Abstract—This paper present a circular patch microstrip array antenna operate in KU-band (10.9GHz – 17.25GHz). The proposed circular patch array antenna will be in light weight, flexible, slim and compact unit compare with current antenna used in KU-band. The paper also presents the detail steps of designing the circular patch microstrip array antenna. An Advance Design System (ADS) software is used to compute the gain, power, radiation pattern, and S 11 of the antenna. The proposed Circular patch microstrip array antenna basically is a phased array consisting of ‘n’ elements (circular patch antennas) arranged in a rectangular grid. The size of each element is determined by the operating frequency. The incident wave from satellite arrives at the plane of the antenna with equal phase across the surface of the array. Each ‘n’ element receives a small amount of power in phase with the others. There are feed network connects each element to the microstrip lines with an equal length, thus the signals reaching the circular patches are all combined in phase and the voltages add up. The significant difference of the circular patch array antenna is not come in the phase across the surface but in the magnitude distribution. Keywords—Circular patch microstrip array antenna, gain, radiation pattern, S-Parameter. I. INTRODUCTION URRENTLY, parabolic dish antenna is at its own pace to receive the KU-band signals. The dish provides the best compromise of high gain, which is about 37dB at 12.5GHZ for 0.6m diameter, 38.5 dB for 0.75m and 40.3 dB for 0.9m [1]. A paraboloid can be considered as a three dimensional profile produced by rotating the parabola about its central axis. In receiving mode, the parabolic shape reflects signals, impinges on its surface to the focal point. In general, the working principle of a parabolic reflector is that a plane wavefront transmitted from satellite would be reflected from the dish surface and converted to a spherical wavefront. A waveguide positioned at the focal point collects the signals [2]. However, it is not necessary that only parabolic dish can be used to receive the KU-band signals, the circular patch microstrip array antenna also can be used to receive the KU- band signals [3]. The proposed antenna has 36 elements arranged in a rectangular grid form and operated in TM 11 mode [4]. Each element has an equal radius and a separation distance from their neighbours . The working principle of this antenna is that the conduction surface is face directly to the Authors are with the INTI International University College, Malaysia. (e-mail: tflai@intimal.edu.my) incoming signals. The voltage will be equally distributed among all the elements. The voltage may superimpose and cancel each other due to the phase different. Hence the resultant voltage appears at the feed point. The microstrip feed networks are designed to do the task of collecting all the induced voltages fed into one point [5]. Comparing the circular patch microstrip array antenna with parabolic dish, it has some advantages such as small dimensions, light weight, slim size and easy manufacturing [6]. II. THE DESIGN ISSUE OF CIRCULAR PATCH MICROSTRIP ARRAY ANTENNA The design of circular patch microstrip array antenna will begin from single element. It then developed into 36 elements and finally the total radiation pattern, gain and S-parameter is computed through ADS. A. Circular patch antenna analysis From the literature review, the effective radius of circular patch is found by [7]: 1.7726 2h r n r 2h r r r eff l 1 (1) Where r = physical radius of circular patch h = height or thickness of the substrate r = dielectric constant The effective area of the patch is then given by [8]: A eff = r 2 eff (2) B. Resonant frequency of the circular patch The resonant frequencies of the circular patch can be analysed conveniently using the cavity model [9], [10], [11]. The cavity is composed of two perfect electric conductors at the top and bottom to represent the patch and the ground plane, and a cylindrical perfect magnetic conductor around the circular periphery of the cavity. Using the synthesis procedure as mentioned in [12], the resonant frequency of a circular patch can be computed as: Circular Patch Microstrip Array Antenna for KU-band T.F.Lai, Wan Nor Liza Mahadi, Norhayati Soin C World Academy of Science, Engineering and Technology International Journal of Electronics and Communication Engineering Vol:2, No:12, 2008 2693 International Scholarly and Scientific Research & Innovation 2(12) 2008 scholar.waset.org/1307-6892/5430 International Science Index, Electronics and Communication Engineering Vol:2, No:12, 2008 waset.org/Publication/5430