The radio frequency current is applied (or in receiving antennas the received signal is produced) between the antenna and ground plane. Microstrip antennas have become very popular in recent decades due to their thin planar profile which can be incorporated into the surfaces of consumer products, aircraft and missiles; their ease of fabrication. A novel cavity-backed slot antenna is proposed and experimentally studied. The antenna consists of a slot cut in a ground plane and backed by shorting strips, forming a backing cavity.
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Microstrip Fed Slot Antenna Backed By A Very Thin Cavity In Back
A Design of Wide Band and Wide Beam Cavity-Backed Slot Antenna Array with Slant Polarization
1College of Electronic Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073, China
2Southwest Electronics and Telecommunication Technology Research Institute, Chengdu, Sichuan 610041, China
Received 11 June 2016; Accepted 29 September 2016
Academic Editor: Jaume Anguera
Copyright © 2016 Huiying Qi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Design of antenna array under the limitation of restricted size is a challenging problem. Cavity-backed slot antenna is widely used because of its advantages of small size, wide band, and wide beam. In this paper, a design of wide band and wide beam cavity-backed slot antenna array with the slant polarization is proposed. To obtain wide band and wide beam with limited size, the inverted microstrip-fed cavity-backed slot antenna (IMF-CBSA) is adopted as the element of 1 × 4 antenna array. The slant polarized antennas and their feeding networks are adopted because of their simple structures. The performance of the proposed antenna array is verified by the simulations and experiments. The measured VSWR < 2 bandwidth is 55% at the center frequency 21.8 GHz, and the gain is larger than 12.2 dB. Experimental results demonstrate that the proposed design achieves wide band and beam with the size of 68 mm × 56 mm × 14.5 mm.
1. Introduction
Slot antennas have advantages of low-profile, light weight, and ease of integration [1, 2]. The cavity-backed slot antenna (CBSA), where the slot is backed with rectangular cavity, achieves unidirectional radiation [3–5]. The CBSA can be fed by probe [5], metal waveguide, substrate integrated waveguide (SIW) [6], and microstrip [7, 8]. With the use of printed circuit board, the structure of the SIW and microstrip is simpler than the probe and metal waveguide. The size of microstrip is smaller than the SIW. Therefore, the microstrip-fed CBSA (MF-CBSA) has simple structure and small size.
The bandwidth of the MF-CBSA element depends on the parameters of the slot. By the slot design, the slot antennas can have wider band than patch antennas. In general, the wide-slot MF-CBSA has larger bandwidth than the narrow-slot MF-CBSA [9, 10]. For example, the bandwidth of the MF-CBSA in [10] achieves up to 35%. The inverted microstrip-fed CBSA (IMF-CBSA) has better performance on the gain and bandwidth than the MF-CBSA [11]. For example, the bandwidth of the IMF-CBSA in [11] is 43% which is larger than that of the MF-CBSA in [10].
Though the IMF-CBSA element has wide beam, the beam widths of the IMF-CBSA arrays in [11, 12] are not enough large because they are plane arrays. To obtain the wide beam array, the element should have wide beam and the array should be a linear array. The purpose of this study is to design an antenna array with the wide band, wide beam, high gain, and slant polarization.
Though the IMF-CBSA arrays in [11, 12] obtain wide band and high gain, the polarization is horizontal polarization and circular polarization, respectively. The slant polarized and circular polarized antennas can receive both vertical and horizontally polarized waves. The slant polarized antennas and their feeding networks are simpler than those circular polarized antennas [13]. The slant polarization can be obtained by two methods: the simultaneously excited horizontal and vertical polarized element or rotating horizontal or vertical polarized element [14–17]. The antenna and feeding network designed by the second method are simpler than those of the first method.
In this paper, a design of wide band and wide beam cavity-backed slot antenna array with the slant polarization is proposed. To obtain wide band and wide beam with limited size, the inverted microstrip-fed cavity-backed slot antenna (IMF-CBSA) is adopted as the element of 1 × 4 antenna array. The 45° slant polarization is achieved by slanting the IMF-CBSA. The good performance of the proposed antenna array is verified by the simulations and experiments. The measured VSWR < 2 bandwidth is 55% at the center frequency 21.8 GHz, and the gain is larger than 12.2 dB.
2. Structure of Slant Polarized IMF-CBSA Array
2.1. Structure of IMF-CBSA Array with Feeding Network
The structure design of the IMF-CBSA array with the feeding network is illustrated in Figure 1. The metal strips are added to fix the structure. The feeding network is designed and added. The exciting port of the array is a coaxial probe. Through a converting structure from the coaxial probe to the shielded microstrip line, the electromagnetic wave is transmitted to the shielded microstrip line. A 1-4 power divided network based on the shielded microstrip line is designed to feed four antenna elements with the equal amplitude and phase. The whole size of the array structure is 68 mm × 56 mm × 14.5 mm.