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A compact planar fixed-beam leaky-wave antenna that radiates its main beam at broadside is presented, that consists of two folded branches of periodically distributed series-fed microstrip patches. The antenna is fed from the center through a 50 transmission line that subsequently feeds two constituent 100 parallel branches, each consisting of eight series-fed microstrip patches. Fixed-beam operation is achieved by the combination of the two oppositely-directed beams that are generated by the two branches. The proposed structure achieves a significant reduction of the longitudinal size by incorporating a 180 bend at the center of each branch, thus effectively folding the antenna in half. This results in a longitudinal size that is 1.8 times smaller than the analogous unfolded antenna. The antenna maintains a measured fixed-beam at broadside over a wide zero beam-squinting bandwidth of 3 GHz in the 28 GHz band, with a radiation efficiency above 60% and a maximum measured gain of 14 dBi at 27.4 GHz, with an overall compact size of 5.8 cm 1.1 cm.

High-speed detection and identification of mobile terminals located in the vicinity of highly directive base stations is essential for future mm-wave communication systems. We propose a novel optoelectronic frequency modulated continuous wave (FMCW) radar system for detection, localization and identification of multiple mobile terminals. The simultaneous localization and identification of multiple mobile terminals is achieved by using frequency scanning mm-wave leaky-wave antennas (LWAs) and backscattering communications. LWAs provide RF-based beam steering for estimating the direction of arrival of the echoes using a FMCW radar signal. Additionally, the implementation of backscattering technology in the mobile terminals allows the identification of users. Hence, simultaneous user localization and identification without the use of any complicated radar signal post-processing algorithms is possible. Finally, the introduced modulated backscattering reflection shifts the signals of the targets at higher frequencies, which exhibit lower noise floor and thus have higher signal to noise ratio (SNR). CA extern

A circularly-polarized metamaterial leaky-wave antenna (LWA) at 5.5 GHz is presented, which exhibits zero beam-squinting (ZBS) at broadside with an increased gain. It consists of two oppositely-directed negative-refractive-index transmission-line (NRI-TL) LWAs. The two LWAs radiate their main beams in opposite directions, and the combination of the two beams results in a broadside beam. The two LWAs are fed through a NRI-TL balun that adds a 180° phase difference between the two output signals. The addition of the balun doubles the gain of the metamaterial LWA, and makes it circularly polarized. The gain of the antenna is 11.75 dBi at 5.5 GHz, 3.35 dBi higher compared to the antenna without the balun. The ZBS bandwidth of the antenna is 0.9 GHz, the axial ratio ranges from 1.1 to 1.4, and the average radiation efficiency is 80%.

An optically reconfigurable metasurface is proposed for use as an antenna radiator at 28 GHz. The metasurface is transmittive and is fed through a horn antenna connected to a multi-core-fibre link, significantly reducing the losses compared to a mm-wave feed. In the proposed system, radiated beams will be photonically controlled using a spatial light modulator, thus not requiring the use of optical fibers. For optical reconfigurability the switching component will be based on silicon instead of photodiodes and varactors, eliminating the need for an active biasing network.

A planar, off-broadside zero beam-squinting leaky-wave antenna operating at 5.5 GHz is presented. It consists of two oppositely-directed branches of negative-refractive-index transmission-line (NRI-TL) leaky wave antennas (LWAs), one operating in the left-handed region and another operating in the right-handed region. The two NRI-TL LWAs are fed through a 50 Ohm transmission line. The two antenna branches each radiate their main beam in opposite directions, and the combination of the two beams results in an off-broadside beam. The antenna maintains its fixed-beam operation for a wide bandwidth of 0.75 GHz, with a gain in excess of 5 dBi and radiation efficiencies greater than 70%.

The objective of this work is to develop and optimize a system to evaluate the effects of RF exposure on biological cell cultures, operating at a wide range of frequencies using multiple specific absorption rate (SAR) distributions simultaneously. In-vitro RF exposure measurements are time-consuming, and in order to show meaningful statistical results, multiple measurements are required. Additionally, many parameters may have to be varied to evaluate the effects of frequency, dosimetry, time, etc., leading to a long series of measurements that can be quite time consuming. Here, we propose a system that is able to achieve multiple optimized SAR distributions by varying the dosage of the cell culture medium in each well of a multi-well plate. Additionally, the setup avoids any resonating modes by using RF absorbers placed around the antenna and the multi-well plate, making it functional at a wide range of frequencies.

We propose the optical control of a negative-refractive-index-transmission-line leaky-wave antenna. This is achieved by implementing optically controlled varactors in the unit-cell structures of the negative-refractive-index-transmission-line leaky-wave antenna. The optically controlled varactors consist of a photodiode and a transimpedance amplifier. By using this topology, the intensity of light is converted into photocurrent at the photodiode and then into voltage at the transimpedance amplifier. Therefore, the capacitance of the varactors can be controlled by varying the incident light intensity at the photodiode. This enables us to control the time delay of each negative-refractive-index-transmission-line unit-cell and therefore steer the radiation beam of the leaky-wave antenna.

A DC voltage boosting technique in radio frequency (RF) wireless power transfer (WPT) systems is proposed. This technique utilizes high PAPR multi-tone waveforms. It is demonstrated that increased efficiencies and DC voltages can be achieved for conventional single- and multi-stage rectifiers. First, the use of multi-stage rectifiers in wireless power transfer as a method to increase the DC output voltage is investigated and it is shown that at low input powers the implementation of a large number of stages can reduce the efficiency dramatically. Then, high PAPR waveforms are presented as an alternative method to multi-stage rectifiers that can increase the DC output voltage without decreasing the efficiency at low input powers. Finally, it is shown that by incorporating high PAPR waveforms with multi-stage rectifiers can decrease the required number of rectifier stages, and hence increase the rectifier efficiency at extremely low input powers.