Radiocrafts

Practical Radio design

• Practical Antennas • PCB-layout for optimum performance

• UART-extentions: Pairing Radiocrafts modules with other equipment

Radiocrafts

Practical Antennas

Quarterwave whip coated with plastic

Quarterwave copper on FR-4 laminate

Yagi: Increased directivity

Helical

Radiocrafts

Practical Antennas• The most easy way to reduce range is by thinking

about antenna as “any piece of wire”• EM-waves are travelling along the antenna conductor

and we want to radiate as much as possible of the power (when we transmit) or receive as much as possible (when we receive)

• To achieve this, the wire should be as long as possible while maintaining resonance to the centre frequency.

• Radiation is prevented by; Nearby grounding, metal obstacles (like metal enclosures…).

• Shorted antennas always reduces range but sometimes is required due to available space

Radiocrafts

Practical Antennas

It is important that the antenna has correct length which is a multiple of a quarter wave. When so, the impedance will be purely resistive in the feeding point, and we will get max power transfer from a resistive source (usually 50 ohm)

Feeding point

λ = c / f x 0.95

Radiocrafts

Antenna “classes”• Monopole: Usually λ/4 or 5/8λ. Electric field dominates• Dipole: Usually λ/2 (can also be 5/8λ). El. field

dominates• Loop (magnetic field dominates). Not covered.• Helical (combination of electric and magnetic)

Antennas containing “elements” of the above• 5/8 λ: Can be either monopole or dipole (Note: serial

inductor is needed for impedance match).• Yagi: Extra Directive antennas (lobe in one direction).

Has one Dipole antenna element and directors + reflectors

Radiocrafts

Monopole vs. dipole

Monopole quarterwave Dipole halfwave

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Radiation patternsGain:0 dBi

5.15 dBi5/8λ: 8.2 dBi

2.15 dBi5/8λ: 5.2 dBi

5-10 dBi(or more)

Radiocrafts

Practical Antenna guidelines• Use quarter-wave stubs with sufficient ground

plane extensionSufficient ground: Preferably the “longest length” the same as the antenna length

• Can be considered as a wire, either in the shape of a “whip” antenna or a PCB-trace.

• Length should be L=(c/f) / 4 x 0.95, i.e:2.9 cm (2.4 GHz), 8.2cm (910MHz), 7.8cm (868MHz) or 16.4cm (434MHz).

• Coated whip antennas: www.procom-dk.com, www.badland.co.uk, www.elcard.fi

Radiocrafts

Radiocrafts Range measurement setup

Antenna quarterwave, from

RC1240DK, approximately 17cm

Cu-side FR4 board size 24x24 cm or at

least 15x15cm, antenna placed in

center

Coax-cable with conducting SMA-connector fastened

tightly to adaptor and connecting to Cu-plane

SMA-SMA adaptor in drilled hole

in PCB

Radiocrafts

Shortened antennas• If not available space, shorter antennas can be used

but an inductor (or more complex matching) must be added at the base to achieve better impedance match. Radiates less! Measure impedance!

• Dielectric antennas: Ceramic material where λ gets shorter. Maintains resonance (see datasheet for req. match) but radiates less. Available for all frequencies 433-2400 MHz (www.fractus.com, www.johansontechnology.com, www.yageo.com )

• PCB-antennas: Can be made more area-efficient by folding the antenna, which also is good for receiving different polarizations. Width: 3mm is OK (the broader the width, the lower the resistive loss)

Radiocrafts

PCB antenna example, 2 layer PCB, λ/4-monopole

”Large” groundplane

”Free space” inside, both layers. Total length of antenna 16.4 cm

Do NOT route antenna close to ground or metallic parts

Note; There is NO gnd in layer 2 under antenna-trace!!

Radiocrafts

Helical antenna at 433/868 MHz

• Radiates in the direction normal to the axis

• Can be seen as monopole antenna shorted by coiling up the whip

• Resonance can be achieved for a much shorter construction

• Higher gain than with a non-helical structure of the same size

• www.stecom.com

Radiocrafts

Helical antenna at 433/868 MHz

Radiocrafts

PIFA-Planar Inverted F-antenna (2.4 GHz)

Feeding point, 50ohm line Ground, GND

Radiocrafts

Practical Antennas cont.

• Usually, FR-4 laminate is used; Thickness and material does not affect length (as the antenna is a wire, not a transmission line)

• If orientation varies (equipment is used both vertical and horizontal), make a 90 degrees bend at the middle

• If there is any length from RF pin of module, use 50ohm trace in PCB until antenna launches (connector or solder joint).

Radiocrafts

Routing guidelines

GNDCTSRTSCONFIGTXDRXDGND

RC1xx0/RC2x00/RC220x

RF

SMA

”50ohm trace”; Width is 1.8 x h for typical FR-4 material. See litterature for general calculations of characteristic impedance ALL vias to ground in entire design; As

close to the pad as possible. One via per ground-pad (do not share with others as this tends to increase length of trace, increasing inductance/impedance to ground)

Gnd-plane in inner- or bottom layer, as large as possible, as un-penetrated as possible.Remember NO ground under PCB-antennas!!

RC-MODULEh=board thickness

Via to ground

Layer 1 RF routing

PCB

Antenna

feeding point or coax launch to external antenna

Radiocrafts

RF Basics• The higher the frequency, the higher the loss in the

air, the lower the range• The higher the data rate, the lower the range

(bandwidth is high=wider internal filter=receiver receives more natural electromagnetic noise, masking a weak signal)

• The higher the frequency, the more straight line the EM signal is following

• Reflections: All EM-signals are reflected, giving local field minimums or maximums. As frequency increases, these min/max occur more frequently

Radiocrafts

UART extentions

www.wiznet.co.kr

Radiocrafts

UART extentions II

www.ftdichip.com

www.oxsemi.com

Radiocrafts

UART extentions III

www.informasic.com