amplifiers, IEEE Microwave Wireless Components Lett 19 (2009), 665–667. 7. P. Colantonio, F. Giannini, E. Limiti, and V. Teppati, An approach to harmonic load-and source-pull measurements for high-efficiency PA design, IEEE Trans Microwave Theory Tech 52 (2004), 191–198. 8. P. Wright, J. Lees, J. Benedikt, P.J. Tasker, and S.C. Cripps, A methodology for realizing high efficiency class-J in a linear and broadband PA[J], IEEE Trans Microwave Theory Tech 57 (2009), 3196–3204. V C 2015 Wiley Periodicals, Inc. Ka-BAND ANTIPODAL FERMI-LINEAR TAPERED SLOT ANTENNA WITH A KNIFE EDGE CORRUGATION Kiran D. Phalak, Zouhair Briqech, and Abderazil Sebak 1515 St.Catherine West, Montreal, QC, Canada, H3G 2W1; Corresponding author: k_phala@encs.concordia.ca Received 23 June 2014 ABSTRACT: An antipodal Fermi-linear tapered slot antenna (AFLTSA) is presented for Ka-band applications. A substrate integrated waveguide is used to excite the tapered slot. The proposed design has a measured 26–40 GHz wide impedance bandwidth with a return loss below 15 dB. It maintains a flat gain of 16 dB over an entire frequency band. The knife edges are corrugation profile of AFLTSA exhibits side lobe level of 214 dB in H plane and 219 dB in E plane. It has a symmetric radia- tion pattern as well as a cross polarization level of 222 dB. V C 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:485–489, 2015; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.28880 Key words: Ka band; tapered slot antenna; corrugation; substrate inte- grated waveguide; symmetry radiation 1. INTRODUCTION Since 1980, cellular communication industry kept adapting to advanced technological generation every decade. The ceaseless demand of high quality internet and streaming services force wireless companies to look for high capacity channels. With modernization in the semiconductor field, high speed switching circuits allow operating data speeds of gigabit per second. As the atmospheric attenuation has a low attenuation window at 28–38 GHz, Ka-band millimeter wave frequencies have a poten- tial for the fifth generation cellular technology to accomplish the bandwidth demand [1]. Due to their planar structure, wide bandwidth, and high gain qualities, tapered slot antennas (TSAs) can be considered as one of the most suitable candidates for communication at millimeter fre- quency range of 28–38 GHz. To attain high gain and narrow beam- width linear tapered slot antenna was introduced by Prasad and Mahapatra in [2], whereas Sugawara discussed Fermi antenna in [3]. Microstrip line fed Fermi shaped TSA is presented in [4] for 60 GHz applications. However, the width of this structure is 2k 0 , and thus, maybe a limitation when used in smart antenna array structures to achieve the beamforming. A further improve- ment of TSA performance can be obtained using knife edge cor- rugations instead of uniform corrugations as discussed later. Various feeding techniques had been proposed for a TSA [2–7]. Similar to microstrip feed lines, slot line feeding exhibits higher insertion loss. Alternatively, substrate integrated wave- guide (SIW) is presented in [6], where the slot is kept closest to the SIW feeding to reduce the overall length of the antipodal lin- ear tapered slot antenna (ALTSA). Therefore, electric field in SIW is only partially coupled with ALTSA. Similar work with improved return loss bandwidth is presented in [7] using coplanar waveguide (CPW) fed SIW feeding. However, as the input impedance of a CPW is sensitive to the width of a slot in CPW, low relative permittivity dielectric material used in [7] obtains an input impedance of 74 X or more. This work is concerned with improving the characteristics of antipodal Fermi-linear tapered slot antenna (AFLTSA) using knife edge corrugation. Three designs with different corrugation profile are studied to achieve the improvement in side lobe lev- els as well as cross polarization level. The shape of the ATSA flare is modified to couple maximum electric field from SIW to TSA. In addition, it has the microstrip line to SIW transition which makes the antenna input impedance equal to 50 X. In this article, design methodology of AFLTSA is discussed in the Section 2. Section 3 elaborates the effect of vital parame- ters on performance of the AFLTSA. Measured results are pre- sented and compared with simulated results in Section 4. 2. DESIGN METHODOLOGY AFLTSA has antipodal structure having a tapered slot sur- rounded by rectangular corrugations as shown in Figure 1 and all the dimensions are given in Table 1. AFLTSA design can be divided into two key parts: SIW feeding section and TSA. 2.1. SIW Feeding Section Periodically placed metallic posts (vias) in two parallel lines form the SIW. The diameter of vias (D) in SIW and the distance between successive vias (p) is chosen to satisfy the following design criteria given in [8]: D < k g 5 (1) p  23D (2) These criteria ensure the electric field is confined in the SIW. Although AFLTSA is wideband, its lowest frequency is limited by the cutoff frequency of SIW. The physical width of SIW is calculated using the formula [8]: W SIW 5 1 2 W eq 1 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðW eq 10:543DÞ 2 2 2d 2 5 r " # 10:273d (3) where W eq is the equivalent width of the dielectric filled rectan- gular waveguide and is given by [8]: W eq 5 c 23f 3 ffiffiffiffi e r p (4) The quarter wave matching section is designed in between SIW and microstrip to reduce the insertion loss. It facilitates the impedance matching between SIW and 50 X microstrip line. 2.2. Tapered Slot Section The opening section of antipodal structure follows the Fermi– Dirac distribution given by [3]: y5 a 12exp 2bx2c ð Þ (5) Unlike design [3] and [4], Fermi curve is not part of the radi- ating tapered slot, but it facilitates the maximum coupling from SIW to TSA due to its shape. DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 57, No. 2, February 2015 485