Journal of Electromagnetic Analysis and Applications, 2011, 3, 368-372 doi:10.4236/jemaa.2011.39058 Published Online September 2011 (http://www.SciRP.org/journal/jemaa) Copyright © 2011 SciRes. JEMAA Rectangular Microstrip Antenna with Air Cavity for High Gain and Improved Front to Back Ratio Kaushik Malakar, Jaydeep Nandi, Souvik Mitra, Prasanta Kumar Gorai, Sudipta Chattopadhyay, Sandip Banerjee Department of ECE, Siliguri Institute of Technology, Siliguri, Darjeeling, India. Email: piyalirekha@yahoo.com Received July 2 nd , 2011 revised July 29 th , 2011; accepted August 12 th , 2011. ABSTRACT A rectangular microstrip patch antenna using conventional Poly Tetra Fluride Ethelene (PTFE) substrate with air cav- ity is proposed and theoretically investigated. Considerably high gain along with improved front to back radiation iso- lation is demonstrated using such proposed antenna. The radiation performance of this new antenna has been com- pared to a conventional microstrip patch for some commonly used aspect ratios (width to length ratio). Compared to conventional microstrip antenna the proposed configuration shows more than 12% increment in peak gain and more than 10% increment in front to back radiation performance in each set of aspect ratio. The elucidation of such im- provement in the radiation characteristics of the proposed antenna is also presented. Keywords: Air Cavity, Front to Back Radiation, High Gain, Microstrip Antenna 1. Introduction Microstrip patch of rectangular or circular geometry etched on a grounded substrate is well known as printed antenna radiating along the broad side. Such a microstrip patch antenna on high dielectric constant substrate suf- fers from poor radiation pattern due to its high surface wave loss. But, sometimes in case of low dimensional devices, it is preferred to use a material with high dielec- tric constant in order to prevent spurious radiation. In those cases, microstrip patch when etched on a high di- electric constant substrate, show poor gain. In order to alleviate the lacunae, a microstrip patch antenna on PTFE-air mixed substrate configuration is chosen as a substrate for the proposed antenna in such a way that, the overall radiation performance can be improved. Several methods have been reported to minimize the surface wave losses such as complete or partial etching of sub- strate underneath the antenna [1-4] or developing few holes in the substrate to perturb the formation of sub- strate modes [5,6]. One very recently reported article on microstrip antenna with composite substrate configura- tion by one of the present authors, show high gain broad beam radiation pattern [7]. Some other composite sub- strate configurations [8] have been reported to enhance the gain of an antenna. But none of the above literatures reported the performance of their proposed antenna from the view of front to back radiation isolation. Actually, the widely used conventional microstrip patch antenna with PTFE substrate produces low gain and poor front to back radiation characteristics. With a view to develop an antenna with high gain along with improved front to back ratio, we have proposed a simple rectangular microstrip patch with full air cavity beneath the antenna. This is done to reduce the effective synthesized dielectric constant below the patch and as a result to increase the peak gain along with improved front to back radiation performance. Larger gain is always a positive requirement but along with that if the front to back radiation isolation can be improved, it will be a promising feature for an antenna to be used as an efficient feed of reflector or minimizing interference in wireless mobile communica- tion systems. In this new antenna, though the air becomes a part of the composite dielectric used, shown in Figure 1, it is still compatible with an integrated circuits and at the same time enjoys the gain enhancing feature as is done using simple air substrate below a patch along with im- proved front to back ratio. The design and implementation of the antenna is sim- ple. An electromagnetic simulator [9] has been used to study the characteristics theoretically and also to search for the physical insight in to this. Its radiation character- istics have been theoretically studied using a set of pro