Independent control of sum and difference patterns in active phase array antennas

For active arrays, the sum beamformer is often used for transmit where approximately equal power is needed at the module inputs, and weighting for the receive sum signal is done in the element modules using variable gain amplifiers (VGAs). A baseline architecture of the T/R module is shown. The amplitude weighting for the receive sum signal must be compensated in the design of the difference combiners. While the coupling values of the circuits within the sum and difference combiners are different, the circuit topology is identical to preserve phase tracking of their monopulse signals. With the advent of the GaAs MMIC (monolithic microwave integrated circuit) technology, it is now possible to provide a separate VGA and phase shifter for each monopulse beam. A block diagram of a module incorporating such a configuration is shown.<>