Wideband meandering probe-fed patch antenna
Student thesis: Doctoral Thesis
Related Research Unit(s)
|Award date||3 Oct 2005|
This thesis presents a novel feeding mechanism for wideband patch antenna, designated as: “meandering probe feed”. This mechanism can increase the impedance bandwidth and suppress the cross polarization of the patch antenna. Based on the working principle of the meandering probe, two alternative feeding mechanisms, the printed meandering strip and the proximity coupled meandering probe, are developed for the patch antenna, which are suitable for mass production. Adding parasitic elements or increasing the width of the meandering probe can further enhance the impedance bandwidth of patch antennas, while increasing the width of the patch to over one wavelength can substantially enhance the gain of a patch antenna. Lastly, the meandering probe is applied for designing circular or dual linear polarization. All antennas are studied by simulation, and then most of them are confirmed by measurements. Firstly, a meandering probe fed patch antenna has been investigated. This antenna has a wide impedance bandwidth of 24.5% and a low cross polarization level of less than –18dB. As the meandering probe can suppress the cross polarization and it is directly connected to the patch, the gain of the antenna is higher than other aperture coupled and the L-shaped probe fed patch antennas, having a value of about 9dBi. The far field radiation pattern across the operating bandwidth is also stable and symmetric in both E and H planes. These results are been confirmed experimentally. A parametric study of the meandering probe fed rectangular patch antenna is carried by simulation, which is used to investigate the effect of the meandering probe’s parameters on the antenna’s input impedance. Moreover, it is found that the meandering probe not only can feed the rectangular patch effectively, but also suitable for the circular and triangular patches. Secondly, for practical implementation, two variations of the meandering probe feed are developed for the patch antenna, including the printed meandering strip and the proximity coupled meandering probe. Both feed mechanisms can excite the patch with wide bandwidth and low cross polarization. With the use of the second order meandering strip, the standing-wave-ratio of the antenna could be improved to SWR of less than 1.2 over a bandwidth of 12%, and to less than 1.1 over a bandwidth of 8% if a third order printed meandering strip is used. The measured cross polarization levels of such antennas are less than –22dB. On the other hand, the proximity coupled meandering probe fed patch antenna has an impedance bandwidth of 17% (SWR<1.5) and a low cross polarization level of less than –15dB over the operating band. Thirdly, in order to further enhance the impedance bandwidth and gain of the patch antenna, several techniques are proposed. One technique is to add coplanar or stacked parasitic elements to the patch antenna. An impedance bandwidth of 37% can be obtained. Another technique is to increase the width of the meandering probe, which has an impedance bandwidth of 47%. The advantages of these bandwidth enhancement techniques are simple structure and low cost. In addition, a gain enhancement technique is proposed, which is achieved by increasing the width of the rectangular patch. The gain of a patch antenna can be increased from 9dBi to 11dBi without adding any parasitic elements, and this antenna still has an impedance bandwidth of 26% (SWR<1.5) and low cross polarization level of less than –15dB across the operating band. The meandering probes are used to feed the patch antenna with circular and dual linearly polarizations. A meandering probe fed patch antenna with truncated corners is presented, and this antenna has 3dB axial ratio bandwidth of 8.8%. The effect of these truncated corners is to generate two orthogonal modes in phase quadrature. Adding another parasitic patch on top of the original patch, the antenna has a wider 3dB axial ratio bandwidth of 13.8%. It generates another two orthogonal modes resulting in the increase of 3dB axial ratio bandwidth. Finally, a dual polarized patch antenna fed by meandering probes is also presented, and this antenna initially has an impedance bandwidth of 14% (SWR<1.5) with isolation below –25dB. The isolation can be improved to less than –30dB by surrounding the antenna with vertical metallic walls. The antenna has gain of 10dBi across the operating bandwidth.
- Antenna arrays, Microstrip antennas, Antenna feeds