Analysis of Dielectric Loaded Complex Horn Gaussian Beam Launcher by Hybrid Technique of FEM and Gaussian Mode Expansion

Summary form only given. High performance Gaussian beam launchers are required in quasi-optical power combing system for the transformation of power from active devices to free space fundamental Gaussian beam mode. The conical corrugated horn appears to be a popular choice (Olver, 1992) which can produce a nearly perfect Gaussian beam. Dielectric cone loaded horn antenna exhibit comparable performance at millimeter waves where the conventional corrugated horn is difficult to construct (Olver et al., 1998). A dielectric lens can be added to the central dielectric corn to obtain a constant phase front over the aperture, which will improve the aperture efficiency of the horn (Olver and Philips, 1993). Imposing a curved profile on the horn will give additional degree of freedom for obtaining better performance, which has successfully been applied in the design of corrugated and dielectric loaded horns (Philips and Olver, 1994). In most cavity-based solid state sources, rectangular waveguide outlets are often used. In this case, rectangular pyramidal launchers are easy to be connected. In this paper, the above stated techniques are applied on the rectangular pyramidal launchers for obtaining high transformation efficiency at D-band. An efficient hybrid technique of finite element method (FEM) and Gaussian mode expansion method has been proposed for the analyses of dielectric loaded complex horn Gaussian beam launchers. The formally exact Gaussian modes are used to express the free space fields. The finite element method is employed to analyze the launcher region. These two methods are combined through the boundary condition on the interface. A matrix equation for discretized electric fields in FEM region can then be deduced. The tangential electric fields on port surface of the launcher are obtained by solving this matrix equation. Then the main mode reflection coefficient can readily be calculated. Meanwhile, the solution to the electric fields on the output port surface can be used to determine the amplitude of each Gaussian mode, and further determine the transformation efficiency of the launcher.