3204 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 59, NO. 9, SEPTEMBER 2011 Very Small Footprint 60 GHz Stacked Yagi Antenna Array Olivier Kramer, Tarek Djerafi, and Ke Wu, Fellow, IEEE Abstract—Millimeter wave applications such as short-range high-speed wireless links require modular, compact-size and high-directivity antennas. In this paper, high-gain compact stacked multilayered Yagi designs are proposed and demonstrated in the V-band. This novel design shows for the first time an an- tenna array of Yagi elements in millimeter wave stacked structure. To demonstrate the proposed concepts and design features, a 4 4 antenna array is created having excellent gain performance as well as very small footprint. A single element stacked Yagi an- tenna fed with microstrip is studied in order to obtain the desired performance. An analysis is performed to define the structure limitations. Measured results of the fabricated antenna prototypes are in good agreement with simulated results The measured Yagi antenna attains 11 dBi gain over 4.2% bandwidth with a size of 6.5 6.5 3.4 mm . A 4 4 array of Yagi antenna using an SIW (Substrate Integrated Waveguide) feeding technique is conceived. Both simulated and measured results match with each other very well. The 4 4 array has a size of 28 24 2.4 mm , and reaches a measured gain of 18 dBi over 7% bandwidth. An alternate con- figuration of the array using angled Yagi antenna elements allows a significant improvement of the side lobe level (SLL) with a low impact on the gain performances. The proposed antennas are excellent candidates for integrated low-cost millimeter-wave and even terahertz systems. The small foot print, the antenna design flexibility as well as its easy adaptation to automatic fabrication processes are good assets for making short range portable imaging systems. Index Terms—Array, circular patch, feeding network, mi- crostrip antenna, millimeter-wave and terahertz, SIW, SLL, stacked antenna, Yagi-Uda. I. INTRODUCTION T HE recent trend on the development of millimeter-wave frequencies systems has led to many innovative tech- niques with their successful demonstrations in different applica- tions. Among those applications, the unlicensed bands around 60 GHz and above provides an opportunity for high-data-rate wireless communications and sensing applications with re- duced energy per bit [1]; 77 GHz automotive radar [2]; and 94 GHz imagers and radiometers [3], where a lower profile array Manuscript received November 25, 2010; revised January 25, 2011; accepted February 23, 2011. Date of publication July 14, 2011; date of current version September 02, 2011. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) and in part by Re- groupement strategique of FQRNT. The authors are with the Département de Génie Électrique, Poly-Grames Research Center, École Polytechnique de Montréal, Montréal, QC H3T 1J4, Canada (e-mail: olivier.kramer@polymtl.ca; tarek.djerafi@polymtl.ca; ke.wu@ieee.org). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2011.2161562 antenna can achieve high gain. Millimeter-wave front-ends necessitate antenna systems with small size, low-power con- sumption and power-efficiency requirements [4], which should be integrated together with circuits to avoid unnecessary transmission line loss. A low side lobe level (SLL) is another important characteristic parameter that must be controlled to minimize the interferences [5]. This is particularly in line with the emerging worldwide discussion on green information and communication technology (Green ICT) policy and its implementations. The physical gain saturation of planar antennas and more specifically planar antenna array is defined by Hall [6], and it is limited to circa 35 dBi for a large number of elements with a significant decrease in efficiency [7]. The stacked Yagi-Uda antenna can overcome this limit by using the third dimen- sion. The classical Yagi antenna has been widely successful thanks to its simplicity and customizable high gain [8]–[12]. It consists of basically three-elements: a half-wavelength driver dipole, a longer reflector backing the driver and a director on the other side. Presented in a previous paper [13] is a stacked Yagi antenna working at 5.8 GHz for the purpose of proof-of-concept, stacking together the reflector, the driver, and the directors printed on substrate. However, the usual spacing between parasitic elements of is quite large at 5.8 GHz and imposes air gaps as the substrate would be too thick. This integration issue is naturally solved at higher frequencies like millimeter-wave and beyond where a completely integrated stacked structure can be achieved owe to wavelength compa- rable with dielectric substrate thickness. Such structures are suitable for multilayer processing techniques including PCB, LTCC and photoimageable thick-film process, which have become more mature in integrated circuit design, fabrication and integration [14], [15]. First of all, a V-band single antenna element is designed and demonstrated, using six elements fed by microstrip line. An analysis of the dielectric loss as well as the effect of coupling in the structure is performed in order to design the 4 4 planar antenna array. The array makes use of an SIW (Substrate In- tegrated Waveguide) network in order to feed a 4 4 array by coupling the radiating elements through rectangular slots. The SIW is used to reduce or even suppress the radiation that gen- erally appears in microstrip feeding structure. Hence, it can be connected to a demodulation circuit without interferences. An alternate configuration of the array is also presented. It is com- posed of Yagi elements oriented in different directions with ge- ometrical offset with respect to each other, allowing for a sig- nificant reduction of SLL. 0018-926X/$26.00 © 2011 IEEE