We have presented a new analytical method for the stub-loaded ridge waveguide that is a candidate of leaky-wave antennas in the millimeter-wave region. This guide has many singular conductor edges, so that its accurate analysis is very difficult. The present method overcomes such difficulty by introducing the singular fields at the edges into the field expressions beforehand. Then we have investigated the dispersion characteristics for various structural parameters, to find a structure suitable to antenna applications. Finally, we have verified their behavioral feature experimentally.

We report here a new mode-coupling effect that occurs on coplanar waveguides of finite width. The coupling occurs between the standard CPW dominant mode and a new dominant mode identified by us for the first time, and called here the CPW dominant surface-wave-like mode. This coupling is different from that which is known to occur when a printed-circuit waveguide is placed in a box or package; here there is no box, and the finite width by itself is sufficient to produce the coupling effect. This effect results in a complicated dispersion behavior, and we investigate it experimentally and theoretically. In addition to this new coupling effect, a new leakage effect on this class of waveguides has been investigated by us for many variant forms. The details will be discussed elsewhere, but a brief discussion of this leakage effect is also included here in order to place the new coupling effect in proper perspective. We also investigate the sets of structural dimensions needed for the coplanar waveguide to operate without leakage. Finally, we perform a set of measurements in X-band on a standard coplanar waveguide of finite width, and it is found that the experimental results agree very well with the theoretical calculations.

We present a design procedure of a leaky-wave antenna with low sidelobes based on the stub-loaded ridge-rectangular waveguide. As a typical example, we desig the antenna with the Taylor distribution of -30 dB sidelobes and fabricated it. The agreement between the measured and the numerical results validate the proposed antenna.

In this paper, an eight-legged resonant element is proposed for a multiband and dual-polarized frequency selective surface (FSS). The FSS element has two resonant frequencies for constructing two reflection bands, of which the separation can be easily controlled by adjusting the shape of the element. The flexibility is demonstrated by the simulated results of transmission responses for various geometrical parameters. And it is shown that introducing resonant-grid and closely-packing techniques can improve the reflection bandwidth. Finally, the good agreement between the measured and the calculated results proves that the eight-legged element is useful for the design of a multiband FSS.

The presence of a new surface-wave-like mode on CPWs of infinite width produces a complex transition region at the onset of leakage, involving the unusual simultaneous combination of a coupling region and a spectral gap. An examination of this region leads to a clear physical explanation of why sharp minima occur in the leakage behavior.

A new mode-matching method is proposed here for printed-circuit analysis, which considers the field-continuity conditions via the singular aperture field at conductor edges expanded into a finite series of known singular functions with unknown coefficients. In this sense, our approach seems to be similar with the spectral-domain method in the handling of singular functions of currents on conductor strips, but the aperture plane on which singular functions are assumed is taken along a perfectly different direction. Effectiveness of this method in numerical handling is proved by the dispersion calculations of microstrip lines with isotropic and anisotropic substrates.

Printed transmission lines have been extensively examined so far, but results obtained there are all concerned with the waveguiding conductors with no loss and zero thickness, except very few results. We have recently studied the transmission characteristics of printed transmission lines in detail, when the waveguiding conductors have finite conductivity and thickness, and we have found an unexpected effect that we call a "mode extinction effect. " This effect results in significant changes in the dispersion behavior of the printed-transmission-line fundamental mode. For a critical thickness, it may turn out that such transmission line can not use in open structural configuration, but must always be used by putting into a packaging box. In this paper, we discuss thoroughly this important effect and related results from the standpoints of both the dispersion behavior and the vector field plots. We also show the measured results of the attenuation constant.

This paper proposes a new type of evanescent-mode waveguide filters consisting of two parallel cutoff waveguide paths, in which a number of swelled portions are provided as resonators. One of two paths (the subsidiary path), mechanically connected to the main path in parallel, achieves the negative coupling to exhibit an elliptic-like feature. This type of filters includes a number of complicated waveguide-junction discontinuities. They are analized accurately by the full-wave analytical method based on the mode-matching method. After deriving the generalized equivalent network, the main-path structure is designed to exhibit the specified passband response by using its approximated network. The specified overall characteristic is then synthesized by a computer-aided design method by using an equivalent network without approximations. Measurements on the filters modeled in both X- and U-bands show excellent agreement with the designed characteristics, and prove the feasibility of two-path cutoff-waveguides for filter applications in the microwave and millimeter-wave regions.

A multimode horn with both a low cross-polarization component less than -30 dB and good VSWR characteristics has been realized at frequency bands 8.6-9.8 GHz and 10.75-11.15 GHz. The improved performance of the proposed horn is verified by comparing with the previous dual-band double-flared horn. The design method for such a horn is based on the mode-matching approach combined with the optimization procedure. This paper proposes an objective function taking account of a spill-over loss and a rotational symmetry in the radiated field instead of an ideal radiation pattern. The effectiveness of our horn is verified by comparison between experimental results in the X band and predicted ones.

This paper discusses an efficient numerical calculation technique for scattering from three dimensional bodies of perfect conductors and dielectric materials. The key of this method is to express the scattering fields by the field generated by the distributed hypothetical dipoles (or the equivalent sources). Since the scattered field should be analytic in each homogeneous sub-domain of general scattering bodies, the equivalent sources to be used for expressing the scattered field in one of those sub-domains should be distributed outside of this space domain. Unknown vector currents of equivalent dipoles are solved by the generalized mode-matching method. Example scatterers discussed here are finite conducting and dielectric cylinders with rotationary symmetry. The results are discussed with comparative data obtained by other numerical method and also with experiments that we took.

We first reported the simultaneous-propagation effect that the leaky dominant mode can be present on conductor-backed coplanar strips at the same time as the conventional bound dominant mode. We have investigated here numerically and experimentally this effect in detail. Consequently, we have found that it occurs under a certain condition of structural parameters, and also have verified that it affects circuit performance significantly.