International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 9, September 2012) 177 Reflection Properties of three different Substrates on Circular Microstrip Patch Antenna Anzar Khan 1 , Puran Gour 2 , Rajesh Nema 3 1,2,3 NIIST, Bhopal (M.P.), India Abstract — Communication Systems are being investigated for S, C, X and Ku bands. For portable systems, the size and cost of the antenna are of great importance. Microstrip antennas show promise due to their small and conformal features, and their ability to be mass manufactured. The bandwidth and return losses are also of great importance. A project is currently underway to examine the characteristics of three dielectric substrates believed suitable for microstrip antenna applications in the X-band. These substrates are Bakelite, ℰr of 4.78 and tan δ of 0.03045, RT Duroid, ℰr of 2.2 and tan δ of 0.0004 and Polyester, ℰr of 1.39 and tan δ of 0.01 specified at 10 GHz frequency. A microstrip antenna is designed with triangular patch of fixed resonant frequency of 10 GHz and fixed height of 1.5 mm. Keywords — Microstrip patch antenna; organic substrates; polyester; X-bands; return loss I. INTRODUCTION Now a days, communication devices need high frequency compact antennas. Microstrip patch antennas are popular choices because of their low profile and conformal structures. The patches can be of different geometry like rectangular, triangular, circular, elliptical or any other shape. In spite of numerous advantages of microstrip patch antennas it is difficult to achieve a better tradeoff between the gain, bandwidth and more prominently the size of antenna. In practice, different dielectric substrates are used for manufacturing microstrip patch antennas. It is believed that dielectric substrates with dielectric dielectric constants in the range 2.2 ≤ ℰr ≤ 12r gives better results. Now a days synthetic or natural materials are also used as substrates to manufacture these antennas. The work presented in this paper is the comparison of synthetic substrate, polyester with the natural dielectric substrates Bakelite and RT Duroid for manufacturing triangular microstrip patch antenna using IE3D Simulator. IE3D has unlimited unknown, magnetic current modeling, iterative matrix solver and Genetic EM optimizer. It also includes the pattern view for full radiation pattern handling capabilities. II. ANTENNA DESIGN Microstrip patch antenna is designed with circular patch. The radius of the patch is calculated by the formula as given below- 1 2 2 1 1.7726 2 r n F F F a h h                        Where a is radius in mm, c is the velocity of light 11 3 10 / mm s   , r E is the dielectric constant of the dielectric substrate. The resonant frequency is taken as 10 GHz and the height of the substrate is 1.5 mm. F is given as- 9 8.791 10 r r F f    The effective radius is given by- 1 2 2 1 1.7726 2 e n r a a a h a h                        Coaxial Feed The Coaxial feed or probe feed is a very common technique used for feeding Micro strip patch antennas. The inner conductor of the coaxial connector extends through the dielectric and is soldered to the radiating patch, while the outer conductor is connected to the ground plane. The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation. A. Bakelite Dielectric constant of Bakelite is r  = 4.78 and loss tangent, tan δ is 0.03045. The radius calculated from the above formula is-