Vol.:(0123456789) 1 3 Journal of Electrical Engineering & Technology https://doi.org/10.1007/s42835-020-00586-4 ORIGINAL ARTICLE Loop‑Shaped Patch Antenna for Conformal Arrays to Minimize the Efects of Adjacent Conducting Skin Sungjun Yoo 1  · Heeyoung Kim 2  · Choulhee Hong 2  · Hosung Choo 3 Received: 22 February 2020 / Revised: 13 May 2020 / Accepted: 15 October 2020 © The Korean Institute of Electrical Engineers 2020 Abstract This article proposes a novel method of designing a loop-shaped slot patch antenna using an extended cavity structure to reduce the infuence of adjacent conducting vehicle skin. The proposed antenna consists of the radiating patch, loop shaped slot, and an extended cavity structure. The radiating patch is directly connected to a hybrid chip coupler to achieve a circu- lar polarization property, and the extended cavity structure is employed to confne the near-feld within the radiating patch that allows to have less infuence of the conducting skin and to increase the efective permittivity of the proposed antenna. To verify the efectiveness of the proposed conformal array antenna, we fabricate 2 × 2 array antenna with and without an adjacent conducting skin, and its performances, such as bore-sight gains and 2-D radiation patterns are measured in a full anechoic chamber. The results confrm that the proposed antenna structure is suitable for elements of the conformal array, which is less afected by the conducting skin of the airframe. Keywords Conformal array antenna · Microstrip patch antenna · Array antenna 1 Introduction Conformal array antennas have been widely used in aeronau- tical applications, such as military aircraft, unmanned aerial vehicles (UAVs), and missiles, to reduce aerodynamic drag and radar cross section (RCS) by incorporating antennas into the curved vehicle skin. Microstrip patch antennas are considered to be most suitable candidate for the conformal array antennas due to their low profle, light weight, and manufacturability [1]. Conformal array antennas have been typically integrated into a conducting airframe to obtain good aerodynamic characteristics and RCS reduction, how- ever; the conducting vehicle surface on which the elements of the conformal array are mounted often afects the array antenna characteristics, such as radiation pattern, impedance matching, and mutual coupling. Therefore, from the per- spective of the overall communication link, it is important to prevent such performance degradations of the conformal antenna due to the efect of the proximity conducting vehicle surface [2]. To prevent such performance degradations, vari- ous studies have been carried out on applying a structurally embedded conformal antenna to vehicles, which extracts some parts of the airframe surface and inserts array anten- nas into the structure. These approaches, however, make it difcult to use space efectively because portions of the air- frame should be extracted much more than required space for the conformal antenna system [3, 4]. Although some papers have reported good results on space-efcient confor- mal array antennas, the array antenna performances can still be afected by conducting vehicle surfaces placed between the individual antenna elements [5, 6]. On the other hand, a great deal of research has also been conducted to prevent such performance degradation by inserting additional struc- tures. For example, techniques of inserting meta-surfaces, * Hosung Choo hschoo@hongik.ac.kr Sungjun Yoo ryoonet@naver.com Heeyoung Kim hykim1220@acetech.co.kr Choulhee Hong chhong@acetech.co.kr 1 Advanced Defense Technology Research Institute Quantum Physics Technology Directorate, Agency for Defense Development, Daejeon, Republic of Korea 2 R&D Center, Ace Technology, 237 Namdongseo-ro, Namdong-gu, Incheon 405-849(21634), Republic of Korea 3 School of Electronic and Electrical Engineering, Hongik University, Seoul, Republic of Korea