A comparison of reflector antenna design for wide-angle scanning

Abstract

Conventional reflector antennas are typically designed for up to -0 beamwidths scan. We compare the ability of six single and dual reflector designs to scan up to 300 beamwidths in order to determine the feasibility of wide-angle scans using reflector antennas. The single reflectors are parabolic symmetric dishes with fD=2 for P1 (Fig. la) and f/D=l for P2 (Fig. lb) and an offset reflector, P3, with f/D=2 (Fig. IC). Scanning is accomplished for the first two designs by tilting the reflector dish. The third design is scanned electronically. The dual reflectors are Cassegrain designs. They are folded versions of the first single reflector design. Scanning is accomplished by tilting the main reflector for C1 (Fig. 2a), tilting the subreflector for C2 (Fig. 2b), and tilting both reflectors for C3 (Fig. 3c). All designs have a circular diameter of 1, OOO wavelengths. Data on extremely wideangle scans of reflector antennas are scarce in the literature [ 1 ].The feeds used are open-ended circular waveguides. For designs P2 and P3 cluster feeds are used to obtain better results. The excitations of the feed elements are chosen to optimize directivity. Results are shown in Figure 3. Conclusions(1) The best results are obtained by PI. This is due to the long focal length and the symmemcal design. The scan loss at 114 BW (8" scan) is only 0.6 dB (Figs. 4a, 4b). The sidelobes increased considerably (from -31 dB to -13 dB). This can be compared to a symmemcal parabolic reflector with f D 4 . 4 that can scan only F I BW with less than 2 dB loss [2]. This problem may be alleviated by using the cluster compensation method [3-71, and needs to be studied. Scan loss is 5.1 dB at 286 BW (20") ( Fig. 4c).(2) The folded version of P1 is the Cassegrain antenna C1. The amount of folding achievable was small (from 2,000 wavelengths to 1,650 wavelengths) due to the size of the feed (r=3 wavelengths). A larger feed is needed in order to obtain more folding.(3) To shorten the f/D from 2 to 1, reflector P2 must rely on a cluster feed to reduce its scan loss. The excitation of the cluster varies as the beam scans. The scan performance of P2 is still not as good as that of P1 (Fig. 5), indicating that a 19-element cluster cannot totaUy compensate the reduction in f D .(4) Tilting the subreflector of a Cassegrain antenna can only achieve a small scan (about f 1 5 BW). It can be used in conjuction with the electrically more effective but mechanically more costly main reflector tilting to achieve a small local scan.cazsscz/m/awnrozee $1.00 01989 IEEE 266

Focal-Plane Arrays With Improved Scan Capabilities

“…Normally, this parameter is a weak spot of traditional reflector configurations. Classical prime-focused reflectors have a very low RATA while scanning, so most of the array elements remain inactive [24], [25]. The complex offset double-reflector model of [10] allows to have about a quarter of the array elements to be active within a ±20 • scan range.…”

Scanning Characteristics of Metamirror Antennas With Subwavelength Focal Distance

“…However, so far, the scanning characteristics of metamirrors have not been studied. It is known that scanning abilities of conventional reflector antennas (parabolic reflectors and reflectarrays) significantly degrade when the focal distance is reduced [11]. Thus, it could be expected that metamirrors with sub-wavelength focal distances would experience the problem of extremely high beam degradation when the feed is laterally displaced from the focal point.…”

Design of W-Band Cassegrain Antenna for Beam Steering

“…기계적인 방법은 주로 반사형 안테나에서 물리적인 방법으로 안테나의 구조를 변경하 여 빔의 방향을 조정하고, 전자적인 방법은 배열 안테나 에서 각 소자에 공급되는 신호의 위상이나 지연시간을 조절하여 빔 방향을 조정한다 [1] . 대표적인 이동체에 탑재된 반사형 안테나의 빔 조향을 위해서는 주반사판을 기울여서 조향하는 주반사판 기울임(main reflector tilting) 방식 [2] 과 안테나 전체를 회전하여 조향하 는 안테나 회전(antenna rotating) 방식 [3] 을 사용한다. 이동 체 내에서 소형, 고이득의 빔 조향 안테나를 구현하기 위 하여 [5] .…”