Circular Waveguide Dual-mode Filter Research Articles

A Circular Waveguide Dual-Mode Filter With Improved Out-of-Band Performance for Satellite Communication Systems

This letter presents a novel design for a 3-D-printed circular waveguide dual-mode (CWDM) filter with a modified cavity shape. The modification leads to a wide spurious-free stopband, which is highly desirable for channel separation in waveguide contiguous output multiplexers (OMUXs) in satellite communication systems. The new resonant cavity design is a result of applying shape deformation to a basic circular cavity in order to move away and suppress parasitic modes. A fourth-order Ku-band channel filter with two transmission zeros (TZs) is designed, fabricated by additive manufacturing (AM) in one piece and measured. In comparison with the state-of-the-art design of a stepped CWDM filter, an improvement of approximately 35% wider spurious-free range is achieved.

A folded dual-mode bandpass filter with circular waveguide

In this article, a folded circular waveguide dual-mode filter without tuning screws is designed for the fifth-generation (5G) mobile communication system. The folded filter is composed of two stacked circular cavities operated at 3.5 GHz. Each cavity has two resonant modes, which can generate and control two transmission zeroes at specific frequencies. Through a coupling iris, the two single-cavity filters are connected together, and can control four poles, which helps to expand the 3dB fractional bandwidth to 11.4%. The measured insertion losses are around 0.5 dB in the passband (from 3.4–3.6 GHz). The experiment results show an excellent agreement with the simulation results. Such folded filters have the advantages of very low insertion loss, compact size, high frequency selectivity, and low cost.

Efficient Design of Waveguide Manifold Multiplexers Based on Low-Order EM Distributed Models

In this paper, a new systematic technique to design manifold-coupled multiplexers in waveguide technology is proposed. The new technique uses generalized low-order electromagnetic (EM) distributed models, which constitute a half-way point between the fast, but imprecise, analytical models, and the more accurate, but costly, full-wave EM models. The method can be applied to contiguous and noncontiguous channel multiplexers, in both $ { E}$ -plane or $ { H}$ -plane configurations. This paper covers the complete design procedure for manifold multiplexers, starting from the required specifications and finishing with the physical dimensions. After explaining the general design technique for multiplexers with channel filters based on transmission-line resonators, the method is specialized for the design of classic multiplexers with circular-waveguide dual-mode filters. As a further application example, the same methodology is also used for the design of a nonconventional tuningless wideband multiplexer with a new type of rectangular waveguide filters. This paper is concluded with a comparison between simulation and measurements for the wideband multiplexer. Excellent agreement between measurements and simulations are demonstrated, thereby validating the complete design procedure.

Correction of manufacturing deviations in waveguide filters and manifold multiplexers using metal insertions

Microwave filters and multiplexers commonly employ tuning screws to compensate for small errors occurring during the fabrication process. Nevertheless, the use of tuning screws has some disadvantages, because the small gaps between the screws and the holes are prone to create unwanted effects when dealing with high-power signals, especially for space applications, and are also the source of potential radiation losses. In this paper, an alternative technique to correct manufacturing deviations is presented, in which tuning screws are replaced by fixed metal insertions. In this case, the correction is made by means of designing new insertion pieces that will be able to correct those small deviations. In order to find the dimensions of the new pieces, a space-mapping technique is applied. For verification purposes, the method has been applied over a circular-waveguide dual-mode filter and later over a manifold multiplexer containing the same type of filters. However, the technique can be directly extended to other types of waveguide filters and multiplexers where tuning screws are also employed.

A Deterministic EM Design Technique for General Waveguide Dual-Mode Bandpass Filters

Circular waveguide dual-mode (CWDM) filters have been widely employed in the manifold-coupled output multiplexer (OMUX) for satellite payloads. In this paper, a deterministic electromagnetic (EM) design technique for fast and accurately computerized prototyping a general CWDM filter is presented. By introducing a generalized K impedance inverter using the generalized scattering matrix of the tuning screw section, the insertion phase and the coupling of the two degenerate modes in a CWDM cavity can be determined by a most effective way. To handle the asynchronously tuned cases, the theoretical formula that relates a self-coupling to its corresponding phase offset is derived. The design technique is based on modal analysis at the center frequency and is deterministic without using optimization or curve fitting. The presented technique enables the full-wave EM design of CWDM filters as easy and accurate as designing conventional single mode waveguide filters. To validate the design technique, practical design of eight-pole symmetric and asymmetric CWDM filters have been studied theoretically and experimentally. An EM design of a complete Ku-band 15-channel contiguous OMUX is also demonstrated.

High-Dimensional Neural-Network Technique and Applications to Microwave Filter Modeling

Neural networks are useful for developing fast and accurate parametric model of electromagnetic (EM) structures. However, existing neural-network techniques are not suitable for developing models that have many input variables because data generation and model training become too expensive. In this paper, we propose an efficient neural-network method for EM behavior modeling of microwave filters that have many input variables. The decomposition approach is used to simplify the overall high-dimensional neural-network modeling problem into a set of low-dimensional sub-neural-network problems. By incorporating the knowledge of filter decomposition with neural-network decomposition, we formulate a set of neural-network submodels to learn filter subproblems. A new method to combine the submodels with a filter empirical/equivalent model is developed. An additional neural-network mapping model is formulated with the neural-network submodels and empirical/equivalent model to produce the final overall filter model. An H -plane waveguide filter model and a side-coupled circular waveguide dual-mode filter model are developed using the proposed method. The result shows that with a limited amount of data, the proposed method can produce a much more accurate high-dimensional model compared to the conventional neural-network method and the resulting model is much faster than an EM model.

Rigorous Mode-Matching Method of Circular to Off-Center Rectangular Side-Coupled Waveguide Junctions for Filter Applications

An accurate and efficient method for analyzing circular to multiple off-center rectangular side-coupled waveguide T-junctions is developed based on a rigorous mode-matching technique. The method is very general and not limited by symmetry or other dimensional constraints to the junction. A new way to match fields on the curved interface between subregions is described in detail. The computer code developed based on this theory is highly efficient. The numerical results match with the results obtained by other methods including experimental ones. The method is used to design a side-coupled circular waveguide dual-mode filter.

Novel modal analysis of a circular-to-rectangular waveguide T-junction and its application to design of circular waveguide dual-mode filters

This paper describes a novel modal analysis of a circular-to-rectangular waveguide T-junction and its application to the design of circular waveguide dual-mode filters with a sidewall coupling iris. The analysis is based on the newly developed finite plane-wave series-expansion technique and the concept of the extended boundary condition. The combination of the two concepts greatly facilitates the modal analysis of complex boundary value problems and eliminates the numerical integration. The proposed modal analysis has been verified both by experiments and commercial software for a wide range of parameters. Design examples of I/O structures for a set of channel filters demonstrate the great value of the new modal analysis scheme in practical applications.

An optimal circular-waveguide dual-mode filter without tuning screws

A novel circular-waveguide dual-mode (CWDM) filter structure is proposed. The coupling between the degenerate modes in the same cavity is provided by an off-centered circular iris built in at the middle of the resonant cavities. Considering the facts of: (1) simplicity of the mechanical process; (2) a potentially high Q; (3) a wide spurious-free frequency band; and (4) the effectiveness of electromagnetic (EM) modeling, the structure can be considered as an optimal coupling structure for CWDM filters when a precise EM design is required. A rigorous mathematical proof is given for explaining its working mechanism. The detailed formulations for designing the new coupling structure is also discussed. To validate the new structure, a narrow-bandwidth four-pole Ku-band elliptic filter is designed, manufactured and tested. Very good agreement is obtained between the calculated and measured responses.

Efficient modal analysis of waveguide filters including the orthogonal mode coupling elements by an MM/FE method

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. >