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Required Equipment in Antenna

Measurements For antenna test equipment, we will attempt to illuminate the test

antenna (often called an Antenna-Under-Test) with a plane wave.This will be approximated by using a source (transmitting) antennawith known radiation pattern and characteristics, in such a way thatthe fields incident upon the test antenna are approximately planewaves

The required equipment for antenna measurements include:

A source antenna and transmitter - This antenna will have a knownpattern that can be used to illuminate the test antenna

A receiver system - This determines how much power is receivedby the test antenna

A positioning system - This system is used to rotate the test

antenna relative to the source antenna, to measure the radiationpattern as a function of angle.

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The Source Antenna should of course radiate well at the desired testfrequency. It must have the desired polarization and a suitable beamwidthfor the given antenna test range.

Source antennas are often horn antennas, or a dipole antenna with aparabolic reflector.

The Transmitting System should be capable of outputting a stable knownpower.

The output frequency should also be tunable (selectable), and reasonablystable (stable means that the frequency you get from the transmitter isclose to the frequency you want).

The Receiving System simply needs to determine how much power isreceived from the test antenna.

This can be done via a simple bolometer, which is a device for measuringthe energy of incident electromagnetic waves. The receiving system canbe more complex, with high quality amplifiers for low powermeasurements and more accurate detection devices.

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The Positioning System controls the orientationof the test antenna. Since we want to measurethe radiation pattern of the test antenna as afunction of angle (typically in spherical

coordinates), we need to rotate the test antennaso that the source antenna illuminates the testantenna from different angles. The positioningsystem is used for this purpose.

Once we have all the equipment we need (and anantenna we want to test), we'll need to place theequipment and perform the test in an antennarange, the subject of the next section.

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The first thing we need to do an antenna measurement is aplace to perform the measurement. Maybe you would liketo do this in your garage, but the reflections from the walls,ceilings and floor would make your measurementsinaccurate. The ideal location to perform antennameasurements is somewhere in outer space, where noreflections can occur. However, because space travel iscurrently prohibitively expensive, we will focus onmeasurement places that are on the surface of the Earth.There are two main types of ranges, Free Space Ranges and

Reflection Ranges. Reflection ranges are designed such thatreflections add together in the test region to support aroughly planar wave. We will focus on the more commonfree space ranges.