924 IEICE TRANS. ELECTRON., VOL.E100–C, NO.10 OCTOBER 2017 BRIEF PAPER Special Section on Microwave and Millimeter-Wave Technology A Simply Structured Transverse Slot Linear Array Antenna in a Quasi-TEM Mode Waveguide Yuanfeng SHE † a) , Member, Masanobu HIROSE † , Nonmember, Yuto KATO † , Takayuki ISHIZONE †† , Satoru KUROKAWA † , Members, Shinya IWASAWA ††† , Nonmember, and Sintaro ARATA ††† , Member SUMMARY This article proposes a simply structured transverse slot linear array antenna with a low cross-polarization in X band on a quasi- TEM (transverse electromagnetic) mode waveguide. The fabrication tech- nology of this antenna is very simple and suitable for mass production. A center fed linear slot array has been designed and measured. The quasi- TEM wave is propagating in the conventional waveguide with dielectrics at sidewalls. The simulation and the measurement results show that the baﬄe plates enhance the gain and reduce the beamwidth eﬀectively. The uncer- tainties of the electric properties of the dielectric and fabrication errors are also discussed. key words: waveguide, array, quasi-TEM 1. Introduction Linear array antennas are wildly used in the current wireless systems. Antennas for marine systems are one of these ap- plications. Due to the typical working conditions for ﬁshing vessels, the antennas for the marine systems are required as follows: the horizontal polarization, the sharp beamwidth in the horizontal plane and the acceptable beamwidth in the vertical plane. The tilted edge-slot array in the waveguide narrow wall or the patch arrays on the printed circuit board (PCB) are popular in the market of marine systems [1], [2]. However, the radiation of the edge-slot array in the waveguide nar- row wall contains the cross polarization and the additional polarization ﬁlter is necessary. In addition, the cost and the weight of the patch array is relatively high and the eﬃciency is relatively low due to the ohmic loss of the material. This article proposes a transverse slot array antenna with a simple structure on a quasi-TEM mode waveguide as shown in Fig. 1. The linearly polarized wave is radiated from the transverse slots in the broadwall of the waveguide. It is fed at the center of the array to be assured that the beam of the radiation does not deﬂect from the boresight. In ad- dition, the baﬄe plates are used to enhance the gain and to reduce the beamwidth in the vertical plane. The dimensions of the antenna are 600 mm × 108 mm × 106 mm (length × height × width). Manuscript received February 13, 2017. Manuscript revised May 31, 2017. † The authors are with AIST, Tsukuba-shi, 305–8563 Japan. †† The author is with Toyo University, Kawagoe-shi, 350–8585 Japan. ††† The authors are with Koden Electronics Co., Ltd., Tokyo, 146–0095 Japan. a) E-mail: yuanfeng.she@aist.go.jp DOI: 10.1587/transele.E100.C.924 Fig. 1 Geometry of a slot array in X band and its magniﬁed cross section. There are three advantages for the proposed antenna as below: 1. The structure of the antenna is simple and easy to design. The manufacture by the sheet metal processing is low cost and suitable for mass production. 2. It radiates the linearly polarized wave and the cross polarization level is very low. Therefore the additional po- larization ﬁlter is not necessary. 3. It is lighter in weight and lower in transmission loss than the conventional dielectric-ﬁlled waveguides and the PCB patch antennas. There are three points of basic knowledge that are re- quired for designing the proposed antenna: 1. Design of the transverse slot for radiation. 2. Baﬄe technique for gain enhancement. 3. Design of the hard wall for the quasi-TEM propaga- tion. In this article, the authors use the reﬂection cancelling slot pair for the array antenna. The reﬂection cancelling slot has been studied in 1990s and has been applied in various slot arrays both on a single mode waveguide and oversized waveguide [3], [4]. The same design procedure is used in the array antenna. In 1950s and 1960s, a baﬄe structure by using the parallel-plate was proposed to suppress the higher order mode and enhance the gain in horn anennas [5]. The side lobe in the H-plane pattern can be suppressed by setting the side walls as the horn antenna [6]. The array antenna in this article uses the sloping baﬄe plate in the horn shape. The distance of the narrow end of the baﬄe is smaller than one wavelength in free space λ 0 . Copyright c  2017 The Institute of Electronics, Information and Communication Engineers