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This work investigates the performance of an envelope detector under high peak-to-average power ratio (PAPR) waveform excitations. First, the use of multi-stage rectifiers is investigated in wireless power transfer systems, as a method to increase the DC output voltage. It is shown that at low input powers, 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. Simulations and experimental measurements with different multi-tone waveforms and modulation schemes are shown. The results demonstrate that the PAPR and complementary cumulative distribution functions (CCDF) of a waveform significantly influence the RF-to-DC conversion. Using a 5-tone input waveform with −10 dBm power and a 100 kΩ load, the DC output voltage was increased by 32.3%, while using a 256 QAM modulation the output voltage was increased by 12.6%. The results show similar behaviour to that of multi-stage topologies but without decreased efficiencies at low input powers. These results suggest that the use of high PAPR waveforms can decrease the required number of rectifier stages, and hence increase the rectifier efficiency at extremely low input powers. 13 14 2457 2463

An implementation of a planar fixed-beam leaky-wave antenna that radiates at broadside is presented, consisting of a periodic arrangement of negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Using an experimental prototype of the antenna, it is shown that each branch of the antenna radiates a beam in opposite directions, and the combination of the two beams results in a symmetric broadside beam over a wide measured zero-beam-squinting bandwidth of 1.1 GHz (23%) around the design frequency of 5 GHz. This is well within the 80% measured -10 dB reflection coefficient bandwith. Furthermore, the antenna has a size of 3.42λ0 × 0.125λ0 × 0.025λ0 at 5 GHz. 17 12 2223 2227

This work proposes sensing CPU voltage noise through wireless electromagnetic (EM) emanations from the CPU. Compared to previous voltage monitoring methodologies, this approach is not intrusive as it does not require direct physical access to the monitored CPU. To prove the effectiveness of this approach, we use EM signal feedback to find the resonant frequency of the CPU power delivery network, and to generate a CPU voltage noise (dI/dt) virus. This study is performed on a modern out-of-order CPU that supports on-chip fine grain voltage monitoring. This on-chip voltage monitoring capability is used to validate the proposed EM methodology. © 2017 IEEE. 17 1 68 71

A novel ring resonator bandpass filter with reconfigurable bandwidth with central frequency at 2.4 GHz is demonstrated. Theoretical analysis for computing the resonant frequencies is shown, and the design approach of implementing $\pi $ -section stubs connected to the ring to obtain the bandwidth reconfigurability is explained. The use of reconfigurable $\pi $ -section allows the alteration of the stub’s effective width and therefore the filter’s bandwidth reconfigurability. p-i-n diodes are used as switching elements to achieve the narrowband/wideband response. Coupled line sections are used for suppressing the higher modes by generating out-of-band transmission zeros, resulting in a significantly enhanced out-of-band rejection. Measurements indicate that the 3-dB fractional bandwidth can be switched from 58.5% to 75% at a fixed center frequency of 2.4 GHz with an insertion loss better than 1.1 dB. Moreover, the −20-dB stopband performance is extended to $2.7f_{0}$ .

In this study, an ultra-wideband (UWB) monopole antenna with a dynamically reconfigurable notch band, along with the associated RF-triggered power management unit (PMU) that enables the dynamic reconfigurability, are presented. The UWB monopole antenna has a rectangular slot which hosts a J-shaped stub, electrically connected with the radiator using one PIN diode switch. When the diode is OFF, the monopole antenna has a UWB characteristic, while when it is turned ON a frequency notch is created at 5.6 GHz. The diode is fed from a PMU that consists of a rectenna and a DC-to-DC active booster. When the rectenna that consists of a patch antenna and a rectifier receives a −11 dBm or higher 5.6 GHz signal, it rectifies the RF signal into a sufficiently high DC voltage. The rectified DC voltage is applied to the cascaded DC-to-DC booster as enabling signal, and the booster provides at its output terminal sufficient DC power to actuate the PIN diode and thus dynamically reconfigure the UWB antenna. The dynamically reconfigurable notch band is created immediately in response to the reception of an external, −11 dBm RF signal at 5.6 GHz, and it disappears in real time immediately after the external RF signal is removed. 13 12 2046 2052

Two rectenna designs consisting of a patch antenna and a voltage doubler operating at 5.6 GHz are presented. Rectenna-1 is matched with a varying input impedance active DC-to-DC booster based on Texas Instruments charge pump IC TPS60300. Depending on the biasing conditions the ohmic impedance varies significantly between 4.2-6.7 KΩ which consists of a design challenge for the rectifier matching. Rectenna-2 is optimized to be terminated with a passive ultra-low-voltage self-powered converter with relatively constant 3.9 KΩ input impedance. The passive converter can only be used if the required rectified power is sufficiently small. 1807 1808

A planar, compact, fixed-beam leaky-wave antenna operating at 26 GHz is proposed, that consists of a periodic arrangement of series-fed microstrip patches. The antenna consists of two oppositely-directed branches of the same periodic structure, and it is center fed through a 50 Ohm transmission line. The two branches of the antenna radiate their beam in opposite directions, and the combination of the two beams results in a broadside beam. To reduce the longitudinal size of the antenna, a 180-degree bend is introduced at the center of each branch. This maintains the fixed-beam operation of the antenna for a wide bandwidth of 1.1 GHz, with a gain in excess of 14 dBi and a radiation efficiency of 65%, while reducing the overall longitudinal size by a half. 1 4

We report a photonic frequency-modulated continuous wave (FMCW) radar system that provides 3D localization with a simple radar frontend. This is achieved by exploiting linearly polarized leaky-wave antennas (LWAs) for simultaneously scanning azimuth and elevation. As such, the FMCW frequency sweep is employed for radar operation as well as LWA beam steering for target angle estimation. The LWAs are based on series fed patches and provide beam steering from -20.7° to +18° in the frequency range of 24-33 GHz in the H-plane and a field of view from -18.9° to 33.3° in the E-plane. The FMCW signal is photonically generated from the wavelength chirp of a low-cost DFB laser. Coherent radio-over-fiber transport with photonic upconversion provides low loss distribution and frequency scaling. Finally, 3D radar localization is experimentally demonstrated by two orthogonal LWAs. A ranging accuracy of better than 4 cm and an angular accuracy of \circ$ have been achieved without any dedicated radar post processing. 1 4

We present a broadband leaky-wave antenna designed using phase-compensated transformation optics. A graded dielectric superstrate is placed above a leaky slot line to produce radiation at a fixed angle off broadside. Geometric phase compensation is applied to mitigate beam distortion due to coordinate stretching and to maintain permittivity values within a practical range. 1 3

A practical implementation of a miniaturized crossover is presented using negative-refractive-index transmission-line (NRI-TL) metamaterial lines. NRI-TL metamaterial theory has demonstrated that by loading a conventional transmission line with lumped LC elements, a large phase shift per-unit-length can be achieved. Employing this technique, the conventional microstrip transmission lines in a three-section branch-line coupler crossover are replaced with 90° NRI-TL lines, and thus a compact NRI-TL crossover with an area 47 times smaller than the area of its conventional counterpart is demonstrated. Measured results demonstrate that the proposed NRI-TL metamaterial crossover exhibits a −10 dB |S11| bandwidth of 33% and a |3 dB| |S31| bandwidth of 26% around 1 GHz.

Worst-case dI/dt voltage noise is typically characterized post-silicon using direct voltage measurements through either on-package measurement points or on-chip dedicated circuitry. These approaches consume expensive pad resources or suffer from design-time and run-time overheads. This work proposes an alternative non-intrusive, zero-overhead approach for post-silicon dI/dt voltage noise generation based on sensing CPU electromagnetic emanations using an antenna and a spectrum analyzer. The approach is based on the observation that high amplitude electromagnetic emanations are correlated with high voltage noise. We leverage this observation to automatically generate voltage noise (dI/dt) stress tests with a genetic-algorithm that is driven by electromagnetic signal amplitude and to obtain the first-order resonance-frequency of the Power-Delivery LC-tank network. The generality of the approach is established by successfully applying it to three different CPUs: two ARM multi-core mobile CPU clusters hosted on a big.LITTLE configuration and an ×86-64 AMD desktop CPU. The efficacy of the proposed methodology is validated through VMIN and direct voltage noise measurements. 573 585

This paper presents a new compact wideband bandpass filter (BPF) with an extremely broad stopband consisting of two parallel coupled-line sections and multiple open-ended stubs, for S-band applications. Due to symmetry of the design, even- and odd-mode analysis method is applied to analyze the proposed filter structure. To further enhance the upper stopband, additional TZ's are generated by attaching two open stubs at the input/output feed lines and a third one in the middle of the structure. The fabricated prototype filter covers the whole S-band frequency range, and has 3-dB fractional bandwidth (FBW) of 66%. The measured insertion loss within the passband is less than 0.8 dB and the measured return loss is greater than 15 dB within the entire passband. In addition, the proposed filter has an appealing compact size of ${0.09\lambda_{\mathrm{g}}}^{2}$ with the upper stopband extended up to $5.96f_{0}$ , for suppression level greater than 20 dB.

A tunable metasurface absorber is presented in this work using an optically-programmable capacitor as the tuning element. The tuning element does not employ conventional semiconductor technologies to operate but rather a bases its tuning by changing the optomechanical properties of its dielectric, poly disperse red 1 acrylate (PDR1A). Doing so there are no conventional semiconductor devices in the RF signal path. The metasurface operates at a design frequency of 5.5 GHz and it achieves an optically-tuned bandwidth of 150 MHz, from 5.50 GHz to 5.65 GHz., Comment: 5 pages, 8 figures, Published in 2018 IEEE International Symposium on Circuits and Systems (ISCAS)

This paper presents a compact reconfigurable phase-shifter based on negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Two inter-switchable NRI-TL metamaterial unit cells are collocated within the same board area, and can be reconfigured based on the biasing polarity of embedded PIN diodes to provide two discrete phase states. The PIN diodes are located on the shunt branches of the metamaterial line in order to reduce losses in the direct signal path. Design limitations in terms of return loss and insertion loss are discussed in relation to the two phase states. A proof-of-concept module with a size of 17.8 × 21.6 mm2 is designed at 1 GHz, with measured insertion phases of −14.5° and +58.5° in the two phase states leading to a differential phase shift of 73°, while exhibiting insertion losses of 1.43 dB and 0.89 dB, respectively. The combined bandwidth for which the reflection coefficient in both states remains simultaneously below −10 dB is 0.46 GHz (46%), from 0.83 GHz to 1.29 GHz.

Chua's mem-components are ideal for creating adaptive metasurfaces for manipulating EM waves given that they hold their state without external biases. In this paper, we propose a generic adaptive reactive element that is in fact a memcapacitor/meminductor. This element makes use of a polymer that demonstrates reversible trans-cis photochemical isomerization, thus making it possible to change the distance between two conductive plates by up to 25%. Furthermore, a design methodology for utilizing these devices is presented., Comment: 5 pages, 7 figures, Published in 2018 IEEE International Symposium on Circuits and Systems (ISCAS)

The use of a tunable power splitter (PS) as a constituent component of a simultaneous wireless information and power transfer (SWIPT) system is discussed. Two varactor diodes are used to achieve a tunable output power ratio P2 : P3 varying from 1 : 1 to 1 : 10 under good matching conditions. The SWIPT system that operates at 2.4 GHz consists of a typical patch antenna, cascaded with the tunable PS, and a voltage doubler rectifier. The constituent components were implemented and tested as stand-alone devices and were subsequently combined in a measurement system using interconnectors. The effect of the tunable PS was explored with respect to the SNR measurements on the port that is intended for the information decoding receiver and the DC voltage measurements on the termination load of the rectifier that is connected directly on the energy harvesting port of the tunable PS. A spectrum analyzer is used for the SNR measurements while the input power is controlled using a signal generator. Both wireless power transmission and on-board measurements verify that the harvested energy can be maximized by using the minimum SNR at the information decoding branch at the expense of DC power consumption required for the biasing of the varactor diodes.

A new technique to miniaturize Yagi antennas utilizing mu-negative (MNG) metamaterial loading is presented. In this method, the director element of the printed Yagi antenna is loaded with MNG-metamaterial unit-cells to introduce a new mu-zero resonance (MZR) which is independent of the size of the antenna, and can be adjusted by changing the amount of loading capacitance. This technique enables the printed Yagi antenna to operate at lower frequencies without changing size of the substrate. As a result of the proposed design, dual band operation is achieved. Lower band of the antenna is defined by the loaded capacitance and for instance for a 3pF loaded capacitance, the antenna operates at 0.78–0.81 GHz. The upper band is controlled by the dipole resonance and depending on the loaded capacitance it operates at different wide bands between 1.15–2 GHz. The proposed method enables the size of the antenna to be reduced by more than 50% compared to existing Yagi antennas with peak gain and front-to-back ratio values of 5.5 dBi and 10 dB, respectively. A sample design of a three-element printed Yagi antenna whose director is loaded with MNG unit cells is presented as a proof-of-concept. 1 3

A unidirectional and wideband resonance-based reflector (RBR) antenna that can be used for biomedical applications, such as thorax imaging, is proposed. One of the main limitations in the design of biomedical systems, which utilize multiple densely spaced antennas, is the mutual coupling created by the radiating elements and the surface waves (SWs). The proposed RBR antenna is designed to achieve an in-phase reflection phase within a wide operating bandwidth. Moreover, it suppresses the SW propagation that reduces the overall mutual coupling by up to 12 dB across the whole operating bandwidth. It consists of a resonance-based loop reflector that is positioned in a perpendicular configuration to a wideband dipole antenna. To increase the electrical size of the loop reflector without physically altering the dimensions of the substrate, its structure is meandered, and a compact side size of $0.22\lambda \times 0.22\lambda $ , which is more than 50% smaller than recent RBR antennas, is achieved. Unlike the majority of conventional double-layer high-impedance surfaces, the proposed RBR antenna consists of a single layer and a single unit cell and utilizes the actual dipole antenna element to achieve a measured wideband unidirectional radiation from 0.83 to 1.9 GHz (79%) with a peak gain of 3.8 dBi and a front-to-back ratio of 9 dB. Due to negligible electromagnetic coupling between RBR antennas, lateral SWs are suppressed, and thus multiple antennas can be located adjacent to each other without experiencing any frequency shift or impedance mismatch.

This study presents a simulation and measurement test-bench to investigate the antenna detuning, impedance mismatch and losses in through-body communications. These parameters are relevant to the efficient design of wearable and implantable antennas for biomedical sensors. The study was carried out using finite-difference-time-domain electromagnetic simulations using realistic high-resolution numerical human body phantom models. S-parameter measurement corresponding to the simulation setup was carried out when an implantable antenna connected to a Vector Network Analyzer was placed in the armpit of a human subject and communication was established with an external wearable antenna. The measured results verified the reliability of the proposed simulation test-bench for biomedical sensor applications. 1 4

Electromagnetic metasurfaces can be characterized as intelligent if they are able to perform multiple tunable functions, with the desired response being controlled by a computer influencing the individual electromagnetic properties of each metasurface inclusion. In this paper, we present an example of an intelligent metasurface which operates in the reflection mode in the microwave frequency range. We numerically show that without changing the main body of the metasurface we can achieve tunable perfect absorption and tunable anomalous reflection. The tunability features can be implemented using mixed-signal integrated circuits (ICs), which can independently vary both the resistance and reactance, offering complete local control over the complex surface impedance. The ICs are embedded in the unit cells by connecting two metal patches over a thin grounded substrate and the reflection property of the intelligent metasurface can be readily controlled by a computer. Our intelligent metasurface can have significant influence on future space-time modulated metasurfaces and a multitude of applications, such as beam steering, energy harvesting, and communications., 10 pages, 8 figures