Rigorous analysis of novel dielectric resonator filters with printed tuning septum

This paper describes the analysis of dielectric resonator filters with printed tuning septum in waveguide sections operating below cutoff. In this design approach a thick dielectric slab of high permittivity is placed longitudinally in the waveguide. A bilateral ladder-shaped metallization determines the resonator and coupling sections (modified finline filter). In contrast to conventional dielectric resonator filters, this approach provides better passband separation and increased stopband attenuation. Furthermore, due to the bilateral tuning septum, the resonator and coupling sections can be manufactured accurately with photolithographic techniques rather than by expensive machining.     

Concept of multiorder multimode resonant optical filters

The idea of implementing optical filters by coupling evanescent waves from several diffracted orders into multiple leaky waveguide modes is studied theoretically. Using a dielectric thin-film structure consisting of a coupling grating placed between adjacent waveguides, guided-mode resonance filters exhibiting multiple reflection peaks within a specified wavelength range can be obtained. These peaks originate in the resonant waveguide modes that are excited by the diffracted waves dispersed by the grating. It is shown that this device can be used to realize multiwavelength as well as wide-band spectral filters.     

Ridged Waveguide for Planar Microwave Circuits (Short Papers)

A TE-mode planar transmission line is analyzed. It has a cross section as a ridged waveguide where the ridges are very thin. It is easily fabricated by photoetching of copper-clad dielectric boards, but can also be made without dielectrics for low-loss applications. Thus, it can be integrated together with other planar transmission lines like, for example, striplines. Besides the simplicity in feeding by stripline, the guide can be made smaller than an ordinary rectangular waveguide. It has applications in filters, resonators, balun-transitions, antenna feeds, etc. The characteristic impedance of the transmission line and its free-space cutoff wavelength are calculated and given in a diagram.     

The relationship between dual mode cavity cross-coupling andwaveguide polarizers

Cross-coupling in dual-mode cavity filters may be obtained by introducing an asymmetry within the cavity cross section at an angle of 45° to the two orthogonal modes. This paper presents a novel formula relating the resulting cross coupling coefficient between the orthogonal resonances to the polarization of a waveguide polarizer. Previous theories for such polarizers may then be applied directly to the dual mode filter situation. Formulas enabling the dimensions of the asymmetries for required coupling coefficients are presented for square and circular waveguide cross sections     

Novel dielectric waveguide components-microwave applications of newceramic materials

Several dielectric-waveguide components utilizing appropriate metallized surface structures on dielectric ceramics are examined. Using magnetic walls, easily realized with ceramics, several dielectric components of a type quite different from conventional hollow waveguide components have been fabricated. Multistage bandpass filters (BPFs) with tandem connection of quarter-wave resonators have been realized on the same dielectric waveguide; multistage BPFs with coaxial resonators in the waveguide are also shown. Components similar to earlier dielectric waveguide components are made smaller by taking the image half-section. Coupling to waveguide can be realized by a probe, in the form of a metallized hole in a dielectric waveguide, or by means of the open surface corresponding to a magnetic wall loaded with the proper metallic surface patterns. These components are described, and experimental performance data are given     

Coupling characteristics of two rectangular dielectric waveguides laid in different layers

The coupling characteristic of rectangular dielectric waveguides which lay in different, parallel layers and one waveguide crossed over the other one are studied. Step-like approximation and the variational method are used for calculating the coupling coefficient which varies with axial distancez. Electromagnetic field expression for the dielectric waveguide mode of rectangular cross section is newly introduced and used. Calculated coupling characteristics are compared with experimental results carried on 50 GHz band. The principle of crossed waveguides leads us to the new design concept of "multilayered integrated circuit."     

Radiation from a homogeneous sphere mounted on a waveguide aperture

The results of an experimental and theoretical study of the effects of placing a dielectric sphere over the aperture of a circular waveguide are presented. A dielectric sphere excited by a Huygens' source is used us the theoretical model to interpret the experimental results. Calculations based on this model show good overall agreement with experimental patterns and directivity measurements. It is concluded that dielectric loaded antennas such as the dielectric sphere excited by a waveguide can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of two wavelengths or less. Measurements of the coupling between these antennas show that they, in general, are not as closely coupled as plain apertures without dielectric object loading.     

Design of Dielectric Waveguide Bandpass Filters Using Parallel-Coupled Gratings

Techniques for the design of narrow-band (of the order of a percent or so), bandpass filters using dielectric waveguide gratings are presented. These filters use both single, uncoupled gratings and parallel-coupled configurations of gratings to form multiresonator bandpass filter structures. Transmission-line equivalent circuits are used to model the dielectric waveguide gratings. Using this model, it is then shown how direct-coupled-resonator theory can be applied to such filter structures to synthesize a prescribed passband having Chebyshev or maximally flat characteristic. On the other hand, the parallel-coupled gratings give these filters broad and strong, absorptive stopbands, as is explained. Experimental results are presented which show good agreement between theoretical and measured results.     

Channel-dropping coupled-line filter

A novel type of channel-dropping filter, constructed in a rectangular dielectric waveguide, is described. The basis of the device is the linear frequency dependence of the coupling coefficient between two identical rods of certain dimensions. An experimental 4-channel filter in the 30?40 GHz band gives losses comparable with those of metal-waveguide commutative filters.     

Design and Performance of Coplanar Waveguide Bandpass Filters

End-coupled resonator bandpass filters built in coplanar waveguide are investigated. The admittance inverter parameters of the coupling gaps between resonant sections are deduced from experiment, and bandpass filter design rules are developed. This allows easy filter synthesis from "prototype" low-pass designs. Measurements of single section resonator quality factors are used to predict filter insertion losses. Several examples of filters realized in coplanar waveguide are presented. Odd-mode coplanar waveguide filter elements that shortcircuit the even coplanar waveguide mode are investigated. Filter tuning, accomplished by adjusting the height of conducting planes above the resonant filter sections, is demonstrated.     

Realization of dielectric loaded waveguide filter with substrate integrated waveguide technique based on incorporation of two substrates with different relative permittivity

In this paper a new structure based on substrate integrated waveguide (SIW), called incorporated substrate integrated waveguide (ISIW), has been used to implement the dielectric loaded waveguide filter in planar structure. Conventional waveguide filter and dielectric loaded waveguide filter have been realized with SIW and ISIW technique, respectively. The use of ISIW structure has reduced the size of the filter, required precision in designing process and the cost of manufacturing process, at the cost of increasing the losses. Thus, while the size of filter and the cost of manufacturing process reduce significantly, there is no need to build the particular dielectric material as resonator and integration with other microstrip devices will be much easier too. Two different excitation mechanism have been considered to cancel the spurious response in the desired frequency band. The SIW and ISIW filters have been fabricated and fairly compared with waveguide filters. Advantages and disadvantages of ISIW structure have been scrutinized in detail. Good agreement between the simulated and measured frequency response of proposed filters has been shown.     

A novel coupled method for dual-mode dielectric resonators andwaveguide filters

A novel method for coupling dual-mode waveguide or dielectric resonator cavities is described and analyzed. The method has advantages of providing a practical, flexible, economic means of replacing irises, of offering easy tunability of the coupling over a wide range of coupling values, and of reducing the length of the coupling structure. Calculation of the resonator's coupling parameters using the mode-matching method yields accurate results and is verified by measurements. Experimental four-pole dual-mode elliptic function filters using the coupling method for empty cavities and dielectric-resonator-loaded cavities were constructed and tested. The test results showed excellent agreement with theoretical analysis     

Narrow-Bandpass Waveguide Filters

A procedure is described whereby narrow-bandpass waveguide filters having ripple in both the passbands and stopbands can be synthesized in the form of coupled waveguide cavities. Orthogonal modes in square or circular waveguides are employed to enable negative coupling elements to be realized. As a consequence, very compact filters can be constructed. Experimental results on an 8-cavity orthogonal-mode narrow-bandpass filter are shown to agree well with theory.     

Simulation Study of Electronically Scannable Antennas and Tunable Filters Integrated in a Quasi-Planar Dielectric Waveguide

Preliminary studies on electronically scannable leaky-wave antennas integrated in a dielectric waveguide are reported. Electronic scan is simulated by a small mechanical motion from which the relation between the scan angle and the necessary change in the dielectric constant can be derived. The work is also applicable to electronically tunable bandstop filters.     

Design of dielectric-filled cavity filters with ultrawide stopband Characteristics

A methodology is presented for the design of small cavity filters, relying entirely on the use of commercial general-purpose design software. Pertinent filter structures comprise resonated segments of ridge waveguide with evanescent-mode inter-resonator coupling sections, supplemented by impedance-transforming port networks. The ridge and evanescent-mode waveguide segments combine to form a metal-clad dielectric core made of either a single dielectric or a composite material. A parameterized equivalent-circuit model is used to describe each segment based on numerical three-dimensional electromagnetic field analyses. For a bandpass filter, the technique yields low passband insertion loss, an ultrawide upper stopband region, and excellent power handling. The approach provides the option to fabricate structures at low per-unit cost with the help of newly available moldable dielectric materials. The efficacy of the technique is demonstrated with an experimental 1-1.45-GHz bandpass filter.     

Properties of the slab modes in photonic crystal optical waveguides

We show that by placing a slab of semiconductor material between two photonic bandgap (PBG) mirrors, waveguide modes at frequencies out of the PBG can be obtained. These modes are similar to the modes of a conventional dielectric slab waveguide. Using these modes, we can obtain very good coupling between a PBG waveguide and a dielectric slab waveguide with similar slab properties. We discuss the properties of these slab modes and outline the guideline for the optimization of the PBG waveguides based on these properties     

Coupling and quality factors in parallelepiped nonradiative dielectric resonators

In this work, the quality factors and the coupling effects have been investigated for parallelepiped dielectric resonators in nonradiative dielectric (NRD) waveguide, in order to achieve fundamental information for the design of various types of advanced filters. The unloaded quality factor has been calculated taking into account both conductor and dielectric losses through a straightforward version of the perturbation method. The electromagnetic coupling as a function of the distance between NRD guide and resonators has been evaluated through proper extensions of typical lumped equivalent circuits, thus quantifying resonance frequency shifts, external and loaded quality factors, etc.. To validate the derived theoretical models, suitable measurements of all these parameters have been performed at microwaves on X-band NRD prototypes.     

A Frequency-Stabilized Microwave Band-Rejection Filter Using High Dielectric Constant Resonators

The high permittivity dielectric resonator is a low loss microwave filter element whose size is substantiality less than metal waveguide cavities. Temperature stabilizing their resonant frequency increases the applicability of such elements. A temperature compensated 3-section band-rejection filter using dielectric resonators has been fabricated and tested. The measured electrical performance was comparable to metal waveguide filters and the frequency stability for temperature variations was comparable to brass waveguide cavity filters which are not temperature compensated.     

Filter-response line shapes of resonant waveguide gratings

The line shape symmetry properties of planar dielectric resonant waveguide-grating filters are theoretically characterized for both TE and TM polarization. Classical antireflection theory is applied to the design of guided-mode resonance filters and it is shown that the symmetry of the line-shape response is determined by the location of the resonance relative to the minimum of the antireflection band. The conditions that allow a single dielectric layer to simultaneously function as both a waveguide grating and as an antireflection thin film are presented. Single-layer antireflection waveguide gratings are shown to yield highly symmetrical filter-response line shapes with suppressed sideband reflectivity and 100% reflectivity at the resonance wavelength. The parametric locations of the symmetrical line-shape responses are predicted approximately by solving the resonance-location equation with the grating thickness set equal to a multiple of a half-resonance-wavelength. Graphical representations of these solutions are provided. Symmetric waveguide-grating filters are shown to yield symmetrical line shapes with near-zero sideband reflectivity, whereas asymmetric filters produce symmetrical line shapes but suffer from increased sideband reflectance that increases as the asymmetry of the filter grows. Numerous calculated examples are presented to demonstrate that ideal reflection filters can be designed by combining thin-film antireflection effects and resonance effects in a single dielectric layer     

Dual-Mode Canonical Waveguide Filters

This paper introduces a new form of dual-mode narrow-bandpass waveguide cavity filter. The filters, which can be constructed from either dual mode circular or square waveguide cavities, can realize the optimum transfer functions (including the exact elliptic function response). One of the unique features of these filters is that all the intercavity coupling irises may take the form of circular holes rather than long narrow slots. Several alternative input-output configurations are described. Experimental results on several filters indicate excellent agreement with theory.