Characterization of dense focal plane array feeds for parabolic reflectors in achieving closely overlapping or widely separated multiple beams

Abstract

[1] In the advent of modern mobile satellite communications requiring rapid and adaptive multiple beams, this work studies the ability of reflector antennas fed by dense focal plane arrays (FPA) in achieving arbitrarily shaped and sized footprints to meet the demands. In this paper, the efficiencies of single off-axis as well as multiple beams of FPA-fed paraboloids are investigated. The offset FPA considered here comprises hard rectangular waveguides. The focal plane field, which the FPA samples, is synthesized by integration of the physical optics induced electric currents over the reflector surface caused by the off-axis incident plane wave arriving at that incidence angle of interest. Full mutual coupling analysis has been performed in the FPA sampling, thereby taking into account mutual coupling losses in the arrays. The fields over the tilted elliptical aperture of off-axis beams needed for calculation of the aperture efficiency are obtained by projecting the usual focal plane fields to this tilted aperture using geometrical optics. Results show that the total efficiency of the offset FPA-fed reflector decreases with increasing beam angle and increases with larger number of FPA elements. It is also found that the maximum directive gain of the reflector radiation patterns falls noticeably with beam angle when the FPA population is low, but the directivity can be maintained well when an adequate number of FPA elements are used. Multiple beams that are either closely overlapping or widely separated are also successfully investigated.Citation: Ng Mou Kehn, M., and L. Shafai (2009), Characterization of dense focal plane array feeds for parabolic reflectors in achieving closely overlapping or widely separated multiple beams, Radio Sci., 44, RS3014,

Wideband radiation enhancement of waveguide arrays operated as feeds for reflector antennas using patch array covers

“…It was also found by Ng Mou Kehn and Shafai [2009] and Ivashina et al [2009] that the coupling effects in FPAs strengthen with reduced interelement separation. Because of this, the decoupling efficiency tends to be poor at low frequencies, due to the close proximity between elements in terms of wavelength.…”

“…The most intensive studies so far on the use of dense arrays comprising electrically small and independently excited elements as FPA feeds for reflector antennas have been the works of Ng Mou Kehn and Shafai [2009] and Ivashina et al [2009]. It has been demonstrated in those articles that a vital factor influencing the overall performance of an FPA‐fed reflector is the decoupling efficiency of the array feed.…”

“…Thus, the bottom line of array matching boils down to the achievement of high decoupling efficiency (over a certain frequency band, if required), for all three forms of arrays, namely, (1) the singly excited array containing an embedded element, (2) uniformly excited and linearly phase‐steered array, and (3) an arbitrarily excited finite subarray. From the findings of Ng Mou Kehn and Shafai [2009] and Ivashina et al [2009], it has been established that this decoupling efficiency constitutes a major degradation factor of the total efficiency of an FPA‐fed reflector system. As such, the importance of array matching cannot be overemphasized.…”

“…The latter form of array covered by a rectangular patch array (RPA) is schematized in Figure 1, as an example of sidewall loaded hard rectangular waveguides (HRW) studied by Ng Mou Kehn and Kildal [2005] as DRPA elements, and later on by Ng Mou Kehn and Shafai [2009] as FPA elements. Such HRW array elements will be reused here for the present study.…”

Double-Reflector Configuration for Optimal Exposure of Wideband Focal-Plane Arrays With Optical Beamforming

“…in radio astronomy [1] and in Ka-band satellite communication [2]. However, the small number of simultaneously active array elements is representing a serious limiting factor for this technology, in terms of number of multiple beams or scan range [3] and level of achievable effective isotropic radiated power (EIRP) [4]. A low EIRP level limits the use of low-cost silicon integrated circuits.…”