A compact high-temperature superconducting (HTS) bandpass filter (BPF) using coplanar waveguide (CPW) meander-line parallel-circuited resonators is proposed for microwave receiver applications. The design theory is presented based on a conventional filter theory with J-inverters. Also, analytical and numerical studies of the meander-line resonator are carried out in terms of equivalent circuit values, the resonant frequency, and the unloaded Q. Two- and four-stage 0.05 dB ripple Chebyshev BPFs at 2 GHz with relative bandwidth 60 MHz are fabricated with the metalorganic deposition (MOD)-derived YBCO films on LaAlO3 substrates and their performance are demonstrated. The measured frequency characteristics and the unloaded quality factors agree well with the theoretical and numerical results and the validity of the design theory is confirmed.

Segmentation of a dielectric resonator enables one to control its spurious property. When a dielectric plate is divided into some planar pieces, the effective permittivity does not change appreciably along the divided plane, while it decreases quite an amount perpendicular to it. This anisotropy is useful for shifting the resonant frequencies of unwanted modes of a dielectric resonator. Since its eigen modes have their own electric field distribution, segmentation of a resonator along the electric line of force of a certain mode will not affect its resonant frequency. When the type of segmentation is changed, we can select the wanted mode, and thus control the resonant frequencies of the unwanted modes. Calculated results with an EM field simulator and experimental results of controlling the resonant frequency are shown for divided dielectric resonators.

The fundamental TE10 mode in a rectangular waveguide of a square cross section is degenerate with TE01 mode. A quarter wavelength resonator made of a dielectric square waveguide is, therefore, applied for a small-sized bandpass filter, just like dual mode filters for base stations in the mobile communication. In this paper, the methods to couple the two modes are first studied, including cutting a corner of the resonator and adding some metal electrodes on its end face. Both methods help to flow the rf current of the odd mode at the corner, resulting in decrease of the series inductance and thus increase of the resonant frequency. The coupling constant, that is proportional to the difference of the odd and even-mode's resonant frequency, can be controlled by the perturbations mentioned above. The coupling to the external circuit is adjusted by an electrode fabricated also on the end face. It is connected to a microstrip line and capacitively couples to the resonant modes. The coupling strength increases with the dimension of the electrode. The adjustment of the resonant frequency is carried out by the similar electrode on the end face and connected to the center of the side of the square cross section. The frequency decreases with the length of the electrode. The unloaded Q is measured to be of around 500 for 5510 mm resonator of εr=93. The optimum aspect ratio for the resonator is found in terms of the Q value. The simplest bandpass filter, i.e., a two-stage bandpass filter is designed and fabricated using 5510 mm resonator. It is mounted in a square hole made in a printed circuit board and excited by a microstrip line. The frequency characteristics are in good agreement with the expected values.

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.

A two stage Combline Bandpass Filter (C-BPF) of the Vertically Installed Planar (VIP) structure has been investigated, which is essentially composed of a strongly coupled microstrip lines terminated with a planar fin and through-hole combined with the tapping feed approach. The principle and performance of this filter is studied approximately by an equivalent circuit model and also by the normalized 3D-FDTD method more exactly. The time domain iteration in the FDTD analysis is performed in an expanded time dimension resulting in a reduced CPU time. Some of the obtained numerical results are compared well with the measured ones. A modified VIP combline BPF has the advantages of simple structure, easy tuning, low cost, versatile bandwidth control and good skirt characteristics brought about by two attenuation poles.

Coupling between resonators are analyzed theoretically on basis of the coupled mode theory. New and basic equations for the coupling coefficient are derived and compared with those of waveguides. They should be useful for understanding the physical background of coupling and designing a new coupling scheme.

The authors propose “Disk-repeater” as a new structure alternative to the conventional resonator repeater. Disk-repeater has a simple structure comprised of just copper plates and wire, non-resonant structure. First, coupling coefficients are measured as functions of disk diameter and wire length to characterize the basic performance of Disk-repeater. It is explained by several experimental evidences that Disk-repeater and resonator are not magnetically coupled but electrically coupled. It is also shown that the transmission distance extends dramatically longer than that of conventional resonator repeater. Further, two-dimensional arrangement, where multiple disks are connected, shows very high efficiency and uniform transmission characteristic regardless of positions of receiving resonator. Disk-repeater gives possibility of unprecedented versatile application with the simple structure.

Unloaded Q of a dielectric image resonator is discussed based on the electromagnetic field distribution. It is shown that a partial air gap and a dielectric sheet with low permittivity between the dielectric resonator and the shield case reduce both the dielectric loss and the conductor loss. Especially, reduction of the conductor loss is significant, since the magnetic field distribution moves from the conductor to the upper part of resonator. A half-cut image resonator with an air gap and dielectric spacer is simulated and measured. The unloaded Q of the dielectric resonator with low dielectric loss is improved by about two times from that of original image resonator.

A miniaturized rectangular resonator made of a novel anisotropic artificial dielectric material is investigated which has advantages of small size and big separation of the higher-modes. To obtain a property of anisotropic permittivity, artificial dielectric material is fabricated by lamination of rectangular metal strips etched on a printed circuit board. Artificial dielectric rectangular resonators are designed to excite TE10δ mode selectively, aligning the rectangular metal patterns along the direction of the mode electric field line. The resonant frequencies and coupling coefficient of artificial dielectric rectangular resonators encapsulated in a metal waveguide are analyzed theoretically, and compared with the experimental result. As a microwave application, a high selectivity TE10δ mode bandpass filter (BPF) using two artificial dielectric rectangular resonators is demonstrated. A two-stage BPF with the center frequency of 1.718 GHz, bandwidth of 78 MHz, and insertion loss of 1.3 dB is successfully realized in a rectangular waveguide.

Existence of a surface wave along the boundary between the semi-infinite materials, one of which is a free-space and the other is a material with either negative permeability or negative permittivity, is theoretically investigated. Surface waves exist in only limited combination of negative and positive signs of the material parameters. In addition, by analyzing the surface wave in a finite-thickness slab with negative permeability, its mode profile has been obtained for two different types of symmetry. From these results, the present paper predicts the possibility of a surface wave directional coupler based on a single slab transmission along its top and bottom surfaces.

A new unified method is proposed to calculate the basic resonator parameters, i.e., the resonant frequency, external Q, unloaded Q and coupling coefficient in the time domain. By exciting the resonator from a weakly coupled external circuit, one can inject only a narrow resonant spectrum from the broad spectrum of the excitation pulse. The resonant frequency is easily counted by the number of zero crossings of the internal field intensity, whereas the Q's are calculated by the decay rate of the field amplitude. The coupling coefficient computed by the energy exchange rate between two resonators completes the new time domain algorithm.

A novel method is proposed to calculate the distributed coupling of dual-modes in a circular resonator. New theoretical expressions are devised to accumulate the infinitesimal coupling between orthogonal modes and their validity is justified by the FD-TD analysis and experiments. The distributed coupling concept of a circular disk resonator is applied to a square disk resonator to calculate its resonant frequency. We have fabricated two types of low-profile dual-mode square dielectric disk resonator BPF, using high dielectric constant material (εr = 93) having a dimension of 5 mm 5 mm 1 mm. The filter characteristics are explained by the transmission line circuit model.

2-pole band-pass filters (BPFs) with tap-excitation are prepared by using high temperature superconductors (HTS). The possibility of realizing superconducting coplanar filters with attenuation poles is revealed.

A new comprehensive method to suppress the spurious modes in a BPF is proposed taking the multi-strip resonator BPF as an example. It consists of disturbing the resonant frequency, coupling coefficient and external Q of the higher-order modes at the same time. The designed example has shown an extraordinarily good out-of-band response in the computer simulation.

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.

A microwave resonator is fabricated by a lump of spherical metal particles for the first time. It is the evidence that those particles constitute artificial dielectrics. The effective permittivity is calculated numerically together with the permeability. Resonant mode frequencies in the experiment are compared with the theoretical result obtained by the effective material constants above. Their reasonable agreement indicates the validity of material constant extraction. The unique diamagnetism of spherical particles could be utilized for improvement of spurious property of a resonator.

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.

Unloaded Q of an image-type dielectric resonator is studied with the simulation and experiment. It is shown that a gap between the dielectric resonator and the shield case reduces both the dielectric loss and conductor loss. The gap moves the electric and magnetic field distributions in the different directions, so that the two losses are reduced. A half-cut image-type resonator with a dielectric spacer inserted into the gap is measured to verify the concept. The unloaded Q is improved by about two times from that without a gap. The proposed structure gives a new packaging method of a dielectric resonator.

Coupling effects between resonators on a laminated Band Elimination Filter (BEF) is studied. The coupling degrades the filter attenuation performance. A new equivalent circuit of coupled-line BEF with loaded capacitors is investigated. The performance is simulated and the improvement by staggered resonators is confirmed. An experimental filter made of Low Temperature Co-fired Ceramics (LTCC) is constructed. It shows good performance.