Dual-mode dielectric or air-filled rectangular waveguide filters

A novel method for realization of dual mode coupling in rectangular waveguide cavities is described and analyzed. This method completely replaces the coupling screw, and therefore can be used to eliminate the need for tuning in dual mode waveguide cavity filters. It also offers a wide range of coupling values and can achieve higher power handling capability than coupling screws. The mode matching method is used to calculate the mode chart of the infinite corner cut rectangular waveguide, the field distributions of each mode, and the resonant frequencies of the cavity. The dual mode coupling parameter is calculated from resonant frequencies and is verified by measurements. A C-band four-pole dual mode elliptic function rectangular waveguide cavity filter using the new coupling method was constructed and tested. The experimental results showed excellent agreement with theory. >

A new polarization filter with no element inside the circular waveguide is presented. It is realized by the insertion of rectangular waveguide sections in a circular waveguide. The validity of this new design is verified on a prototype model.

The physical processes occurred in the waveguide-dielectric structure that has the form of a section of rectangular cut-off waveguide with dielectric insertion, which completely fills the cross section of the waveguide have been considered. The electromagnetic fields in the classic waveguide-dielectric resonator without devices for its excitation and a coupling element with two sections of the cut-off waveguide have been calculated. The expressions for the reflection and transmission coefficients of the structure under consideration are presented. The positions of poles and zeros of the reflection coefficient have been investigated with a fractional-rational approximation and they have been compared with the natural frequencies. The obtained results are useful for measuring the properties of dielectric materials with the aid of waveguide methods.

In this paper, a rectangular waveguide probe with a ridge-loaded straight slot (RLSS) is presented for a near-field scanning microwave microscope (NSMM). The RLSS is located laterally at the end wall of the cavity and is loaded on double ridges in a narrow straight slot to improve the spatial resolution compared with a straight slot. The probe consists of a rectangular cavity with an RLSS and a feed section of a WR-90 rectangular waveguide. When the proposed NSMM is located at distance of 0.1mm in front of a substrate without patches or strips, the simulated full width at half maximum (FWHM) of the probe improve by approximately 31.5 % compared with that of a straight slot without ridges. One dimensional scanning of the E-plane on a sample under test was conducted, and the reflection coefficient of the near-field scanning probe is presented.

Oscillators in the microwave and millimeter-wave region were constructed wherein the resonators consisted of sections of rectangular dielectric waveguide. While adding thin blocks of dielectric to increase the mechanical length of the resonator, the power output and frequency were measured. Using this technique, the experimental value of the wavelength in the longitudinal direction, lambda/sub g/, was determined. These experimental data were then compared with calculations predicted by optical theory. Good agreement was found where the bulk wavelength was small compared with the cross-sectional dimensions of the dielectric. If the half-wavelength in the dielectric was comparable with the dielectric dimensions, the values of lambda/sub g/ were greater than the theoretical values. In the process of carrying out these experiments, a new type of oscillator is described which provides a power ontput comparable with diodes in metal-walled cavities. In addition, the new dielectric cavities are simple in construction and are compatible with dielectric waveguide, image line, or microstrip systems.

<div class="htmlview paragraph">In the Sabatier reactor, oxygen is recovered (as water) by hydrogenation of carbon dioxide. Half of the reacted hydrogen is contained within the product water, the other half forms methane (CH<sub>4</sub>). To close the hydrogen loop, we are investigating methods for the efficient recovery of hydrogen from CH<sub>4</sub>. This paper describes microwave plasma-based methods for the thermal decomposition (cracking) of methane to produce hydrogen, elemental carbon, and related carbonaceous substances. Two primary reactor configurations have been employed in this work: 1) a quartz tube vertically oriented within a section of rectangular waveguide, and 2) waveguide transmission through a quartz window into a cylindrical vacuum chamber based multimode cavity. Hydrogen recoveries of up to 98% have been obtained. Three primary mechanisms of methane decomposition have been identified: methane pyrolysis, methane oligomerization, and methane aromatization. In the multimode plasma chamber methane pyrolysis experiments, we have observed the formation of a highly dendritic form of elemental carbon which may be beneficial in the minimization of potential problems associated with carbon deposition. Alternatively, by optimization of the reactor to promote volatile oligomerization products, carbon formation is minimized.</div>

The experimental investigation of a reflectometer for measuring return loss magnitude and phase at submillimeter wavelengths is presented. The reflectometer, which is designed as a proof-of-principle demonstration, is based on the sampled-transmission line architecture and its design and operation are described. The instrument is a relatively simple implementation of the six-port network analyzer introduced by Engen and consists of a section of rectangular waveguide and an ensemble of Schottky diode power detectors. Design considerations for the instrument are presented and measurements in the 270 GHz to 285 GHz range are discussed.

In this work, two different types of evanescent mode rectangular waveguides filters are proposed, designed and fabricated, using a hybrid manufacturing strategy. On the one hand, the evanescent waveguide filter section is filled with dielectric material made of ABSplus, commonly employed by 3D printers based on Fused Deposition Modeling (FDM). On the other hand, the metallic external structure of the filters has been built by means of standard machining computer numerical control (CNC) procedures. Some guidelines on how to properly combine the dielectric and metallic pieces are provided. As design examples, two different fifth order C-band Chebyshev bandpass filters have been designed and tested. The first filter is composed of a single ABSplus dielectric piece (&#x03F5;<inf>r</inf> = 2.55) drilled with elliptical airholes, and then aligned in the metallic waveguide housing. The second filter is loaded with five elliptical dielectric post resonators distributed along the metallic evanescent waveguide section. In both cases, the return losses are higher than RL = 18 dB, the fractional bandwidth within the range 3%-4.6%, whereas the spurious free range is around 1 GHz. Due to the nowadays limitations of the quality of available dielectric materials for 3D-printers, the insertion losses of the filters are high within the passbands (around IL = 4.3 dB). Nevertheless, the overall performances are satisfactory, showing the promising usefulness of this kind of filters for low cost implementations, based on combining additive manufacturing techniques with standard CNC processes.

An efficient hybrid mode-matching finite element (MM/FE) method is applied for the rigorous analysis of waveguide filters composed of homogeneous standard waveguide cavities together with waveguide coupling sections of nearly arbitrary cross-section. To demonstrate the efficiency of the method, a simple two-pole circular waveguide dual-mode filter is analyzed where the orthogonal modes are coupled by obliquely positioned rectangular post elements with rounded edges and the coupling to the rectangular port waveguides is provided by rectangular irises with rounded corners. Moreover, a four-pole filter is shown where the dual-mode coupling is achieved by asymmetrically located irises. The theory is verified by excellent agreement with measurements. >

This work presents the design techniques to realize highly compact inline generalized Chebyshev dielectric waveguide filters based on novel nonlinear frequency-variant coupling (NFVC) inverters. The discontinuities in the form of a pair of metalized blind holes placed at half-wavelength intervals in the broad wall of a rectangular dielectric waveguide operate as NFVC inverters. The NFVC produces a transmission pole in between a pair of fully controllable transmission zeros (TZs). The pole is added to the passband to increase the order of the filter without augmenting its physical volume. The simulated results for 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> and 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order inline dielectric waveguide filters with quasi-elliptic-type filtering response are presented to validate the design theory.

The behavior of several lower order modes in a sectoral waveguide is investigated. It is shown that their sequence order depends on the flare angle of the sector. It is found that, at an angle smaller than 135°, the waveguide may operate in a single-mode regime with the H 01 mode. The per-unit-length attenuation of the H 01 mode in a sectoral waveguide is analyzed and compared to the attenuation of the H 10 mode in a rectangular waveguide.

A full-wave numerical approach is proposed for analyzing rectangular waveguides with periodic slots. The approach is based on an aperture magnetic field integral equation in one unit cell. The presented technique can analyze both bound and leaky modes on rectangular waveguides with periodic slots that have a rather arbitrary shape on either the broad or narrow wall. Besides, the method can be used for a uniformly slit rectangular waveguide by taking the limit of the period. Using the proposed method, it is found that an air-filled rectangular waveguide with periodic longitudinal slots supports a leaky waveguide mode but no slot mode, while a uniformly slit rectangular waveguide (air-filled) can support a leaky waveguide mode as well as a slot mode. It is also found that an air-filled rectangular waveguide with cross slots supports a surface-wave mode in addition to a leaky waveguide mode.

Rectangular waveguide section with two partial-height transversal inserts located side by side is examined. Such a section acts as a resonator providing two transmission zeros and one transmission resonance located between these zeros simultaneously. Thus, the number of transmission zeros is twice more than the number of waveguide sections. The broadband quarter-wavelength resonator filter using such sections provides two stopbands and one passband simultaneously. Their bandwidths and locations are controlled both by the section geometry and the distance between the sections. Two closely spaced sections providing two independent stopbands are proposed as a perspective block for a filter with complicated frequency response.

The computer‐aided analysis and design of direct‐coupled and quarter‐wave‐coupled bandpass filters utilizing monomode rectangular waveguides with 1‐dimensional offset discontinuities are described. The equivalent networks of these discontinuities, which consist of a shunt reactance and additional transmission lines connected at both sides, have been derived from the rigorous field‐theoretical investigations of E‐plane and H‐plane displacements in rectangular waveguide. Both network elements are tabulated in terms of geometry and wavelength with fine steps to allow accurate interpolation by means of computational methods, Simple design formulae for the filter geometry as a function of the electrical specifications are given which are based upon narrow‐band approximations. The analytical relationships required for a computer simulation of the filter's wide‐band performance are summarized. The predicted frequency characteristics showed such close agreement with the experimental results obtained on two X‐band filter models that neither tuning elements in the waveguide sections nor final adjustments of the offset widths had to be provided.

The integral-equation method has been applied along with perturbation theory to investigate the leaky-wave parameters of the fundamental mode in the regular waveguide with a narrow longitudinal slot on its broad wall, opened into shielded semispace. Then, the simple analytical formulas have been derived for the engineering synthesis of radiating elements (REs), which are formed by a nonuniform waveguide section with a nonregular slot on its broad wall. The long slot was cut in the longitudinal direction along certain curved or several connected broken lines, forming small local angles with the waveguide axis. The synthesis of RE's by single-mode approximation has been carried out for the condition of good uniformity of radiating electrical-field distribution along the RE axis near the slot. Good agreement of theoretical and experimental results was obtained.