Super-Wideband Planar Monopole Antennas

Abstract

Over the past few years, wireless communication systems have been developed with an astonishing rate and wireless terminals for future applications are required to provide diverse services. This rising demand prompts the need for antennas able to cover multiple bandwidths for various systems. Since the allocation of UWB frequency spectrum (3.1 GHz to 10.6 GHz) by the Federal Communications Commission (FCC) for ultra wideband (UWB) wireless communications, UWB has been rapidly evolving as a potential wireless technology and UWB/SWB antennas have consequently drawn more attention from both academia and industries worldwide. A competent UWB/SWB antenna should be capable of operating over an ultra-wide bandwidth as assigned by the FCC and also cover cellular and radar communication frequency bands. At the same time, a small and compact antenna size is highly desired, due to the integration requirement of entire UWB systems. This thesis focuses on SWB planar monopole antenna design and analysis. Studies have been undertaken covering the areas of UWB fundamentals and antenna theory. Extensive investigations were also carried out on two different SWB antennas. The first type of antenna studied in this thesis is elliptical planar monopole antenna. The conventional microstrip feed line replaced with tapered microstrip feed line to enhance the operating bandwidth substantially. The trapezoid ground plane is also utilized to get impedance matching at lower frequency bands. The antenna has achieved the simulated impedance bandwidth of 62.5:1 in the frequency range of 0.4-25 GHz and measured bandwidth of 28.5:1 in the frequency range of 0.7-20 GHz. The proposed antenna also exhibits stable radiation patterns and good gain over the entire bandwidth. The second type of antenna is planar hexagonal monopole antenna. The feeding mechanism is same as the first antenna to achieve enhanced impedance bandwidth. In this design, two parasitic elements are used with the main patch radiator to match the impedance at lower frequencies as well as to minimize the effect of radiations caused by feed line. Simulations and measurements are carried out and it is observed that the antenna is capable of operating over an extremely wide bandwidth. The simulated ratio bandwidth is 147:1 in the frequency range of 0.17-25 GHz while the measured one is 66.6:1 in the range of 0.3-20 GHz. Good radiation patterns and gain are also obtained from the proposed antenna. It is also observed that the proposed antennas are smaller in size than the previously reported SWB antennas. These features have demonstrated that the proposed antennas can be an excellent choice for various wireless communication systems. It is needed to mention that the proposed antennas are measured till 20 GHz due to the limitation of SMA connector.