Cassegrain antenna

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

The higher order modes in the feeds of the satellite monopulse tracking antennas

Abstract: Corrugated horns have been widely applied as optimum feeds for reflector antennas due to the characteristics associated with their rotationally symmetric radiation field patterns which have very low side lobe and cross-polar levels. Most ground stations now use Cassegrain antennas with conical corrugated feed horns for satellite tracking and control as they are optimum systems which can support high gains, better efficiencies, and low cross-polar components. These systems utilize the hybrid HE/sub 11/ mode for the main signal and one or two of the following modes, TM/sub 01/, TE/sub 01/, (HE/sub 21/ or TE/sub 21/) for creation of the error signals that are used by the automatic tracking units to derive the angular tracking information. The antenna systems use both the TM/sub 01/ and TE/sub 01/ modes for monopulse tracking. Nearly all the antenna systems now extract the tracking information from the HE/sub 21/ or TE/sub 21/ modes in corrugated or in smooth waveguides respectively. The. tracking mode sensor extracts the higher-order-mode signal from a circular overmoded waveguide section following the corrugated antenna feed. It is explained how the tracking information can be extracted from the HE/sub 21/ or TE/sub 21/ signals.

A Simplified Feed Model for Investigating the Cross Polarization Reduction in Circular- and Elliptical-Rim Offset Reflector Antennas

Abstract: An analytic model for the primary feed of offset reflector antennas is presented that facilitates a more general investigation of the cross polarization reduction in both asymmetric and inter-cardinal planes. It includes both first and second order azimuthal modes, primarily the TE11 and TE21 type modes, and allows selection of symmetric and asymmetrical patterns, with different field tapers in the principal planes. Using this model first the influence of the second order TE21 mode on the cross polarization of an offset reflector with a circular rim is investigated. Then, the problem for an offset reflector with an elliptic rim is also studied. It is shown that minimizing the cross polarization in the asymmetric plane does not necessarily reduce it globally, as in the inter-cardinal plane it remains high. The procedure for reduction of the cross polarization globally and its effects on the sidelobe levels of the reflector antenna are also investigated. With the proposed feed model, the aperture efficiency of the reflector antenna is improved compared with a standard Gaussian feed with the same edge taper. Based on this study, a dual-mode circular waveguide horn is also proposed and designed. Its performance on an offset reflector antenna is studied and shown that the cross polarization levels are reduced quite satisfactorily within a respectable frequency band.

L-band radar antenna array

Abstract: A stripline horizontally polarized dipole and passive director antenna ar, operative at L-band (1220-1280MHz), mounted in a 90° corner reflector constructed of a grid of cylindrical rods which are hinged along its apex permitting folding of the reflector over the antenna array to protect the elements of the array, for example, during transport.

Cylindrical antenna coherent feed system and method

Abstract: Systems and methods are disclosed for illuminating multiple columns of antennas to provide a desired wave front without introducing non-coherent combining. The preferred embodiment feed network provides elevation scanning for a multiple beam antenna system on a per antenna beam basis. In a preferred embodiment columns of antenna elements are divided into phase-centers having a relative phase shift introduced there between. Phase differentials are introduced into the antenna beam signals of each phase-center of antenna elements in order to provide a phase progression which steers the antenna beam a predetermined angle from the broadside. The phase differentials are independently provided for each antenna beam signal to thereby allow independent steering of each antenna beam.

The ALMA Front End Optics—System Aspects and European Measurement Results

Abstract: The Atacama large millimeter/submillimeter array (ALMA) is a radio telescope array with 50 Cassegrain style antennas that is currently being built in the Atacama desert in Chile. The telescopes are designed for a frequency range from 30 to 960 GHz with two orthogonal linear polarizations. Due to the extremely wide range, ten receivers are needed to cover the band, the divisions coinciding with the atmospheric windows. All receivers are built into a common cryostat on separate cartridges. The front end optics include the optical elements between the mixers and the secondary reflector. There are three different generic optical layouts. The two lower frequency bands use lenses that double as vacuum breaks. The next two frequency bands use ambient-temperature mirror systema and the upper six frequency bands have their complete optics cooled to cryogenic temperatures. In addition to the very demanding performance requirements, the optics design needs to take into account the constructional and operational aspects. As a large number of front ends will be built, the design must be robust with respect to mechanical and alignment tolerances. The exchange of receivers must be easy and should require as few alignments as possible. During operation, no mechanical adjustments are allowed. Measurement results are shown for the ALMA baseline bands. These measurements were made for single cartridges with the IRAM near-field measurement system and at SRON. The results of these measurements validate the design approach.