Intermediate frequency transmit/receive modules for low-sidelobe phased array application

Low sidelobe performance in a small, active phased array requires very tight amplitude and phase tolerances in the transmit/receive (T/R) modules and beamforming network. An L-band T/R module is described in which the required precision is realized through the use of 12-b, voltage-controlled attenuators and phase shifters operating at an intermediate frequency rather than at a radio frequency. All control voltages are derived from a single multiplexed 12-bit D/A converter. The modules were evaluated in a 32-element, linear array. Near-field measurements proved that the amplitude and phase of array elements could be set with errors of less than 0.02 dB and 0.2 degrees RMS. Antenna patterns were obtained with average peak sidelobes at least 35 dB below an isotropic radiator