Non-planar log-periodic antenna feed for integration with a cryogenic microwave amplifier

The bandwidth of a microwave reflector telescope is limited by the size and figure accuracy of the mirror elements and by the feed which couples focused radiation to the receiver. A single or hybrid-mode feedhorn can efficiently illuminate a telescope aperture with low ohmic loss. Its gain varies quadratically with frequency, however, limiting its effective bandwidth to less than an octave. A log-periodic antenna (LP) can illuminate a telescope aperture over multi-octave bandwidths, but it has greater spillover and ohmic loss than a well-designed feedhorn. This paper describes a non-planar log-periodic antenna feed to which cryogenic electronics can be attached without the need for a long, lossy section of transmission line. With appropriate reflector optics to minimize defocusing with phase travel and baffles to redirect sidelobes onto the sky, this antenna offers a low noise, wideband alternative microwave feed for astronomical and SETI applications. It is currently being adapted for use on the Allen telescope array.