Thomas Sieverding

Automated design of waveguide components using hybrid mode-matching/numerical EM building-blocks in optimization-oriented CAD frameworks-state of the art and recent advances

Fast hybrid mode-matching/boundary-contour (MM/BC) and mode-matching/finite-element (MM/FE) waveguide building blocks are described for the optimization-oriented use in powerful circuit computer-aided design (CAD) tools and the automated design of waveguide components. The efficient electromagnetic (EM) CAD technique allows the accurate design of a comprehensive class of rectangular and circular waveguide components including realistic structures of higher complexity. The efficiency and flexibility of the hybrid CAD method is demonstrated at advanced EM design examples, such as broad-band circular-to-rectangular waveguide transitions including octagonal cross sections, waveguide resonator filters with rounded corners, optimum-shaped bends, dual-mode filters with coupling sections without tuning screws, ridged waveguide filters with rounded corners, and multiplexers. The designed components are directly amenable to cost-efficient fabrication techniques like computer-controlled milling methods. The theory is verified by available measurements.

Field theoretical CAD of open or aperture matched T-junction coupled rectangular waveguide structures

The rigorous computer-aided design of rectangular waveguide structures coupled by open or rectangular iris loaded E- or H-plane T-junctions is described. The design theory is based on the full wave mode-matching method for the key-building-block T-junction element associated with the generalized S-matrix technique for composite structures. The waveguide structures may be arbitrarily composed of the T-junction and already known key-building-block elements (such as the double step and the septum discontinuity) combined with homogeneous waveguide sections between them. The E- or H-plane T-junction effect, large apertures, finite iris or septum thicknesses, and higher-order mode interactions at all step discontinuities are rigorously taken into account. Typical design examples, like rectangular iris coupled T-junctions, narrow-stopband waveguide filters, high return loss E-plane T-junction diplexers, an elliptic function E-plane integrated metal insert filter and a simple ortho-mode transducer demonstrate the efficiency of the method. The theory is verified by measurements. >

Rigorous CAD of multiport coupled rectangular waveguide components

Based on the simple mode-matching key-building block of the single double-plane step discontinuity, a general modal admittance formulation is presented for the rigorous CAD of longitudinal multi-channel or -aperture coupled rectangular waveguide structures of arbitrary size and location. The theory involves an arbitrary number of rectangular coupling structures, different size and finite thickness of the coupling elements, as well as immediate higher-order mode interaction of all discontinuities. The efficiency of the design method is demonstrated at two new filter examples: a metal insert Ku-band bandstop filter (12-18 GHz, WR-62) with an E-plane bypass waveguide structure, and a low-cost lowloss Ku-band four-aperture iris coupled bandpass filter. The theory is verified by comparison with measured results.

Modal analysis of the magic tree

The full-wave modal S-matrix of the magic-T-junction is derived by applying the mode-matching technique. Four standing-wave solutions in suitably chosen subregions for the four side arms are superimposed in the common cavity region in the middle section. This yields rapid convergence and accurate results, since the electric wall boundary conditions in the waveguide ports are met rigorously. The theory is verified by measurements at a magic-T-junction with standard X-band (WR 90) rectangular waveguide ports.<<ETX>>

Mode-matching CAD of rectangular or circular multiaperture narrow-wall couplers

A rigorous and efficient mode-matching computer-aided design (CAD) method for rectangular waveguide H-plane couplers is presented. The couplers employ multiple large rectangular or circular apertures of different sizes and nonuniform distance. The decomposition of the coupler structure into adequate mode-matching key-building blocks, i.e., the T-junction, double-plane step discontinuity, and rectangular-to-circular waveguide transition, together with the homogeneous intermediate waveguide sections of finite lengths yield the desired high flexibility. Both the finite wall thickness and the higher order mode interaction between all discontinuities are accurately taken into account by the combination of the individual building blocks of the generalized scattering matrix technique. Design examples for rectangular and circular aperture provide coupling values of -10.7, -10, -8.1, -5.3, -4.7, -3, -2.6, and -2.3 dB in Ku-band (12-18 GHz), thus demonstrating the flexibility and the efficiency of the method. The theory is verified by excellent agreement with measurements.

Rigorous analysis of the rectangular waveguide six-port cross junction

The modal S-matrix of the general rectangular waveguide six-port cross-junction building block is derived by applying the mode-matching technique. Rapid convergence and accurate results are achieved by the superposition of six standing wave solutions in the common cavity regions which meet the electric wall boundary conditions in the waveguide ports rigorously. The theory is verified by measurements at a six-port cross with standard Ku-band (WR 62) rectangular waveguide ports.<<ETX>>

Optimum field theory design of broad-band E-plane branch guide phase shifters and 180 degrees couplers

Optimum rectangular waveguide E-plane branch guide phase shifters and 180 degrees branch guide couplers are designed with the rigorous method of field expansion into normalized eigenmodes. The design includes both the higher order mode interaction between the step discontinuities and the finite step and branch heights. The phase shifter design applies the Schiffman principle to branch guide couplers where two ports are short-circuited. The 180 degrees coupler design combines the advantage of the broadband potential of multiple-branch couplers with the low-insertion-loss qualities of E-plane stub-loaded phase shifters. A computer-optimized phase shifter prototype for the waveguide Ku-band (12-18 GHz) shows a 90 degrees +or-1 degrees differential phase shift with reference to an empty waveguide within about 23% bandwidth. Five-branch three-stub coupler prototypes, designed for 3+or-0.2 dB coupling, for the waveguide Ku- and Ka-bands (26-40 GHz) achieve a 180 degrees +or-1 degrees differential phase shift at the output ports within about 19% bandwidth, as well as more than 30 dB isolation and return loss. The theory is verified by measured results. >

Novel remote controlled dual mode filter providing flexible re-allocation of center frequency and bandwidth

A novel TE113 dual mode cavity filter design is introduced that provides remote controlled reallocation of center frequency and bandwidth. The reconfiguration principle1 considers both end-walls of the cavities to be independently moveable along the cavity axes. This allows convenient control of cavity resonance frequencies (cavity length) and filter couplings (i.e., field strength in front of the coupling means inside the cavity). Higher order filters are realized by side-wall cavity arrangements using synchronous movement of all cavity end-walls with only two actuation units. EM analyses and measured results of a 2-order filter design at 11.2GHz prove the feasibility of the new solution.

Compact Rx/Tx channel duplexer with tuning capability for integration in a 26GHz high capacity short haul radio equipment

A novel Ka-band Rx/Tx channel duplexer1 design with tuning capability is established for the 26GHz band. Thus, only a single hardware is necessary to serve all duplex channel combinations of the overall radio frequency band - a prerequisite for large scale low cost unit production. The applied filters consider optimal tailored transfer functions with transmission zeros, realized with compact planar overmoded TE103 cavity structures to accommodate the extreme rejection demands while maintaining low insertion loss. A further design aspect has been easy integration and interfacing into the waveguide subsystem of the radio equipment. The complete duplexer structure has been designed using a mode matching based CAD. To satisfy the stability of the responses for the given outdoor environmental conditions it has been realized from silverplated INVAR sheets - a technique supporting the low cost issue. Good agreement of computed and measured results and the successful testing of the tuning capability verifies the design.

Comments on "Fast and accurate analysis of waveguide filters by the coupled-integral-equations technique" [with reply]

For original paper see F. Arndt et al., ibid., vol.45, pp.747-60 (1997). In the original paper, the authors analyzed a four-resonator H-plane filter with both the mode-matching technique (MMT) and a coupled-integral-equation technique (CIET). In this paper we applied the MMT utilizing all features described by them to the same filter and verified the total central processing unit (CPU) time. A reply by the original authors to our comment is included.