The application of the segmentation method in the design of compact single-feed circularly and linearly polarised microstrip patch antennas

Lee, Sin Keng (2007) The application of the segmentation method in the design of compact single-feed circularly and linearly polarised microstrip patch antennas. Doctoral thesis, Northumbria University.

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Abstract

This thesis presents the application of coplanar circuit analysis in the design of compact single-feed circularly polarised (CP) and linearly polarised (LP) microstrip patch antennas. A CP nearly square patch antenna and a CP truncated corners square patch antenna are designed. Also a LP U-slot rectangular patch antenna is designed. In order to obtain a faster computational run-time, coplanar circuit analysis and segmentation method are applied for the impedance calculations. The coupling and self impedance formulas for both rectangular and right-angled isosceles triangular segments are given. Explicit formulas for the coupling impedance between a perimeter port and a probe port, and also the probe self impedance on both of these segments are new and are derived in detail. A CP nearly square patch antenna is designed using both the cavity and equivalent circuit models. New and simple design equations are derived to determine the dimensions of the patch with a feed in any given position. For a microstrip feed offset from a corner of the patch, the area of perturbation segment is increased which reduces the effect of manufacturing errors. A simple matching network consisting of a short length of microstrip line is designed to achieve a more compact form of the matched antenna. The results obtained from both models are good agreement. A CP truncated corners square patch antenna with a microstrip feed offset from the centre is presented. In previous work the design is a feed along the centre line and the areas of the deleted segments are very small so the performance of the antenna is very sensitive to manufacturing errors. Hence an offset feed is proposed in order to increase the perturbation area and so reduce the effect of the manufacturing errors. The segmentation method is used for which a new explicit matrix input impedance formula is derived. The impedance formula requires a computer run time less than half that required by simulation (full-wave software, Ansoft Ensemble). The change in area of the perturbed segment and input impedance with the microstrip offset feed position is examined. A compromise offset feed position was chosen so as to maximise the area of the perturbation segment and achieve good impedance matching for a compact antenna structure. A LP probe feed U-slot rectangular patch is designed and the input impedance is determined. A set of initial design equation is used to produce a first-pass design. In applying segmentation method a new explicit input impedance formula for the antenna is derived. The basic system of eleven coplanar circuit equations is reduced to seven equivalent circuit equations from which the explicit impedance formula is derived. The dimensions of the patch are adjusted to give good impedance matching. In respect of computational efficiency, the run time of the new matrix input impedance formula is at least 10 times faster than is required by simulation. A thicker substrate is also used in order to improve the bandwidth. The predicted, simulated and measured results of the above three compact patch antennas are in good agreement. Mathcad programming is used to implement the design calculations of the compact patch antennas.

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