Abstract - This paper presents the radiation performance of a square patch antenna having two triangular notches on opposite edges designed on glass epoxy FR4 substrate and its performance is compared with a simple square patch antenna without any notch. The simulated results for this antenna are obtained by varying notch angle and compared with the measured results. The results indicate that square patch antenna with both notch angles equal to 168o resonates not only at two different frequencies but also offers a much higher bandwidth in comparison to a normal square patch (without notches). Both these resonance frequencies lie in the median band (3.25 to 3.85 GHz) allotted by IEEE 802.16 working group for WiMAX systems. The performance of antenna is optimized considering different conditions to obtain an antenna with dual band and high bandwidth performance. The radiation patterns, gain and radiation efficiency of antenna are also determined. Index Terms— Microstrip antenna, dual band operation, bandwidth and gain

Microstrip antennas have many advantages over conventional antennas such as low profile, ease of integration with active and passive devices, ability of mounting on planar, nonplanar and rigid exteriors to form MICs and low manufacturing cost due to use of printed circuit technology [1-3]. In case of planar antennas designed for wireless communication systems, it is necessary to have a compact size antenna configuration that can be integrated with other devices. Since the physical area of the microstrip antenna is inversely proportional to the frequency, it is difficult to achieve a compact size antenna for modern communication systems for WLAN, WiMAX and WiFi applications, particularly with normal patch geometries having acceptable efficiency and isolation values. There is often a tradeoff in realizing compact antennas while maintaining their performance characteristics. Traditional patch antenna using rectangular, circular or triangular geometries under normal conditions resonate at a single frequency and have inherent low bandwidth and gain values limiting their potential applications. Present day communication systems need dual or triple frequency operation with higher bandwidth. Microstrip antennas for dual frequency applications have been realized by exciting patch geometry by using a single [4] or dual feed [5] arrangements. Several researchers have studied the performance of bow-tie microstrip antennas and have reported either enhancement in bandwidth [6-8] or possible operation at two or more frequencies [9]. Some other works [10–12] applied different kind of notches in regular shaped microstrip antennas to improve their impedance bandwidth or to obtain multiple resonant frequencies with same antenna. Chen and Chia [11] applied suspended notched square probe fed plate over the ground plane to attain impedance bandwidth around 20 %. Shackelford et al. [12] considered a probe fed notched square patch antenna with a shorting post to attain bandwidth of the order of 13 %. In the present communication, we have considered a more simplified antenna structure by applying triangular notches on opposite edges of a square patch antenna and changed the depth of notch tip to optimize and attain best performance. This geometry is somewhat like a bow-tie antenna which are planar equivalents of the biconical antenna [13] that has wideband characteristics. However, in this communication, variations are made in the simple rectangular patch geometry where the notch tips are relatively far away than that in bow tie antenna. II. ANTENNA GEOMETRY AND RESULTS In the present paper, radiation performance of a square patch antenna with two nothes on its opposite edges is considered and is compared with a normal square patch antenna. The antennas are simulated using IE3D [14] and later designed on glass epoxy FR4 substrate (Єr = 4.4, tanδ = 0.002, substrate thickness 0.158 cm) with copper as its ground plane [15].