The basic numerical steps of a method to analyze dual offset reflector antennas are reviewed. The technique employs an alternative approach to calculating the secondary pattern of an arbitrarily shaped offset dual reflector antenna, and is based on the application of the geometrical theory of diffraction from the subreflector and physical optics (PO) scattering from the main reflector. The PO integral is evaluated using the Jacobi-Bessel series expansions, and numerical results are presented for the off-axis scan performance of an offset clear aperture Cassegrain antenna. Results indicate that the equivalent paraboloid concept can be used to determine the location of displaced feed and define the local optimal focal plane, and the scan performance of the Cassegrain reflector can be improved if the feed is located on the true opimal surface.

Scan performance of dual offset reflector antennas for satellite communications

This paper presents the results of a study to determine the satellite capacity enhancement obtainable by using syllabic compandors. Syllabic companding applied to the speech channels of tDDM-rm carriers can increase satellite capacity by as much as 100 percent, depending on the number of channels per carrier. Syllabic compandors presently produced by integrated circuit technology are small and inexpensive. Compandors permit a higher level of satellite circuit noise and hence an FM index (and bandwidth) which is smaller than that required for uncompanded channels. The results presented in the paper are based on compandor advantage measurements and singleand multi-channel amplitude distribution measurements for both companded and uncompanded speech signals. For data transmission, it is estimated that about 2-dB degradation may be encountered when long terrestrial access circuits are interconnected via a companded satellite circuit for international transmission. *This paper is based upon work performed at COMSAT Laboratories under the sponsorship of the International Telecommunications Satellite Organization (INTELSA r).

Enhancement of FDM-FM satellite capacity by use of compandors

http://ieeexplore.ieee.org/iel6/8251/25856/01148516.pdf

Optimum feed locus for general three-dimensional beam scanning in offset Cassegrain antenna

http://ieeexplore.ieee.org/iel6/8250/25855/01148322.pdf

D. DiFonzo

Papers

Optimum feed locus for beam scanning in offset Cassegrain antennas