An overview of advances in filter design techniques in the framework of the evolution of the microwave area is presented in this article. Several types and implementations of filters developed during the last decades to satisfy the demands of modern communication services are described, emphasizing the new technologies and designs that fulfill the stringent electrical, mechanical, time and production cost requirements 4 actual system. In this context, this article revisits some of the advances in this area, where the role of Computer Aided Design (CAD) has enormous impact on the microwave industry.

High-performance DRs and filters are widely used in wireless and satellite communication systems due to their superior characteristics, such as high unloaded Q, excellent temperature stability, and smaller size compared to their air-filled counterpart. Temperature-stable high-Q dielectric materials with a wide range of dielectric constants from 20 to 100 are available. The properties of a DR such as resonant frequency and unloaded Q can be accurately determined by full-wave EM simulations. TEoi single-mode filters offer the advantages of design simplicity and flexibility in layout options over HEn dual-mode filters, while dual-mode filters have significiint advantages in the mass and volume of the products. Mixing the TEoi and HE\\ modes, dielectric loaded resonator filters achieve the advantages of dual-mode HEn DR filters and the excellent spurious performances of the TEqi mode ring resonator filters.

An extremely wideband ridge waveguide filter is presented. The fractional bandwidth of the filter can be greater than 115%. An input and output transition from ridge waveguide to stripline and then to coax is also designed. The analysis is done with mode matching method and verified with Ansoft HFSS. For validation purpose, a test filter with pass band from 3 GHz to 9 GHz has been designed. The results by both mode matching method and Ansoft HFSS are presented. Excellent agreement is obtained. The test filter is designed using air filled ridge waveguide; however the same design procedure can be equally applied to other manufacturing techniques such as LTCC.

Energies of ions emitted from large rare gas clusters irradiated by high intensity femtosecond laser pulses have been measured and the dependence of the average energy of ions on cluster sizes have been studied experimentally.

A novel type of tunable high Q dielectric loaded resonator and its application to filters and multiplexers are presented. The tunable dielectric loaded resonator has high unloaded Q, wide tuning range, and high temperature stability by using the ring shape DR and dielectric tuning element. The tuning properties of the resonator, such as tuning range, spurious mode, unloaded Q, and effect on couplings are investigated. Several PCS band filters and multiplexers for CDMA base station applications were designed and tested. Excellent measured frequency responses were obtained.

A novel type of filter power combiner, consisting of a plurality of tunable dielectric loaded resonator channel filters and using a multiple half-wavelength coaxial resonator common transformer is presented. The dielectric loaded resonator channel filters can be efficiently coupled to the common transformer resonator by opening the aperture at maximum magnetic field positions of the common resonator. Optimal mechanical layout and electrical performance can both be achieved. A PCS band 4-channel tunable CDMA combiner is designed and tested. Excellent measured frequency responses were obtained and verify the theory.

A practical triple-mode dielectric monoblock band pass filter integrated with a wide bandwidth pre-select mask bandpass filter and a microstrip low pass filter for WCDMA base station application is presented. The dielectric monoblock triple-mode filter was designed and optimized using 3D EM simulation software incorporating the equivalent circuit model. The pre-select filter and low pass filter were used to clean up the spurious response of the triple-mode filter up to 12 GHz. Both triple mode and mask filters are directly mounted on the PCB to minimize the cost and loss.

The electric coupling probe for combline resonators and filters is rigorously modeled by the full-wave mode matching method for the first time. The coupling structure is considered as a cascaded network of the resonator and stripline discontinuities, and is solved by cascading the generalized scattering matrices of all the discontinuities. As a result, the electric probe couplings of both rectangular and cylindrical combline resonators and filters can be accurately determined. The validation and accuracy of the method are verified by comparing the numerical results with the measured data and shown to be in good agreement.

Tunable dielectric resonators with dielectric tuning disks in rectangular enclosures are modeled by mode matching method. Tuning properties of T E01 mode such as tuning ranges, spurious mode separation, and couplings, etc., are investigated for both rod- and ring-type dielectric resonators.

A new ultra-stable sapphire resonator combined with a specially designed enclosure with semi spherical sidewall is presented and modeled by mode matching method. Stair steps are used to approximate the semi spherical sidewall to simplify the modeling procedure. The characteristic equation of the sapphire resonator can be obtained by solving the discontinuities of the cylindrical region and the spherical region. Resonant frequency, field distribution and unloaded Q of the resonant mode are obtained. Accurate and reliable results of the resonator can be obtained. Good separation of a whispering Gallery mode is obtained by optimizing the structure dimensions.

Rigorous mode matching method, incorporating perturbation techniques was introduced to the modeling, analysis and design of the resonant frequency-temperature characteristic of the combline resonator. Methods for temperature compensation of the resonator are accurately modeled and implemented. The accuracy of the modeling results is verified by comparing with the measured results and shown to be in good agreement.

Full wave modeling of the coupling structure between a double ridge waveguide and dielectric resonator in a rectangular cavity through an iris is presented. Eigen modes of the double ridge waveguide, and the discontinuities of the structures are obtained by rigorous mode matching method. By applying the cascading procedure, the reflection coefficients of the coupling structure can be obtained. From the phase variation of the reflection coefficient and circuit theory, resonant frequency and input/output coupling of the structure are accurately determined. An equivalent circuit model of the resonant structure is established. The computed results are compared with those obtained by other methods and shown to be in good agreement, which verifies the theory.

Modeling of the generalized multilayer cylindrical anisotropic dielectric loaded resonator structure by rigorous mode matching method is presented. Eigen modes of the multilayers two parallel plates waveguides are obtained. By cascading the radial discontinuities of the structure, resonant frequency, field distribution and the unloaded Q of the resonator are obtained. The computed results are compared with the experimental data for higher order Whispering Gallery (WG) modes and shown to be in good agreement.

A new configuration of conductor loaded resonator filters using two different sized conductor loaded resonators is presented. The spurious performance of the conductor loaded resonator filters are significantly improved. A rigorous mode matching method is used to compute the resonant frequency, unloaded Q and the field of the resonant mode of the conductor ( solid or ring) loaded resonators. The coupling coefficients between two resonators are computed using small aperture theory by Levy's approach. An 8-pole elliptic function filter is designed, constructed and tested. Experimental results verify the theory.

Full wave modeling of conductor loaded resonators in rectangular enclosures and associated coupling structure is presented. The generalized scattering matrices of the planar conductor loaded resonator in rectangular waveguide are obtained. By applying the short condition and cascading procedure, resonant frequency, field distribution of the resonator, and coupling between two cavities through an iris are obtained. The computed results are compared with the measured data and both are in good agreement. A 4-pole dual mode elliptic function filter using a planar structure cavity is designed, constructed and tested. Excellent measured frequency responses of the filter are obtained.

A new class of dual mode filters consisting of cylindrical waveguide cavities loaded with perfect conducting cylindrical resonator are introduced. A 4 pole dual mode elliptic function filter was designed, constructed and tested. Excellent filter frequency response with wide band spurious performance is obtained.

A new kind of dual mode filter consisting of high temperature superconductor (HTS) patch loaded circular cavity resonators is presented. The resonator is analyzed using full wave mode matching method. The generalized scattering matrices of the HTS patch loaded circular cavity are obtained. After performing cascading procedure and applying boundary conditions, resonant frequencies, field distribution, unloaded Q of the resonator and the coupling between two cavities through irises are obtained. Two 4-pole dual mode elliptic function patch conductor loaded cavity filters are designed, constructed and tested. Excellent measured frequency responses of the filter are obtained.

A rigorous technique for full wave modeling of the generalized double ridge waveguide T-junction has been developed, Eigen modes in each ridge waveguide region are obtained using mode-matching technique. Based on the eigen mode expansion method, combining the cascading procedure and computation of the magnetic fields of each mode at the shorted ports, the generalized admittance matrices and scattering matrices of all three ports are obtained. The method is general and very efficient, The accuracy and versatility of the method are verified through several numerical examples, The computed dominant mode's S-parameters are compared with that by finite element method (HFSS) and shown to be in good agreement.

The effects of several practical tuning structures on resonant frequencies and slot couplings in combline filters are investigated using a rigorous mode matching model. As an application, an 8-pole combline elliptic function filter is designed, built, and tested. Experiments verify the accuracy and validate the analysis.

A rigorous method for analysis of coupled dielectric quarter wavelength combline resonators is presented. The resonant frequencies and coupling coefficients of the resonators coupled by different coupling structures are investigated. A filter design technique based on the results of numerical analysis is described. A slot coupled filter and a monoblock elliptic function filter are designed. Excellent experimental results verify the theory.