Reduction of amplitude-phase distortions of movable microwave coupling circuit for antenna field measurements

A radio holography system for measuring the amplitude-phase distribution of antenna fields in the aperture is described. The system incorporates a movable microwave coupling circuit between the amplitude-phase meter and the scanning probe which is designed to prevent the amplitude-phase distortions of the microwave circuit from influencing the measurement results. This is achieved by determining the instabiliy of the electrical length of the circuit at every moment and accordingly correcting the measurement results by computer. The block diagram of the system is presented, and the transformation of the signal as it passes through the system is analyzed. In order to reduce errors caused by signals reflected from the metal surfaces of the microwave devices, all metal members of the scanner are coated with an absorbing material. By doing this, the total error resulting from the added microwave devices does not exceed a few tenths of a degree in phase, and approximately 0.1 dB in amplitude.