Manuel Sanchez-Renedo

Tunable combline filter with continuous control of center frequency and bandwidth

A new combline filter structure with a continuous tunability for both the center frequency and bandwidth is presented in this paper. The passband-width tunability is achieved by placing variable coupling reducers between the filter resonators. The coupling reducers, operating as bandwidth control subnetworks, are designed as detuned resonators made up of a line segment ending in a variable capacitor. The proposed filter structure is experimentally validated with the design, construction in suspended stripline technology, and characterization of a low-cost filter prototype for terrestrial digital video broadcasting receivers operating in the UHF band (470-862 MHz). Other relevant factors, such as the intermodulation distortion produced by the varactors used to control the bandwidth electronically or the power-handling performance of the constructed filter, are also discussed. The reconfigurable filter module described in this paper is very suitable for the design of flexible multifunction receiver subsystems simultaneously supporting signals with a different bandwidth.

A Class of Microwave Transversal Signal-Interference Dual-Passband Planar Filters

A new type of microwave dual-passband planar filter exploiting signal-interference techniques is presented. The described filter approach consists of transversal filtering sections shaped by two transmission lines connected in parallel. This transversal section, operating under feedforward signal-combination principles, allows dual-band bandpass filtering responses with several transmission zeros to be synthesized. A set of analytical formulas and guidelines for the design of the dual-passband transversal filtering section are provided. Moreover, its practical usefulness is verified through the development and testing of a microstrip prototype for the 1.4/2.6-GHz dual band.

Microwave Dual-Band Bandpass Planar Filters Based on Generalized Branch-Line Hybrids

A new class of microwave dual-band bandpass planar filter is reported. It uses an original generalized branch-line hybrid topology devised here, operating as dual-passband transversal filtering section. This type of filter network, under feedforward signal-interaction concepts, enables dual-band bandpass filtering actions with transmission zeros to be generated. Some design formulas and guidelines helping to synthesize the proposed dual-passband transversal filtering section are given. Furthermore, to prove its practical viability, theoretical, simulated and experimental results of two manufactured sharp-rejection dual-band bandpass microstrip filter prototypes are shown.

Signal-Interference Stepped-Impedance-Line Microstrip Filters and Application to Duplexers

In this letter, signal-interference filtering sections shaped by two in-parallel stepped-impedance transmission lines are applied to frequency-asymmetrical microstrip filter design. When realizing single-passband filters, a different selectivity for the lower and upper stopband can be generated, making them appropriate for duplexing devices. In the case of double-passband filters, fully-asymmetrical dual bands in terms of bandwidth, cutoff slopes and class of filtering transfer function can be shaped. Examples of design curves to adjust the performances of the synthesized signal-interference section filtering profile are given, e.g., bandwidth or in-band ripple level for Chebyshev-type functions. To show practical viability, a duplexer and a spectrally-asymmetrical dual-passband filter circuit are also built and characterized.

Low-Pass and Bandpass Filters With Ultra-Broad Stopband Bandwidth Based on Directional Couplers

The design of planar sharp-rejection low-pass and bandpass filters (LPFs and BPFs) featuring a very broad stopband is addressed in this paper. For the LPF case, two new classes of bandstop signal-interference transversal filtering section (TFS) consisting of power directional couplers in reflection mode are proposed. In the BPF application, additional short-circuit stubs are inserted at the TFS input/output accesses. Based on these filtering cells, the devised LPF and BPF approaches are then derived from the cascade of multiple TFSs with frequency-contiguous stopbands. Thus, an overall attenuated band showing an ultra-large spectral width and deep rejection levels through the generation of several transmission zeros (TZs) is synthesized. Furthermore, such unprecedented filtering performances are obtained for much lower circuit complexity than available solutions. The operating principle of the conceived LPF and BPF topologies and guidelines for their realization are detailed. This includes formulas for their analytically designable TZs. For practical validation, three LPF prototypes and one wideband BPF circuit are also fabricated in microstrip technology and tested.

Application of generalized Bagley-polygon four-port power dividers to designing microwave dual-band bandpass planar filters

A new type of microwave dual-band bandpass planar filter based on signal-interference techniques is reported. The described filter approach consists of transversal filtering sections made up of generalized Bagley-polygon four-port power dividers. This transversal section, by exploiting feedforward signal-interaction concepts, enables dual-band bandpass filtering transfer functions with several transmission zeros to be obtained. A set of closed formulas and guidelines for the analytical synthesis of the dual-passband transversal filtering section are derived. Moreover, its practical usefulness is proven with the development and testing of a 2.75/3.25-GHz dual-band microstrip prototype.

Microwave filtering power-distribution planar networks

In this paper, a new concept of single/multi-band microwave planar two-way circuit featuring a dual RF power-dividing/ filtering functionality is presented. This circuit, based on signal-interference techniques, is applied to develop multi-stage power-distribution networks with intrinsic filtering capability. Design equations and rules for the proposed dual-function circuit, helping in the synthesis of a given transfer function, are provided. Moreover, for experimental validation, two broadband microstrip prototypes corresponding to eight-way single-band and four-way quintuple-band networks are manufactured and characterized.

A new electronically tunable combline filter with simultaneous continuous control of central frequency and bandwidth

A new reconfigurable band pass filter with electronically continuous control of both central frequency and bandwidth is presented in this paper. The bandwidth tuning is achieved by means of an ingenious method to modify the electrical couplings of the filter resonators. The propose structure employs varactor capacitors as variable reactance elements. Finally, a filter prototype is designed, constructed and measured in suspended stripline technology in the UHF band (470-862 MHz).

Microwave single/multi-band planar filters with Bagley-polygon-type four-port power dividers

This work reports a planar signal-interference filter structure based on Bagley-polygon-type four-port power dividers. It is shaped by the cascade of two identical transversal filtering sections made up of this power splitter and applied to synthesize single/multi-band responses with sharp-rejection characteristics. Analytical equations helping in the theoretical design of this filter approach are provided. Besides, its practical viability is proven with the building and testing of three microstrip filter prototypes.

A Type of Planar Array-Antenna Feeding Network With Single/Multiband Filtering Capability

A dual-function circuit carrying out both the RF power-division and single/multiband filtering action is presented. It is used as building element to develop highly frequency-selective power-distribution networks for planar array-type antennas. The operating principle of this filtering/feeding circuit, exploiting transversal signal-interference techniques, is described. Also, formulas and guidelines helping in its theoretical design are given. As proof of concept, microstrip prototypes of four-way single- and triple-band filtering/feeding networks are built and tested.