A holographic technique for millimetre-wave antenna near-field/far-field transformation

The move to higher operating frequencies in communication systems has presented new problems in the measurement of antenna radiation patterns. At millimetre wave frequencies, for electrically large antennas, the many benefits of conventional near-field techniques become outweighed by the need to acquire excessively large data sets and by the difficulties in measuring the phase of the received signal. The semicompact antenna test range (SCATR) has been proposed to solve the former problem and its use has previously been validated at 35 GHz. The paper addresses the remaining problem and describes a new scheme which avoids the measurement of phase by utilising the well-known holographic principle. The approach presented differs from previous holographic antenna measurements in that it is applied over a complete cylinder in the close near-field region. Furthermore, interpolation techniques are used to sample the data as a function of sin cp, where cp is the cylindrical angular co-ordinate. This procedure is found to be particularly beneficial in extracting the required phase information from the holographic data. The scheme also proposes the possibility of offsetting the antenna under test (AUT) from the centre of the turntable so that a desirable constant reference signal can be employed from coaxial cable or a beam waveguide system