Broadband millimeter‐wave planar antenna array with a waveguide and microstrip‐feed network

Abstract

In this paper, we describe a fixed-beam broadband planar antenna array at millimeter-wave frequencies. The antenna is fed by waveguide-feed and microstrip-feed networks. In order to ensure fixed beams and a broad bandwidth, a subarray concept is introduced. For efficient coupling, a novel waveguide-to-slot transition consisting of a slot pair and a narrow conductive bar is proposed. Simulated and mea- INTRODUCTIONWith the growth of millimeter-wave communications, especially broadband multimedia wireless services, the demand for a lowcost broadband planar-array antenna has increased. Although microstrip patch antennas with a microstrip-feed network are widely used because of their low fabrication cost, they have serious problems in millimeter-wave large-array applications, such as large feed-line loss and gain degradation [1]. In contrast, slottedwaveguide array antennas have low loss and high efficiency, but high fabrication costs [2]. To obtain both low cost and low loss, standing-wave waveguide/microstrip feed networks have been reported [3, 4]. However, the arrays fed by these standing-wave feed networks have a very narrow bandwidth because the peak position of the E-and H-fields of the standing wave shifts with the operating frequency. Another problem of standing-wave arrays is the frequency-dependent main-beam direction. These characteristics restrict their application within a narrow band [5].This paper presents a beam-fixed broadband array antenna with high gain operating at 40.5-43.5 GHz. To reduce the feed-line loss, the antenna is fed by a waveguide-feed network in the E-plane direction. The microstrip-feed network is distributed in the H-plane direction in order to decrease fabrication costs. The two feed networks are coupled using the waveguide-to-microstrip transition proposed in this paper. The proposed transition consists of a slot pair and a conductive bar and is more efficient than a conventional transition. We also introduced the subarray concept, which widens the reflection bandwidth and fixes the main-beam direction for variant frequencies. The whole array is divided into four subarrays that consist of eight coupling slots and 30 ϫ 8 antenna elements. Figure 1 shows the geometry of the proposed waveguide-to-microstrip transition. The incident wave from Port 1 is coupled through the slot pair and propagates toward Ports 2 and 3 where the microstrip feed network is attached. The slot pair consists of two center-inclined slots that are placed equidistant from the center of the slot pair. The slot is 3.3 mm in length and 0.6 mm in width and is etched on the ground plane of the substrate. The etched ground plane also serves as the upper conductor plate of the waveguide. The dielectric constant of the substrate is 2.2 and its height is 10 mil. Figure 2 shows the ratio of the coupled power to the input power for various slot spacings d. The simulation has been performed using Ansoft's finite-element-method simulator HFSS [6]. The coupled power is calculated as sum of the square of scatterin...

High Gain Superstrate Loaded Membrane Antenna Based on Substrate Integrated Waveguide Technology

“…The SIW based structures can be implemented by various manufacturing processes such as conventional printed circuit board process (PCB) [8,9], multilayer PCB process [10], photoimageable thick film technology [11], and low-temperature cofired ceramic (LTCC) technique. There are many techniques to improve the gain, either by using large arrays [12,13], which in turn increases losses from the feed network especially at the high frequencies, or by using superstrates [14,15]. This technique is simple and efficient to improve the gain.…”

Design of a High-Gain Cavity-Backed Slot Antenna With Mushroom Cells and Bent Ground Walls

“…For a very high gain, the array should contain a lot of elements if the gain of each element is not high, which not only increases the size of the array, but also decreases the efficiency of it [1][2][3]. Superstrates are also used for gain enhancement [4][5][6][7].…”

Gain improvement of a cavity‐backed slot antenna

“…Antennas with high‐gain have many applications in wireless communication systems as they produce focused and narrow beamwidth, which allow for more precise targeting of the signal. Therefore, various gain enhancement techniques for antennas have been studied in the past decades [1–25]. Specifically, there are three important methods to achieve this purpose: (1) using antenna array, (2) adding superstrate, and (3) using intrinsically high gain antenna.…”

“…Antenna array is one of the most commonly used methods for gain enhancement. However, when a very high gain is expected, the array should contain a lot of elements if the gain of each element is not high, which not only increases the size of the antenna, but also decreases the efficiency of it [1–4]. The gain can also be improved by proposing a corrugated slots array with a space larger than a wavelength, which in turns increases the array size [5].…”