# Circularly Polarized Broadband Printed Antenna for Wireless Applications
## 1 Introduction  
Circularly polarized (CP) microstrip antennas have been popularly used in various contemporary wireless communications systems, such as for satellite communication, WLAN (Wireless Local Area Network) and WiMAX (Worldwide Interoperability for Microwave Access), GPS (Global Positioning System), RFID (Radio-frequency identification) tag and RFID readers because of the versatile orientation of the transmitter and receiver [1,2]. Systems utilizing CP antennas in both transmitter and receiver ends have observed they improved upon cross polarization discrimination and present better immunity to multipath propagation. With the latest interest in high-speed transmission for wireless communications, the marketplace demand for CP antennas with a broad impedance and AR (Axial Ratio) bandwidth are in popular. Several types of antennas with different shapes for the patch, feed line, and different slots in the ground and radiating patches, which can generate considerable wideband CP properties, have been reported in the literature. Among the reported research, dielectric resonator antennas (DRAs) [3, 4, 5], cross dipole antennas [6, 7, 8, 9] and magneto-electric dipole antennas [10, 11, 12] was designed for broadband CP characteristics. The DRA designed by [3] to achieve ARBW (Axial Ratio Bandiwdt) of 46% while the magneto-electric dipole antenna proposed by [12] yielded IBW (Impedance Bandwidth) of 65%, 3 dB ARBW of 71.5%. However, the thickness of DRA is comparatively large and complex designstructure, and a dipole antenna requires a distance of quarter wavelength from the radiator to the ground plane, which makes these antennas relatively bulky. To solve the issue, array antennas [13; 14] and multilayer antennas [15; 16] were suggested. However, array antennas require a complex feeding network while multilayer antennas pose complexity in the alignment and integration process. Besides, these type of antennas suffers narrow bandwidth. To minimize the above drawbacks, various recently reported CPW (Coplanar Waveguide) antennas, monopole antennas, reactive impedance surface based UWB (Ultra Wideband) antennas and different shape slot antennas were studied [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34]. To enhance the performance of the small antenna especially gain and impedance bandwidth, several researchers were used reactive impedance surfaced metamaterial [17]. Using planar-patterned metamaterial concepts, broad bandwidth and high gain rectangular patch antenna were designed [18; 19]. A coupled capacitive-inductive circuit is formed using the patterned patch and ground plane. The dimension of [18] is 28 mm \(\times\) 32 mm, and the bandwidth is covering from 5.3-8.5 GHz with the gain above 4 dBi. Rectangular radiating patches, which are asymmetrically positioned concerning the microstrip line, attain an impedance bandwidth of 136% and AR bandwidth of 77% with large dimensions [20]. An approximately 60% large AR bandwidth was obtained through the inverted L and U-shaped monopole strip and a slotted ground plane [21]. The 61.96% CP bandwidth has been attained with an inverted asymmetric arm L-shaped microstrip and slotted ground plane, but the dimensions of the antenna were large [22]. An asymmetrical Y-shaped feeding line is used to produce the CP radiation for X band applications and a through via in series with an inductive strip is employed to achieve an impedance bandwidth of 31.4% [23]. A wideband CP printed triangular monopole antenna is also proposed in [24]. By asymmetrical excitation of a trilateral ground plane and a planar triangular wideband circular polarization is achieved, which is covering 1.42 to 2.7 GHz (62%). Though the antenna does not cover a compact dimension. The overall dimension of the antenna is 79.2 \(\times\) 112 mm\({}^{2}\). A simple and compact broadband CP antenna was presented with a slotted ground plane and semicircular slot.