arrays in October

of the same year, and rigid line optimization

in early 2004. Currently configured for

nine channels (including two standby

services), the first services went on-air in

April 2004, with the others joining in the

following months.

The project as a whole was undeniably

a team effort—not only between the

consultant, Merrill Weiss, and RFS, but

also between the tower and transmitter

designers, installation and construction

crews, the site owner, and the four

broadcasters themselves. After extensive

theoretical design and modelling, the

physical realization of the individual

components, and the ultimate installation

and commissioning, the RF broadcast

system met all performance objectives

right from the start.

combining. Dual sub-systems

also allow greater flexibility for

main/standby services, as well as

accommodating the different

pattern tailoring requirements

of the stations.

Sculpting the signalAccurate sculpting of the broad-

cast signal was one of the

primary performance require-

ments of the system. A number

of channels required signal

restrictions over Mexico or

toward San Diego to the south-

east, and it was desirable to

reduce wasted power over the

ocean for all channels, while

ensuring premium coverage

for all of Los Angeles and its

western satellite cities. The only

way of achieving this level of

pattern sculpting, without compromising

performance, was through use of broadband

panel arrays.

The dual, 10-level broadband panel arrays

deployed at Mount Wilson were designed

by RFS in close collaboration with Merrill

Weiss. Early in the project, it was decided

to use panels arrayed on three faces of a

five-sided column, with panels omitted on

the two northern faces, since coverage was

not required over the nearby mountains to

the north. Using sophisticated computer

modelling techniques, the effects of

electrically tilting the three faces individually,

coupled with power distribution and

phasing adjustments, were assessed to

determine the optimum pattern for

each antenna.

This antenna pattern optimization process

involves numerous variables. The act of

changing the beam-tilt on individual faces

leads to ‘transition regions’ in the pattern

that require careful analysis during the

design process. Also, the effect of

signal phasing on the pattern is tightly

integrated—such that a change of phasing

on one face has cascaded effects on other

antenna parameters. Finally, due to the

broadband nature of the antenna (580 to

756 MHz), any adjustments for one

frequency lead to follow-on effects across

the bandwidth, so that the design is

effectively four dimensional.

The process of ensuring optimum coverage

for each of the services—and particularly,

that the signal restrictions over Mexico

didn’t degrade the performance of those

channels not requiring it—involved many

iterations of the key design variables.

Interference issues and the challenge of

achieving the required gain within specified

power limitations were also taken into

account, with the ultimate result being

two separate stacked panel arrays (each

capable of handling up to 195 kW total

average power input) that meet the

stringent performance requirements of all

four broadcasters.

The advent of digital television and simulcast

digital/analogue services has undeniably

changed the face of global broadcasting.

With mountain real estate often at a

premium, plus escalating potential for

interference and the considerable cost of

deploying new infrastructure, many broad-

casters have made the bold move toward

multi-service systems.

For four Los Angeles broadcasters (KDOC,

KJLA, KOCE, and KXLA) seeking to add

DTV to existing analogue services, these

considerations ultimately have led to

the deployment of a shared broadcast

facility atop the city’s premier site—Mount

Wilson. Envisaged, co-designed and

overseen by broadcast consultant, S. Merrill

Weiss, the solution incorporates a dual,

broadband panel antenna/combiner system

designed and manufactured by Radio

Frequency Systems.

As an experienced provider of broadband

RF solutions, RFS joined the project when it

became clear that a shared system was

required. Not only is the Mount Wilson site

highly congested, but since adjacent

channels were involved, each of these

services needed to be broadcast from the

same location to prevent interference. In

order to move the analogue services from

elsewhere to Mount Wilson, plus deploy

the new digital services, a shared system

was imperative. It also offered the

advantage of economy of scale.

For the seven channels to be broadcast

(32, 44, 48, 49, 50, 51, and 56), dual

antenna/combiner sub-systems were

conceived for a number of reasons. The first

of these was to simplify the combiner system,

removing the need for adjacent channel

6 C O V E R S T O R Y

An innovative, shared broadcast system atop Mount Wilsonprovides four LA broadcasters with high performance—and highlysculpted—digital and analogue television coverage.

Shared and sculpted:LA broadcast ing in the l imel ight

Dual broadband panel arrays from RFS providesculpted digital/analogue signals for four Los Angeles broadcasters at Mount Wilson.

The panel arrays wereinstalled in four sections

in October 2003.7

The panel arrays are supported by a pair ofparallel RFS directional waveguide combinerchains—including a new ‘full-wavelength’directional waveguide combiner.

“We put a lot of thought into this with the

development of CELLFLEX ‘A’,” explains

Chris Adams. “We knew crush strength was

vital in the field, so we didn’t compromise

the CELLFLEX crush resistance, while

dropping attenuation up to six per cent.”

Make the connectionDressing or ‘connectorizing’ the cable—

finishing the cable so it is fitted with a

universal 7/16-inch DIN connector—is the

second area where Wilson sees problems.

These, he believes, are often caused by

cable manufacturers. “There are some

brands out there that have three different

types of connectors and connector tools, to

do three different cable models, all by the

same manufacturer!” Wilson says. He

firmly believes this is a recipe for disaster—

and he’s witnessed the results. “We’ve

actually just repaired a site where the

installer made the wrong connector fit

the cable. There was no signal strength

at all—it was completely open!” The

well-known cable brand name matched

that of the connector, but the models didn’t

match up.

Worse yet, the wide variety of tools can be

expensive, bulky and difficult to use. As

Wilson explains, it can be an uphill battle

ensuring you have just the right tool for

each job.

RFS’s Adams agrees that cross-range and

backward compatibility of connectors, plus

simplicity of tooling is an essential in

getting it right at site. Equally important

though, is ensuring the RF and electrical

robustness of the connector design itself.

There are three basic designs for connectors

—two of which rely on clamping down on

the outer of the cable, which is ultimately

problematic.

“Smooth-wall cable is an entirely glued

assembly—inner conductor to dielectric to

For these reasons, the appearance of

smooth-wall feeder cable on the base

station scene is something of a curiosity.

“To-date, rigid smooth-wall feeder cable

hasn’t been seen much in European base

station applications, but it’s common all

over the world in its ‘native’ application—

that of cable television (CATV) signal

routing,” says RFS’s Adams. “Here, it’s

buried deep beneath the ground—where

the thermal conditions are comparatively

stable—and routed in long straight runs

with few bends, so it thrives.”

In the vastly different environs of the cellular

base station, things are quite different.

“When we get called out on a site repair

where rigid smooth-wall cable has been

used, we always check for the kinks first,”

says Wilson. “We also check the ground

kits and connectors—cutting into the outer

conductor seems to be a common problem

with smooth-wall installs. If it’s cut, then

thermal contraction and expansion

eventually make an opening for water

to get in.”

Some ‘high-performance’ (reduced attenu-

ation) cables can also pose site problems. In

the quest to minimize attenuation, some

manufacturers have used dielectric foams

with densities so low that crush resistance is

severely compromised. “They’re looking at

gaining a quarter of a dB, but losing crush

strength in a big way,” Wilson says. “When

you take the cable out and put a hoisting

grip on it, it puts indentations in the

cable 'cause it's so thin.” This, he says,

becomes an even greater problem on

collocation sites, where obstructions and

bends are many.

corrugated cable, and rigid smooth-wall cable

—plus a dizzying range of accompanying

connector systems and tools. There is also

wide diversity in installation crews’ skill levels

and experience, plus a broad range of site

layouts, weather conditions and so on. This

mix makes achieving repeatable long-term

feeder performance a challenge.

“We were well aware of this real-world,

multi-variable situation when we developed

our CELLFLEX ‘A’ high-performance

corrugated feeder cable,” says Chris

Adams, Global Product Manager of

Transmission Lines with Radio Frequency

Systems. “All too often, feeder cable

technology groups focus too hard on

achieving performance in one or two key

areas—say attenuation, flexibility, or

connector VSWR. The end result is they

have something that might perform well in

the laboratory, but is a disaster in the field.

end-to-end wireless project development

services, from site acquisition and base

station design, through to installation,

commissioning and maintenance.

And it is at the maintenance end that

Wilson sees feeder costs really blow-out.

“We often get called out to repair faults on

non-CMS Wireless sites. The majority of the

feeder cable problems we see here are as a

result of poor connectorization, problems

at bends, and cuts and crush faults in the

cable run,” says Wilson. These manifest in

poor signal strength, or intermodulation

problems.

According to Wilson, it’s a frustrating and

costly business for the operator. “The end-

user is putting out maintenance money to

repair what should’ve been done right in

the first place,” he says. The cost isn’t limited

to that of raw maintenance; there are also

the costs of base station down-time, and

resultant subscriber churn.

Wilson cites the limited nature of the feeder

system commissioning/testing regime as a

something of a problem. The common

voltage standing wave ratio (VSWR)

‘sweep’ test simply doesn’t truly measure

the long-term quality of the install. “You

can tighten a connector down and make

the sweep pass today, but over time and

temperature cycles a poor install will

deteriorate,” he says. “You’ll start seeing

reflective power over time.”

The challenge facing both operators and

installation crews is dealing with the

number of variables in the transmission line

‘equation’. These include a wide selection

of feeder technologies—such as corrugated

cable, low-attenuation ‘high-performance’

The ubiquitous coaxial feeder cable provides

the RF link on cellular base stations from

Moscow to Minneapolis. Bought by the

metre, its ‘buy and install’ cost is negligible

on the total base station price scale. In

many quarters, the feeder system is regarded

merely as a network ‘consumable’. Some

believe that ‘a cable, is a cable, is a cable’.

“Wrong,” say the experts—the network

operators and planners, and the site

installation and maintenance crews. If

poorly selected and managed, the potential

total life-cycle costs of a transmission line

system can be very high indeed.

”We attach great importance to the

reliability and quality of feeder cables, as

they directly influence both the quality of

the services we provide our subscribers, and

the ongoing expansion costs of the system

as a whole. It is for this reason we search

out a specific grade and quality of cable,“

says Valery Ulianov, Director of Regional

Network Development and Technical

Director of Moscow region with leading

Russian cellular operator, Vimpelcom.

Ulianov is involved in the operator’s massive

network expansion program that will see

Vimpelcom’s popular ‘BeeLine GSM’ service

further expanded in the so-called macro-

regions of Russia.

Mounting costsFast forward from base station planning

and roll-out, to where the feeder system

costs really mount up: during long-term

maintenance and repair. Aaron Wilson is

Technical Maintenance Manager with CMS

Wireless, an Arkansas USA-based wireless

base station developer. His company provides

8 F E E D E R S Y S T E M S 9

Connect ions, corrugat ions andcosts—the feeder cable debateMaking sense of the base station feeder cable technology debate is noeasy task.The best place to start is where it all begins and ends: at the basestation site with the site crews and network development teams.

It’s about striking a balance, and remem-

bering that the feeder systems are ultimate-

ly destined to be installed by real installers

on real base station sites, not in labs!”

Bend and crushAccommodating cable bends—sometimes

up to six bends in a single run on a modern

urban site—is an area where problems can

occur. Most problematic is the rigid

smooth-wall feeder cable. Without the

corrugations of conventional cable, it

exhibits minimum bend radii of up to two

and a half times that of corrugated cable,

and bending moments as much as six times

greater. “From an installer’s point of view,

this is the hardest cable to install,” says

Wilson. “It’s hard to bend, and if you

re-bend, it tends to kink. If you bend it

once and need to bend it back, it

generally snaps.”

The ‘kinks’ that ultimately occur in rigid

smooth-wall cable represent a great deal

more than visual blights—they are weak

points that crack or deteriorate over time,

and ultimately reduce signal strength.

RFS uses a slotted brass finger claw onthe RAPIDFIT connector to maximize thecontact with the outer—this providesaround twice the electrical contact, andbetter long-term performance.

just what is installed at site and how. “Stick

with what works,” advises CMS Wireless’s

Wilson. “To me, that’s corrugated cable.

My suggestion is to find a cable with just

one type of connector and stick with it.

Make sure you keep the crush strength up

there, as well.”

While feeder cable might be purchased as a

site-consumable, its potential long-term

cost implications are in the ‘major capital

item’ league. Ulianov’s experience with

Vimpelcom suggests this is very much the

case, and is the core reason Vimpelcom

opts for CELLFLEX ‘A’. ”The vastness of

Russia, coupled with the fast-paced and

all-embracing nature of our services

expansion program, forces us to work

under diverse economic and climatic

conditions,” Ulianov concludes. ”At the

same time, we insist on providing unique

quality standards in all the services we offer.

For this reason we take the choice of the right

cable systems very seriously”. The bottom

line, it would seem, is that subscribers the

world over justifiably expect operators to

get it right the first time. There are no

‘second chances’—feeder technology

needs to be chosen accordingly.

The wireless component of the project is

divided again into two elements, the

‘transport’ or backbone links, and the

‘access’ links. The transport links provide

high-capacity point-to-point microwave

connectivity over longer distances

(20 to 120 kilometres), at data

throughputs of either 45 or 155 Mbps. The

access links are shorter microwave hops

(10 to 40 kilometres), providing connectivity

between the transport network and remote

facilities.

The Canadian arm of global communications

solutions provider, Alcatel, was appointed

by Bell in the second half of 2003 to provide

the RF equipment radios (antennas and

associated equipment) that make up the

2,000-kilometre/60-hop transport network.

Alcatel, in turn, selected Radio Frequency

Systems to provide all the necessary

microwave antennas, waveguide, and

associated installation hardware.

Hops in timeThe 60 microwave hops are located across

the province within 44 wireless ‘service areas’

(see map on page 13). Each hop is powered

by Alcatel’s MDR-8000 low to high-capacity

microwave digital radios. These are coupled

with RFS’s high-performance single-polarized

DA series microwave antennas, using RFS’s

low-loss FLEXWELL elliptical waveguide to

form each radio-to-antenna link.

“The reason we selected the RFS DA series

antennas was to ensure we got the best RF

performance,” says Alcatel Canada’s Senior

Account Director, Terry Pettigrew. The RFS

DA series, he says, provides premium

front-to-back performance, and the

precision radiation pattern envelope (RPE),

sharp beamwidth and reduced side lobe

radiation demanded by the Canadian

spectrum authority, Industry Canada.

A further, and equally important, reason

was RFS’s ability to deliver a proven product

in accordance with a demanding delivery

schedule. “The timeline was certainly one

of the biggest challenges,” says RFS Area

Ingenious conceptSuperNet is ingenious in its concept and

design. The network is made up of two

elements—a ‘base area’ and an ‘extended

area’ network. The base area network is

optical fibre-based, and provides gigabit

connectivity to 27 larger communities. The

extended area network is made up of a mix

of optical fibre and microwave wireless

technologies, and extends SuperNet’s

connectivity to 395 smaller communities

across the province. For many of these

smaller locations, access to high-speed

internet services is an entirely new

experience.

The complete network is being built by

leading next-generation communications

company, Bell, and independently managed

by Axia SuperNet, a subsidiary of the

broadband networks project group Axia

Netmedia. This ensures cost-controlled

access for all service providers, plus a

healthy and competitive ISP market from

which subscribers can choose.

In some parts of the world, rolling out

community-wide broadband network

infrastructure is far from straightforward.

Alberta, Canada’s fourth largest province, is

a case-in-point. Half its three million people

live in just two cities, Edmonton and

Calgary. The balance is thinly distributed

across far-flung rural and semi-rural centres.

The province is roughly the same size as

France, and its terrain varies wildly from

mountains, to rolling hills and plains,

through to marshy peat lands. As a result,

providing cost-efficient broadband access

to most of Alberta’s population is

challenging, to say the least.

In early 2001, the Government of Alberta

took this challenge head-on. It

conceptualized a province-wide broadband

network—the Alberta SuperNet. Its core

goal was to ensure affordable high-speed

network connectivity to schools, libraries,

businesses and homes in 422 communities

across Alberta.

Alberta SuperNet—broadband for the future From Alberta’s Rocky Mountains to its northern ice lakes, RFS microwaveantenna solutions play an important role in realizing province-widebroadband connectivity.

outer conductor to jacket. This means you

can’t flare the outer to electrically clamp it

from both sides, as you do with corrugated

cable connectors,” Adams says. As a result,

the cable outer is clamped from the outside

only, using a ‘slip ring’. “Over time, the

outer starts to collapse under the slip ring

and gives way. Installers tell us that you can

leave an installation nice and tight, then

return to find the connector can almost

spin on the cable. This leads to inconsistent

behaviour, dropped calls, intermodulation

and so on.”

The other basic design that applies pressure

to the cable outer conductor, is one used

with some corrugated cable connectors.

While the outer is flared and clamped in the

conventional manner, a ring of ball-bearings

within the connector head is used to

achieve extra electrical connection on the

ridge of one corrugation. “This design is

flawed, as the bearing ring only grabs a

small portion of the available conductor.

Instead, RFS uses a slotted brass finger claw

on the RAPIDFIT connector to maximize the

contact with the outer,” Adams says. “It

gives us around twice the electrical contact,

and better long-term performance.”

The water mythWater ingress in the cable is another area of

debate. The rigid smooth-wall camp claims

its cable’s glued construction prevents water

ingress, whereas flexible corrugated cable is

susceptible. Nonsense, say the users. “I

have been using corrugated cable here in

North Germany for many years now, and

have never experienced water ingress

problems,” says Stefan Kraege, Project

Leader with the German installation group

Hestra-Antennenmontage. “If the connectors

are correctly installed and sealed, you have

no problems. We have base stations that

are almost a decade old, and none have

experienced water problems.”

Adams concurs with this view. “The glued

assembly of the rigid smooth-wall cable

stops water moving from within its connector

to the cable. But water in the connector in

a cellular installation is enough to totally

disrupt transmission!,” he says. “Our view

is that the only place water belongs is outside

the transmission line. Where it gets in is

either via a cut in the cable outer, or via a

poor quality connector. Keeping water out

of the connector comes down to two

factors—simplicity of connectorizing and

quality three-point sealing, rather than

simple ‘crest-seal’ O-rings.”

Minimizing feeder system total life-cycle

costs, it would seem, starts and finishes with

M I C R O W A V E 11

Aaron Wilson, Technical Maintenance Manager with Arkansas USA-based wirelessbase station developer, CMS Wireless.

10 F E E D E R S Y S T E M S

The balance of

the 60 transport

hops are expected

to be installed and

commissioned before the end

of September 2004, marking a

significant milestone in the development of

SuperNet. “Once we got things rolling and a

process established, it all went incredibly

smoothly,” says Pettigrew. “Of all Bell’s

suppliers, I know they are very pleased with

RFS and Alcatel and the work we have done.”

The responsiveness of the RFS/Alcatel team,

coupled with the tried and proven nature of

the RFS DA series microwave antenna and

the Alcatel MDR-8000 radio, have played

an important part in the success and

efficiency of the transport network rollout.

“There was no experimentation, beta-version

radio software or unproven RF systems,”

says Zoberi. “What we offered in the DA

antenna was world class, proven technology

—nothing less. It was the optimal choice

for the SuperNet.”

service level agreement, Alcatel opted to

use ‘quad diversity’—a combination of

both space and frequency diversity—on the

single hop.

“We use either space or frequency diversity

in other hops, but this is the only link on this

project where we’ve actually combined

them together,” says Alcatel’s Director

Wireless Communications Division, Marc

Vandeberg. To achieve the space diversity,

Vandeberg explains, the link uses a massive

pair of 15-foot diameter RFS DA antennas,

plus a pair of 12-foot diameter antennas,

each mounted with around 60 metres of

vertical separation. While the balance of

the SuperNet transport hops operate in

the 8-GHz band, the Fort Chipewyn-to-

Birch Mountain link uses channels in the

lower 6-GHz band, to reduce the hop

attenuation. Two pairs of non-adjacent

channels, separated by 177.9 MHz, are

used to achieve the link’s frequency

diversity.

Trials and successJointly designed by Alcatel, the project’s

lead contractor, Morrison & Hershfield, and

design group Planetworks, the link was

simulated and trialled in early April 2004 at

Alcatel’s two US facilities (Longview and

Plano). The radios were connected to long

lengths of microwave waveguide to model

the space diversity in the 120-kilometre

hop. Fixed and variable paths were used

to simulate fading activity, plus test

equipment to simulate dispersive fade

characteristics.

Once the link was proven in the factory, the

Alcatel radios were air-freighted from

Edmonton, Alberta, to the remote Fort

Chipewyn and Birch Mountain sites, where

they joined the already-installed 15-foot

and 12-foot diameter RFS DA antennas.

On the first weekend in July 2004, the Bell

installation and commissioning crews

finally proved the design was correct—one

of the world’s longest OC3 microwave

links was up and running, and ‘Fort Chip’

was on the air!

Product Manager, Asad Zoberi. “While we

had completed microwave projects of this

scale before—for example, State-wide

deployments in Florida and Philadelphia—

the time lines were more spread out.”

The first deliveries of RFS antenna systems

and Alcatel radios to Bell were in October

2003, with the entire program completed

by the end of the second quarter of 2004.

The antennas and radios are progressively

being delivered and installed at the

120 sites by the project’s installation

contractors, Radian and West Tower.

Time was tight on this project due in part to

Alberta’s unique seasonal and geographic

conditions. An example is the marshy peat

lands in the north-east of the province—

sites in this area are only accessible by road

during the winter months, via ice roads cut

through the snow. After the spring thaw,

the only option for moving equipment into

these sites is via helicopter—a prohibitively

costly option.

Long-distance linkOne particular ice road-accessed hop also

proved to be the project’s most technically

demanding—the hop linking the remote

centres of Fort Chipewyn and Birch

Mountain, in the province’s far north-east.

Located in the project’s wireless service area

‘J’, the 120-kilometre microwave hop runs

over boggy marsh lands and alongside the

vast Wood Buffalo National Park, home to

2,200 rare wood buffalo. “We had to get

the antennas and radios in no later than the

second week of March,” recalls Pettigrew.

“I think we had one of the last trucks on the

ice road to get in and out of there!”

The long hop distance—the link is

understood to be one of the longest

‘Optical Carrier Level 3’ (OC3) microwave

links in the world—presented a great

challenge to the link’s designers. This was

exacerbated by the ponds and marshes

scattered along the link, which represented

reflection and multipath sources. As the

Government of Alberta specifies ‘five

nines’ reliability (99.999 per cent) in its

12 M I C R O W A V E 13

The RFS DA antenna series is a high-

performance solid-body antenna family,

providing reduced side lobe suppression for

more exacting applications. Available in 4,

6, 8, 10, 12 and 15-foot diameters, the

DA single-polarized antenna series features

RPE that meets applicable international

A microwavesolut ion for Alberta

standards such as ETSI, FCC, Industry

Canada and so on. The antennas also

feature low VSWR performance and high

front-to-back ratios, and are designed for

the harshest of environments, with a

survival wind speed of 200 km/h.

RFS FLEXWELL elliptical waveguide

provides superior flexibility and installation

efficiency, when compared with

conventional, rigid rectangular waveguide.

Available in a wide selection of frequency

bands from 2 to 40 GHz, FLEXWELL

provides both low loss and low VSWR

performance.

The 15-foot and 12-foot diameter RFS DAantennas mounted with around 60 metresof vertical separation at Fort Chipewyn.

Alberta

Bri

tish

Co

lum

bia

Saskatchew

an

Legend

Wireless service areaWireless service area JNational park area

Bitumount

Birch Mountain

Fort ChipewynLake Mamawi

Lake Athabasca

Fort Mackay

0 100 km 200 km

ROCKY M

OUNTAINS

Edmonton

J

Wood BuffaloNational Park

CalgaryBanff NationalPark

that the thickness of solid radomes is always

dependent on the wavelength (and hence

frequency) to be used in the application.

Assuming a dielectric constant between 2.5

and 3, typical solid radome thicknesses for

different frequencies would be: 6 mm (14 GHz),

4 mm (22 GHz), and 2.4 mm (38 GHz).

It is important to note that if a radome of

incorrect thickness is used, the transmitted

power will be reduced, and consequently

Accounting for angleFigure 2 is valid for the ‘ideal’ case, where

wave fronts hit the wall perpendicularly.

Now consider the situation for signals

not having this ideal orientation. Given

the longer effective wave path through

the radome material as they hit the

wall obliquely, the optimum thickness

is now also dependent on the angle of

incidence (θ), measured as the deviation

from the normal.

In practice, however, angles of incidence of

up to 20 degrees have negligible effect on

the optimum radome thickness. This is

illustrated for flexible radome materials in

Figure 3, which shows the relationship

between angle of incidence (θ) and d/λο

(where λο is the free space wavelength),

for achieving 95 per cent power trans-

mission through materials with different

dielectric constants. For values of θ up to

20 degrees, the optimum thickness is barely

impacted—particularly for low loss materials,

which should be those considered for

radome design purposes.

A similar relationship holds for solid

radomes. These relationships have been

exploited in practical fashion by many

microwave antenna designers. A small

degree of tilt of the main beam—

around 5 degrees—actually improves the

performance of the antenna, by directing

spurious reflections within the antenna away

from the microwave feed system.

The influence of typical thin wall or flexible

radomes can be seen in Figure 4, which

compares the radiation patterns, with and

without radomes, of microwave antennas

operating at 6.4 GHz and 33.4 GHz.

At 6.4 GHz it is evident the radome has

negligible effect on the radiation pattern.

However, at 33.4 GHz the gain of the

antenna is decreased by 1 dB due to

attenuation by the radome. Once again, to

achieve the same link budget the radio

power has therefore to be increased

by 1 dB, causing a higher interference

potential outside the main beam. The

the antenna gain also reduced. Greater

radio power would then be required to

achieve the desired radiation power, resulting

in a corresponding increase of side lobe

radiations. This illustrates the fact that

correct radome design is critical not only

for optimizing link budget, but also for

interference control, since an increase in

side lobe radiations would raise the potential

for interference.Over the past decade microwave links

have proven a popular solution for the

telecommunications industry. The relative

ease and economy of installation has seen

them deployed in an increasing number

of point-to-point and point-to-multipoint

applications—from communications back-

bones, to branch links and distribution

networks, not to mention applications in

the broadcast industry and private enterprise.

With the rise of new cellular operators

and new technologies, overall microwave

network density is undeniably escalating.

Yet this intensification of microwave

communications brings added challenge.

The greater the number of point-to-point

links in a given area, the greater the

potential for these to interact with one

another and cause interference. Since any

distortion of the signal reduces the quality

of service, controlling interference is now

the mandate of any radio network operator

and national authority. A good starting

point for consideration is the design and

location of the source of the signal—the

microwave antenna (Figure 1).

Figure1 shows the main beam at 0 degrees,

plus side lobes that are significant to

about ±90 degrees from the main beam.

It is these side lobes that can cause

interference with adjacent point-to-point

links, and it is these side lobes that must be

minimized through careful antenna design

and installation.

Optimizing the radomeRadomes are used for two main applications

in radio link antenna design. The first is to

cover the antenna feed system in order to

protect it from the dirt, snow and ice of our

natural environment. In addition, a radome

significantly reduces the windload of an

antenna system, by preventing the dish and

shield from ‘catching’ wind. However, both

radome material selection and thickness need

to be carefully considered to optimize the

power transmitted through the radome,

while at the same time ensuring the side

lobes are not increased to detrimental effect.

Figure 2 shows a plot of the reflection

characteristics at a plane wall radome for

different materials. Each of these materials

are characterized by a relative dielectric

constant of εr = 2; however each material

has a different loss parameter, tan δ, where

tan δ ranges from 0.0018 (low loss) to

18 (high loss). Figure 2 shows that for low

loss materials, there exists two distinct

minimum values of the reflection coefficient,

for which a radome wall will allow maximum

transmission of incident power. These

correspond to design values where the ratio

of radome wall thickness (d) to microwave

wavelength in the sheet (λ) is close to either

zero or 0.5.

The first case of d/λ≈0 is practically realized

as d<λ /10, and leads to flexible radome

materials with typical thicknesses of 0.4 to

0.6 millimetres—essentially as thin as is

practical! Flexible radomes are commonly

used for larger antennas (greater than

4 feet), to avoid the bulk and weight of

solid radomes.

The second design case of d/λ≈0.5 is more

complex, and leads to the design of solid

radomes, which are more economical to

produce at the smaller sizes (less than 6

feet). The practical implication of d≈λ /2 is

14 T E C H N O L O G Y F O C U S

Microwave antenna opt ions for minimiz ing interference

With microwave network density on the rise, the potential for signalinterference is also increasing. Dr Daniel Wojtkowiak, Vice President of Microwave Antenna Systems RFS, looks at ways of minimizing interference-causing distortion of radio frequency signals.

15

Amplitude reflection coefficient [R]

Thickness in free-space wavelengths (d/λ0)

ε= 2 εo

ε= 4 εo

ε= 6 εo

ε= 9 εo

ε= 16 εo

Figure 1—Illustration of microwave antenna configuration

Figure 2—Reflection characteristics at a plane wall radome

Figure 3—Dependence of flexible radome design on incidence angle

Am

plit

ude

refle

ctio

n co

effic

ient

[R]

Thic

knes

s in

free

-sp

ace

wav

elen

ghts

(d/λ

ο)

No matter how carefully a microwave

antenna radome is designed, the potential

increase in side lobes remains. This must be

taken into account during other aspects of

design and installation of the antenna in

order to minimize interference.

Removing rim reflectionsThe basic ‘standard performance’ microwave

antenna consists of an open dish and a

feed system. Usually lacking a radome

(although a moulded radome is an

option), standard performance antennas

are economical solutions for specific

applications. Aside from the lack of

environmental protection of the feed

system, the main drawback is the

diffraction of microwave power at the rim

of the dish; these result in significant

backward reflections at azimuth angles of

±100 degrees, which can seriously interfere

with adjacent point-to-point links.

To literally block these backward rim

reflections, antenna designers place a

shield around the circumference of the

antenna, to which a planar radome is

usually attached (Figure 5). These ‘high

performance’ microwave antennas may be

further enhanced by the application of an

absorbing foam to the inside of the shield,

resulting in ‘ultra high performance’

microwave antennas. The foam absorbs

spurious reflections within the antenna

and dramatically improves performance

through limiting the side lobes.

Radiation pattern envelopes for standard,

high, and ultra high performance antennas

are compared in Figure 6. The improvement

in side lobe reflection control of the ultra

high performance antenna over both other

antennas is evident. Interestingly though,

the high performance antenna exhibits

poorer performance than the standard

performance antenna between 20 and

60 degrees—the result of additional

reflections off the shield. It nevertheless

proves significantly better at preventing

backward reflections. Selection of the

appropriate microwave antenna clearly

depends on the intended application, and

the expected interference potential in a

given area.

Evading the environmentIt is important that, once installed, the

performance of a microwave network

should not deteriorate due to environmental

impact. While a radome might protect the

sensitive feed system from the elements,

only a stable construction can protect the

dish itself from wind. Mechanical stability

of an installed antenna is critical for it to

maintain its point-to-point link, as well as

restricting its potential for interference with

adjacent links, if its orientation changes.

Different antenna manufacturers use

different methods of rating the antenna

resistance to wind. Radio Frequency Systems

defines the ‘operational windspeed’ rating

of an installed antenna as that for which

temporary deflection of the main beam is

within one-third of the half-power beam

width of the antenna. (Half-power beam

width is defined as the angle, relative to

the main beam axis, between the two

directions at which the measured co-polar

pattern is 3 dB below the value on the main

beam axis.) Within this operational wind-

speed—of which typical values are 190 to 230

kilometres per hour—the point-to-point

link will be satisfactorily maintained.

Other standards consider the operational

windspeed as that for which the main

beam is not deviated by more than

0.1 degree. Whatever the method used,

it is important to take the deflection

of the mounting structure into

consideration during calculation of the

beam deflection.

The positional mounting of antennas must

also be considered by operators seeking to

minimize interference. Typical multi-antenna

tower installations, with their many side

lobe radiations, are a breeding ground for

17

presence of the radome also leads to

increased side lobe levels, clearly visible in

Figure 4 at azimuth angles between 20 and

60 degrees.

This effect of the radome on the 33.4 GHz

antenna is due to the fact that at higher

frequencies, flexible radome design

16

Gain [dBi]

Figure 6—Performance comparison of standard, high, and ultra high performance antennas

Normalised radiation [dB]

Figure 7—Illustration of the significant reflections that may arise when an antenna ismounted too close to a solid structure

Normalised radiation [dB]

Figure 4—Effect of flexible radomes on antenna performance at 6.4 GHz and 33.4 GHz

interference; while in other cases, the

mounting structure may directly impact the

performance of the microwave link

through shielding and the generation of

reflections from outside of the antenna

itself. This is particularly the case when

antennas are mounted on the face of

buildings and solid towers, while Figure 7

shows the significant reflections that arise

when an antenna is mounted too close to a

solid structure to the side. Such structure-

generated reflections are likely sources

of interference, and are often not taken

into consideration by operators during

installation.

Managing interference is not a new issue,

but it has certainly become more critical

as the prevalence of radio networks has

grown. Judicious antenna selection,

design and installation is more essential

than ever to minimize the interfering

effect of spurious emissions, and to

maximize performance of the microwave

link network.

becomes more sensitive to the practical

constraints on material thickness and stability.

Whereas the design ratio of d/λ ≈0.01 can

be achieved for the 6.4 GHz antenna, the

best possible case for the 33.4 GHz antenna

is just d/λ≈0.05, which is not as close to the

ideal zero.

Figure 5—Typical high (or ultra high) performance microwave antenna (including shield)

Nor

mal

ised

rad

iatio

n [d

B]

Gai

n [d

B]

Nor

mal

ised

rad

iatio

n [d

B]

T E C H N O L O G Y F O C U S

As of September 2004, Budapest audiences

will enjoy increased picture quality and

viewing flexibility, with Radio Frequency

Systems launching initial digital terrestrial

television (DTT) services for Antenna

Hungária. After successful DTT trials in

Budapest, a new 20-kW antenna system—

being designed, delivered and installed

by RFS—will increase digital coverage for

the city.

According to Hans-Peter Quade, RFS Area

Product Manager Broadcast, the biggest

challenge has been the tight schedule

imposed. “Normally the delivery of such an

antenna system is around 12 weeks—we

will be doing it in six!” he said. “The other

factor is that in order to use the existing

tower mast and meet Antenna Hungária’s

This coming October will see Radio Frequency

Systems return to China’s largest tele-

communications/IT event, PT/Expo Comm

China 2004, to be held in Beijing. At this

important exhibition, RFS will display its

comprehensive suite of cellular base station

solutions, with a special focus on helping

mobile operators to meet current network

optimization and future third-generation

(3G) migration objectives.

According to Chloe Yao, RFS China

marketing communications officer, Chinese

mobile operators are starting to look

seriously at 3G options in the face of exten-

sive technology trials during 2004. “A

series of outdoor 3G trials are being held

by potential license-holders in Beijing,

Shanghai and Guangzhou,” she

said. “Insiders expect that the 3G licenses

may be granted as early as next year, so

PT/Expo Comm China will be an important

forum for all the industry players to meet

and discuss this exciting next step.”

RFS’s base station solution set includes high-

performance cellular antennas, microwave

antennas, flexible transmission line and RF

conditioning components. Highlights of the

RFS PT/Expo Comm China display will include:

• Cross-polarized Optimizer antennas

with variable electrical tilt and optional

remote tilt control (APXV series)

• Dual tower mount amplifier

(ATM201712D series) for universal

mobile telecommunications system

(UMTS) applications

• New three-foot CompactLine

microwave antenna (SB3 series) for

point-to-point applications in the

7 to 22 GHz range.

RFS at PT/Expo Comm China 2004:China International Exhibition Center, Beijing, 26 to 30 October, 2004Hall 8, Stand 8300

18

RFS shinesthe DTT l ightin Hungary

Base station technology—an RFinterface evolutionFew technology advances have impacted

on life and the way we do business to

the extent brought about by cellular

communications. The technology itself has

undergone dramatic change over the past

two decades, as it evolved from the earliest

analogue networks to the powerful

third-generation (3G) digital networks of

today. Advances in base station RF

technology—both passive and active—

have underpinned each and every

milestone in this industry’s fast-track

developments.

In the next issue of STAY CONNECTED, we

explore the recent and near-future

advances in base station RF technology—

the technology leaps that are supporting

the global transition from second to third-

generation cellular and beyond. We look,

in particular, at the increasingly important

role played by active base station RF

technologies, minimal environmental

impact antenna solutions, and emerging

‘intelligent’ microprocessor-based RF

technologies. Precision levels of footprint

control, superior network optimization,

and innovative overlay solutions are the

exciting outcomes.

3G focusfor Chineseexpo

PREVIEW

At the IBC 2004 exhibition in Amsterdam

this September, Radio Frequency Systems

will display its comprehensive portfolio of

total RF system solutions for European

digital terrestrial broadcasting.

“We will be exhibiting solutions for the

entire RF chain—from the output of

the transmitter to the top of the

mast,” said Paul Newsome, RFS Senior

Sales Manager for Broadcast and Defence

Systems. “Whether broadcasters are seeking

to overlay existing analogue services with

digital or deploy new digital infrastructure,

RFS has the product portfolio to meet their

total RF system requirements.”

According to Newsome, RFS is also expanding

its European manufacturing capability. “In

response to the continuing demand for

complete broadband systems in Europe, we

are increasing the volume of panel array

manufacture and the size of our local

support team,” he said.

In support of Europe’s transition to digital

broadcasting, RFS will be launching three

new RF filtering/combining products at the

IBC 2004 exhibition: an ultra-compact

manifold UHF combiner (see page 5 of

this issue of STAY CONNECTED), a

family of DAB Band III filters (see page

5 of this issue of STAY CONNECTED),

and a low-power integrated VHF combiner.

Also exhibited at RFS’s IBC 2004 stand

will be other elements of the RF chain:

broadband panel antennas, a high-power

waveguide combiner module, HELIFLEX

air-dielectric coaxial transmission lines, and

patch panel with optional digital RF

monitoring technology.

RFS at IBC 2004: RAI Amsterdam, 10 to 13 September, 2004 · Hall 5, Stand 5.221

In support of Kerrang! 105.2 FM, the latest

regional radio station serving the UK’s West

Midlands, Radio Frequency Systems has

supplied Crown Castle UK with a custom-

built FM combiner for its transmission site

at Sutton Coldfield, near Birmingham. The

RFS combiner enables the broadcast of a

new 2-kW FM service from an existing

broadband antenna, which also transmits

three existing FM radio services—one of

which operates at a frequency just 500 kHz

distant from that allocated to the new

FM service.

According to RFS Senior Systems Engineer,

Dave Thickett, utilizing the existing antenna

was a key objective for the broadcaster and

site owner, Crown Castle. “Since this was

to be the first channel combiner in the UK

Kerrang! rocks with FM solut ion

to achieve 500-kHz spacing, Crown Castle

developed a theoretical solution using

computer modelling, then approached

RFS in late 2003 to confirm its feasibility,”

said Thickett. “The main challenge was

to manage the effect of group delay

introduced by a combiner of such close

frequency spacing.”

Installed in April 2004, the resulting RFS

combiner is a modification of its three-pole

filter module (CA3P400IB), where the filter

apertures have been reduced in size and

carefully tuned to accommodate the

500-kHz channel spacing, as opposed to

the design-spacing of 800 kHz. The new

combiner was inserted between the exist-

ing three-channel combiner system and

broadband antenna.

19I N T O U C H

STAY CONNECTED4th quarter 2004

In support of DTT services, RFS willside-mount UHF panel arrays at

Antenna Hungária’s Budapest site.

IBC 2004: RFS to displaydigita l solut ions

pattern-tailoring requirements, the antennas

need to be side-mounted to the structure.”

To meet these specifications, RFS is providing

three UHF panel arrays from its PHP series

and flexible air-dielectric feeder cable from

the HELIFLEX range. A 20-kW four-level

three-sided panel array will transmit two

digital channels (43 and 51) and three

analogue channels (24, 41 and 48)—this

will be mounted at the top of the 130-metre

mast and fed via 170 metres of 3-1/8-inch

HELIFLEX cable. Below this, two smaller

panel arrays will transmit analogue

channels 47 and 26 respectively.

This configuration, devised by RFS, will

optimize coverage over the Budapest area

without dissipating power over the city’s

mountains to the north-west. Quade

reported that RFS and its partners, Hoeller

and Frequenz Plus, plan to realize the

venture as a total turnkey project with no

disruption to broadcast services.

I N T O U C H

R A D I O F R E Q U E N C Y S Y S T E M S

T h e C l e a r C h o i c e ™

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