Range Distance Requirements for Large Antenna Measurements for Linear Aperture with Uniform Field Distribution

Gain reduction on measurement of distance and on sizes of test and probe antennas are discussed. We consider only the case of linear antenna with uniform field distribution. The analysis is based on time-domain (TD) physical optics (PO) method of field calculation [1]. We show that in determining the level of the side lobe there are two competing effects: (i) the decrease in the amplitude of the signal in the direction of the side lobe and (ii) reducing the maximum signal level in the direction of zero-angle. We show the optimal measurement distance with respect to the acceptable small errors of antenna gain. It is shown that optimal relation beta = b/a is about similar to 0.4 (a and b are the sizes of the antenna under test and the probe antenna). For this optimal relation, the well-known far-field distance criterion R-0 = 2D(2)/lambda can be reduced by 2 times (D is the diameters of the antenna under test and lambda is wavelength). Note that when b is optimal, the errors in determining of the sidelobe levels are also small and do not exceed 0.5 dB.