A metallic waveguide that has an array of dielectric rods located at a distance from the side wall of approximately one quarter the waveguide width was previously proposed for single mode propagation over a wide frequency range. In this study, the S parameters of such a waveguide were measured for the TE10 mode.

A system that has an array of dielectric rods at the center of a waveguide was previously suggested for single mode propagation with a wide frequency range. However, it is difficult to introduce the wave source from a coaxial cable, due to use of the TE10-like and TE20-like modes. In this investigation, an asymmetric setup of the dielectric rods is proposed for better coupling efficiency of the TE10 mode.

A metallic waveguide with dual in-line dielectric rods can propagate electromagnetic waves more than two times higher than the cutoff frequency region and without higher modes [1]. If the straight portion in the waveguide has even symmetry, then dielectric rods are only required in the bent portion. Connection losses between the portions are improved by adding other dielectric rods.

Characteristics of a class of stepped-impedance resonators (SIRs) which is loaded with two dielectric rods, are investigated by a Finite-Difference Time-Domain (FDTD) method. Dielectric rods to be inserted between a strip conductor and the ground plane have higher relative permittivity than that of the substrate. When a tapped half-wavelength (λ/2) microstrip resonator is loaded with two dielectric rods, the electric length of a loaded λ/2 resonator becomes longer than λ/2, which makes its fundamental resonant frequency () to be generated on the region lower than that of an unloaded λ/2 resonator (fr) and its first spurious response (fsp1) is generated on the region higher than 2. Therefore, to shift back to fr, the resonator's length is to be reduced, and this, in turns, suppress the spurious responses. Then, the resonant characteristics of an SIR employing the proposed method has also been investigated, and it is found that this is capable of suppressing the spurious responses in wideband together with an attenuation pole in the stopband, and of further reducing the resonator's length. Therefore, wide exploitation of the presented method can be expected in the filter design based on the LTCC technique.

This paper presents a new method to improve the resonant characteristics of a microstrip resonator. The improved characteristics have been achieved by inserting two dielectric rods between strip conductor and the ground plane. Dielectric rods to be inserted have higher relative permittivity than that of the substrate. Therefore, it is suitable to realize by Low-Temperature Cofired Ceramics (LTCC) technique. Several model of microstrip resonators employing the proposed method are analyzed by a Finite-Difference Time-Domain (FDTD) method, and their resonant characteristics are discussed. One of the advantages of the proposed method is that an attenuation pole (fl or fh) in each side of the fundamental resonant frequency (fr) and improved-spurious responses can be realized together by a capacitive-coupling tapped resonator loaded with dielectric rods. The proposed method is also effective to achieve sharp skirt characteristics and wide stopband of a direct-coupling tapped resonator which can be used either as a wideband lowpass filter or a band-elimination filter. Another interesting feature of the analyzed resonators is that about 60% reduction in resonator's length has been obtained compared to a basic half-wavelength (λ/2) microstrip resonator. Therefore, wide exploitation of the proposed method can be expected in the filter design based on the LTCC technique.

An image NRD guide-fed dielectric rod antenna, which is suitable for use at millimeter-wave frequencies, is presented in this paper. The antenna is composed of a linearly tapered dielectric rod connected to the image NRD guide. First, radiation characteristics of the dielectric rod antenna directly protruded from the end of the image NRD guide are investigated by FDTD analysis and measurements at 30 GHz band. For this case, the degradation of the radiation pattern and the decrease of the gain, which are due to the strong radiation from the guide-to-antenna discontinuity, are observed. In order to minimize this radiation and to realize reasonable radiation characteristics, a transition from the image NRD guide-to-rod antenna is proposed. A simple procedure to determine the optimum dimensions of the transition is described. This procedure is based on parametric study of the transition's dimensions, and is performed using FDTD analysis. Based on the results, the dielectric rod antenna having a length of 10 λ0 is designed, and its performance is analyzed and measured. The results show that radiation patterns with the half power beamwidth of 22, sidelobe level of -21 dB and reasonable gain of 18.5 dBi can be realized by employing the transition having the optimum dimensions.

The dielectric rod waveguides with corrugation consisting of nonintegral-ratio period waves are investigated numerically. The leakage characteristics of HE11-type wave in the waveguide is analyzed by applying Yasuura's method. The complex propagation constants and the far field patterns are presented. The radiation pattern of a fabricated waveguide with corrugation agrees well with the calculated value. The dependence of radiation characteristics on the corrugation form is discussed. It is shown that the leakage directions and the intensity of leaky waves are controlled independently one another. The radiation pattern can be synthesized by choosing the geometric parameters of the corrugation properly.

An image type resonator method is proposed as a method to evaluate precisely the temperature dependence of dielectric material. At first, the temperature coefficients of the resonant frequencies, TCf are measured separately using the shielded dielectric resonators of three types; that is a parallel plate type, and an image type, and a MIC type resonator. Secondly, an intrinsic temperature coefficient of the resonant frequency TCf0, which is defined as the temperature coefficient of a resonant frequency when all the stored energy is confined inside a dielectric, is estimated from these measured TCf. Actually, the TCf0 values of a sapphire and (ZrSn) TiO4 rod are estimated from the TCf values measured for the resonators of three types. As a result, for the parallel plate type, the precision of TCf0 is about 0.1 ppm/. For the image and MIC types, the errors of about 0.5 ppm/ in the TCf0 values arise from the errors in the linear expansion coefficients of the resonators, rather than from the experimental errors in TCf. Then, another image type resonator is designed to estimate TCf0 within error of 0.1 ppm/. In this design, dimensions of the shielding cavity is determined to reduce the influence of the errors in the linear expansion coefficients on precision of the TCf0 estimation. Finally, for a (ZrSn) TiO4 ceramic rod, a TCf0 value estimated from TCf measured for the image type resonator is obtained with accuracy of about0.1 ppm/.

A dielectric rod waveguide applicator for microwave heating such as microwave hyperthermia is described. The applicator consists of the acrylic cylinder filled with deionized water. By circulating the deionized water, the dielectric rod waveguide applicator acts as a surface cooling device, so that it doesn't need any bolus. This surface cooling device enables the dielectric rod waveguide applicator to control the site of effective heating region along the depth axis. Useful pattern of the circular or spheroidal shape and axially symmetric effective heating region were obtained. Furthermore metal strips provided on the aperture of applicator control the shape of the heating pattern.