In this article we review state-of-the-art concepts of space mapping and place them con- textually into the history of design optimization and modeling of microwave circuits. We formulate a generic space-mapping optimization algorithm, explain it step-by-step using a simple microstrip filter example, and then demonstrate its robustness through the fast design of an interdigital filter. Selected topics of space mapping are discussed, including implicit space mapping, gradient-based space mapping, the optimal choice of surrogate model, and tuning space mapping. We consider the application of space mapping to the modeling of microwave structures. We also discuss a software package for automated space-mapping optimization that involves both electromagnetic (EM) and circuit simulators.

Space mapping

Nonradiative wireless power transfer using magnetically coupled coils is studied in order to transfer a predetermined amount of power at the maximum efficiency. Accordingly, a conceptual wireless power transfer system and a tuning method are presented. Such a study is essential for effectively exploiting the inherent ability of a given pair of coupled coils. With the equations for inductance and resistance calculations, the system performance is evaluated and verified with well-known experimental results and circuit simulations.

A Study of Loosely Coupled Coils for Wireless Power Transfer

The evolution of microwave filters and multiplexers for space application is described. The many advances are described within the context of the design of the overall communication subsystem. Emphasis is placed on the multipaction and passive intermodulation (PIM) considerations in designing high-power multiplexers. The impact of microwave filter technology in the channel characterization of satellite systems is described. The future directions of research and development are briefly discussed. >

Innovations in microwave filters and multiplexing networks for communications satellite systems

The concept of the conventional coupling matrix is extended to include designs of dual- and triple-band filters. The multiband response is created by either placing transmission zeros within the bandwidth of a wideband filter or using higher order resonances. Realizable topologies both in planar and waveguide technologies can be imposed and associated coupling coefficients enforced during optimization. The design process is verified by measurements and comparison with results of commercially available field solvers

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Coupling-Matrix Design of Dual and Triple Passband Filters

A compact circularly polarized (CP) co-designed filtering antenna is reported. The device is based on a patch radiator seamlessly integrated with a bandpass filter composed of coupled stripline open-loop resonators, which are designed together as a system. In the proposed design, the patch functions simultaneously as the radiator and the last stage resonator of the filter, resulting in a low-profile integrated radiating and filtering module with a small overall form factor of $\mathbf{0.53{\lambda _0} \times 0.53{\lambda _0} \times 0.07{\lambda _0}}$ . It is shown that the filtering circuit not only ensures frequency selectivity but also provides impedance matching functionality, which serves to broaden both the impedance and axial ratio bandwidths. The designed filtering antenna was fabricated and measured, experimentally achieving an $\mathbf{{S_{11}} , an axial ratio of less than 3 dB and a gain higher than 5.2 dBi over a bandwidth from 3.77 to 4.26 GHz, i.e., around 12.2%, which makes it an excellent candidate for integration into a variety of wireless systems. A linearly polarized version of the integrated filtering antenna was also demonstrated. In addition, further full-wave simulations and experiments were carried out to verify that the designed CP filtering antenna maintains its properties even when mounted on different positions of the human body with various body gestures. The stable impedance and radiation properties also make it a suitable candidate as a wearable antenna for off-body wireless communications.

A Compact, Wideband Circularly Polarized Co-designed Filtering Antenna and Its Application for Wearable Devices With Low SAR

Foreword Preface Acknowledgments 1 Radio Frequency (RF) Filter Networks for Wireless Communications-The System Perspective PART I: INTRODUCTION TO A COMMUNICATION SYSTEM, RADIO SPECTRUM, AND INFORMATION PART II: NOISE IN A COMMUNICATION CHANNEL PART III: IMPACT OF SYSTEM DESIGN ON THE REQUIRMENTS OF FILTER NETWORKS 2 Fundamentals of Circuit Theory Approximation 3 Characterization of Lossless Lowpass Prototype filter functions 4 Computer-Aided Synthesis of Characteristic Polynomials 5 Analysis of Multiport Microwave Networks 6 Synthesis of a General Class of the Chebyshev Filter Function 7 Synthesis of Network - Circuit Approach 8 Coupling Matrix Synthesis of Filter Networks 9 Reconfiguration of the Folded Coupling Matrix 10 Synthesis and Application of Extracted Pole and Trisection Elements 11 Microwave Resonators 12 Waveguide and Coaxial Lowpass Filters 13 Waveguide Realization of Single- and Dual-Mode Resonator Filters 14 Design and Physical Realization of Coupled Resonator Filters 15 Advanced EM-Based Design Techniques for Microwave Filters 16 Dielectric Resonator Filters 17 AllPass Phase and Group Delay Equalizer Networks 18 Multiplexer Theory and Design 19 Computer-Aided Diagnosis and Tuning of Microwave Filters 20 High-Power Considerations in Microwave Filter Networks Appendix A Appendix B Appendix C Appendix D Index

Microwave Filters for Communication Systems: Fundamentals, Design and Applications

Following a brief review of different types of multiplexer configurations, a systematic design approach has been outlined for the design of manifold-coupled multiplexers. The piecewise approach, optimizing parts of the multiplexer separately in repeated cycles while converging upon an optimal solution, has proved to be very effective for most practical applications. The technique is readily applicable to manifold multiplexers incorporating an arbitrary number of channels, regardless of their bandwidths and channel separations. There are no restrictions on the design and implementation of channel filters onto the manifold; they may be asymmetric, and may incorporate transmission zeros, group delay equalization zeros, or both. The manifold itself is a transmission line, be it a coaxial line or a rectangular waveguide or some other low-loss structure. The costly EM simulation is used economically on manifold junctions and channel filters through the use of space-mapping optimization techniques, where EM-based simulators are used to fine-model each multiplexer channel and coupling matrix representation is used to coarse-model the performance. Fine details such as tuning screws may be included in the design process. This design procedure takes into account the effects of dispersion and spurious modes and, as a result, the overall design and final tuning time can be significantly reduced.

Design of manifold-coupled multiplexers

This paper presents new ideas for the design and implementation of microwave filters with single and dual stopbands. They can be realized with waveguide, coaxial, dielectric resonators, or in a planar technology. The new methods represent an advance over present methods in that the resonators are direct coupled, thus avoiding the need for transmission line phase lengths between resonator stubs that tend to degrade performance due to their dispersion and are difficult to adjust during tuning. Three bandstop (BS) configurations are presented. The first will accommodate even or odd characteristics and also asymmetric responses, although some negative or diagonal cross-couplings will be needed. The second resembles the cul-de-sac configuration for bandpass filters and needs no diagonal or negative couplings even for asymmetric characteristics. The third is an application of the cul-de-sac synthesis technique to dual-band bandstop (DBBS) filters. All these BS designs are very similar to regular bandpass filters in their design and realization. The design of a DBBS filter is presented and compared with an equivalent bandpass filter to demonstrate its advantages. Finally, the simulated and measured results of a fourth-degree BS filter design in the novel cul-de-sac configuration are presented.

Direct-coupled microwave filters with single and dual stopbands

The invention relates to a single mode multi-cavity microwave filter that includes a housing formed with a plurality of walls which define at least two rows of side-by-side dielectric loaded cavities, wherein sequential cavities are coupled to one another via slots formed in the walls therebetween and at least one pair of non-sequential adjacent cavities are coupled via a probe. The coupling via the slots is defined mathematically as positive coupling. The probe is selectively configurable to provide positive or negative coupling relative to the sign of the slot coupling. Further, at least one non-adjacent, non-sequential pair of cavities is coupled via a second probe that may be configured to provide either positive or negative coupling relative to the sign of the slot coupling. The filter housing supports a plurality of adjustable fins which extend into the slots, one fin to each slot, to selectively adjust the size of the slot.

Folded single mode dielectric resonator filter with cross couplings between non-sequential adjacent resonators and cross diagonal couplings between non-sequential contiguous resonators

This paper presents a novel adaptive predistortion technique for general cross-coupled microwave/RF filters with improved insertion loss and group-delay equalization. The method enables many potential applications of an almost abandoned technique, and permits a lower Q implementation technology to emulate the performance of a higher Q filter. 10-4-4 filters were built and tested at C- and Ku-band to verify the validity of the new method. The impact to satellite communication channels was also analyzed. Another novel concept of over-predistortion was proposed and evaluated and should lead to significant improvement for applications such as satellite transponder input multiplexers, where insertion loss can be traded off for in-band flatness, mass, volume, and even overall system performance.

Richard J. Cameron

Papers

Microwave Filters for Communication Systems: Fundamentals, Design and Applications

Design of manifold-coupled multiplexers

Direct-coupled microwave filters with single and dual stopbands

Folded single mode dielectric resonator filter with cross couplings between non-sequential adjacent resonators and cross diagonal couplings between non-sequential contiguous resonators

Predistortion technique for cross-coupled filters and its application to satellite communication systems