Patch type circuits for wireless communications
Student thesis: Doctoral Thesis
Related Research Unit(s)
Microstrip patch elements are used in wireless communication systems for its well-known advantages that include ease of construction, strong mechanical structure, low profile, and low cost. However, its relatively large size and narrow bandwidth limits its practical applications. This thesis covers different approaches to solve these technical challenges. These approaches each provide the detailed design guidelines for existing configurations, and can be used to develop new components to extend their potential. First of all, to compress the bulky size of patch elements, a patterned ground plane structure is proposed and verified. Four different patterns are etched into the ground plane to reroute the current distribution in the patch, and they all achieve different size reductions and with different complexity. For demonstration purposes, the patterned ground plane structure is applied to a four port network, rectangular patch hybrid coupler, achieving a significant size reduction of up to 72.3% compared to the conventional one. In addition, the patterned ground plane structure is proposed and verified to achieve frequency agility in the solution of the narrow bandwidth problem. An auxiliary patch is introduced into the patterned ground plane as a mechanism for changing the characteristic of the patch element, to realize frequency agility. This is achieved because the capacitance between the upper patch and ground plane can be controlled by loading tunable capacitors via the auxiliary patch. A frequency agile rectangular patch hybrid coupler with varactor loaded patterned ground plane is designed to operate over a frequency range of 50% with good return loss, small amplitude imbalance and quadrature phase characteristics. Besides the frequency agile approach, the broad band slot coupled structure is employed as one of the most straightforward way to solve the problem with bandwidth. The vertically installed slot coupled patch is proposed as an alternative to implement broadband characteristics with uniplanar topology. The pattern on the ground plane underneath the vertical substrate is introduced to enhance the coupling strength, increase the design freedom, and compress the circuit height. To demonstrate its simple structure and good performance compared with previous coupled line structures, the design of broadband 3 dB quadrature coupler and a broadband differential phase shifter will be demonstrated. Integrating multiple functions within a simple patch element is another proposed method for the size reduction of patch elements. Out of phase equal power division and bandpass filter characteristics are combined within one patch element. The novelty of the proposed structure is to use simple asymmetric cross slots in the patch element to achieve this integration. Coplanar waveguide/microstrip broadside coupling is then investigated to enhance the performance of the patch balanced filter and eliminate narrow coupling gaps and microstrip lines. Subsequently, transition between microstrip and coplanar waveguide is then added to the patch element by targeting certain electromagnetic coupling methods for higher level integration without introducing additional loss.
- Wireless communication systems, Electronic circuits