Reactively steered adaptive array using microstrip patch elements at 4 GHz

Experimental and theoretical results are presented for a Reactively Steered Adaptive Array (RESAA) consisting of five microstrip rectangular patch elements resonant at 4.0 GHz. RESAA differs from other adaptive arrays in that only a single element is connected to a receiver, and the RESAA pattern is formed according to the values of the reactive terminations on the remaining elements which are parasitics. Instrumental measurements and an adaptive control simulation were performed using the steepest descent algorithm of Bekey and Karpens (1968) to adjust the terminations. The results demonstrate that a useful degree of pattern control can be achieved. It was found that in a power inversion mode a null with a depth of 30 dB and width of about 25 deg can be steered toward an interferer, with minimal distortion of the pattern towards other directions; and that in a mode using a reference signal the pattern can be shaped to steer a null toward interference and a lobe toward a desired signal. The nulling bandwidth is 40 MHz. An estimate shows that a beamforming time of 1.6 ms could be achieved by using a microprocessor controller. The advantages and disadvantages of the RESAA are discussed.