Cassegrain antenna

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

Adaptive beamforming with a multiple beam antenna

Abstract: Adaptive array processing is seen as one possible solution to the severe bandwidth and power restrictions in a communications system between a geostationary satellite and a mobile terminal. This paper considers the use of an offset parabolic reflector with an array feed, referred to as a multiple beam antenna (MBA), as a way of combining the high gain of the reflector with the spatial filtering ability of the antenna array. A signal model is developed in which the key quantity is the steering vector which represents the response of the antenna array to a plane wave arriving from a given angle. The steering vector for the MBA is found numerically by finding the secondary field of each of the antenna elements, and then using the principle of reciprocity to relate this field to the received amplitude. Statistically optimum beamforming on the MBA is demonstrated followed by a simulation of the direct matrix inversion (DMI) algorithm.

Investigation of Virtual Array Antennas With Adaptive Element Locations and Polarization Using Parabolic Reflector Antennas

Abstract: A novel multi-phase center parabolic reflector antenna is investigated that utilizes a single hardware system to displace the antenna phase center location electronically in any direction, while generating identical broadside secondary radiation patterns at the far-field region to convert the reflector antenna into a virtual array. The primary feed is a dual-mode circular waveguide operating at the TE11 and TE21 type modes. The combination of these modes with different polarizations, amplitude ratios, and phase differences are considered. It is shown that the phase center location of the antenna can be displaced from the physical center of its geometry by changing the excitation amplitude and phase of each mode, and more importantly by employing different mode orientations. This results in a virtual array antenna with element locations that can be displaced in any direction, depending on the polarization of each mode, by a simple signal processing procedure without mechanically moving the antenna itself. The antenna developed using this technique has potential applications as a transceiver antenna in precise positioning systems, radars with moving platforms, and virtual smart antennas. The operating frequency is 10 GHz. The proposed multi-phase center virtual antenna concept is verified experimentally exhibiting excellent agreement with the numerical results.

Reflector surface error compensation in cassegrain antennas

Abstract: Two focal plane parabolic reflectors 2.8 m in diameter were used to test the feasibility of compensating for reflector surface profile errors by figuring the surface of a Cassegrain mirror. The paraboloids had been designed originally for frequencies less than 7 GHz, and therefore the surface errors had a significant effect on the antenna performance in the 27-40 GHz range. For these frequencies a template could be used to measure the surface profile. The first reflector had a prominent axially symmetrical surface error component. Compensating for this alone simplified the construction of the subreflector and improved the overall aperture efficiency at 34 GHz from 12 percent to 24 percent. The second reflector had a more random distribution of surface errors. Its efficiency was improved from 35 percent to 48 percent at 34 GHz, the improvement in gain varying from 1.1 dB at 28 GHz to 2.3 dB at 40 GHz, the shortfall being within 1 dB of the possible improvement predicted from the measured surface errors. For both reflectors the illumination efficiency set by the feed horn was about 50 percent. The linear cross polarization discrimination on axis increased from 29 dB to 38 dB at 34 GHz. The sidelobe levels and gain improvement obtained suggest that effective rms errors of about 0.45 mm with correlation distances of about 30 cm remained on the reflector surface after compensation, consistent with the estimated accuracy of the measuring and construction techniques adopted.

Hybrid array fed reflector antenna solution for broadband satellite communications

Abstract: An hybrid array fed reflector antenna solution is described in this paper, combining a focused geometry in one plane and an imaging (defocused) geometry in the orthogonal plane This doubly curved reflector geometry can be combined with a stack of linear phased arrays, introducing some re-configurability at a moderate cost when compared to more conventional imaging reflector solutions using planar phased arrays A simple analytical formulation is derived to define the proposed doubly curved surface and numerical results are presented for a multiple beam mission at Ka-band This hybrid antenna solution is considered of interest for broadband payloads to be embarked on future communication satellites

Design of high efficiency Fresnel zone plate antennas

Abstract: With a family of ideal radiation patterns, the theory for designing high-efficiency phase-correcting FZP (Fresnel zone plate) antennas is presented. The optimum 3-dB beamwidth of the feed pattern as a function of F/D (focal length/diameter) of the plate, the relation between the phase efficiency of the antenna and the number of subzones used in each full-wave zone, and the total efficiency limits of various versions are given. It is found that the maximum efficiency of a practical FZP antenna is usually less than 70%. The theory has been employed in designing a four-layer experimental FZP reflector antenna, and good agreement between the theoretical expectation and the measured value is obtained. >