Design of Coaxial Fed Microstrip Patch Antenna for Wi-MAX/ IMT Applications

In this paper, a single layer, single co-axial feed, broadband, compact rectangular microstrip patch antenna is proposed. This proposed antenna is constructed by cutting a -shape slot under a Pi-shape slot in the patch fabricated on a substrate with relative permittivity 2.33 and thickness 8mm using simple coaxial feeding technique. In addition, four circular slots have been cut into the radiating edges of patch for broadband operation to cover both Wi-MAX (3400MHz-3690MHz) & IMT (3900MHz-4400MHz) communication standards. Basically, the use of these circular slots has effectively excited multi-resonant modes together with good impedance bandwidth. A thick substrate helps broaden the bandwidth for covering the entire frequency range of Wi-MAX & IMT communication standards. The proposed slot loaded patch antenna resonates at 2.66 GHz and has a broadband from 3.4 GHz to 4.5 GHz with the corresponding bandwidth of 108 MHz and 1.14 GHz and return losses of -16.0 dB and -22.6 dB respectively. The antenna gives a stable radiation performance with gain greater than 7dB over the entire broadband. The simulation has been performed by using CST Microwave Studio, which is a commercially available full wave electromagnetic simulator based on the method of finite difference time domain technique. Meanwhile, the proposed antenna exhibit almost omni-directional radiation pattern, relatively high gain and low cross polarization. Results for reflection coefficient and far-field radiation pattern of the designed antenna are presented and discussed. The analysis of the simulated results confirms successful design of co-axial fed microstrip patch antenna (MPA).