Indian Journal of Radio & Space Physics Vol. 39, April 2010, pp. 107-113 Design and analysis of a gap coupled split circular patch with elliptical slot filled with elliptical patch Dheeraj Bhardwaj 1 , Komal Sharma 1 , D Bhatnagar 1,$,* , S Sancheti 2 & B Soni 3 1 Microwave Laboratory, Department of Physics, University of Rajasthan, Jaipur 302 004, India 2 National Institute of Technology, Surathkal 575 025, India 3 ISRO Satellite Centre, Bangalore 560 017, India $ E-mail: dbhatnagar_2000@rediffmail.com Received 29 May 2009; revised 12 February 2010; accepted 17 February 2010 The paper presents radiation performance of a gap coupled split circular patch with elliptical slot filled with elliptical patch. Initially, a circular elliptical ring slot antenna is taken and it is modified step by step to achieve an end product with desired performance. The performance of designed antenna after each step is presented systematically. The simulated and measured results of proposed antenna are compared with that of a circular elliptical ring slot antenna. The gap between two gap-coupled semi circular elliptical ring structures and the length of major and minor axis of inserted inner elliptical patch are optimized to achieve best performance. It is observed that with proposed modifications in circular patch geometry, impedance bandwidth, gain and radiation efficiency of antenna are improved considerably. The resonance frequency of end product is lower than that of a circular elliptical ring slot antenna which indicates that for achieving identical resonance frequencies from circular elliptical ring slot antenna and modified circular patch geometry, effective patch size of modified antenna must be reduced. The outcome results into a further compact circular patch antenna with much improved performance. Keywords: Gap coupled antenna, Microstrip antenna, Return loss, Impedance bandwidth, Impedance gain PACS Nos: 84.40 Ba; 75.50 Gg 1 Introduction Printed planar microstrip antennas are gaining tremendous popularity for modern communication systems due to their inherent features including compact size, low cost and ease of fabrication 1 . These antennas may be neatly integrated into the handsets without protruding outside as protruded antennas may break easily with little mishandling making the device useless. Though extensive work on simple microstrip geometries including rectangular, circular and triangular shaped structures have been reported 2–6 in recent past, still these antennas in their conventional form could not attract consumer market due to their inherent narrow bandwidth, low gain and capability to operate at single resonance frequency corresponding to their dominant mode. Various techniques to improve the matching over a broad bandwidth have also been proposed. For high data rate communication systems, smaller patch antennas with improved bandwidth are desired. Hence, several conventional patch geometries were modified in recent times to make them useful for modern communication systems. Among these geometries, perhaps circular patch geometry is the most extensively analysed geometry and extensive experimentation and alterations in this patch geometry have been reported to improve its performance 6-9 . Bao & Ammann 10 proposed the design of a compact circularly polarized wideband circular patch antenna embedded in a narrow annular ring which uses an unequal cross- slotted ground plane. Recently, Azenui & Yang 11 have proposed a transmission line fed crescent patch antenna for wideband applications with displaced center of circular region from centre of outer ellipse. In the present paper, the performance of a gap coupled split circular patch with elliptical slot filled with elliptical patch has been reported. By varying the gap between two gap-coupled semi circular elliptical ring structures and the lengths of major and minor axis of inner elliptical patch, antenna structures are optimized to obtain improved performance. 2 Antenna structure and results (a) Circular elliptical ring slot antenna (CERSA) First a circular patch microstrip antenna with radius ‘r’ having a concentric elliptical slot with length of