Microwave bandpass filters consisting of rectangular waveguides with 1‐dimensional offsets

An accurate design technique of dual-mode microwave dielectric or air-filled rectangular waveguide filters is described. Dual-mode coupling is realized by a section of rectangular waveguide with square-corner-cut. The unequal couplings between dual-mode pairs of the cavities is provided by a section of evanescent mode waveguide. Rigorous analyses are applied to characterize the microwave junctions and to obtain the design parameters for the filter. The design procedure used to determine the dimensions of the waveguide junctions with a minimum of computational effort is described. The design is demonstrated by four-pole and six-pole dual-mode rectangular waveguide elliptic function filters. Excellent agreement between computer simulation and experimental results with absolutely no tuning justifies the design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene-based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying the electrical length of a resonator. The presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene-based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. A frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene-based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene–metal combined waveguide resonators are proposed in order to preserve the excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

Substrate Integrated Waveguide (SIW) is a new kind of microwave transmission structure appeared in recent years. The SIW technique makes it possible that a complete circuit including planar circuitry, transition, and rectangular waveguide are fabricated in a planar form using a standard printed circuit board (PCB). From analysis of the susceptance of symmetrical window and designing process of Chebyshev bandpass filter in rectangular waveguide, an X-band filter based on SIW is designed and fabricated in this article. The simulated results show that the bandwidth of the filter is 5%. The insertion loss is about 1.4 dB, and return loss is about 25 dB at 10 GHz. The measured insertion and return losses are about 2.9 dB and about 13 dB, respectively at mid-band frequency. The filter has a small insert loss and good frequency selective performances from 9.82GHz to 10.20GHz. It is suitable for designing millimeter-wave circuits, and can be produced with batches to be widely used in the microwave systems with the simple structure.

This paper presents the simulation, design and implementation of bandpass filters in rectangular waveguides. The filters are simulated and designed by using a numerical analysis program based on the Wave Iterative Method (WIM) called WFD (Waveguide Filter Design) simulation. This simulation program can analyze the electrical network of filters. The sample waveguide filter is designed based on a proposed structure consisting of three circuits serving as a simple bandpass filter with two inductive irises and three inductive irises in a cascade. We determined that the operating frequency was equal to approximately 4.20-4.84 GHz. The waveguide filters were then implemented using an aluminum material. The analyzed results for the inductive iris obtained with the WFD program agree well with the results of CST Microwave Studio®. Finally, the measured results of sample waveguide filters are consistent with the simulation tool.

Spoof surface plasmon polaritons (SSPPs) are developed in a rectangular waveguide (RWG) to realize a controllable band-pass propagation feature for millimeter-wave applications. The proposed SSPP structure consisting of a single row of corrugated metallic blocks, is embedded inside the closed structure of an RWG. The dispersion property of the RWG-based SSPP (RWG-SSPP) has tunable lower and upper cut-off frequencies, and a band-pass filter with flexible bandwidth has been designed using an RWG-SSPP structure. The proposed band-pass filter is based on an RWG-SSPP with an all-metal structure, which is of great potential for millimeter-wave applications due to small losses.

Monopole antennas are widely used in communication systems because of features such as pure vertical polarization and omnidirectional radiation patterns in the horizontal plane. Conventionally, monopole antennas are fed through a ground plane by a coaxial probe. Recently, monopole antennas fed by printed transmission lines have attracted increasing attention. However, to the best of our knowledge, monopole antennas are seldom fed by a rectangular waveguide. We consider the problem of this type of feed because of our interest in designing an omnidirectional antenna at millimeter wave bands. At millimeter wave frequencies, rectangular waveguides are preferred to coaxial or microstrip lines because they exhibit very low loss, have a large power handling capacity and other waveguide components are readily available. The paper presents a design for monopole antennas fed by a rectangular waveguide. In order to achieve a good transition from a rectangular waveguide to the monopole antenna, a ridged waveguide section is introduced, and the vertical monopole is attached to the ridge through a circular aperture opened on the upper broad-wall of the rectangular waveguide, which is part of the ground plane. Two examples are provided and experimental tests of one of these antennas shows that the monopole can achieve about 24% bandwidth and 5 dBi gain.

A common strategy to reduce the cost of a filter is to use a manufacturing technique with an intermediate accuracy and use tuning elements to compensate for the manufacturing errors. However, including tuning elements in the final EM simulations, and tuning the filters after manufacturing, can be quite challenging. In this context, therefore, we review in this paper two powerful filter design procedures based on Aggressive Space Mapping (ASM), and two semi-automatic tuning techniques. As a validation, we describe in detail the design and tuning of two types of filters that are commonly used for both space and ground applications, namely, a six-pole inductive filter in rectangular waveguide, and a more complex five-pole filter based on dual-mode resonators.

In this paper the design of rectangular waveguide filters in Ka-band with constant bandwidth is discussed. Only the cavities are assumed to be tuned, while the couplings must be dimensioned in order to get constant the bandwidth in the tuning bands. The tuning elements are implemented by means of dielectric rods driven by a single stepper micro-motor. As a result, all the rods are assumed to have the same penetration in the cavities for each tuning band. The design of a filter with 500 MHz bandwidth tuned in the band 29-31 GHz is presented, together with the preliminary simulation results.

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.

Latching phase shifters, consisting of a waveguide section containing a ferrite toroid, are widely used as digital steering elements in microwave array antennas. The theoretical determination of device performance cannot be obtained exactly, since these structures are inhomogeneous along both transverse directions. The present study presents an approximate method to evaluate phase shift and losses in the case of a rectangular toroid. An approximately equivalent structure (twin slab), for which an exact resolution method is available, is considered first. The changes due to the upper and lower sections of the toroid are then evaluated by means of a variational principle. Experimental results show good agreement with computed values for several practical cases considered. Finally, the range of validity for this approximate method is determined.

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

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.

Context. The problem is to systematize and improve the models of a resonance ferrite isolator in the rectangular waveguide for the antenna-feeder devices, generating, receiving, measuring microwave equipment containing ferrite decoupling devices: ferrite isolators and circulators. Objective. The goal of the work is to verify the formula for the losses of the resonant ferrite isolator in the direct and reverse directions, as well as the isolator ratio. Method. The research method of the work is a critical analysis of literary sources, which was carried out, but did not bring the desired results, since it did not allow to verify the correctness of the derivation of the formula [17]. Therefore, a number of hypotheses were put forward, what the formula might mean. The difficulty lay in the presence in the formula of the product of trigonometric functions that can be attributed to frequency properties, which was taken as an initial hypothesis, which was not subsequently confirmed. The check included transformation of formulas using mathematical physics in terms of microwave electrodynamics, trigonometry and algebra. The beginning was the formula of the classics [16], similar to the formula of [18], accepted without proof. As it is known, for the main type of wave in a rectangular waveguide, the components of the magnetic field strength, obtained as a solution to the wave equation under the boundary conditions inherent in a rectangular waveguide. One component of the magnetic field strength is along the direction of wave propagation, and the second one is in the transverse direction in the section of the waveguide are proportional to the trigonometric functions cosine and sine with the same arguments. The equality of the two components of the strengths is traditionally uses to find the plane of circular polarization where to place the ferrite isolator, and so the authors use this proportionality to trigonometric functions in their derivation, namely the formulas of trigonometric functions of a double angle, the basic trigonometric identity sine squared plus cosine squared is equal to one for replacing the propagation constants with trigonometric functions, this allows to get rid of radicals in the formulas, these radicals in the formula are due to the phenomenon of dispersion in a rectangular waveguide. The rest of the manipulations with the formula are the reduction of similar terms. Results. There was obtained analytical expressions for the losses of the resonant ferrite isolator in the forward and reverse directions, as well as the isolator ratio by strict mathematical transformations. There was performed such transformations. The ratios of the longitudinal propagation constant to the transverse propagation constant are replaced by the ratios of the trigonometric functions sine and cosine, since they are continuous as opposed to tangents and cotangents. Such a transformation allows to avoid square roots in the formula for the losses of the ferrite isolator in the forward and reverse directions, which are associated with the presence of dispersion in the waveguide, as in the formula for wavelength in the waveguide. The conversion is based on microwave electrodynamics. The formulas are used for the distribution of fields in a rectangular waveguide for the main type of wave. Further transformations consist in taking the common factor out of brackets and other arithmetic transformations. Conclusions. Тhrer was obtained results partially coincide with the well-known [17], the derivation of the formula [17] was obtained for the first time, the studies carried out allowed us to reject the hypothesis that the product of cosines and sines in the loss formula of a ferrite isolator is a frequency characteristic, it appears as a result of arithmetic transformations. To take into account the frequency range, it is used that there is circular polarization at the middle frequency, there will also be circular polarization at the extreme frequency of the range, but the plane of circular polarization will shift in comparison with the position of the plane of circular polarization at the middle frequency. That is, a peculiar system of two equations is obtained with respect to two positions of the polarization plane relative to the wide side of the rectangular waveguide section. The scientific novelty consists in systematization and generalization of the formulas of the loss of the resonance ferrite isolator, the connection between the formulas from different literature sources, both foreign and domestic, is proved, which saves time for researchers of ferrite isolators for the verification of the formula. The practical significance. It may be useful for teaching purposes and in optimization of the ferrite isolator design.

This article presents an approach to the development of band-reconfigurable tunable bandpass filters (BPFs) using a mode-switching concept. The key to realize this feature is that the first higher-order mode TE201 can be switched to the diagonal modes TE201 and TE102 using tuning elements in a square waveguide cavity. A pair of tuning elements are deployed along the diagonal line of a cavity while the other pair are arranged at its anti-diagonal line. If the two pairs of tuning elements have the same depths in the cavity, the first higher-order mode TE201 can be formed, and its resonant frequency can be tuned effectively. If the tuning elements have different depths, the TE201 mode can be switched to the diagonal modes TE201 and TE102, whose resonant frequencies can be tuned individually. Accordingly, the corresponding tunable BPF can be reconfigured between single- and dual-band states. Moreover, a flexible number of transmission poles can also be implemented in the dual-band state. For experimental verifications, two band-reconfigurable tunable BPFs are designed, fabricated, and measured in Ku-band. The first design has 2 and 2+2 poles in the single- and dual-band states, respectively, whereas the second design introduces one transmission zero (TZ), which has 3 and 3+2 poles in the single- and dual-band states, respectively. Regardless of single- and dual-band responses, each band can be frequency-tuned.