Impact of Delays on Antenna-Array Noise

Abstract

Antenna arrays are increasingly being used in radio telescopes that operate with large bandwidth and demand very-low-noise performance. Designing the receivers for these telescopes involves the use of equations that were developed for narrowband receivers. One of the impeding factors in receiver design is array mutual coupling that degrades system noise performance. The effects of mutual coupling can be mitigated completely, provided the receiver is designed to noise match the active array for a single scan direction. This type of matching was developed for narrow band receivers where signal delays between antennas can be safely ignored. This work develops equations and techniques for matching wideband active arrays to the receiver while taking into consideration the propagation delays in the array that become relevant with large bandwidth. Matching the receiver to the active array requires matching the individual LNA separately to the active array, which is not ideal. For this reason, matching the active array to identical LNAs while minimizing receiver noise is also explored. The equations developed are verified using simulation of antenna arrays designed for radio astronomy use. Finally, minimizing array noise for multiple scan directions while using identical LNA in the receiver is discussed.