Multi-Mode Array Feed Operations with the Westford Radio Telescope

This article describes a new UHF Multi-Mode Array Feed (MMAF) built for the Westford Radio Telescope. The MMAF consists of a dual-linear focal plane array installed con-centrically with the existing cryogenic Ultra-Wideband (UWB) feed on the telescope. This combined system is capable of transmit or receive on UHF radar and satellite communications frequen-cies between 400 and 500 MHz simultaneous with reception from 2 to 14 GHz. To the authors' knowledge, the MMAF represents the first demonstrated use of a concentric eleven-style feed topology to extend the capabilities of a preexisting antenna system to lower frequencies. The multiple degrees of freedom provided by the MMAF also enable advanced capabilities at UHF for dynamic beamforming and spatial filtering to suppress interfering signals. This enables a user to maximize signals of interest for radar or communications, as well as enabling determination of spatial separation for signal sources. Simple algorithms to maximize the SNR of satellite downlinks and suppress unwanted Radio Frequency Interference (RFI) sources have been demonstrated that can be run in real time with consumer grade software radios and computer hardware.