Cassegrain antenna

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

A Dual-Focus Reflector Antenna for Spaceborne SAR Systems With Digital Beamforming

Abstract: Future spaceborne synthetic aperture radar (SAR) missions shall benefit from digital beamforming (DBF) techniques with the goal of generating high-resolution wide-swath imagery. The basic idea is to replace parts of the analog receiver hardware by digital components, increasing the flexibility of such systems. The limited transmit power rises the need of large antennas capable of electronically steering the antenna beam over a large angular domain. An innovative concept is the usage of large unfoldable mesh-reflector antennas in combination with digital feed arrays. An inherent problem of such systems is, that every feed element illuminates, after reflection from the main reflector, an essentially non-overlapping angular domain in the far field. In case of an element failure the radar system would be `blind' in the specific direction. To circumvent costly redundant receiver hardware a new approach to increase the reliability of such systems has been studied. The approach is based on a so called defocused reflector which grants visibility of the complete angular domain under failure conditions. This article presents the electromagnetic considerations leading to the defocused reflector concept. The performance of the defocused reflector system is evaluated in comparison to a conventional parabolic reflector system, utilizing digital beamforming techniques.

Analysis of radiation pattern and G/TA for shaped dual-reflector antennas

Abstract: An accurate calculation of the radiation pattern from shaped Cassegrain-type dual-reflector antennas is given. In the forward axial region this is achieved by using the classical methods of physical optics and aperture field. Elsewhere we use the g.t.d. in the analysis, utilising a recent solution for the double knife-edge diffraction phenomenon between the two reflector edges. The result is used to compute the antenna temperature TA at a number of frequencies in the 1–100 GHz region commonly used for radio astronomy and space communications. The use of shaped reflector profiles to maximise G/TA consistent with other requirements such as acceptable sidelobe levels is discussed.

Analysis of Offset Antennas in Radio Telescopes

Abstract: We present an analysis on the performance of two popular dual offset antennas design, i.e. the offset Cassegrain and Gregorian reflector antennas. In our study, we have adopted the design parameters for the Cassegrain configuration used in the Atacama Large Milimeter Array (ALMA) project. Modifications on the original parameters are made so as to meet the design requirement of the offset configurations. To reduce spillover loss, we have adjusted the angle between the axis of the primary reflector and that of the sub-reflector to 0.20o. The results obtained from the physical optics computation show that the amplitude at the main lobe of the Gregorian configuration is approximately 74.02 dB, while that of the Cassegrain configuration is approximately 74 dB. The maximum (relative) side lobe level, SLLdB for the Cassegrain and Gregorian configurations are found as -3.67 dB and -3.69 dB respectively. Although the magnitude of the main lobe for both configurations is comparable, the Gregorian antenna gives relatively lower SLLdB. In other words, the Gregorian configuration performs relatively better than its Cassegrainian counterpart.

Analysis of radiation patterns and feed illumination of the reflector antenna using the physical and geometrical optics

Abstract: Reflector antennas are characterized by very high gains (30 dB and higher) and narrow main beams. They are widely used in satellite and line-of-sight microwave communications as well as in radar. Reflector antennas operate on principles known long ago from the theory of geometrical optics. The first reflector system was made by Hertz back in 1888 (a cylindrical reflector fed by a dipole). The radiation fields from aperture antennas, such as slots, open-ended waveguides, horns, reflector and lens antennas, are determined from the knowledge of the fields over the aperture of the antenna. In this paper, we analyzed the effects of feeds relating to the parabolic reflectors such as waveguide and horn. We show the variations of the gain in the electric and magnetic planes (E and H) according to the angle of incidence. In our case, we use the origin to be at the focus.

Optical-mechanical scanning antenna device used for scanning imaging

Abstract: The invention discloses an optical-mechanical scanning antenna device used for scanning imaging. The optical-mechanical scanning antenna device used for scanning imaging comprises a main reflecting surface (6), a feed source (5), an auxiliary reflecting surface (7), a spinning motor (3) and a detector, wherein a certain angle is formed between the central axis of the auxiliary reflecting surface (7) and the central axis of the main reflecting surface (6). According to the optical-mechanical scanning antenna device used for scanning imaging, due to the fact that the auxiliary reflecting surface of a Cassegrain antenna is inclined by a certain angle, antenna wave beams deviate from the central axis of the main reflecting surface by a certain angle; due to the fact that the inclined auxiliary reflecting surface spins around the central axis of the main reflecting surface of the antenna, circular scanning is achieved through spinning of the antenna wave beams which deviate from the central axis of the main reflecting surface by the certain angle.