Circular polarised microstrip antenna design using segmental methods

Lim, Eng G. (2002) Circular polarised microstrip antenna design using segmental methods. Doctoral thesis, Northumbria University.

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Abstract

Research into the modelling and analysis of microstrip patch antenna have been reported in many studies. These include Transmission Line Modelling, Cavity Modelling, Coplanar Multiport Modelling and Full wave Modelling. Since the electromagnetic field elements are time harmonic, the phasor-form of the Maxwell field equations is used. In this thesis results are presented of the research that has been carried out into the segmental approach for the analysis of the microwave patch antennas. The segmental approach includes the "Segmentation" and the "Desegmentation" methods. In the segmentation method two distinct structural forms have been identified, cascade and shunt types. In the cascade type all consecutive segment elements share a common boundary, while for the shunt type, all appended segment elements have no common boundary. In the case of the shunt type structure a generalised input impedance matrix formula, for any number of appended segment elements, has been obtained. For the desegmentation method a generalised input impedance for any number of deleted segment elements, has been obtained. The above research studies have been applied in the design of a circular polarised two corner deleted square patch microstrip antenna with a single feed. For this structure the design involves both square and triangular patch geometries. The overall patch geometry for circular polarised is determined using perturbation analysis to determine the size of the deleted triangular segment elements. New computationally efficient impedance coupling expressions for the interconnecting port impedances on a rectangle, and, on a right angled isosceles triangle shaped antenna patch have been derived. In the determination of the input impedance of the overall antenna structure the coupling impedances constitute the elements of the individual segment coupling matrices. The matrices are used in a general multiport matrix circuit analysis to obtain the input impedance formula. It is established that, where applicable, the desegmentation method is computationally more efficient than the segmentation method. The new results obtained have been applied to the design of a corner deleted square patch antenna, and, the design procedure is fully described. The computer program implementation evaluates the perturbation quantity, and, the antenna input impedance. The structural properties of the coupling matrices, which are used for efficient computation, are described in detail. All the results from the above work show close agreement with full-wave software simulation and practical results. SIGNIFICANT RESEARCH ACHIEVEMENTS: Both segmentation and desegmentation methods have been studied and it has been shown that the desegmentation approach, when applicable, is in general significantly more computationally efficient. In the segmentation method two structural forms, cascade and shunt have been identified. In the latter case a new generalised input impedance matrix formula has been obtained for any number of appended segment elements. A new generalised input impedance matrix formula has been obtained for any number of deleted segment elements in the desegmentation method. New computationally efficient expressions for the coupling impedances have been derived and used in test applications. New computationally efficient expressions for the offset input impedance of a linear polarised rectangular patch, and, an isosceles right-angled triangular patch have been derived and experimentally verified. A program implementing the design procedure for the corner-deleted truncated square patch circular polarised microstrip antenna has been constructed using MATHCAD programming.

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