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We present the design of a novel K-band radar architecture for short-range target detection. Applications include direction finding systems and automotive radar. The developed system is compact and low cost and employs substrate-integrated-waveguide (SIW) antenna arrays and a $4\times 4$ Butler matrix (BM) beamformer. In particular, the proposed radar transmits a frequency modulated continuous-wave (FMCW) signal at 24 GHz, scanning the horizontal plane by switching the four input ports of the BM in time. Also, in conjunction with a new processing method for the received radar signals, the architecture is able to provide enhanced resolution at reduced computational burden and when compared to more standard single-input multiple-output (SIMO) and multiple-input multiple-output (MIMO) systems. The radar performance has also been measured in an anechoic chamber and results have been analyzed by illuminating and identifying test targets which are 2° apart, while also making comparisons to SIMO and MIMO FMCW radars. Moreover, the proposed radar architecture, by appropriate design, can also be scaled to operate at other microwave and millimeter-wave frequencies, while also providing a computationally efficient multi-channel radar signal processing platform.

We propose a compact circularly polarized series-fed patch array with enhanced radiation performance at $S$ -band. To our best knowledge, no similar single-layer structure has been designed, measured, and reported in the literature with equivalent radiation performances in terms of reduced sidelobe level (SLL) and aperture efficiency as well as compactness and simplicity. The planar array consists of a 50- $\Omega $ microstrip single feed point, offering uniform and efficient excitation of all its elements that enable a broadside beam with high-gain and low sidelobes. A feeding network for such aperture control is designed and optimized to provide good impedance matching with a two-point excitation per radiating element, which is based on 0° and 90° meander lines to enable circularly polarized radiation. A structure made by a $4\!\!\times \!\!1$ arrangement of square patches is simulated, optimized, and manufactured, providing a realized gain of about 10 dBic and an SLL below −15 dB. Very good axial ratios and high efficiencies are obtained. The proposed antenna may be of interest for next-generation far-field wireless power transmission systems and other applications including target tracking, radar, and internet of things technologies requiring efficient circularly polarized radiation.

This paper describes an innovative remote surface sterilization approach applicable to the new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The process is based on the application of a liquid film on the surface or object under sterilization (OUS). A beacon signal is used to self-steer the transmitted power from the designed retrodirective antenna array (RDA) towards the OUS using circularly polarized fields; then, the sterilization is completed by raising and maintaining the required temperature for a certain time. Results suggest that the process takes 5 minutes or less for an angular coverage range over 60 degrees whilst abiding by the relevant safety protocols. This paper also models the power incident onto the OUS, providing consistent results with full-wave simulations. A practical RDA system is developed using a 2 × 1 microstrip patch array operating at 2.5 GHz and tested through the positioning of a representative target surface. Measurements, developed by sampling the power transmitted by the heterodyne RDA, are reported for various distances and angles, operating in the near-field of the system. To further validate the methodology, an additional experiment investigating virus deactivation through microwave heating was also developed. Measurements have been performed with an open cavity microwave oven on the Coronavirus (strain 229E) and egg white protein in a cuvette. This demonstrates that the temperature increases of aqueous films up to 70 [Formula: see text]C by remote microwave-induced heat can denature proteins and deactivate viruses. Possible applications of the method include sterilization of ambulances, medical equipment, and internet of things (IoT) devices.

Automotive engineers are repeatedly faced with the issue of choosing radars with the best angular resolution while having reduced processing times. In this paper, a novel extrapolation method is presented to estimate the amplitudes and phases for virtual antenna elements at the receiver periphery. This method has shown to resolve two targets where the (real) baseline receiver antenna cannot. Furthermore, a comparison study is provided which considers different extrapolation methods that can be applied to the system. Together with other techniques for improving resolution, such as Multiple-Input Multiple-Output (MIMO) radars, beamsteering for increased power distribution, and compressed sensing for optimising sampling requirements, a radar system based on the fusion of these techniques can provide a powerful new platform which can fast process and accurately detect targets.

This article describes a full-bridge rectifier and a receiving antenna array for operation within an innovative wireless power transmission (WPT) system. A high-power transmitter using circularly polarized free-space waves and based on a retrodirective antenna array technology is also employed to boost the overall received RF power at the input of the rectenna. To the best of our knowledge, the proposed rectifier circuit and active antenna configuration are the first demonstration of a high-power beam tracking system for WPT scenarios, being different from previously reported near-field coupling and other lower power harvesting schemes. The main focus of this article is the rectifier design, its bench-top measurements, and operation in such a retrodirective, self-tracking microwave system. A novel approach based on in-phase multitone input signals is also developed to improve rectifier efficiency. The rectifier size is 4.5 cm by 2 cm and can offer more than 86% and 75% RF-to-dc rectification efficiency at 27 dBm for an input signal at 1.7 and 2.4 GHz, respectively. This rectifier circuit component can also be employed in other communication applications or WPT systems, for example, to convert to dc received RF signals or power in the radiating near- and far-field in order to wirelessly charge the batteries of home electronics, such as smartphones, tablets, or Internet of Things (IoT) devices.

International audience; An isolation technique, which does not require conventional circulators, is proposed for the realization of a simple and low-cost aperture-coupled circularly polarized antenna for application to full-duplex devices. The approach is based on the use of slotlines loops to provide surface current cancellation in specific regions of the antenna structure, leading to improved axial ratio and isolation between the ports in excess of 50 dB. Circular polarization is achieved by introducing a double-box hybrid coupler, which is optimized to obtain good matching and isolation of the quadrature signals. On this basis, both right- and left-hand circularly polarized beams are achieved by interchanging the transmitting and receiving antenna ports, enabling full-duplex operation and reconfigurability. While the antenna structure is designed for 2.45 GHz operation, one can take advantage of the proposed approach to tune the frequency of maximum isolation. Both single-element prototypes as well as a 2 × 2 array are fabricated and measured, showing good agreement with the simulations and validating the proposed isolation approach. The beam steering capabilities as well as the application to a Van Atta retrodirective antenna array and the possibilities of achieving delta and sum patterns for monopulse operation are also reported. The proposed full-duplex antenna can also represent an excellent solution for narrowband wireless power transmission systems. © 2013 IEEE.

A retrodirective antenna (RDA) array for wireless power transmission (WPT) is presented. Applications include the wireless charging of mobile phones and other handheld devices. The reported RDA defines an active high-power transmitter module that retrodirects a received beacon tone back to a mobile unit by circularly polarized (CP) free-space radiation. In addition, this RDA architecture uses a network of four subarrays, defined by a total of 16 radiating patch elements, in an effort to boost the transmit gain while also reducing the supporting RF hardware requirements when compared to a more conventional RDA. Measurements and simulations in the reactive near-field of the system are in agreement in terms of the tracking capabilities of the high-power CP-RDA. Power levels in excess of 27 dBm were measured at 2.4 GHz at a receiver module, and when this RF power was rectified, more than 350 mW at dc was observed. To the best knowledge of the authors, this is the first demonstration of a WPT system using a mixer-based analog RDA. Previous low-power demonstrations were more complex computer-controlled systems that did not offer any real-time tracking ability. Other applications for the proposed RDA include target tracking, sensor charging, and other WPT systems.

In this paper, a novel millimetre-wave radar for collision avoidance and automotive applications is presented. The system uses frequency modulated continuous-wave (FMCW) transmission based on multiple input multiple output (MIMO) substrate-integrate waveguide (SIW) antennas operating in the K-band regime. The continuous sawtooth time-domain wave transmitted from two SIW antennas, by time-domain multiple access (TDMA), is detected with a half-lambda spaced four-element SIW receiver array at a distance of 4 meters in a calibrated anechoic chamber and verified with simulations. The high bandwidth and omnidirectionality of the SIW antennas in the horizontal plane, together with digital-beamforming for the achieved MIMO virtual array, offers an overall field-of-view of 130 degrees for the radar system. Also, the MIMO radar achieves an angular resolution of 14 degrees and offers a range resolution of 10 cm at a cost of only 6 transmitter and receiver elements in total.

This paper describes the design and measurement of a full-bridge rectifier and a receiving antenna array operating at 2.4 GHz for wireless power transmission system applications, and with motivations to wirelessly charge an electronic device in the radiating near-field. A retrodirective antenna array (RDA) was also used in the system with high power gain to boost the overall received RF power at the input of the rectenna. In particular, the RDA offered automatic tracking of the rectenna module in 3D space by employing phase conjugating mixers. The diode rectifier of our rectenna, which is the focus of the present work, offers full-wave-rectification and exhibits a 76% efficiency for an RF input power of 26 dBm and 74% at 27 dBm, while also providing more than 60% of RF-to-DC conversion efficiency at 2.4 GHz when considering an input RF power level ranging from 15 dBm to 29 dBm.

In this paper, a retrodirective antenna (RDA) array for wireless power transmission (WPT) is presented. Applications include the charging of mobile device batteries wirelessly. Thanks to the principle of phase conjugation in mixers, retrodirectivity can be achieved in the far-field. More specifically, the reported RDA architecture deals with an active transmitter module to retrodirect a received beacon tone, with increased power, from a mobile unit and with circularly polarized (CP) radiation. Measurements and simulations show a good agreement in terms of the retrodirective tracking capabilities. In addition, a new RDA architecture is also proposed for WPT, using sub-arrays, in order to boost the overall received power at the mobile while also not significantly increasing the costs of the active transmitter module. Other applications for the proposed RDA circuit element include target tracking, low-cost sensor charging, and other WPT systems.

International audience; This paper presents low cost, low complexity, dual-circularly polarized patch antenna designs. The aperture coupled antennas employ simple square slotline loop elements to provide surface current cancellation in the critical regions of the antenna structure. High isolation (below 50 dB) is then obtained between the two antenna inputs, one for each polarization state. Circular polarization (CP) is produced thanks to the use of a planar hybrid coupler, feeding the antenna with two quadrature signals. Reciprocity of these components allows for the use of one port as the input (Tx) and the other one as an output (Rx), making the antenna work in full duplex mode. Also, both right-hand and left-hand circular polarizations are possible by interchanging the Tx and Rx ports, bringing a valuable degree of versatility. The proposed antenna design is also grouped in a 2x2 array for operation at C band (2.45 GHz), and its corresponding results are reported. Possible applications for the single-element and the low profile array include modern short range wireless communications, polarization diversity, direction finding, radar, and other beam steering array applications. © Institution of Engineering and Technology.All Rights Reserved.