This paper presents a new set of results concerning the use of higher/lower order modes as a means to implement bypass or cross coupling for applications in elliptic filter design. It is shown that the signs of the coupling coefficients to produce a transmission zero (TZ) either below or above the passband are, in certain situations, reversed from the predictions of simpler existing models. In particular, the bypass coupling to higher/lower order modes must be significantly stronger than the coupling to the main resonance in order to generate TZs in the immediate vicinity of the passband. Planar (H-plane) singlets are used to illustrate the derived results. This study should provide very important guidelines in selecting the proper main and bypass couplings for sophisticated filtering structures. Example filters are designed, built, and measured to demonstrate the validity of the introduced theory.

Characteristics of cross (bypass) coupling through higher/lower order modes and their applications in elliptic filter design

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.

A new family of all-inductive dual-mode filters

In this paper, patent pending substrate integrated waveguide (SIW) bandpass filters with moderate fractional bandwidth and improved stopband performance are proposed and demonstrated for a Ka-band satellite ground terminal. Nonphysical cross-coupling provided by higher order modes in the oversized SIW cavities is used to generate the finite transmission zeros far away from the passband for improved stopband performance. Different input/output topologies of the filter are discussed for wide stopband applications. Design considerations including the design approach, filter configuration, and tolerance analysis are addressed. Two fourth-order filters with a passband of 19.2-21.2 GHz are fabricated on a single-layer Rogers RT/Duroid 6002 substrate using linear arrays of metallized via-holes by a standard printed circuit board process. Measured results of the two filters agree very well with simulated results, showing the in-band insertion loss is 0.9 dB or better, and the stopband attenuation in the frequency band of 29.5-30 GHz is better than 50 dB. Measurements over a temperature range of -20degC to +40degC show the passband remains almost unchanged.

Substrate Integrated Waveguide Filter With Improved Stopband Performance for Satellite Ground Terminal

This contribution presents new design dimensions for the ridge waveguide septum polarizer. Emphasis is placed first, on including the finite septum thickness in the analysis; second, demonstrating its influence on the polarizer performance; third, including a stepped approach for extremely thick septa; fourth, optimizing components without the need for additional phase-adjusting structures; and fifth, providing the application engineer with some design guidelines. Examples for varying septum thickness and/or number of sections are given for C-, X-, R120-, Ku- and K-band applications. The analysis is based on an efficient mode-matching technique. Evolution-strategy methods are used for optimization. Both algorithms are translated into PC-operational software. Results are compared with previously published theoretical/experimental polarizer data and with a finite-element analysis, and are found to be in good agreement. >

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Ridge waveguide polarizer with finite and stepped-thickness septum

In this paper, we propose a simple, yet reliable methodology to expedite yield estimation and optimization of microwave structures. In our approach, the analysis of the entire response of the structure at hand (e.g., $S$ -parameters as a function of frequency) is replaced by response surface modeling of suitably selected feature points. On the one hand, this is sufficient to determine whether a design satisfies given performance specifications. On the other, by exploiting the almost linear dependence of the feature points on the designable parameters of the structure, reliable yield estimates can be realized at low computational cost. Our methodology is verified using two examples of waveguide filters and one microstrip hairpin filter and compared with conventional Monte Carlo analysis based on repetitive electromagnetic simulations, as well as with statistical analysis exploiting linear response expansions around the nominal design. Finally, we perform yield-driven design optimizations on these filters.

Rapid Yield Estimation and Optimization of Microwave Structures Exploiting Feature-Based Statistical Analysis

An improved type of asymmetric-iris coupled-cavity filters is introduced which utilizes the dual mode resonance and interference characteristics of the fundamental mode and the next-higher-order odd mode in suitably optimized resonators. This design achieves additional stopband poles which may advantageously be used to improve the edge steepness and the rejection characteristic in the second stopband. Based on the modal scattering matrix method. The rigorous design takes into account both the finite iris thickness and the higher-order mode interaction at all step discontinuities. Computer-optimized design examples of asymmetric inductive and resonant iris coupled resonator filters for the waveguide Ku-band (12-18 GHz) and W-band (75-110 GHz), respectively, demonstrate the improved stopband behavior. The theory is verified by available measured results. >

Asymmetric iris coupled cavity filters with stopband poles

The authors present a rigorous design method for corrugated septum orthomode transducers (OMTs) which combines the compactness advantage of the stepped septum structure with the phase matching potential of corrugated waveguide polarizers. The structure under investigation is composed of standard field theory key-building blocks, the double-step discontinuity, the waveguide-to-ridged-waveguide transition, and the transition waveguide to septated waveguide. Based on the modal scattering matrix method, the design takes into account the influence of both the finite septum thickness and the higher-order mode interaction at all discontinuities. Computer-optimized design data are given for a Ku-band waveguide corrugated septum polarizer, achieving a return loss of more than 20 dB together with a 90 degrees +0 degrees /-3 degrees differential phase shift for about 10% bandwidth. The theory is verified by measurements. >

Field theory design of a corrugated septum OMT

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

Rigorous CAD of multiport coupled rectangular waveguide components

The authors describe the rigorous CAD (computer-aided design) of a class of cavity filters composed of rectangular and circular waveguide structures. Based on the rectangular-to-circular and circular-to-circular waveguide junction key-building block modal S-matrices, the design takes rigorously into account both the finite iris thickness and the higher order mode interaction at all step discontinuities, as well as asymmetric irises. This allows the stopband characteristic to be included in the filter design, and dual-mode resonance effects may be utilized to achieve improved edge steepness and rejection characteristics. The theory is verified by measurements. >

Modal-S-matrix design of microwave filters composed of rectangular and circular waveguide elements

A new design of compact, lightweight, broad-band and low-insertion-loss diplexers for satellite conununication systems is introduced utilizing E-plane corrugated and below-cutoff waveguide filters in the septate waveguide sections of E-plane furcated power dividers with asymmetrical transformer heights. The rigorous optimization technique comprises the complete component, including all discontinuities as well as the higher order mode interaction between them. Results are given for a computer optimized design exmnple for a minimum input port return loss of about 22 dB over the transmit (3.7 - 4.3 GHz) and receive (5.83 - 6.5 GHz) frequency band. The theory is verified at a R- 48 waveguide diplexer example which was milled from a solid block.

U. Papziner

Papers

Asymmetric iris coupled cavity filters with stopband poles

Field theory design of a corrugated septum OMT

Rigorous CAD of multiport coupled rectangular waveguide components

Modal-S-matrix design of microwave filters composed of rectangular and circular waveguide elements

Rigorous Field Theory Design of Compact and Lightweight Broadband Diplexers for Satellite Communication Systems