Dietmar Schmitt

A new family of all-inductive dual-mode filters

In this paper, we describe a new family of dual-mode filters that is based on the use of simple inductive discontinuities in a rectangular waveguide environment. The proposed filter structure can be analyzed and optimized very efficiently using multimode equivalent network representations, thus leading to a simple and rapid development procedure. In addition to theory, the measured performance of a number of filter structures is also presented, thereby fully validating the proposed filter concept.

The electric-field Integral-equation method for the analysis and design of a class of rectangular cavity filters loaded by dielectric and metallic cylindrical pucks

Rectangular cavity filters loaded by metallic and dielectric cylindrical pucks represent a wide class of structures used for the realization of compact microwave filters for space and terrestrial communications. The electric-field integral-equation method has been applied here to develop a software tool for the design of such a class of filters. Resonators simultaneously containing a number of dielectric and metallic cylindrical pucks can be analyzed using the method presented here. Dielectric loaded rectangular waveguide filters and comb-line filters are two typical examples where this approach can be applied. The input and inter-cavity couplings realized by slots have been modeled using the proposed integral-equation method. The full-wave analysis and optimization of an entire filter can be performed using the software presented here. Dielectric and metallic losses have been taken into account and the tuning screws have been also included into the analysis. The prototype of a single resonator and complete passband dielectric loaded rectangular waveguide filter have been realized and measured to test the software, and a commercial software has also been used to validate the code. A number of examples are presented here. A very short computation time of the order of 1-s/frequency point for the analysis of an entire filter has been obtained, making the full-wave optimization of an entire filter an affordable task.

Dimensional synthesis for wideband waveguide filters

Broadband waveguide filter designs are widely used for telecommunications, space and terrestrial applications. Fairly accurate design procedures giving equivalent circuit information are well known, but this data needs to be converted into physical dimensions, i.e. waveguide cavity lengths and iris dimensions. The aim of this work is the description of a novel procedure giving dimensions of such filters directly for wide and narrow band applications. The results obtained demonstrate very good equi-ripple performance up to bandwidths of approximately 20% in frequency or 40% in terms of guide wavelength.

Investigation of Multipaction Phenomena in Passive Waveguide Filters for Space Applications

This paper presents an investigation on multipaction risk in microwave bandpass filters. The study reveals higher multipaction risk for narrower bandpass filters. To alleviate the problem with multipaction generation, different filtering structures are proposed. Results demonstrate that using the new structures multipaction risk can be reduced as much as 30% with regard to the initial design

Study of the Multipactor Effect in Bandpass Wedge-Shaped Waveguide Filters

Recently developed high-power radio-frequency discharges prediction tools have suggested that wedge-shaped waveguides are more resistent to multipactor effects than the equivalent rectangular waveguides. As a result of several research activities performed in cooperation with the European Space Research and Technology Centre of the European Space Agency, a filter structure based on wedge-shaped cavities is designed and manufactured, thus proving the previous theoretical results with a passive device widely used in the output (high-power) stage of satellite payloads. Experimental results are presented that confirm the developed prediction models. Finally, a discussion of advantages and potential limitations of this new filter topology is included, and further improvements for this waveguide topology are also suggested.

Computer-aided design of Y-junction waveguide diplexers

Waveguide diplexer designs are widely used for telecom- munications, space, and terrestrial applications. Although mathemat- ical models and design procedures for waveguide fllters are known, diplexer designs still remain complex and time consuming. This pa- per describes how to obtain an equivalent circuit network model and a complete design of non-contiguous diplexers using a computer-aided approach with a classic Y-junction. Results are satisfactory in terms of reduced design time and performance. Examples including physical dimensions are provided.

Polarization-Preserving Quadruple-Ridge Waveguide Filter and Four-fold Symmetric Transformer

Current astrophysical and space applications require waveguide filters to exhibit wide stop-band performances and to preserve the dual polarization states of the electromagnetic field. The aim of this work is to present a waveguide filter that exhibits four-fold symmetry and significant stop-band improvements over the performances of standard circular and square waveguide technologies. Positive results have been achieved using quadruple ridge waveguide cross-sections and attenuation poles. This work also presents a polarization preserving transformer that converts a quadruple ridge waveguide cross-section into a square cross-section. Design examples are presented to show good performances of both filter and transformer

Efficient full-wave CAD tool of passive components based on coaxial waveguide junctions

An efficient full-wave CAD tool dedicated to coaxial waveguide junctions is presented. The tool is well suited to treat both standard coaxial lines and rectangular-circular coaxial waveguides. The case of offset internal conductors and dielectric filling are contemplated as well. The tool is very efficient and accurate, which allows to be used by iterative optimization procedures for the design of coaxial waveguide components such as low-pass and bandpass filters, and impedance transformers among other structures. Direct coaxial excitations in rectangular waveguides can be characterized as well.

Innovative manufacturing technology for RF Passive devices combining electroforming and CFRP application

In this paper an innovative manufacturing technology is presented that combines electroforming and CFRP (Carbon Fiber Reinforced Plastic) application and thus could be an enabling technology to achieve tuningless lightweight RF passive hardware with complex geometries. In order to demonstrate the performances achievable with this manufacturing process, a highly sensitive 0.14% fractional bandwidth dual mode filter centered at 19.8GHz was fabricated and tested. The flange interface of the filter was an integral part of the hardware and the total weight four times lighter than an equivalent part made from INVAR.

Resonator Voltage Prediction in Microwave Bandpass Filters

The prediction of peak voltages in high-power bandpass filters is presented using a new method in order to overcome the limitations of previously reported techniques. The concepts of coupling matrix, frequency transformation, and resonator stored energy are used to arrive at a compact formulation, which accounts for both circuital and electromagnetic (EM) filter characteristics. The resulting expression is independent of the detailed filter design. An analytical method is therefore obtained, enabling RF power-handling studies of bandpass filters without restrictions on filter bandwidth or resonator geometry. Explicit formulas are derived and applied to examples representative of a variety of applications, i.e., rectangular-waveguide TE101-mode Chebyshev and coaxial TEM-mode Bessel filters. EM simulations and experimental results verify the validity of the presented method.