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Abstract-A modified technique to design directional ultra-wideband (UWB) antenna with slotted ground structure approach on the ground plane has been presented for applications in C-and X-bands. Initially, elliptical slot is inserted into ground and thereafter, the axis of ellipse is rotated 45 degrees in direction of the substrate. Minor axis of the ellipse is optimized to locate it symmetrically around the circular patch in order to obtain the full C-and X-band operations and also to enhance directivity. Thereafter, for further improvement in the directivity as well as gain, an elliptical slot in circular patch has also been introduced. The impedance bandwidth approximates about 95% covering the frequency ranging from 4.18-11.50 GHz. The return losses (S 11 ) are −38 dB and −43 dB through simulation, which are −24 dB and −32 dB by measurement at 6.3 GHz, 9.3 GHz resonant frequencies, respectively. Simulated gain and half power beam width (HPBW) are 2.5-8.4 dB and 49-22 degrees in 4.18-11.50 GHz band, respectively. Gain and half power beam width (HPBW) of the proposed antenna improves by 1-2 dB and 5-10 degrees, respectively compared with previously designed antennas. Simulation of the antenna has been carried out on Computer Simulation Technology (CST) software on an FR-4 substrate having dielectric constant 4.3 of thickness 1.6 mm. The measured results show good agreement with equivalent circuit model and CST simulation.

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This work presents a novel structure of semi-circular floral shape slotted antenna for an ultra-wideband (UWB) including WCDMA, Bluetooth and Wi-Max applications. Initially, a semicircular floral shape radiator is designed by inserting an elliptical slot in patch with partial rectangular ground plane. Further, three rectangle symmetrical stepped slots are inserted in ground below 50 ohm micro-strip (MS) feed line which is integrated with stepped quarter wave transformer to achieve an ultra-wide impedance bandwidth. The proposed antenna structure achieves UWB of 4-18 GHz which cover 127% (S 11 < −10 dB) fractional bandwidth (FBW). Furthermore, ground plane is modified by loading three asymmetrical capacitive folded strip resonators (CFSR), which provide an additional lower frequency communication bands 2100 MHz (2-2.2 GHz), 2400 MHz (2.34-2.47 GHz), and 2700 MHz (2.69-2.75 GHz) for applications of WCDMA, Bluetooth, and Wi-Max, respectively. An optimized dimension of the proposed antenna is 30 × 30 mm 2 (1.1λ 0 × 1.1λ 0), which is designed and fabricated on an FR-4 substrate having thickness 1.6 mm and dielectric constant 4.3. The proposed design is computed by Electromagnetic (EM), ADS simulator, and simulation results are validated with measured results. 1. INTRODUCTION Recently, the demand of ultra-wideband (UWB) antenna is increased day by day in modern communication system. Federal Communications Commission (FCC) released an unlicensed UWB 3.1-10.6 GHz for commercial applications [1]. Compact size, matching bandwidth, and stable radiation characteristics are main challenges for the design of UWB antennas. Presently, compact single antennas are the major requirement for modern communication systems to cover the entire allotted wireless communication bands. In recent years, the design of dual-band antenna with UWB has an active research area without affecting UWB performance [2-9]. A number of dual-band antennas have been reported by researchers having UWB characteristics. Chu and Ye, Yildirim et al., and Gupta [10-12] proposed 42 × 46 mm 2 wideband antennas having lower frequency bands, but size of these antennas is large. However, a few UWB antennas have also been proposed with the integration of low frequency wireless bands. Antoniades and Eleftheriades, Samadi Taheri et al., and Mishra et al. [13-15] designed a fork shaped, L-shaped and rhomboidal monopole multiband antennas with attaching extra loaded strips, but these antennas did not have UWB characteristics. Further, Bod et al. and Foudazi et al. [16, 17] proposed 25 × 28 mm 2 antennas with compact size, but bandwidth is very small. Rahanandeh et al. and Li et al. [18, 19] designed a dual-band compact antenna by loading three additional strips to cover Wi-Max, WLAN, and Bluetooth frequency bands, but the antenna did not cover the entire UWB. Aravind et al. [20] designed a rectangle patch with a coupled folded stub for UWB and long-term evaluation system, but the antenna size is very large. Mahamine et al. and Naidu [21-23] proposed a circular ring with t...