This paper presents a novel dual-band comb-line filter using a pair of hybrid resonators. The resonator consists of a half-wavelength stripline resonator short-circuited at both ends and a quarter-wavelength resonator of coplanar waveguide that is nested in the half-wavelength resonator. Numerical calculations by an electromagnetic simulator clarify the characteristics of dual-frequency resonance of the hybrid resonator when the structural parameters are changed. The surface current density on the resonator is also investigated at the resonant frequencies. A typical model of the resonator is fabricated and its resonance frequency characteristics are measured.

A simple method for improving out-of-band characteristics of a planar microwave filter is proposed. We clarify the close relationship among 'tap connection,' 'attenuation pole' and 'spurious responses' in filter design, theoretically and experimentally. Firstly, the basic characteristics of the resonator depending on the excitation method are examined. We show that skirt characteristics can be improved and spurious responses can be suppressed by using the tap connection technique. Secondly, the application examples of bandpass filters (BPFs) on the basis of the resonator with our principle are provided. It is confirmed that the resonator depending on the excitation method is useful for improving out-of-band characteristics of the planar microwave filter.

New bandpass filters (BPFs) with stub resonators are proposed for creating multiple attenuation poles. Firstly, the stub-dependent characteristics of the distributed-element stubs are examined theoretically. Secondly, the new BPFs with resonators of combined stubs are proposed. An advantage of these filters is the possibility of controlling the number of attenuation poles. The design of the proposed filter is carried out based on the general filter design with the narrow-band approximation technique. The transmission and reflection characteristics of the proposed BPFs are also examined theoretically and experimentally. The miniaturization of the filters is also carried out using the resonator with loaded-element stubs. The discussions lead us to the conclusion that the proposed design method of the filters are useful for controlling the number of attenuation poles of the BPF.

Properties of a quarter-wavelength coplanar waveguide resonator such as resonant frequency, external quality factor (Qe) are characterized by a theoretical approach and verified by the experiment. The unloaded quality factor (Q0) of the resonator is also examined experimentally. After new types of combline bandpass filter (BPF) made of these resonators are realized, their transmission and reflection characteristics are examined theoretically and experimentally. A new combline BPF having attenuation poles are also realized. A simple method to produce two-port equivalent circuit of these BPF is presented in this paper. The transmission characteristics including such as the control of attenuation poles of these filters are explained by the created equivalent circuit with the concept of even and odd modes. A new method of describing attenuation poles is established.

In a partially coupled-line bandpass filter (BPF), a combination of two microstrip line resonators which are partially coupled, are considered, where one resonator is half-wavelength (λ/2)-long, and another whose one end is grounded, is only quarter-wavelength (λ/4)-long. Therefore, the length of a coupled-line section can be varied based on the position of the grounding end, and five conditions of the movable coupling length have been simulated which will greatly influence the spurious responses of a BPF. This property is numerically investigated in this paper. The analysis shows that, based on the grounding position, this method is capable of realizing the improved out-of-band characteristics by locating the multiple attenuation poles in the stopband and improved spurious responses up to five times of the center frequency (5f0). A few empirical models of BPF are fabricated, and the numerical results are ensured by comparing with the experimental results.

A method for estimating complex permittivity of a material using a rectangular waveguide with a flange is presented by the finite difference time domain (FDTD) method. An advantage of the present method is that it is not necessary to vary the material structure in order to insert it into the waveguide. Therefore estimation errors related to the dimensions of the material are almost negligible. In this case, fluoridated rubber is chosen as the low-loss material. The comparison of the complex permittivity of the material determined by the present method with FDTD and the conventional waveguide method at 10 GHz is performed. It was confirmed that the present method is effective for estimating the complex permittivity under the condition that the length of the flange is about 50 mm (1.7λ) square.

A design methodology of bandpass filters (BPFs) using λ/4 resonators for improving out-of-band characteristics is proposed. Firstly, the basic characteristics of various λ/4 resonators are examined. In this study, we focus on four types of λ/4 resonators, i.e., (1) direct-coupled λ/4 resonator, (2) loaded-element λ/4 resonator, (3) tapped λ/4 resonator and (4) loaded-element tapped λ/4 resonator. Secondly, the application examples of BPFs with improved out-of-band characteristics are provided. We examine the improvement of filter characteristics, i.e., sharp skirt characteristics and low spurious responses. The results of this study lead us to the conclusion that the methodology is very useful for improving the out-of-band characteristics of the BPFs using the λ/4 resonators.

Basic characteristics of a short-ended coplanar waveguide (CPW) resonator of good spurious suppression property is studied. The resonator is loaded with open tubs at its middle position and makes a fully planar structure. The length of the resonator is shortened almost by half and the first spurious resonance goes up to more than 3 times of the fundamental resonant frequency without degradation of unloaded Q(Q0). The origin and property of spurious response is thoroughly investigated to show the advantage and the limit of this configuration. The external Q(Qe) and fundamental resonant frequency of the resonator are also clarified theoretically and experimentally. Using those result, a bandpass filter (BPF) is designed on the basis of the narrow band approximation is realized and its transmission characteristics are examined theoretically and experimentally. The spurious suppression characteristics have been realized by the present filter in accordance with the expectation.

Basic characteristics of a short-ended half-wavelength resonator made of a coplanar waveguide (CPW) and their applications to bandpass filters (BPFs) are discussed. The first part of this paper gives the essence for improving out-of-band characteristics of the BPF by describing the basic characteristics of a tap-coupled resonator. Secondly, a new BPF with attenuation poles using the short-ended half-wavelength CPW resonators is proposed and realized. It is confirmed that our methodology is useful for improving out-of-band characteristics of the BPF using the short-ended half-wavelength CPW resonators without complicated filter design.

The aim of this study is to examine the effectiveness of various open-ended resonators. According to the required filter responses, the application to microwave filters based on presented open-ended resonators is systematically examined as well. First, the resonance property of the basic open-ended resonator is discussed based on even-and odd-mode analysis. The intrinsic property of a tapped open-ended resonator is also discussed here. Second, the basic properties of a stepped impedance resonator (SIR) and a loaded-element resonator are examined theoretically for improvement of spurious responses and the dual-passband response. The basic operations of these resonators are also explained based on even- and odd-mode analysis. Examples for filter applications based on presented resonators are also provided. We found that the intrinsic properties of the open-ended resonators are very useful for practical filter responses.

In this paper, the amplitude coefficient in each mode of leakage waves is calculated by using the amplitude level of the electric field about these unwanted waves under Ministry of Economy, Trade and Industry (METI) definition for measuring the leakage waves irradiated from door portion at the time of microwave oven manufacture, and the percentage of each mode included in leakage waves is also calculated by using finite difference time domain (FDTD) method. Furthermore, shielding effectiveness (SE) of choke structure for suppressing the leakage waves is calculated using combined waves composed of higher order modes as each percentages. As a result, the percentage of each mode included in the leakage waves is examined quantitatively. The approximation analysis for the SE of the choke structure can also be carried out. Therefore, efficient method for evaluating the door structure of the oven at the time of manufacture has been established without the use of the memory in the calculation.

This paper focuses on the characteristics of tunable half-wavelength resonators and their applications to bandpass filters (BPFs). First, the resonance characteristics of various tunable half-wavelength resonators are examined for the tunabilities of transmission zeros and the center frequency of the proposed BPFs. We examine four types of tunable half-wavelength resonators, namely, an end-coupling resonator and three types of tap-coupling resonators. Secondly, the proposition and design of two types of BPFs using acquired resonators are carried out. The fabrication and experimental application of the resonators and designed BPFs are also performed based on coplanar waveguide (CPW) technologies. Their calculated and measured results are compared with each other. The results show that tunabilities of the transmission zero and the center frequency of the proposed BPF are obtained as expected.

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.

In this paper we describe the investigation of design methodology of a planar duplexer consisting of BPFs using mixed tapped resonators. Firstly, we propose the planar duplexer consisting of bandpass filters (BPFs) using a tapped open-ended λ/2 resonator and a tapped λ/4 resonator. The duplexer is designed based on the general filter theory with narrow band approximation and tap-coupling technique. The actual duplexer is fabricated using a coplanar waveguide (CPW). Secondly, downsizing of the planar duplexer is carried out based on the BPF using stepped impedance resonators (SIRs). Lastly, another type of duplexer consisting of different BPFs using mixed tapped resonators is investigated in the same manner. The results of this study lead us to the conclusion that the design methodology is useful for realizing the high-performance planar duplexer fabricated without increasing the number of elements.

An epoxy-modified urethane rubber mixed with carbon particles is now chosen as the millimeter-wave absorber material in our study. The absorption characteristics of the absorber is measured under temperature changes. The weatherability of our absorber is also clarified based on absorption characteristics, thickness and hardness of the sample. As a result of the temperature characteristics of the absorber, the difference of the maximum absorption frequency under temperature changes is about 1 GHz, however the absorption of 20 dB or more is obtained between 54 and 58 GHz. The result of accelerated artificial exposure test is that 2.8% of the thickness of our sample is shrunk after 1000 hour exposure, and the hardness of rubber is hardened with increasing test time. It is also confirmed that the deterioration of the absorption ranges from 1 to 3 dB, although the absorption of about 20 dB is kept at the frequency range. As a consequence, it is confirmed that the wave absorber using the epoxy-modified urethane rubber mixed with carbon particles has good weatherability including our desired temperature characteristics, and it is suitable for outdoor use.

This paper focuses on the realization of low spurious responses by various bandpass filters (BPFs) using open-ended λ/2 resonators. The first part of this paper gives the resonance characteristics of the open-ended λ/2 resonators when the excitation methods are chosen. Secondly, various BPFs obtained with our methodology are provided. For constructing the BPF, (1) point-coupled resonators, (2) comb-line resonators, (3) quasi comb-line resonators and (4) parallel-coupled resonators are used. It is verified that the presented BPFs can be used to obtain low spurious responses both theoretically and experimentally.

An intrinsic property of a tapped resonator is elucidated here, and a novel bandpass filter (BPF) with improved skirt characteristics based on a tapped half-wavelength resonator is proposed by this intrinsic property. "Tapping" for both I/O and interstage couplings of the resonator is the key concept here because a resulting open-ended resonator makes shunt open stubs which give anti-resonance near the center frequency. Multiple attenuation poles appear near the center frequency, namely, close to the passband. A BPF is designed on the basis of the general filter theory with a narrow band approximation. An experiment is carried out to confirm the concept by using a coplanar structure. The expected bandpass characteristics with multiple attenuation poles have been obtained by the novel BPF designed by the present concept.

In this paper, the method of locating multiple transmission zeros by the tap-coupling technique is described for bandpass filters (BPFs), using short-ended λ/2 resonators and its application to a duplexer. First, the method of locating the transmission zero using the short-ended λ/2 resonators is examined with various excitation methods. We focus on four types of short-ended λ/2 resonators: the end-coupling type, tap-coupling type, capacitive tap-coupling type and inductive tap-coupling type. Secondly, the BPFs based on the basic characteristics of the respective resonators are proposed and designed on the basis of a general filter theory with narrow band approximation. Lastly, we propose and design new duplexers consisting of the proposed BPFs. The results lead to the conclusion that the basic characteristics of the short-ended λ/2 resonators are useful for realizing a BPF with multiple transmission zeros and a high-performance duplexer fabricated without increasing the number of elements.

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.

This paper is focused on the measurement of the complex permittivity of a liquid phantom by the transmission line method using a coaxial line for measuring high-permittivity and high-loss materials. First, the complex permittivity of the liquid phantom material is measured under various physical lengths of the coaxial line for accurate measurement. Secondly, comparison between the measured result and the result obtained by the coaxial probe method is carried out in the frequency range from 0.5 to 3 GHz. Finally, the measurement error included in the complex permittivity is estimated quantitatively. The discussions lead to the conclusion that accurate measurement of the liquid material with high-permittivity and high-loss is possible by the presented method.