UWB microstrip antenna based on circular patch topology with stepped blocks and defected ground structure / Mohd Aizat Sulaiman

The growth of wireless communications technology over the past few years resulted in increasing number of wireless terminals worldwide. This also led to massive increase of user capacity, which is critical in maintaining the quality of services in a wireless communication system. Therefore, the development of breakthrough technologies that provides a new method of increasing the efficiency of frequency usage, and developing new frequency resources are essential. UWB uses very low energy pulses and transmit in a way which allows it to co-exist with other traditional narrowband and continuous carrier wave systems operating in the same frequency band. Corresponding to this development, research and design of UWB-capable antennas are essential for implementation and commercialization of UWB systems. UWB antennas are challenging and difficult to design because the antennas should be able to operate efficiently throughout the UWB frequency range as defined by the FCC. At the same time, due to integration requirement of the UWB system, the UWB antennas must be small, compact, and able to transmit stable signals. This thesis focuses on the design of UWB antenna in order to achieve stable return loss and stable radiation pattern in the range of UWB which are presented into four types of UWB antennas. The first design of the UWB antenna studied in this thesis consists of a circular microstrip monopole antenna with partial ground plane. However, this design did not cover all UWB range and the radiation pattern diverges at high frequency range of UWB. To overcome these problems, rectangular open stub lines and quarter wave transformer were introduced in the second design. The rectangular open stub line is used to maintain the return loss and the radiation pattern while quarter wave transformer is used to distribute 50ohm of impedance at the end of the feedline. The third design introduced the Wing open stub line structure at the both side of circular microstrip monopole antenna to improve the result from previous design. The fourth design was focused on the miniaturization of the UWB antenna from the third design while maintaining the antenna performance by applying Defected Ground Structure (DGS) concept. All the antennas were designed on Rogers 5880 printed circuit board (PCB) with overall size of 26 x 40 x 0.787 mm³ and dielectric substrate, εr = 2.2. The performance of each designed antennas was analyzed in terms of bandwidth, gain, return loss, radiation pattern, and verified through actual measurement of the fabricated antennas.