Design of An Asymmetric T-slot Coupled Circular Microstrip Antenna for GPS Application Jayanta Ghosh 1 , Neela Chattoraj 2 , Jibendu Sekhar Roy 3 1 ECE Department, Asansol Engineering College, Asansol, West Bengal e-mail: gh_jayanta@rediffmail.com 2 ECE Department, BIT, Mesra, Ranchi-835215, Jharkhand e-mail: nila_chwdhry@yahoo.com 3 School of Electronics Engineering, KIIT University, Bhubaneswar-751024, Orissa e-mail: drjsroy@rediffmail.com Abstract – Design of a slot-coupled microstrip antenna, for GPS application is presented in this paper. A circular microstrip antenna is excited by an asymmetric T-slot, which produces very good circular polarization, required for GPS application. Simulated results using IE3D software are verified with measured results. Index Terms– Slot-coupled, circular microstrip antenna, asymmetric T-slot, GPS. I. INTRODUCTION The increasing use of microwave mobile communication systems demand the antennas for different systems and standards with properties like reduced size, broadband, multiband operation, moderate gain etc. [1-10]. One of the important frequency bands for wireless communications is Global Positioning System (GPS) which operates at 1.575 GHz. The GPS system uses low earth orbiting satellites that transmit signals continuously to the earth based receivers. There are two categories of GPS services: civilian and military. Civilian GPS system operates at a center frequency of 1575.42 MHz (L1 band) with a bandwidth of 20 MHz. The required polarization is circularly polarized with axial ratio of 3dB or better and required antenna gain is 4 dBi. A user terminal may use linearly polarized antenna, but in that case it will suffer 3 dB power loss. The GPS antenna should have a wide hemispherical coverage in the upper half plane. Slot-coupled microstrip antennas are very attractive for wide bandwidth and also due to various controlling parameters of these antennas, it is easier to achieve desired characteristics [1,2,11-15]. In Slot-coupled (also known as aperture-coupled) microstrip antenna, the radiating patch in one substrate, is excited by a microstrip line on other substrate, via an aperture or slot. The shape of the slot may be of various shapes. In this paper, design of a slot-coupled circular microstrip antenna is reported. The antenna is circularly polarized and designed at the centre frequency of 1.575 GHz, which is used for GPS. The slot is in the form of an asymmetric T. Asymmetric T-slot means the length of the arm1 and arm2 of the T-slot are unequal, as shown in Fig 1. (a) Antenna configuration (b) Asymmetric T-slot Fig.1. Asymmetric T-slot coupled circular microstrip antenna