It is a difficulty problem to measure permittivity of a dielectric material accurately whose permittivity is very close to unit. Open cavity method and interferometer method have been used in the past. In this paper, the sensitivity of these two methods to a small disturbance of permittivity is simulated and compared. Based on the simulation a new approach combining merits of the open cavity method and the interferometer method is proposed, and its advantages are described.

Finite-difference time-domain (FDTD) full-wave analysis of several waveguide junction circulators with full-height ferrite posts of arbitrary shapes is presented. The structures contain T-junction, irregular T-junction, Y-junction, and Y-junction with a bend. Two ferrite shapes of interest are studied, including circular cylinder and triangular post, and the performance of the circulators is presented. Calculation results of the waveguide-junction circulators with circular ferrite post and triangular ferrite post obtained by the present analysis are compared with those from the field-matching and finite-element methods, respectively, as a reference, and better agreement is found in this study.

An electromagnetic beam that is not the solution to the paraxial wave equation but is the solution to Maxwell's equation is simulated directly by the finite-difference time-domain method. Electrical and magnetic field components of the beam are presented graphically. Then the diffraction of the electromagnetic beam pulse by an aperture in a conducting screen is analyzed. The fraction of the beam power through the aperture is defined and calculated. The fields in the time domain near the aperture, which show the diffraction by the aperture, are presented graphically.

Field structures of waveguide Y -junction circulators containing irregular shaped ferrite material,suc h as Y -junction with partial-height cylinder/triangle ferrite posts and metal step impedance transformer, Y -junction with a ferrite sphere, and dual higher order modes circulator,whic h are classified as different junction resonance modes, are depicted to illustrate the circulating process. The analysis method used is a combination of the mode expansion method and finite element method,whic h is based on the weak form of Helmholtz equation. Calculated results (return loss,insertion loss and isolation) of these structures are shown and compared respectively to those in literatures. Consistencies have been observed.

This paper is aimed at analyzing the focal field of some axially-symmetric diffractive lenses with small F-number and electrically large radii which are used in millimeter wave focal imaging, especially for the case of a plane-wave incident onto the lenses obliquely, by using the method of moments (MoM). The analysis of a diffractive lens whose radius is as large as 78.3λ can be performed using appropriate pairs of basis functions and test functions in the MoM, and specific integration methods are adopted to integrate the oscillatory integrals which occurr in the MoM when it is applied on a body of revolution (BOR) for which the rotational symmetry of the BOR has been utilized. Comparison of the simulated results with the experimental data shows that the simulation is valid. An imaging experiment is carried out to show the ability of diffractive lens in a millimeter imaging system.