University of California, Radio Astronomy Lab, …（加州大学射电天文学实验室,u2026）.pdf

Non-planar log-periodic antenna feed for integration with a cryogenic microwave amplifier G. Engargiola University of California, Radio Astronomy Lab, Berkeley, CA 94720, greg@ 1 Introduction 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. Moreover, in contrast to a horn, an LP is a large open structure, requiring a long twin-lead or coaxial cable to carry signals away from the near field region, before amplification. Loss in such cables can be greater than 1 dB, contributing more than 60 K to the receiver noise temperature. Also, motion with frequency of the phase center along the antenna axis may require a mechanical actuator to move the feed into focus for good illumination efficiency of the telescope. Figure 1a. Photograph of prototype log-periodic This paper describes a non-planar log-periodic antenna feeds, LP1 (left) and LP2 (right). LP2 antenna feed to which cryogenic electronics can has a finline attached to the inner face of each be attached without the need for a long, loss