Showing papers on "Radio frequency published in 2019"

Dual mode communications device with remote device feedback and methods for use therewith

Abstract: In accordance with one or more embodiments, a communication device includes an antenna array configured to receive first millimeter wave (MMW) signals from a remote device in a millimeter wave (MMW) frequency band and to transmit second millimeter wave (MMW) signals to the remote device in the MMW frequency band. A base transceiver station is configured to generate a consolidated steering matrix in accordance in a radio frequency (RF) band based on a consolidated feedback matrix in accordance with the RF band, wherein the MMW frequency band is above the RF band. A remote radio head is configured to: process the first MMW wave signals received from the remote device to recover an original feedback matrix in accordance with the MMW frequency band; convert the original feedback matrix in accordance with the MMW frequency band to the consolidated feedback matrix in accordance with the RF band; convert the consolidated steering matrix to a converted steering matrix that facilitates the transmission of the second MMW signals to the remote device in the MMW frequency band, and is further configured to generate the second MMW signals in accordance with the converted steering matrix.

Observations of fast radio bursts at frequencies down to 400 megahertz

Abstract: Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes likely arriving from far outside the Milky Way galaxy. This phenomenon was discovered at radio frequencies near 1.4 GHz and to date has been observed in one case at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies. Here we report detections of FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. We present 13 FRBs detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show a variety of temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper. Our low-scattering events suggest that efforts to detect FRBs at radio frequencies below 400 MHz will eventually be successful. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium (ISM) in the Milky Way.

Advanced Adaptive Photonic RF Filters with 80 Taps Based on an Integrated Optical Micro-Comb Source

Abstract: We demonstrate a photonic radio frequency (RF) transversal filter based on an integrated optical micro-comb source featuring a record low free spectral range of 49 GHz, yielding 80 micro-comb lines across the C -band. This record high number of taps, or wavelengths for the transversal filter results in significantly increased performance including a Q RF factor more than four times higher than previous results. Furthermore, by employing both positive and negative taps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using a Gaussian apodization, together with a tunable center frequency covering the RF spectra range, with a widely tunable 3-dB bandwidth and versatile dynamically adjustable filter shapes. Our experimental results match well with theory, showing that our transversal filter is a competitive solution to implement advanced adaptive RF filters with broad operational bandwidth, high frequency selectivity, high reconfigurability, and potentially reduced cost and footprint. This approach is promising for applications in modern radar and communications systems.

Analytical Performance Assessment of THz Wireless Systems

Abstract: This paper is focused on providing the analytical framework for the quantification and evaluation of the joint effect of misalignment fading and hardware imperfections in the presence of multipath fading at terahertz (THz) wireless fiber extenders. In this context, we present the appropriate system model that incorporates the different operation, design, and environmental parameters. In more detail, it takes into account the transceivers antenna gains, the operation frequency, the distance between the transmitter (TX) and the receiver (RX), the environmental conditions, i.e., temperature, humidity, and pressure, the spatial jitter between the TX and RX antennas that results to antennas misalignment, the level of transceivers' hardware imperfections, and the stochastic characteristics of the wireless channel. Based on this model, we analyze and quantify the joint impact of misalignment and multipath fading by providing novel closed-form expressions for the probability and cumulative density functions of the composite channel. Moreover, we derive exact closed-form expressions for the outage probability for both cases of ideal and non-ideal radio frequency (RF) front-end. In addition, in order to quantify the detrimental effect of misalignment fading, we analytically obtain the outage probability in the absence of misalignment cases for both cases of ideal and non-ideal RF front-end. In addition, we extract the novel closed-form expressions for the ergodic capacity for the case of the ideal RF front-end and tight upper bounds for both the cases of ideal and non-ideal RF front-end. Finally, an insightful ergodic capacity ceiling for the non-ideal RF front-end case is provided.

A 28-GHz CMOS Phased-Array Transceiver Based on LO Phase-Shifting Architecture With Gain Invariant Phase Tuning for 5G New Radio

Abstract: This paper presents a 28-GHz CMOS four-element phased-array transceiver chip for the fifth-generation mobile network (5G) new radio (NR). The proposed transceiver is based on the local-oscillator (LO) phase-shifting architecture, and it achieves quasi-continuous phase tuning with less than 0.2-dB radio frequency (RF) gain variation and 0.3°C phase error. Accurate beam control with suppressed sidelobe level during beam steering could be supported by this work. At 28 GHz, a single-element transmitter-mode output ${{\mathrm {P}}_{\mathrm {1\,dB}}}$ of 15.7 dBm and a receiver-mode noise figure (NF) of 4.1 dB are achieved. The eight-element transceiver modules developed in this work are capable of scanning the beam from −50° to +50° with less than −9-dB sidelobe level. A saturated equivalent isotropic radiated power (EIRP) of 39.8 dBm is achieved at 0° scan. In a 5-m over-the-air measurement, the proposed module demonstrates the first 512 quadrature amplitude modulation (QAM) constellation in the 28-GHz band. A data stream of 6.4 Gb/s in 256-QAM could be supported within a beam angle of ±50°. The achieved maximum data rate is 15 Gb/s in 64-QAM. The proposed transceiver chip consumes 1.2 W/chip in transmitter mode and 0.59 W/chip in receiver mode.

A Rydberg atom-based mixer: Measuring the phase of a radio frequency wave

Abstract: Rydberg atoms have been shown to be very useful in performing absolute measurements of the magnitude of a radio frequency (RF) field using electromagnetically induced transparency. However, there has been less success in using Rydberg atoms for the measurement of the phase of an RF field. Measuring the phase of a RF field is a necessary component for many important applications, including antenna metrology, communications, and radar. We demonstrate a scheme for measuring the phase of an RF field by using Rydberg atoms as a mixer to down-convert an RF field at 20 GHz to an intermediate frequency on the order of kHz. The phase of the intermediate frequency corresponds directly to the phase of the RF field. We use this approach to measure the phase shift on an electromagnetic wave from a horn antenna as the antenna is placed at different distances from the Rydberg atom sensor. The atom-based RF phase measurements allow us to measure the propagation constant of the RF wave to within 0.1% of the theoretical value.

Observations of Fast Radio Bursts at Frequencies down to 400 Megahertz

Abstract: Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes likely arriving from far outside the Milky Way galaxy. This phenomenon was discovered at radio frequencies near 1.4 GHz and to date has been observed in one case at as high as 8 GHz, but not below 700 MHz in spite of significant searches at low frequencies. Here we report detections of FRBs at radio frequencies as low as 400 MHz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. We present 13 FRBs detected during a telescope pre-commissioning phase, when our sensitivity and field-of-view were not yet at design specifications. Emission in multiple events is seen down to 400 MHz, the lowest radio frequency to which we are sensitive. The FRBs show a variety of temporal scattering behaviours, with the majority significantly scattered, and some apparently unscattered to within measurement uncertainty even at our lowest frequencies. Of the 13 reported here, one event has the lowest dispersion measure yet reported, implying it is among the closest yet known, and another has shown multiple repeat bursts, as described in a companion paper. Our low-scattering events suggest that efforts to detect FRBs at radio frequencies below 400 MHz will eventually be successful. The overall scattering properties of our sample suggest that FRBs as a class are preferentially located in environments that scatter radio waves more strongly than the diffuse interstellar medium (ISM) in the Milky Way.

Rydberg-atom-based digital communication using a continuously tunable radio-frequency carrier.

Abstract: Up to now, the measurement of radio-frequency (RF) electric field achieved using the electromagnetically-induced transparency (EIT) of Rydberg atoms has proved to be of high-sensitivity and shows a potential to produce a promising atomic RF receiver at resonance between two chosen Rydberg states. In this paper, we study the extension of the feasibility of digital communication via this quantum-based antenna over a continuously tunable RF-carrier at off-resonance. Our experiment shows that the digital communication at a rate of 500 kbps can be performed reliably within a tunable bandwidth of 200 MHz near a 10.22 GHz carrier. Outside of this range, the bit error rate (BER) increases, rising to, for example, 15% at an RF-detuning of ±150 MHz. In the measurement, the time-varying RF field is retrieved by detecting the optical power of the probe laser at the center frequency of RF-induced symmetric or asymmetric Autler-Townes splitting in EIT. Prior to the digital test, we studied the RF-reception quality as a function of various parameters including the RF detuning and found that a choice of linear gain response to the RF-amplitude can suppress the signal distortion. The modulating signal can be decoded at speeds up to 500 kHz in the tunable bandwidth. Our test consolidates the physical basis for reliable communication and spectral sensing over a wider broadband RF-carrier, which paves a way for the concurrent multi-channel communications founded on the same pair of Rydberg states.

Microwave and RF Photonic Fractional Hilbert Transformer Based on a 50 GHz Kerr Micro-Comb

Abstract: We report a photonic microwave and radio frequency (RF) fractional Hilbert transformer based on an integrated Kerr micro-comb source. The micro-comb source has a free spectral range (FSR) of 50 GHz, generating a large number of comb lines that serve as a high-performance multi-wavelength source for the transformer. By programming and shaping the comb lines according to calculated tap weights, we achieve both arbitrary fractional orders and a broad operation bandwidth. We experimentally characterize the RF amplitude and phase response for different fractional orders and perform system demonstrations of real-time fractional Hilbert transforms. We achieve a phase ripple of <0.15 rad within the 3-dB pass-band, with bandwidths ranging from 5 to 9 octaves depending on the order. The experimental results show good agreement with theory, confirming the effectiveness of our approach as a new way to implement high-performance fractional Hilbert transformers with broad processing bandwidth, high reconfigurability, and greatly reduced size and complexity.

An Efficient Broadband Slotted Rectenna for Wireless Power Transfer at LTE Band

Abstract: A compact and broadband rectifying antenna (rectenna) which consists of a novel slotted antenna and an efficient rectifying circuit is presented for wireless power transfer at LTE-2300/2500 band. Three different broadband antennas have been investigated and compared. It is found that the newly designed antenna which combines the annular slot radiation patch and a slotted ground plane (GP) has the widest bandwidth and the best matching characteristic. A new broadband dual-stub matching network is proposed to maximize the transmission of wireless power and enhance the reliability of the rectifier when the input power and load varies. In addition, the ground of the rectifier is directly connected to the GP of the antenna for compactness and low energy loss. The proposed designs have been simulated, fabricated, and tested. The results indicate that the proposed receiving antenna performs well at LTE band with a wide bandwidth from 2 to 3.1 GHz. The maximum efficiency of the proposed rectenna reaches 70% at 2.5 GHz under the input power of 5 dBm. Furthermore, the rectenna remains at a relatively efficient power conversion when the load varies in a wide range from 2 to 20 $\text{k}\Omega $ under different low input power, which is of great significance when the ambient radio frequency(F) signal is weak. Therefore, the rectenna is potentially applicable to a wide range of low-power electronic devices by harvesting RF energy at LTE band.

Microcomb based photonic RF signal processing

Abstract: Microcombs are powerful tools as sources of multiple wavelength channels for photonic radio frequency (RF) signal processing. They offer a compact device footprint, large numbers of wavelengths, and wide Nyquist bands. Here, we review recent progress on microcomb-based photonic RF signal processors, including true time delays, reconfigurable filters, Hilbert transformers, differentiators, and channelizers. The strong potential of optical micro-combs for RF photonics applications in terms of functions and integrability is also discussed.

Weak electric-field detection with sub-1 Hz resolution at radio frequencies using a Rydberg atom-based mixer

Abstract: Rydberg atoms have been used for measuring radio-frequency (RF) electric (E)-fields due to their strong dipole moments over the frequency range of 500 MHz-1 THz. For this, electromagnetically induced transparency (EIT) within the Autler-Townes (AT) regime is used such that the detected E-field is proportional to AT splitting. However, for weak E-fields AT peak separation becomes unresolvable thus limiting the minimum detectable E-field. Here, we demonstrate using the Rydberg atoms as an RF mixer for weak E-field detection well below the AT regime with frequency discrimination better than 1 Hz resolution. A heterodyne detection scenario with two E-fields incident on a vapor cell filled with cesium atoms is used. One E-field at 19.626000 GHz drives the 34D5/2 → 35P3/2 Rydberg transition and acts as a local oscillator (LO) and a second signal E-field (Sig) of interest is at 19.626090 GHz. In the presence of the LO, the Rydberg atoms naturally down convert the Sig field to a 90 kHz intermediate frequency (IF) signal. This IF signal manifests as an oscillation in the probe laser intensity through the Rydberg vapor and is easily detected with a photodiode and lock-in amplifier. In the configuration used here, E-field strength down to ≈ 46 μV/m ± 2 μV/m were detected with a sensitivity of ≈ 79 μVm−1Hz−1/2. Furthermore, neighboring fields 0.1 Hz away and equal in strength to Sig could be discriminated without any leakage into the lock-in signal. For signals 1 Hz away and as high as +60 dB above Sig, leakage into the lock-in signal could be kept below -3 dB.

Hybrid RF-Solar Energy Harvesting Systems Utilizing Transparent Multiport Micromeshed Antennas

Abstract: The design of a hybrid radio frequency (RF) and solar energy harvesting (EH) system utilizing a transparent multiport antenna for indoor applications is described. The system incorporates an eight-port transparent antenna, operating in the unlicensed 2.4-GHz band, and is constructed from transparent copper micromeshed planar conductor. The antenna is integrated on the top surface of a solar cell with rectifiers positioned underneath to form a hybrid RF-solar indoor EH system. A key advantage of this approach is that the surface area of the solar cell is reused for the antenna saving space. Another novelty is the use of a multiport antenna for increasing the RF harvested energy. It is demonstrated that with a light intensity of 360 lux, the solar cell can obtain 1.68-mW power while the rectenna can achieve an additional 4.8%–45.8% harvested power when the incident RF input power density is varied from 13.30 to 52.96 mW/m2. The transparent antenna achieves 72.4% efficiency and is one of the highest reported results. In addition, the rectifiers obtain 53.2% RF-to-dc conversion efficiency for an RF input power of −10 dBm. These results demonstrate that the proposed RF-solar energy harvester can increase harvested energy and provide energy diversity.

RF Energy Harvesting Wireless Communications: RF Environment, Device Hardware and Practical Issues

Abstract: Radio frequency (RF) based wireless power transfer provides an attractive solution to extend the lifetime of power-constrained wireless sensor networks. Through harvesting RF energy from surrounding environments or dedicated energy sources, low-power wireless devices can be self-sustaining and environment-friendly. These features make the RF energy harvesting wireless communication (RF-EHWC) technique attractive to a wide range of applications. The objective of this article is to investigate the latest research activities on the practical RF-EHWC design. The distribution of RF energy in the real environment, the hardware design of RF-EHWC devices and the practical issues in the implementation of RF-EHWC networks are discussed. At the end of this article, we introduce several interesting applications that exploit the RF-EHWC technology to provide smart healthcare services for animals, wirelessly charge the wearable devices, and implement 5G-assisted RF-EHWC.

An Ambient RF Energy Harvesting System Where the Number of Antenna Ports is Dependent on Frequency

Abstract: We describe the design of a multiport rectenna system for ambient radio frequency (RF) energy harvesting where the number of ports utilized is dependent on frequency. A unique aspect of the design is the use of different numbers of antenna ports for harvesting RF energy at different frequencies. This allows the available area for the rectenna to be fully utilized at all frequencies. In particular, the proposed antenna is designed to have four ports for harvesting energy from the GSM-900 frequency band and 12 ports for the GSM-1800 frequency band in the same area. The design for the rectifiers for the GSM-900 and GSM-1800 frequency bands with direct current (dc) combining is provided and prototypes are demonstrated. Field-test measurements show that the proposed rectenna can provide an output dc voltage of more than 3.2 V, an output dc power of more than −10 dBm, and an RF-to-dc efficiency of greater than 42% when the power density is greater than $1400~\mu \mathrm {W/m^{2}}$ . Measurements in an ambient RF environment at a university campus with commercial GSM-900 and GSM-1800 systems in operation show that the proposed rectenna can achieve output dc voltages of up to 2.2 V and dc power up to −13.6 dBm.

Multi-Band MIMO Antenna Design with User-Impact Investigation for 4G and 5G Mobile Terminals

Abstract: In this study, we propose a design of a multi-band slot antenna array applicable for fourth-generation (4G) and fifth-generation (5G) smartphones. The design is composed of double-element square-ring slot radiators fed by microstrip-line structures for easy integration with radio frequency (RF)/microwave circuitry. The slot radiators are located on the corners of the smartphone printed circuit board (PCB) with an overall dimension of 75 × 150 mm2. The proposed multiple-input multiple-output (MIMO) antenna is designed to meet the requirements of 4G and 5G mobile terminals with essential bandwidth for higher data rate applications. For −10 dB impedance bandwidth, each single-element of the proposed MIMO design can cover the frequency ranges of 2.5–2.7 GHz (long-term evolution (LTE) 2600), 3.45–3.8 GHz (LTE bands 42/43), and 5.00–5.45 GHz (LTE band 46). However, for −6 dB impedance bandwidth, the radiation elements cover the frequency ranges of 2.45–2.82 GHz, 3.35–4.00 GHz, and 4.93–5.73 GHz. By employing the microstrip feed lines at the four different sides of smartphone PCB, the isolation of the radiators has been enhanced and shows better than 17 dB isolation levels over all operational bands. The MIMO antenna is implemented on an FR-4 dielectric and provides good properties including S-parameters, efficiency, and radiation pattern coverage. The performance of the antenna is validated by measurements of the prototype. The simulation results for user-hand/user-head impacts and specific absorption rate (SAR) levels of the antenna are discussed, and good results are achieved. In addition, the antenna elements have the potential to be used as 8-element/dual-polarized resonators.

The More (Antennas), the Merrier: A Survey of Silicon-Based mm-Wave Phased Arrays Using Multi-IC Scaling

Abstract: Phased-array antenna technology has had a broad impact for more than half a century, spanning radio astronomy and radar, and is about to ignite a significant shift in the operation of mobile communications. Its general principle is to use an array of wireless transmitters (Txs) or receivers (Rxs) to focus and steer energy. The focus is achieved by creating an interference pattern from the antenna array to enable constructive interference in the desired direction and destructive interference in all of the other directions; the steering is accomplished by modifying the delays at each antenna element in the array to control the directions of constructive and destructive interference [1]-[3].

Avoidance of Time-Varying Radio Frequency Interference With Software-Defined Cognitive Radar

Abstract: Congestion in the RF spectrum is rapidly increasing, which has motivated the need for efficient spectrum sharing techniques. A cognitive radar system has been developed to implement a perception action cycle, for spectrum sharing, in which the RF spectrum is sensed, other RF signals are identified, and the radar frequency band of operation is adapted to avoid interfering signals in the spectrum. The system operates in real time and is capable of coexisting with common communications signals. A system with this capability requires efficient programming that pushes the limits of the technology available. In order to properly test the performance of a radar system designed for this kind of reactive spectrum sharing, a rigorous set of synthetic interference signals is generated and several informative evaluation metrics are defined. Additionally, the system's performance is evaluated with common communications signals such as LTE and GSM. The performance of the system is found to be adequate for avoiding signals that are either varying in frequency or turning on and off at rates on the order of 10 ms.

High-Efficient Broadband CPW RF Rectifier for Wireless Energy Harvesting

Abstract: In this paper, the implementation of a compact, wideband, single layer, and simple RF rectifier design is discussed. The proposed rectifier configuration is based on the coplanar waveguide transmission line. The rectifier is constructed using the voltage doubler circuit in conjunction with a broadband matching network. To obtain a small circuit size, the matching circuit is constituted with a series dual-inductive lumped element. The overall rectifier dimensions are very compact $22.5\times 31\,\,\text {mm}^{2}$ . In order to accurately characterize the rectifier performance, the electromagnetic and harmonic balance simulations are conducted using the Agilent, ADS software. The comparison shows good agreement between the simulation and measurement results. For instance, the peak measured efficiency is 74.8% at 10-dBm RF input power and the corresponding simulated value is 75% with a terminal load of 1 $\text{k}\Omega $ . The efficient frequency range is extending from 0.1 to 2.5 GHz, with an efficiency of more than 45% at input power 10 dBm.

Opportunistic Ambient Backscatter Communication in RF-Powered Cognitive Radio Networks

Abstract: In the present contribution, we propose a novel opportunistic ambient backscatter communication (ABC) framework for radio frequency (RF)-powered cognitive radio (CR) networks. This framework considers opportunistic spectrum sensing (SS) integrated with ABC and harvest-then-transmit (HTT) operation strategies. Novel analytic expressions are derived for the average throughput, the average energy consumption and the energy efficiency (EE) in the considered set up. These expressions are represented in closed-form and have a tractable algebraic representation which renders them convenient to handle both analytically and numerically. In addition, we formulate an optimization problem to maximize the EE of the CR system operating in mixed ABC—and HTT—modes, for a given set of constraints, including primary interference and imperfect SS constraints. Capitalizing on this, we determine the optimal set of parameters which in turn comprise the optimal detection threshold, the optimal degree of trade-off between the CR system operating in the ABC—and HTT—modes and the optimal data transmission time. Extensive results from respective computer simulations are also presented for corroborating the corresponding analytic results and to demonstrate the performance gain of the proposed model in terms of EE.

Multi-Target Concurrent Vital Sign and Location Detection Using Metamaterial-Integrated Self-Injection-Locked Quadrature Radar Sensor

Abstract: A new architecture of self-injection-locked (SIL) quadrature radar sensor based on a metamaterial (MTM) leaky-wave antenna (LWA) to detect multi-target vital sign and location simultaneously is proposed for the first time. The angular information of targets is obtained by a 1-D MTM LWA with −50° to +30° beam-steering angle when the frequency varies from 1.85 to 2.85 GHz. Furthermore, the distance from the radar sensor to the targets is obtained by imposing the frequency-shift keying (FSK) modulation on the radar waveforms. Meanwhile, the vital sign signals of multiple targets can be extracted from the Doppler frequency spectrum. For the proof of concept, two frequencies, 2.24 and 2.45 GHz, are chosen to detect two targets at different locations, which correspond to the scanning angle at −10° and −40°, respectively. A first-order microwave differentiator followed by a quadrature coupler is employed to convert the radio frequency (RF) signals from the output of the MTM LWA to in-phase (I) and quadrature (Q) RF signals with frequency-dependent amplitudes, thereby eliminating the null point issues for radar detection. Experimental results show that the proposed SIL MTM radar sensor can detect the target location accurately, while the obtained vital sign results agree well with the ground truth.

Embedding a Rydberg Atom-Based Sensor Into an Antenna for Phase and Amplitude Detection of Radio-Frequency Fields and Modulated Signals

Abstract: We demonstrate a Rydberg atom-based sensor embedded in a parallel-plate waveguide (PPWG) for amplitude and phase detection of a radio-frequency (RF) electric field. This embedded atomic sensor is also capable of receiving modulated communications signals. In this configuration, the PPWG antenna serves two functions. First, the PPWG antenna acts as a source for a local oscillator (LO) field. The LO is required to use an atomic vapor cell (a glass cell containing a Rydberg atom vapor) as a Rydberg atom-based mixer, which detects the amplitude and phase of a second RF field incident from some remote location. The second function of the PPWG antenna is to capture the RF field arriving from a remote location and concentrate it at the location of the atomic vapor cell for detection. To demonstrate this, we show several examples of phase and amplitude measurements of an RF field with the embedded Rydberg-atom sensor. We also demonstrate the discrimination of the polarization of an RF field and the ability to receive phase-modulated carrier communications signals with this integrated atomic sensor. Embedding the atomic sensor in an antenna allows for the full characterization of a radio frequency field, in that the magnitude, phase, and polarization of an RF field can be measured with one compact integrated quantum-based sensor. Furthermore, the embedded sensor head allows one to easily vary the LO in order to maximize the ability to measure phase and amplitude of the field or modulated signal.

A Generic Receiver Architecture for MIMO Wireless Power Transfer With Nonlinear Energy Harvesting

Abstract: This letter investigates a multiple-input multiple-output (MIMO) wireless power transfer system under practical nonliner energy harvesting (EH) models. We propose a new generic energy receiver (ER) architecture consisting of $N$ receive antennas and $L$ rectifiers, for which one power splitter is inserted after each antenna to adaptively split the received radio frequency (RF) signals among the $L$ rectifiers for efficient nonlinear RF-to-direct current (dc) conversion. With the proposed architecture, we maximize the total harvested dc power at the ER, by jointly optimizing the transmit energy beamforming at the energy transmitter and the power splitting ratios at the ER. Numerical results show that our proposed design by exploiting the nonlinearity of EH significantly improves the harvested dc power at the ER, as compared to two conventional designs.

Frequency-Scanned Monopulse Pattern Synthesis Using Leaky-Wave Antennas for Enhanced Power-Based Direction-of-Arrival Estimation

Abstract: The synthesis of frequency-scanned monopulse radiation patterns using an array of two leaky-wave antennas (LWAs) is demonstrated The LWA array must be designed with appropriate shifted frequency-dispersion responses to fulfill the desired monopulse-scanning specification over the required bandwidth and number of channels This is demonstrated using two manufactured LWAs in half-width microstrip technology, designed to scan in the band from 239 to 265 GHz covering a field of view (FoV) from −80° to +80° and using three frequency channels Also, this paper addresses the procedure to estimate the direction of arrival (DoA) of an incoming beacon RF signal composed by prescribed tones distributed in the scanning band This type of multicarrier beacon signals can be produced in wireless systems which allow for frequency-hopping operation It is demonstrated that the proposed monopulse DoA-estimation technique combines good angular resolution and wide FoV using a simple passive antenna structure

Observation and stabilization of photonic Fock states in a hot radio-frequency resonator

Abstract: Detecting weak radio-frequency electromagnetic fields plays a crucial role in a wide range of fields, from radio astronomy to nuclear magnetic resonance imaging. In quantum optics, the ultimate limit of a weak field is a single photon. Detecting and manipulating single photons at megahertz frequencies presents a challenge because, even at cryogenic temperatures, thermal fluctuations are appreciable. Using a gigahertz superconducting qubit, we observed the quantization of a megahertz radio-frequency resonator, cooled it to the ground state, and stabilized Fock states. Releasing the resonator from our control, we observed its rethermalization with nanosecond resolution. Extending circuit quantum electrodynamics to the megahertz regime, we have enabled the exploration of thermodynamics at the quantum scale and allowed interfacing quantum circuits with megahertz systems such as spin systems or macroscopic mechanical oscillators.

Symbol-Level Precoding for Low Complexity Transmitter Architectures in Large-Scale Antenna Array Systems

Abstract: In this paper, we consider three transmitter designs for symbol-level-precoding (SLP), a technique that mitigates multiuser interference (MUI) in multiuser systems by designing the transmitted signals using the channel state information and the information-bearing symbols. The considered systems tackle the high hardware complexity and power consumption of existing SLP techniques by reducing or completely eliminating fully digital radio frequency (RF) chains. The first proposed architecture referred to as, Antenna Selection SLP, minimizes the MUI by activating a subset of the available antennas and thus, reducing the number of required RF chains to the number of active antennas. In the other two architectures, which we refer to as RF domain SLP, the processing happens entirely in the RF domain, thus eliminating the need for multiple fully digital RF chains altogether. Instead, the analog phase shifters directly modulate the signals on the transmit antennas. The precoding design for all the considered cases is formulated as a constrained least squares problem and efficient algorithmic solutions are developed via the Coordinate Descent method. Simulations provide insights into the power efficiency of the proposed schemes and the improvements over the fully digital counterparts.

Radio frequency timing analysis of the compact jet in the black hole X-ray binary Cygnus X-1

Abstract: We present simultaneous multiband radio and X-ray observations of the black hole X-ray binary Cygnus X-1, taken with the Karl G. Jansky Very Large Array and the Nuclear Spectroscopic Telescope Array. With these data, we detect clear flux variability consistent with emission from a variable compact jet. To probe how the variability signal propagates down the jet flow, we perform detailed timing analyses of our data. We find that the radio jet emission shows no significant power at Fourier frequencies f ≳ 0.03 Hz (below ∼30 s time-scales), and that the higher frequency radio bands (9/11 GHz) are strongly correlated over a range of time-scales, displaying a roughly constant time lag with Fourier frequency of a few tens of seconds. However, in the lower frequency radio bands (2.5/3.5 GHz), we find a significant loss of coherence over the same range of time-scales. Further, we detect a correlation between the X-ray/radio emission, measuring time lags between the X-ray/radio bands on the order of tens of minutes. We use these lags to solve for the compact jet speed, finding that the Cyg X-1 jet is more relativistic than usually assumed for compact jets, where β=0.92+0.03−0.06 and (⁠Γ=2.59+0.79−0.61⁠). Lastly, we constrain how the jet size scale changes with frequency, finding a shallower relation (∝ν−0.4) than predicted by simple jet models (∝ν−1), and estimate a jet opening angle of ϕ ∼ 0.4–1.8 deg. With this study we have developed observational techniques designed to overcome the challenges of radio timing analyses and created the tools needed to connect rapid radio jet variability properties to internal jet physics.