Indian J Phys- 75B (3), 171-173 (2001) U P ® — an international Journal Microstrip miniaturised antennas Sanjeev Gupta*. Pankaj Kanti Nath and B K Sarkar Society for Applied Microwave Electronics Engineering and Research, III Campus, Powai, Mumbai-400 076, India E-mail sanjecv@samcer emel.in Abstract This paper deals with the various techniques for reduction in the size of the antennas A small microstrip patch antenna is presented The probe-fed microstrip patch incorporates a single shorting post which significantly reduces the overall si/c ofthe antenna Theoretical impedance behaviour and radiation characteristics of the modified patch arc given. keywords Microstrip antennas, design and simulation results PACS No. 84.40 Ba 1. Introduction In the present scenario of increase in demand by the system designers for the implementation of more complex functions in reduced space, there is an increase in the demand for the active integrated microstrip patch antennas with lower size and weight. This paper addresses these demands by describing various techniques to satisfy the severe constraints on the physical dimensions, the need for “miniaturisation” of the patch antennas. Such light weight and low volume antennas could find applications in land, mobile and personal communication systems and airborne antenna systems. The half-wavelength (A/2) open-circuited microstrip patch antenna is used because of both its conventional property and relative ease to manufacture. M iniaturisation of the resonant nuciLstrip patch antennas can be accomplished by loading. Loading can take various forms, namely (i) use of substrates and/or superstrates of higher permittivity, (ii) modification of basic patch geometry and (iii) use of short-circuiting posts These are briefly described below. Loading the resonant antenna with the high permittivity dielectric material reduces the size of the antenna [1]. Although the reduction of antenna dimensions by dielectric loading has been carried out since antennas were first used, practical implementation has been closely tied to the availability and competitive and economical cost of dielectric materials in industry. On one hand high permittivity substrates can improve some antenna characteristics, they are, on the other hand, invariably ceramic-based which require specialized machining equipment as compared to that required for plastic substcates. To achieve smaller planar antennas operating at the same frequencies as conventionally configured antennas requires a more complex geometry. One of the geometry is C-patch microstrip antenna formed by cutting a small area in one of the radiating edges of the antenna [2]. A similar technique uses H-shaped or rectangular ring microstrip patch, which consists of a strip of metal, H-shaped or rectangular ring- shaped supported on the grounded dielectric sheet. It has a size about half that of the rectangular patch, with larger beamwidth but smaller bandwidth. Other miniaturisation shapes include the double C-patch (two stacked C-shaped antenna elements connected together with a vertical ground plane) [3], annular slot and the annular sector. Some of the other shapes make inefficient use of the available area and an adequate performance can only be achieved either by super-conducting material or thick low-loss substrates. Common technique to reduce the overall size of a microstrip patch antenna is to terminate one of the radiating edges with a short circuit [4]. The short circuit can be in the form of a metal clamp or a copper sheet wrapped around the Corresponding Author © 2001 lACS