Cassegrain antenna

About: Cassegrain antenna is a research topic. Over the lifetime, 3207 publications have been published within this topic receiving 28278 citations.

Study of efficiencies and phase centers of broadband log-periodic feeds for large offset dual-reflector antennas using formulas for bodies of revolution (BOR/sub 1/ extraction)

Abstract: The Allen Telescope Array (ATA) is a new instrument being built by the SETI institute. It is an array of offset Gregorian reflector antennas with a very large bandwidth, covering 0.5 GHz to 11 GHz. The feed consists of four log-periodic arms, together forming a pyramid. In the center of the pyramid, a metallic pyramid is located, holding low noise amplifiers and cryogenics. We present a method for analyzing dual reflector systems based on BOR/sub 1/-extraction and use it to analyze the performance of the ATA feed in the offset Gregorian dual reflector. With a good corrugated feed in a paraboloid or Cassegrain antenna, the spillover efficiency is typically around -0.5 dB for the subtended angle giving the highest efficiency. The spillover efficiency for the ATA feed is around -1 dB, which is caused by high sidelobes. In order to increase the performance of the system, the sidelobes should be reduced. We have found that 0.5 dB gain can be accomplished by changing the shape of the ground pyramid in the center of the feed to a cone. This reduces the spillover and increases the BOR/sub 1/ efficiency. With optimized placement of the feed in the reflector, the reduction of phase efficiency due to phase center movement is better than -1 dB. Considering the bandwidth of the feed, this is very good.

Variable beamwidth dual reflector antenna

Abstract: The growth of remote sensing by an airborne platform and the use of satellite communication from elliptical orbits indicate the need for a reflector antenna where the beamwidth of the main radiation pattern can be varied dynamically. The requirement is to make the radiated beam spot diameter independent of the antenna platform height and the scan angle. There are various other applications at microwave and millimetre wavelengths where a uniform footprint or precise changes in the beam spot diameter are required, for example, metrology from satellites, fire control radars and military communications. This paper describes a variable beamwidth dual reflector antenna which fulfils their specification. Parametric studies and an experimental verification of the concept are performed.

Cross-polarization in satellite and earth-station antennas

Abstract: Cross-plarization in axially symmetric reflector antennas can be reduced, theoretically, to zero by use of special feeds like the Huygens' source. Alternatively, paraboloidal reflectors with large f/D ratio do not deteriorate further the cross polarization level relative to the value due to the feed itself. The Cassegrainian optics is equivalent to a large f/D paraboloid. The reflector of linearly polarized off set fed antennas contribute more cross-polarization than symmetrical reflectors fed by the same feed. With symmetrical reflectors the cross-polarized component generated by the reflector vanishes in the principal planes and is confined to four main lobes that have peak values in planes at 45° to the principal planes. In the case of offset fed reflectors cross-polarization vanishes in the plane of symmetry and has its peak in the plane of asymmetry. The reflector generated cross-polarization with offset fed antennas may be reduced by use of small offset angles and large f/D ratios. Feed offsetting has but little effect on the peak level of cross-polarization. This is usually accompanied with an asymmetry in the cross-polarization radiation pattern. Feed offsetting also results in spatial tilt in the copolarized and cross-polarized lobes with the cross-polar minimum always coinciding with the main beam peak. The effect of surface errors on the antenna cross-polarization is to partly fill the cross-polar along boresight. The peak cross-polarization, however, changes but slightly.

A Reconfigurable Satellite Reflector Antenna

Abstract: The paper describes a means to change the coverage zone of a spacecraft antenna by reconfiguration of the reflector surface. By using a realistic model for an offset mesh reflector, reconfiguration is successfully demonstrated for the case of two future INTELSAT regional beams. Suggestions are made concerning both the mesh characteristics and the means by which it might be controlled.