Wideband and dual-band patch antennas for wireless communications

Abstract

This thesis presents novel techniques to improve the performance of the wideband and dual band monopolar patch antennas. Top loaded monopole technique was proposed in the literature in 1999 for enhancing the bandwidth for monopolar patch antennas. With the utilization of a multi-resonating structure and top-loaded monopole feeding technique, a compact wide bandwidth monopolar patch antenna with good performance can be achieved. In addition, this multi-resonating structured antenna, employing passive CMRC filters, with U-bridge feeding technique, can perform a wide dual bandwidth. Firstly, the small wide bandwidth monopolar patch antenna is studied. In this new design, the size reduction is achieved with the two pairs of shorting strips from the truncated corner of the upper patch to the ground. The upper and lower patches form a parallel plate, introducing a capacitance to cancel out the probe inductance. A very wide impedance bandwidth (SWR<2) of 76% is obtained which is attributed to two critical parts of the antenna structure. The first one is due to the square disc coupling feed which is formed by the coaxial probe feed with a small square patch which is coupled to the upper truncated corner patch with shorting strips to the ground. The second one is due to the folded upward wall on the upper patch. Without the upward wall, the antenna exhibits a 33% impedance bandwidth (SWR<2), by choosing a certain height of the upward wall, the impedance bandwidth can be well matched in the lower band and the impedance bandwidth is enhanced up to 76%. Then, a small dual band patch antenna for wireless communication applications is studied. The antenna consists of a folded patch, 4 shorting strips and excited by a U-shaped bridge feed. With the introduction of shorting strips and folded wall, the total size reduction achieves about 60%, as compared to the conventional TM01 mode monopolar radiating patch. Wide impedance bandwidths of 43.2% and 31.4% (SWR<2) in the frequency bands of 2.03 to 3.15GHz and 5.34 to 7.33GHz, respectively, have been obtained experimentally. Finally, the compact dual bandwidth monopolar patch antenna integrated with CMRC filters is investigated. The antenna consists of a cross-shape copper plate folded as an upward cap, which is integrated with passive CMRC filters, excited by a coaxial probe feed. With the introduction of the CMRC filters, the unwanted 2nd harmonic radiation is blocked and stable radiation patterns with low ripple levels are achieved in the two operating frequency bands. This single structure patch antenna performs a dual wide impedance bandwidths of 23.5% and 27.8% (SWR<2) in the frequency bands of 2.25 to 2.85GHz and 5.58 to 7.38GHz, respectively.

Date of Award	16 Jul 2007
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kai Ning Edward YUNG (Supervisor)