Summary
International Symposium on Antennas and Propagation
2009
Session Number:3A2
Session:
Number:3A2-2
Bandwidth Enhancement Techniques for Printed Compound Air-fed Array Antennas
Zhi-Hang WU, Wen-Xun ZHANG,
pp.779-782
Publication Date:2009/10/21
Online ISSN:2188-5079
Summary:
Over the last decade, a class of high-gain printed antennas: the reflectarray (RA) [1-2], transmitarray (TA) [3-4], and Fabry-Perot resonator (FPR) [5-8], summarized as air-fed array [9] were developed, which avoid the serious loss due to feeding network. The traditional RA or TA consists of the printed radiator array illuminated by a feed apart from the array approximately the aperture size of array, which has high profile in structure. The traditional FPR antenna has much lower profile as half wavelength [5-7] but usually owning very narrow bandwidth due to the high quality factor of resonant cavity, and lower efficiency due to the non-uniformity of aperture distribution. In order to enhance the bandwidth and efficiency, but keep its low-profile structure, an improved antenna named as printed compound air-fed array (PCAFA) as shown in Figure 1 was developed [9-10] successively. The original design of PCAFA consists of three components: a tapered FSS as cover for phase compensation of illuminated rays, an inversely tapered HIS as base for phase compensation of multiple reflection rays, and an embedded broadband radiator as printed feed. Alternatively, in this paper the cover is a uniform FSS with partial reflectivity; the base is a mixed HIS with prescribed reflection phase. It can further improve the gain bandwidth of PCAFA by proper designing. Let us briefly review the ever existed techniques in advance, as well known that the main cause of narrow bandwidth to PCAFA is the mechanism of high-Q resonance, similar as so-called EBG resonator antennas [11-17]. A simplest method is to decrease the Q-factor by decreasing the reflectivity of cover [11- 13], however such approaching benefits its bandwidth with the scarification of gain and aperture efficiency. The second method is to combine double layers of FSS for getting an increasing slope of reflection phasefrequency response rather than decreasing response [14-15], however the cost is the rising spacing between FSS layers and then the volume of antenna. The third method to greatly enlarge the bandwidth of gain-drop is fed by a radiator array [16-17], but it needs a complex feeding network again. The technique for enlarging the gain-bandwidth product proposed in this paper is to perform a flat gainfrequency response with small ripple inside, and with abrupt slope-down outside the band, by means of combined techniques. Firstly, choose a proper FSS as cover with stable frequency response of reflectivity and reflected phase to minimize gain deterioration caused by reflectivity and phase variation. Secondly, adopt mushroom-patch HIS rather than patch-HIS as base to suppress the lateral waves including surface wave and parallel guide wave. Thirdly, properly arrange two or more kinds of size of HIS elements to get a flat gain-frequency response. These steps provide the possibility to approach maximal gain-bandwidth product based on a low profile structure with the height less than half-wavelength and single feed only. The detailed principle and design procedure will be presented, and then a designed example of PCAFA antenna is simulated, which exhibits 9.9 % (14.1 %) relative bandwidth of ?1dB (?3 dB) gain-drop from peak gain (19.1 dBi) corresponding to 71 % aperture efficiency.