Sidelobe suppression considerations in the design of an electronically steered IFF antenna

This paper deals with considerations in the design of an electronically steered IFF antenna which is to provide sidelobe suppression through the use of a difference beam with gain higher than that of the sum beam everywhere outside of the mainlobe region. The influence of the suppression requirement upon illumination design tradeoffs in beamwidth, sidelobe levels, and taper efficiency is demonstrated theoretically for an array restricted to 16 elements. The sidelobe suppression performance for this array, with appropriate choices for amplitude taper, number of phase shifter bits and randomizing phase function, is examined in detail for susceptibility to failures in elements, failures in individual phase shifter bits, and random phase and amplitude illumination errors. In the case of random errors, performance variability with steering direction is examined and a criterion involving the radiation patterns at both the transmit and receive RF frequencies is defined as a measure of performance. It is seen that the design analyzed is successful in reducing the corresponding performance degradation to very low levels in even the worst cases. Expressions are presented for estimating the effects of increasing the number of elements upon improvements in performance in the presence of component failures or random errors.