Jose-Maria Munoz-Ferreras

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.

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.

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.

A Review on Recent Progress of Portable Short-Range Noncontact Microwave Radar Systems

This paper reviews recent progress of portable short-range noncontact microwave radar systems for motion detection, positioning, and imaging applications. With the continuous advancements of modern semiconductor technologies and embedded computing, many functionalities that could only be achieved by bulky radar systems in the past are now integrated into portable devices with integrated circuit chips and printed circuits boards. These portable solutions are able to provide high motion detection sensitivity, excellent signal-to-noise ratio, and satisfactory range detection capability. Assisted by on-board signal processing algorithms, they can play important roles in various areas, such as health and elderly care, veterinary monitoring, human-computer interaction, structural monitoring, indoor tracking, and wind engineering. This paper reviews some system architectures and practical implementations for typical wireless sensing applications. It also discusses potential future developments for the next-generation portable smart radar systems.

Motion compensation for ISAR based on the shift-and-convolution algorithm

ISAR (inverse synthetic aperture radar) is a coherent technique that obtains images of targets by processing the echoes returned during the dwell time. A higher angular resolution than the antenna beamwidth may be obtained. In this paper we report high resolution ISAR images, which have been obtained from data captured by a millimeter-wave LFMCW (linear frequency modulated continuous wave) radar. The target translational motion compensation is achieved by means of a new parametric algorithm, which makes use of the shift-and-convolution technique. This image autofocusing algorithm is compared with prominent point processing (PPP) and phase gradient autofocus (PGA). Simulated and real data from the millimeter-wave LFMCW radar are used to verify the proposed technique, although the method is also applicable to any kind of coherent radar.

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 Deramping-Based Multiband Radar Sensor Concept With Enhanced ISAR Capabilities

This paper explores the field of multiband radar as a further step in the research into advanced remote-sensing systems with enhanced capabilities. Specifically, a deramping-based multifrequency radar concept is addressed. Several multiband radar architectures are discussed and compared in terms of performances and hardware complexity. For the minimum-hardware multifrequency radar configuration, a proper design for its multiband waveform is suggested which enables the exploitation of all the operation features expected for such a system. Simulated inverse-synthetic-aperture data for a linear-frequency-modulated continuous-wave (LFMCW) dual-frequency radar emphasizes the usefulness and limitations of this multiband radar approach.

A Portable FMCW Interferometry Radar With Programmable Low-IF Architecture for Localization, ISAR Imaging, and Vital Sign Tracking

This paper presents a portable radar system for short-range localization, inverse synthetic aperture radar imaging, and vital sign tracking. The proposed sensor incorporates frequency-modulated continuous-wave (FMCW) and interferometry (Doppler) modes, which enable this radar system to obtain both absolute range information and tiny vital signs (i.e., respiration and heartbeat) of human targets. These two different operation modes can be switched through an on-board microcontroller. To simplify the system, the proposed radar utilizes the audio card of a laptop to sample the baseband signal. The FMCW mode of the radar uses operational-amplifier-based circuits to generate an analog sawtooth signal and a reference pulse sequence (RPS). The RPS is locked to the sawtooth signal to obtain coherence for the radar system. For the interferometry mode, a low-intermediate-frequency modulation method is implemented to avoid the slow vital signs from being distorted by the high-pass filter of the audio card. Several experiments were carried out to reveal the capability and distinct operational features of the proposed portable hybrid radar. The experiments also showed that the system can easily detect glass, which is usually difficult to identify for optical-based sensors. In addition, 2-D scanning in a complex environment revealed that the proposed radar was able to differentiate human targets from other objects. Moreover, ISAR images were used to isolate moving human targets from surrounding clutter. Finally, the proposed radar also demonstrated its ability to accurately measure vital signs when a human subject sits still.

Short-Range Doppler-Radar Signatures from Industrial Wind Turbines: Theory, Simulations, and Measurements

Industrial wind turbines are large constructions that require in-field monitoring. In this paper, short-range Doppler radar signatures of wind turbines are both mathematically analyzed and practically verified through simulations and experiments. Two custom-designed radar prototypes that operate at the C and K bands, respectively, are employed in the acquisition campaign. The unique features of the radar signal-in particular, some observed energetic flashes in the time-Doppler map-appear as curved lines for specific acquisition scenarios and/or for nonstraight blades. Furthermore, it is demonstrated that the use of high-frequency radar systems is beneficial in terms of improved spectrogram resolution. Experimental results coming from a 50-m-height wind turbine and a curved-blade 12-m-height turbine are also discussed, in this paper, in the context of the provided theoretical and simulation frameworks. This paper paves the way for noncontact structural health monitoring of industrial-type wind turbines through portable low-cost Doppler radar sensors.

Isolate the Clutter: Pure and Hybrid Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Indoor Applications

Radars are among the best exponents of radio-frequency (RF)/microwave devices for remote sensing [1], [2]. Long-range radars have demonstrated outstanding potential not only for defense/security environments, such as the detection, location, and tracking of targets, but also on a plurality of civilian scenarios, such as meteorological/weather measurement tasks, imaging of the Earths surface through synthetic aperture radar (SAR) techniques, monitoring of animal migrations, and many others [3]-[7].