Roberto Gomez-Garcia

Systematic Method for the Exact Synthesis of Ultra-Wideband Filtering Responses Using High-Pass and Low-Pass Sections

A systematic consistent and analytical method for the exact synthesis of ultra-wideband bandpass filtering responses using the isolated cascade connection of high- and low-pass sections is presented in this paper. Through the described synthesis technique, the optimum values for the design parameters of the high- and low-pass sections are computed from the initial specifications of the intended bandpass filtering profile. The theoretical results are validated with a synthesis example for both the Butterworth and Chebyshev cases. Furthermore, to prove the practical viability of the ultra-wideband filter topology based on high- and low-pass sections, a prototype at 4 GHz is designed, constructed in hybrid technology, and characterized. The main advantages of this wideband microwave bandpass filter solution are also highlighted

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.

Application of Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Tracking of Vital Signs

This paper focuses on the exploitation of linear-frequency-modulated continuous-wave (LFMCW) radars for noncontact range tracking of vital signs, e.g., respiration. Such short-range system combines hardware simplicity and tracking precision, thus outperforming other remote-sensing approaches in the addressed biomedical scenario. A rigorous mathematical analysis of the operating principle of the LFMCW radar in the context of vital-sign monitoring, which includes the explanation of key aspects for the maintenance of coherence, is detailed. A precise phase-based range-tracking algorithm is also presented. Exhaustive simulations are carried out to confirm the suitability and robustness against clutter, noise, and multiple scatterers of the proposed radar architecture, which is subsequently implemented at the prototype level. Moreover, live data from real experiments associated to a metal plate and breathing subjects are obtained and studied.

Reconfigurable Multi-Band Microwave Filters

An original and simple approach to the design of fully reconfigurable multi-band microwave bandpass filters (BPFs) with an arbitrary number of passbands is reported in this paper. It exploits the use of an innovative quasi-BPF configuration made up of different sets of controllable mono-frequency resonators to separately shape each tunable passband. Thus, high-selectivity multi-band bandpass filtering transfer functions exhibiting independent control in terms of center frequency, bandwidth, and transmission zeros can be synthesized. Furthermore, as an unprecedented frequency-agility feature of the proposed reconfigurable multi-band BPF structure when compared to the state-of-the-art, its passbands can be merged together to form broader, and for certain realizations, higher order transmission bands. This allows even more degrees of reconfiguration to be achieved in the devised circuit, which can also operate as ultra-wideband BPF with flexible in-band notches or self-equalized flat-group-delay quasi-elliptic-type BPF. The theoretical foundations of the described reconfigurable multi-band BPF scheme, along with guidelines for its design and a triple-passband filter synthesis example based on the coupled-node formalism, are expounded. In addition, as an experimental proof-of-concept, two microstrip prototypes with high- Q tuning implemented through mechanically variable capacitors are manufactured and tested. They are a wideband dual-band BPF and a quadruple-band BPF with narrow-bandwidth passbands.

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.

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.

RF Front-End Concept and Implementation for Direct Sampling of Multiband Signals

The placement of the analog-to-digital converter as near the antenna as possible is a key issue in the software-defined radio receiver design. Direct sampling of the incoming filtered signal is a compact solution enabling channel simultaneity. In this brief, in the context of evenly spaced equal-bandwidth multiband systems, sufficient conditions for the channel allocation assuring that the minimum sub-Nyquist sampling frequency does not imply aliasing are provided. Subsequently, as a validation example, the design of a minimum-sampling-frequency acquisition system for quad-band applications within a ultrawideband frequency range is shown. Moreover, an innovative solution for its radio-frequency front end, basically consisting of a signal-interference multiband bandpass filter, is reported. Experimental results of the built microstrip-filter prototype for the proposed 1-3-GHz-range quad-band system are also given.

Flexible Filters: Reconfigurable-Bandwidth Bandpass Planar Filters with Ultralarge Tuning Ratio

The objective of this overview article is to report the latest research findings in the research into RF/ microwave reconfigurable-bandwidth bandpass planar filters with ultralarge passbandwidth tuning ratio. This means filtering devices with much higher flexibility, showing reconfigurable bandwidths between narrow/moderate-band and ultrawideband states. Specifically, two different solutions we recently proposed are described, with emphasis on their operating principles and achieved electrical performances. They consist of 1) transversal signal-interference switchable-bandwidth bandpass filters and 2) tune-all bandpass filters simultaneously exploiting MMRs and quality-factor control to achieve unprecedented reconfiguration levels in terms of center frequency and instantaneous passbandwidth. Some other modern filtering topologies proposed by other authors, which have clear interest to attain very high levels of bandwidth variation, are also expounded.