IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012 1261 High-Ef ficient Patch Antenna Array for E-Band Gigabyte Point-to-Point Wireless Services Nasser Ghassemi, Student Member, IEEE, and Ke Wu, Fellow, IEEE Abstract—This letter presents a low-cost, high-gain, and high-ef- ficiency 4 4 circular patch array antenna for gigabyte point-to- point wireless services at E-band (81–86 GHz). The antenna struc- ture consists of two layers. The feed network is placed at the bottom layer, while the circular patches are on the top layer. To increase the efficiency of the antenna array, substrate integrated waveguide (SIW) is used to feed the circular patches through longitudinal slots etched on the top metallic surface. Low-cost printed circuit board (PCB) process is used to fabricate the antenna prototype. Simu- lated and measured bandwidths of the antenna array are 7.2%, which covers the desired frequency range of 81–86 GHz. Measured gain of the 4 4 antenna array is 18.5 dBi, which is almost con- stant within the antenna bandwidth. Measured radiation efficiency of 90.3% is obtained. Index Terms—Antenna array, E-band antenna, gigabyte wire- less spectrum, millimeter-wave, substrate integrated waveguide (SIW). I. INTRODUCTION F REQUENCY bands of 71–76 and 81–86 GHz are al- located by the Federal Communications Commission (FCC) [1], [2] as gigabyte wireless spectrum. Over this fre- quency window, the atmospheric absorption drops to less than 1 dB/km and provides the capability of long-range gigabyte point-to-point wireless services. Thanks to the wide bandwidth and low atmospheric absorption, a wide range of applica- tions, such as broadband metropolitan or local area networks, and emerging millimeter-wave back-haul systems for LTE and future base-station connectivity, are evolving quickly in E-band [3]. Antenna is one of the most important components in such wideband point-to-point wireless systems. A low-cost, high- gain, and high-efficiency antenna that covers the whole system bandwidth is highly needed. Microstrip patch antennas have been used since several decades for microwave applications due to their low-cost planar structures. As frequency increases to millimeter-wave region, the efficiency of microstrip lines suf- fers from serious losses at the bends [4]. On the other hand, classical waveguide technology is pop- ular in the design of high-performance millimeter-wave sys- tems. However, they are not suitable for low-cost and mass production because of their expensive and bulky structures. In Manuscript received September 09, 2012; accepted October 03, 2012. Date of publication October 19, 2012; date of current version November 20, 2012. The authors are with the Poly-Grames Research Center and Center for Ra- diofrequency Electronics Research of Quebec (CREER), Department of Elec- trical Engineering, Ecole Polytechnique (University of Montreal), Montreal, QC H3V 1A2, Canada (e-mail: nasser.ghassemi@polymtl.ca; ke.wu@ieee.org). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2012.2224087 addition, the nonplanar structure of the waveguide makes it dif- ficult to get interfaced with planar active components. Substrate integrated waveguide (SIW) was proposed to address the above- mentioned issues [5]. SIW has the advantages of waveguide, but it is also low-cost and in planar form. The structure can easily be connected to the coplanar waveguide (CPW) and microstrip lines [6]. As such, antennas based on SIW can easily be inte- grated with active devices. Recently, SIW-based antenna arrays and beamforming networks have been developed [7]–[13]. This letter presents a 4 4 patch array antenna for E-band (81–86 GHz) applications. A network based on substrate inte- grated waveguide is used to feed the antenna patches through longitudinal slots etched on the top metallic surface of SIW. Low-cost printed circuit board (PCB) process is used to fabri- cate the antenna array prototype in two layers. Good agreement is obtained between the simulated and measured results. Com- pared to the SIW-based slot arrays [7], [8], the proposed antenna presents more gain, larger bandwidth, and better radiation effi- ciency. Compared to the SIW-based antennas [12], [13], the fab- rication process of the proposed antenna is much easier, and it is thinner while it has almost the same gain over the bandwidth. II. DESIGN OF THE ANTENNA ARRAY The schematic of the 4 4 array antenna is shown in Fig. 1. The antenna structure consists of two layers. The bottom layer is used to support the design of the SIW feeding network and power dividers, which are made of a 20-mil Rogers/Duroid 6002 substrate. The top layer involves circular patches that are fed through longitudinal slots etched on the SIW top surface. The slots are placed half a wavelength apart to feed the patches in phase. To align the slots at peaks of the standing wave along the SIW structure, SIWs are terminated by short circuits that are three quarter-wavelengths away from the center of the last slot. The slots are placed half a wavelength apart, at the center frequency, in order to be allocated at the standing wave peaks, and also get excited with the same phase. The design proce- dure of the slots is similar to that of the SIW slot array that was presented in [8]. One T-type and two V-type power dividers are used to feed the 1 4 array antennas in phase. Simulated and of the Y- and T-shaped junctions are presented in Fig. 2. It is noted that the T-junction leads to a higher reflec- tion coefficient than the Y-junction due to the existence of 90 bends in this structure, while the T-junction has a smaller foot- print and also is shorter, especially at the first stage. Note that dielectric and metallic losses have been considered in the simu- lation results of the power dividers. Due to the shorter length of the T-junction, it is less lossy. The circular patches are designed on Rogers/Duroid 5880LZ substrate. To reduce mutual coupling 1536-1225/$31.00 © 2012 IEEE