A novel broadband RF-to-DC rectifier using an uncomplicated matching approach is proposed and tested. The proposed rectifier is based on a voltage doubler-type configuration and broadband matching is achieved by simply adding two inductors in series with each of the diodes, canceling out the large capacitance inherent in the diodes as well as producing resonances over a wide bandwidth. This uncomplicated matching network allows for a smaller circuit footprint while providing a wide bandwidth. The proposed rectifier is validated via simulation and measurement. The results demonstrate that a rectification efficiency of more than 50% is maintained over a bandwidth of approximately 83% (0.54-1.3 GHz) at 5-dBm input power, with the maximum rectification efficiency of 80% at 10-dBm input power.

The performance of time-reversal (TR) based far-field wireless power transfer (WPT) from an antenna array in a complex propagation environment is investigated in comparison with conventional array-based beamforming (BF). A two-step experiment is performed, namely 1) the propagation stage and 2) rectification stage. In the propagation stage, signal transmission is measured between the transmit array and receive antenna in an indoor multipath environment, for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. The results demonstrate that TR results in higher peak voltage compared to BF given the same average transmit power. In addition, while BF loses its ability to selectively send waves at the receiver due to impairment of the beam from multipath, TR can selectively focus waves at the receiver by inherently taking advantage of multipath. In the rectification stage, the resulting signals from the propagation stage are fed into a broadband rectifier for RF-to-DC conversion. It is shown that the signals received using TR lead to higher rectified DC voltage and rectification efficiency. The overall results suggest that TR can outperform BF with higher rectification efficiency given the same average transmit power. Through optimization of the TR pulse interval, array configuration and transmit power, further improvement in the performance of TR based WPT in a complex propagation environment is possible.

Nonlinear radars can be utilized to detect electronic devices, which are difficult to detect with conventional radars due to their small radar cross sections (RCS). Since the receiver in a nonlinear radar is designed to only receive harmonic or intermodulated echoes from electronic devices, it is able to separate electronic devices from non-electronic scatters (clutter) by rejecting their echoes at fundamental frequencies. This paper presents a harmonic-based nonlinear radar scheme utilizing frequency-modulated continuous-wave (FMCW) signals for the detection of various electronic devices at short range. Using a laboratory experiment setup for FMCW radar at S-band for Tx (C-band for Rx), measurements are carried out to detect electronic devices of various sizes. The results show that the detection of small electronic devices is possible with nonlinear FMCW radar when appropriate system parameters are selected. Furthermore, we also discuss the maximum detectable range estimation for electronic targets using the radar range equation for FMCW nonlinear radar.

The detection of visually obstructed small nonlinear targets in a through-the-wall (TTW) environment is difficult because of linear scatterers and strong wall reflections. In this letter, harmonic-based nonlinear TTW detection is introduced as a method to effectively detect small nonlinear targets behind the wall. Nonlinear TTW detection allows for the suppression of linear scatterer responses and wall reflections by detecting only the harmonics generated from nonlinear targets. Here we apply the decomposition of the time-reversal operator (DORT) for the detection and separation of multiple nonlinear targets behind the wall. DORT extracts the eigenvalues and eigenvectors of nonlinear targets and allows for selective focusing (imaging) of each detected target. In addition, we utilize linear frequency modulated (LFM) pulses, which allow for the compression gain in the detection processing. To validate the proposed concept, we conducted simulation and measurements of various configurations of nonlinear TTW detection. The results demonstrate that nonlinear targets behind the wall can be effectively detected and located.

Nonlinear radars detect nonlinear (harmonic or intermodulation) responses excited from semiconductor junctions within electronic targets, allowing for the detection of small targets that are otherwise difficult to detect. To properly detect the nonlinear responses from targets, which are typically much lower than the responses at the fundamental frequency, the transmit, and receive antennas in a nonlinear radar, must ensure high isolation between the transmit and receive ports to suppress unwanted harmonics from the transmit side interfering with target responses. In this letter, a circularly polarized dual-band shared-aperture antenna, applicable to nonlinear radar, is presented. The S -band part of the antenna has a center frequency of 3 GHz for transmit, while the C -band part is designed to operate at the second-harmonic band of 6 GHz for receive. The proposed antenna is designed to exhibit high isolation between the transmit and receive ports in both bands. The characteristics of the proposed antenna are demonstrated via simulation and measurement, where it shows good circular polarization (CP) characteristics at both S -and C -bands with high isolation between ports. Furthermore, the performance of the proposed antenna for nonlinear detection is verified through an experiment where a nonlinear target is detected.

There has been growing interest in the field of wireless power transfer (WPT), especially for a high-power (Watt-level) applications. Rectifiers are essential components for WPT, as they convert incoming RF into DC power. However, conventional Schottky diodes used in WPT exhibit their highest efficiency at low power levels typically less than few Watts. To address this limitation, we introduce a power dividing rectenna system that can handle beyond several Watts of input RF power. The proposed rectenna consists of a single patch antenna integrated with a radial power divider, whose output ports are connected to rectifiers. In this way, incident RF power can be distributed into lower levels at which Schottky diode-based-rectifier can accommodate. Via simulation and measurement, we demonstrate that the input power (about 10 W) received through the proposed structure can be uniformly distributed to each output port of the divider to be rectified at lower power levels, which are then combined at DC to provide several Watts of DC power. The proposed rectenna can be utilized in WPT applications requiring beyond several Watts. Furthermore, by configuring the proposed structure into an array, even higher power handling can be achieved for applications that require hundreds of Watts.