Cancelling non-linear processing products due to strong out-of-band interference in radio astronomical arrays

Radio astronomy instrumentation uses phased array feeds to provide radio telescopes with wider fields of view and enhanced beam control for detection and interference suppression. The standard assumption in Radio Astronomy is that receiver amplifiers operate in a linear region. In the presence of strong radio-frequency interference (RFI), however, it is possible to drive the amplifiers non-linear. This can cause out-of-band RFI to become non-linear and mix harmonics into the filter passband. In this scenario, classical RFI-mitigating beamformers may not be very good at suppressing the interference. This paper analyzes the effect of several beamformers in suppressing interference resulting from non-linear amplifiers. Experimental results show that a subspace projection beamformer is able to suppress the interference despite the nonlinear RFI.