Digitally Controlled 10.5 GHz Complex Weight Circuit for Null Steering Arrays

Null steering array antennas require proper selection of the amplitude and phase on the excitation of each element. This paper describes a microstrip PIN-diode circuit that is capable of changing amplitude and phase at X-band frequencies. The device consists of a pair of variable attenuators and one-bit 180°phase-shifters. Digital control circuits have been built that use pre-stored calibration data. Measurements indicate that accurate attenuation and phase change can be obtained over all four quadrants of the complex plane.