Far field

Category: 

Far-field measurements

Overview

No deadband

Antenna characteristics and parametres measurement in far field can be conducted as in outdoor or indoor ranges. In any case testing and subsidiary (transmitting) antennas should be installed in a distance, that is the borderline of far field.

D — antenna’s dimension
λв — wavelength, equal to the upper frequency of spectrum

An advantage of measuring with the help of short pulse signals is that measurement of output signals of testing antenna is conducted in limited time interval, called time window. It allows to select radar clutters effectively. In addition, minimal time window (necessary time for useful signals registration)is determined by pulse width characteristic of antenna.

On this basis, the required antenna height is determined:

τ — length of pulse antenna characteristic;
c — light speed.

During the measurement of antenna pattern, the testing antenna ritates round the bearing turning device in two angles (azimuth and place angle). While measurement of diagram flat sections, the turning is carried on azimuth only, and testing and subsidiary antennas are set for measurement the required polarization field component in the required flatness.

The subsidiary antenna radiates short ultrawideband pulse signal. Signals and their complex spectra are registered in testing antenna output. Based on complex spectra, the required characteristics and parameters of the testing antenna are defined simultaneously in the whole operating frequency band without generator rearrangement of probing signal.

Measurement parameters:

Amplitude pattern
Phase pattern
Gain
Polarization
Position phase center

Major elements:

UWB programmed stroboscopic receiver in standard 19-inch package Ulta short pulse generator
Programmed positioner
Transmitting antennas set
Reference antennas set
Windows® operating system 9x/Me/XP/2000

Technical characteristics

Parameter name Parameter meaning
Frequancy 50 MHz-18 GHz (30, 40 GHz)
Amplitude range >76 dB (>90 dB with interpolation)
Amplitude pattern and Gain measurement accuracy-in range to -25dB-in range to -40dB < 0,2 dB < 0,35 dB
Phase pattern measurement accuracy — in range to -25 dB — in range to -40 dB < 2° < 3,6°
Angular resolution 2 angular minutes
Load on the positioner to 500 kg
Amplitude pattern and Phase pattern measurement time at one place angle from 1 minute