Resorting to the temporal excitation synthesis of a time-reversal mirror (TRM), we develop a method of how to physically generate the desired microwave fields in a predefined area. The new method composes the desired field patterns with a number of the time-reversal (TR) focusing fields generated by a TRM. We first decompose the region of the desired pattern into a number of spatial grids and then probe the system by situating a probe antenna at these grids one by one. After all TRM elements capture their responses to the probing signals emitted from all grids, we synthesize the TRM excitation with these responses based on the TR method. Thanks to the space-time focusing property of TR, a set of TR focusing fields is simultaneously generated when the TRM is excited by the synthesized excitation. These focusing fields are spatially distributed with their focal spots spaced by the grids. If the grids are closely spaced, the focal spots will overlap with each other and eventually produce a smooth microwave field of the desired shape. We successfully demonstrate the generation of different desired microwave fields in an aluminum cavity. Theoretically, this method can be exploited to generate arbitrary electromagnetic fields.

In this paper, a beam-scanning seven-element microstrip quasi-Yagi-Uda antenna working at terahertz (THz) frequencies is presented. This antenna is printed on the surface of a silicon dioxide substrate. The directing elements are made from metal and extended to the length of the reflecting element by graphene. Metal and graphene strips are printed on the bottom of the dielectric substrate. The H-plane radiation pattern of the quasi-Yagi-Uda antenna can be deflected from −70° to 70° by controlling the bias voltage of graphene on the upper and lower substrate surfaces. The proposed antenna configuration has potential applications in THz beam scanning antennas.

By utilizing two optically controlled microwave switches (OCMSs) to control two independent narrow-band complementary split ring resonators, an optically controlled aperture ultrawideband antenna capable of generating reconfigurable multiband notches is proposed. Four reconfigurable states are achieved in the 3.1–10.6-GHz band: 1) a full FCC-allowed band; 2) a WiMax-notched band; 3) a WLAN-notched band; and 4) a WiMax-WLAN-notched band. These bands are useful to detect the available spectra or block the harmful interference from WiMax and/or WLAN systems by simply changing the ON/OFF states of the OCMSs with no more than 100-mW optical powers for each switch. A prototype of the proposed antenna is fabricated and measured. Both simulations and experiments demonstrate the proposed design.

Resorting to power accurate delivery for wireless power transfer (WPT) based on microwaves, a theory and method based on time reversal (TR) for WPT in 3D indoor environments are presented in this paper. Conventional WPT methods have the limitations of requiring that the elements on power source array (PSA) must have the same structure and regular arrangement. Unlike those conventional methods, the PSA used in this paper can be constructed by any omnidirectional antenna elements with any structure and any arrangement, whose principles are based on the auto-match of antenna radiation and environment adaptability of TR. Moreover, compared with those conventional methods, which perform complex multi-objective optimizations of beam pattern cost-functions at each frequency for getting excitation of PSA, the proposed algorithm can obtain PSA's excitation over a wide frequency range only by a single run of TR and Fourier transform operations. In addition, by weighting the time reversed charging request signal from powered devices, the interference caused by different observing elevation angles and amplitude difference among each channel can be suppressed effectively. At last, multi-powered devices placed arbitrarily can be charged simultaneously, and get similar power from PSA without power unfairness by our proposed algorithm.

The radiating effect of metal ground is rarely considered in most antenna designs. In this communication, we show that a properly designed metal ground can serve as a cooperative lower frequency radiator for reducing the antenna dimensions, broadening impedance bandwidth, and achieving almost uniform omnidirectional patterns over a wide frequency band. By introducing a ground-cooperative radiating structure (GCRS) into the metal ground of a prototype defected hexagonal monopole antenna (HMA), a more compact and broadband planar antenna of almost uniform omnidirectional patterns and stable linear polarizations is developed. The new antenna exhibits excellent omnidirectional radiation uniformity over the frequency range of 2.38≤ f (GHz) 11.80, together with group delay of τ _g ≤0.8 ns and a compact size of 27 × 31 mm ² , which makes it very promising for applications in wireless local area network (WLAN), long-term evolution (LTE), and ultrawideband (UWB) systems as a compact multifunctional antenna to reduce the number of antennas installed in wireless devices for accessing multiple wireless networks.

In order to continuously power movable sensors, we present an autotracking continuous-wave time reversal (TR) wireless power transfer (ACTR-WPT) system of a novel low-profile planar transmitter. The new transmitter is designed with a radio-frequency (RF)–channel cascaded structure, which couples only a little energy of the amplified feeding signal of each radiating element to the following cascaded one. Such RF-channel cascaded transmitter makes the decrease or increase of the number of the radiating elements quite flexible. The transmitting circuits are highly integrated with a microstrip antenna for every radiating element, which benefits the planar transmitter with the profile of less than 3 mm and the weight of each radiating element of less than 40g. Meanwhile, we develop an autotracking algorithm for the ACTR-WPT system, which inherently depends on the adaptive focusing mechanism of the TR technique. With the newly developed autotracking algorithm, we successfully demonstrate the experiments of powering the devices arbitrarily moving within a range from 1m to 7 m and the angle from -45° to +45°. The received dc power ranges from 1mW to 250 mW. The demonstration results are exciting for applications in charging or powering the movable sensors of low power consumption within a mid-range region.