Modal expansion analysis of monopole and microstrip antennas

Abstract

Antenna problems are traditionally treated as open-region problems and solved by formulating one or two integral equations, whose solutions can be found analytically or numerically. Unlike most previous techniques available in the literature, this thesis presents an accurate and versatile technique for many canonical antenna problems. The proposed method treats the models, which are very close to the actual structures for practical engineering applications, in a very rigorous way. After properly introducing a boundary, the open-region antenna problems are transformed into "closed-region" guided-wave problems, which are then solved by the full-wave, formally exact modal expansion method. The distinguishing advantage of this approach to many antenna problems is that it can easily take into account all the effects of the feed line, junction discontinuities, and conductor thickness.

A number of techniques are introduced in this thesis to efficiently implement the modal expansion analysis. The "perfectly matched boundary", which is the combination of an electric wall and a magnetic wall, is used to truncate the free-space domain. An improved formulation for cascaded waveguide junctions is developed to save the computational effort involved in the modal expansion analysis.

Successful applications of the technique to various monopole and microstrip patch antennas are demonstrated. The input impedance and radiation pattern of various monopole antennas, including conventional monopole, sleeve monopole, dielectric-buried monopole, multilayer insulated monopole, and monopole on a finite ground plane, are thoroughly investigated by the proposed modal expansion method. Single and stacked circular and annular-ring microstrip patch antennas are also studied in detail in the thesis. Extensive computed results are presented for all the antenna structures considered.