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Frequency Band: 850-942MHz

Transmitting Power: 360 kW peak280 kW specified peak power12-13 kW average power

Antenna Parameters: Parabolic Reflector stabilized for roll and pitch 7.3m/24 ft wide,4.3m/14.2 ft high

Rotating ClearanceBeamwidths:

8.7m/28.4 ft diameter 3.3-3.3 azimuth

Gain 28.5 dB

Scan rate 6 or 12 rpm

Range 250 nm

Range Accuracy: 0.03 nmi

Azimuth Accuracy: 0.5 deg

PRF 280, 800, 1000 pps

Pulse width 125 microsecond

Solid antennas have more ideal characteristics but are troublesome because of weight and

high wind load. Mesh and wire types weigh less, are easier to construct and have nearlyideal characteristics if the holes or gaps are kept under 1/10 of the wavelength.

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Antennas

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The antenna is a conductor which enables electromagnetic waves to be sent and received

by a system

The output from a coherent source (e.g. an oscillator) is directed out into free space using

an antenna. The signal source is linked to the antenna by some kind of waveguide(microwave guide, light fibre, or whatever). The antenna acts as a sort of transformer. It

takes the electromagnetic field pattern, moving along the guide and transforms it into

some other pattern, which is radiated out into free space.

An antenna does not produce the power- it is a passive device. It also has the

characteristic of reciprocity

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RR is the antenna's Radiation Resistance value; it represents the antenna properties which

allow power to radiate away. R is the Loss Resistance; it represents the ways power isdissipated, warming up the antenna. X is the antenna reactance; this represents any ways

the antenna can store energy, returning it to the generator after a delay.

For a perfect antenna

Zg = RR , R = 0 , and X = 0

Antenna Near FieldThe close-in region of an antenna where the angular field distribution is dependent upon

distance from the antenna. The limit is usually defined by 2D 2/

Antenna equations

Beamwidth radiansD

=

3

RZg Rg

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Gain2

4

effA

Far field at

22D

Fresnel Zone radius21

21

dd

dd

+

4

d1

1000m

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The maximum recorded levels are around 0.869 mW/cm2 This is 33% of the NationalRadiological Protection Board (NRPB) power density level. However, it is 4.3 times the

International Commission for Non-ionising Radiation Protection (ICNIRP) power density

level or more than twice the ICNIRP voltage level.

In the report the MoD state:

(para 4 on p. Ev60) "It should be borne in mind that UK safety thresholds are based on

NRPB guidelines and not those of ICNIRP..."

The Ripoff antenna provides high gain omnidirectional coverage using the earth andionosphere as a waveguide. It operates at 200GHz and incorporates the latest ripoff

technology so it is especially useful in high noise areas and underground.

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Parabolic Antenna

The feed is located at the focus of the parabola and directs radiation onto the dish.Position of feed is such that the the phase of the radiation at every point in the plane of

the aperture is the same. Antenna is simple and relatively inexpensive to make

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Phased Arrays

Until the 70's, radars used reflector antennas which were rotated to allow beam steering.Then phased array antennas with a multiplicity of radiating elements, each equipped with

phase control, were introduced. They allowed much faster electronic beam steering to

detect and to trace targets, and to help reduce interfering signals.The main constituents of such antennas are the radiating elements, the amplifier modules

and the beam formers. Unlike passive arrays, they can generate several beams

simultaneously. Phased array and active phased arrays have a great potential forcommunications applications, for example to track a communications satellite from a

moving vehicle, ship or aircraft, or to track a mobile phone user from a cellular base

station..

2 dipoles Radiation Pattern

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le Dipole Radiation Pattern

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2

isotropes 1/4apart in phase 2 isotropes 1/2apart in phase

2

isotropes 1 apart in phase 2 isotropes 6apart in phase

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2 isotropes 1/2apart antiphase

4 isotropes 1/4apart in phase9

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A wave guide slot array antenna designed for real aperture radar

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aveguide slot array for a radar

hased array

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Types of Electronically Scanned Antennas (ESAs)

Passive

An electronically controlled phase shifter is placed immediately behind each radiating

element. The phase shifter is controlled by a processor.

Active

This is much more complex than a passive ESA. Each element of the antenna has its own

transmit/receive module. This module contains a multi-stage high power amplifier, a

duplexer, a protection circuit to block leakage from the transmit to the receive part of themodule, and a low noise amplifier. Each of these devices can be implemented with

integrated circuits. As the LNA and HPA are placed immediately behind the radiators the

noise of the device is considerably better than the passive equivalent. Additional

advantages include:

Amplitude as well as phase can be controlled

Multiple independent steerable beams can be provided

Different frequencies uses the same aperture can be used

Each transmit module can use a reliable SSPA rather than a TWT

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F35Northrop Grumman Electronic Systems is developing the advanced electronically

scanned array (AESA) AN/APG-81 multi-function radar. The AN/APG-81AESA willcombine an integrated radio frequency subsystem with a multifunction array. The radar

system will also incorporate the agile beam steering capabilities developed for the APG-

77.

Other Types of Antenna

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BladeFeed array

helix patch

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Yagi Antenna

GT = 1.66 * N

Where N is the number of elements (dipoles) in the Yagi-Uda antenna.

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