Raul Loeches-Sanchez

Single/multi-band Wilkinson-type power dividers with embedded transversal filtering sections and application to channelized filters

This paper addresses the exploitation of signal-interference concepts for the realization of single/multi-frequency Wilkinson-type filtering power dividers in planar/lumped-element technologies. By embedding transversal signal-interference filtering sections into the arms of conventional Wilkinson-type power-divider topologies, RF/microwave power-distribution actions with intrinsic mono/multi-band bandpass filtering capabilities can be obtained. Analytical equations and rules for the theoretical synthesis of this dual-function device are derived. The generalization of the approach to multi-stage schemes for enhanced-performance designs or for the shaping of frequency-asymmetrical responses is also discussed. Furthermore, for practical demonstration, three prototypes are developed and characterized. They are a microstrip quad-band circuit for the 1-5 GHz range, a dual-band lumped-element device for the band of 0.2-0.6 GHz, and a new type of two-branch channelized active bandpass filter at 3 GHz that makes use of single-band versions of this dual-behavior component as signal-division/combination blocks.

Hybrid Acoustic-Wave-Lumped-Element Resonators (AWLRs) for High-

A new class of bandpass filters with quasi-elliptic frequency response, small physical size, and effective quality factors (Qseff) of the order of 1000 are presented. They are based on novel hybrid acoustic-wave-lumped-element resonator (AWLR) modules that enable the realization of bandpass filters with fractional bandwidths (FBWs) that are much larger (0.91-5.1 kt2) than the electromechanical coupling coefficient (kt2) of conventional acoustic wave (AW) resonator filters that exhibit FBWs between 0.4-0.8 kt2. In addition, they exhibit Qseff that are 25-50 times larger than in traditional lumped-element filter architectures. Quasi-elliptic single-pole bandpass filters (one pole and two zeros) made up of commercially available one-port surface AW resonators and surface-mount-device components are manufactured and measured at 418 MHz. Various passbands with FBW between 0.07% and 0.4% and insertion loss below 1.25 dB (i.e., Qseff in the range of 1525-5150) are demonstrated. Second-order bandpass filters (two poles and four zeros) with 0.24% FBW and less than 1.15 dB of insertion loss (i.e., Qseff of 4000) are also shown to improve the passband selectivity and out-of-band rejection. These filters feature dynamic stopband characteristics by tuning the position of their transmission zeros. The operating principle, theoretical analysis, and design guidelines of the AWLR module, as well as a comparison with traditional all-AW ladder-type filters, are also reported. An original and rather simple RLC-circuit equivalent of AW resonators that facilitates the incorporation of spurious modes into a simple Butterworth-Van-Dyke model for a more accurate synthesis of AWLR-based filters is extracted from measured two-port S-parameters.

Q

A novel technique to design lumped-element-based analog filters is presented. It exploits the application of signal-interference principles to a class of transversal filtering section made up of two in-parallel discrete-element transmission lines. This circuit network, through destructive and constructive signal-energy interactions, enables high-selectivity filtering actions to be generated. Moreover, this can be done in the same circuit topology independently of the type of transfer function to be synthesized. Design equations and guidelines for this lumped-element analog filter approach are given. Besides, for experimental validation, simulation results of two synthesis examples consisting of a lowpass and a bandpass filter implemented at the layout level are shown.

Bandpass Filters With Quasi-Elliptic Frequency Response

Double-functionality microwave planar circuits hybridizing filtering and impedance transformation capabilities are reported in this work. They are based on signal-interference transversal filtering sections (TFSs) whose design equations are generalized to synthesize the filtering functionality between any pair of real port impedances. Thus, an inherent impedance-transformation action is added to the signal-interference filter in its passband(s). The devised dual-functionality circuit concept is valid for other types of TFSs, as well as for both single- and multi-band designs. For experimental verification, two double-function microstrip prototypes for dual-band and ultra-wideband single-band filtering specifications which feature transformation ratios of 2:1 are synthesized, constructed, and characterized.

A type of lumped-element-based analog filters based on transversal circuit networks

An original and simple method to design high-performance microwave planar bandpass filters (BPFs) is reported. It makes use of traditional low-order coupled-resonator BPF networks properly modified in base of signal-interference techniques. Thus, through these mixed coupled-resonator/signal-interference BPF schemes, high-selectivity bandpass filtering functions also exhibiting low in-band group-delay variation can be synthesized. A detailed explanation of the proposed BPF concept is provided. Furthermore, as experimental validation, several prototypes are developed in microstrip technology and characterized.

Transformers with incorporated filtering capabilities exploiting signal-interference principles

A technique to design analog signal-interference narrow-band bandpass filters by merging transmission lines and surface-acoustic-wave (SAW) resonators is reported in this work. By inserting one-/two-port SAW resonators into the transversal filtering sections (TFSs) of the signal-interference filter, narrowband filtering actions with remarkable electrical properties can be synthesized. The latter particularly refers to the untypically-high effective unloaded quality factor (Qu) associated with the generated bandpass filtering response given its fully-planar realization. This leads to perceptible benefits in terms of in-band transmission loss and occupied physical area when compared to a classic pure signal-interference filter design. Moreover, for a given type of SAW resonator, adjustable bandwidth and transmission zeros (TZs) can be produced to attain a large variety of high-selectivity filtering functions. For practical validation, a three-stage microstrip narrow-band bandpass filter with measured S-parameters of a 433.9-MHz one-port SAW resonator is shown. The spurious-mode effect of the measured SAW resonator, as a limiting factor in the overall filter performance, is also discussed.

Microstrip filters with selectivity improvement using the new concept of signal-interference source/load coupling

An original type of lumped-element analog filters based on signal-interference techniques is proposed in this paper. To this aim, a novel class of two-path transversal filtering section shaped by a lumped-element quadrature power coupler arranged in reflection mode is devised as basic building block. Thus, under feedforward signal-interaction effects generated in this circuit network, high-performance filtering functions can be produced. As synthesis examples, two different multi-stage designs corresponding to ultra-wideband single-band and dual-band bandpass filters are demonstrated. Furthermore, for the previous ultra-wideband bandpass filter example, two alternative implementations at the layout level are developed for practical verification.

Analog signal-interference narrow-band bandpass filters with hybrid transmission-line/SAW-resonator transversal filtering sections

The design of RF/microwave planar differential-mode single/dual-band bandpass filters (BPFs) based on signal-interference principles is addressed in this work. To this aim, transversal filtering sections (TFSs) that consist of bi-path in-parallel-transmission-line-type cells are embedded into the two identical parts of a balanced circuit. The engineered filtering devices feature sharp-rejection capabilities in their differential-mode transfer function through multi-transmission-zero (TZ) generation along with higher in-band power attenuation levels in their common mode of operation when compared to most of the related prior-art architectures. Furthermore, the proposed concept of balanced BPF can be extrapolated to other classes of signal-interference TFSs as well as to configurations with more-than-two passbands. For experimental verification, a demonstrative two-stage single-band balanced BPF centered at 2 GHz is synthesized, manufactured in microstrip technology, and characterized.

Lumped-element-based single/dual-passband analog filters using signal-interference principles

This paper focuses on the application of signal-interference techniques to develop planar multi-band Wilkinson-type power dividers. By inserting transversal signal-interference multi-band filtering cells into the branches of the classic Wilkinson-type power-divider scheme, multi-band power-splitting/combining actions with added filtering operation can be attained. Design formulas for this dual-behavior filtering/power-dividing device for a particular class of embedded multi-band filtering cell are provided. Moreover, a 1.6/3/4.4-GHz triple-band microstrip prototype is built and tested for practical validation.

A class of differential-mode single/dual-band bandpass planar filters based on signal-interference techniques

A new family of signal-interference planar bandpass filters (BPFs) with frequency-asymmetrical transfer function is reported. They are made up of modified transversal filtering sections (TFS) having short-circuit-ended stubs in their signal-propagation paths. Through this technique, by synthesizing the load stubs as in-band resonating nodes in both single- and multi-band BPF realizations, higher selectivity when compared to that of their conventional counterparts is achievable. Furthermore, as experimental verification, a dual-band BPF prototype in microstrip technology with strongly-asymmetrical passbands for the double band 0.56/1.28 GHz has been built and measured.