Showing papers on "Radio frequency published in 2018"

Ambient Backscatter Communications: A Contemporary Survey

Abstract: Recently, ambient backscatter communication has been introduced as a cutting-edge technology which enables smart devices to communicate by utilizing ambient radio frequency (RF) signals without requiring active RF transmission. This technology is especially effective in addressing communication and energy efficiency problems for low-power communications systems such as sensor networks, and thus it is expected to realize numerous Internet-of-Things applications. Therefore, this paper aims to provide a contemporary and comprehensive literature review on fundamentals, applications, challenges, and research efforts/progress of ambient backscatter communications. In particular, we first present fundamentals of backscatter communications and briefly review bistatic backscatter communications systems. Then, the general architecture, advantages, and solutions to address existing issues and limitations of ambient backscatter communications systems are discussed. Additionally, emerging applications of ambient backscatter communications are highlighted. Finally, we outline some open issues and future research directions.

Thin film lithium niobate electro-optic modulator with terahertz operating bandwidth.

Abstract: We present a thin film crystal ion sliced (CIS) LiNbO3 phase modulator that demonstrates an unprecedented measured electro-optic (EO) response up to 500 GHz. Shallow rib waveguides are utilized for guiding a single transverse electric (TE) optical mode, and Au coplanar waveguides (CPWs) support the modulating radio frequency (RF) mode. Precise index matching between the co-propagating RF and optical modes is responsible for the device’s broadband response, which is estimated to extend even beyond 500 GHz. Matching the velocities of these co-propagating RF and optical modes is realized by cladding the modulator’s interaction region in a thin UV15 polymer layer, which increases the RF modal index. The fabricated modulator possesses a tightly confined optical mode, which lends itself to a strong interaction between the modulating RF field and the guided optical carrier; resulting in a measured DC half-wave voltage of 3.8 V·cm−1. The design, fabrication, and characterization of our broadband modulator is presented in this work.

Photonic RF and microwave reconfigurable filters and true time delays based on an integrated optical Kerr frequency comb source

Abstract: We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave

Multiport Pixel Rectenna for Ambient RF Energy Harvesting

Abstract: We describe the design of a multiport pixel rectenna for ambient radio-frequency (RF) energy harvesting consisting of an optimized triple-port pixel antenna and a triple-port rectifier with dc combining. The advantages of the multiport pixel approach include enhanced harvested RF power for a given area as well as a reduction in the antenna matching requirements. We formulate the design of the triple-port pixel antenna as a binary optimization problem with an objective function related to harvested RF power in the GSM-1800 band for specified power angular spectrums without the need for antenna matching components. The optimization of the triple-port pixel antenna is obtained by using successive exhaustive Boolean optimization. The design for the triple-port rectifier with dc combining is also provided and a prototype is demonstrated. The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size. The overall RF-to-dc efficiency of the multiport pixel rectenna is also evaluated and shown to be 19% when the total input RF power is −20 dBm. The effects of nonuniformity in the input RF power across antenna ports are also investigated.

Advanced RF and microwave functions based on an integrated optical frequency comb source.

Abstract: We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave signal processing functions for applications including radar and communication systems.

A Radio Frequency Channelizer based on Cascaded Integrated Micro-ring Resonator Optical Comb Sources and Filters

Abstract: We report a broadband RF channelizer based on an integrated optical frequency Kerr micro-comb source, with an RF channelizing bandwidth of 90 GHz, a high RF spectral slice resolution of 1.04 GHz, and experimentally verify the RF performance up to 19 GHz. This approach to realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

Orthogonally Polarized RF Optical Single Sideband Generation and Dual-Channel Equalization Based on an Integrated Microring Resonator

Abstract: We demonstrate narrowband orthogonally polarized optical radio frequency (RF) single sideband generation as well as dual-channel equalization based on an integrated dual-polarization-mode high- Q microring resonator. The device operates in the optical communications band and enables narrowband RF operation at either 16.6 or 32.2 GHz, determined by the free spectral range and TE/TM mode interval in the resonator. We achieve a very large dynamic tuning range of over 55 dB for both the optical carrier-to-sideband ratio and the dual-channel RF equalization.

Zero-static power radio-frequency switches based on MoS 2 atomristors.

Abstract: Recently, non-volatile resistance switching or memristor (equivalently, atomristor in atomic layers) effect was discovered in transitional metal dichalcogenides (TMD) vertical devices. Owing to the monolayer-thin transport and high crystalline quality, ON-state resistances below 10 Ω are achievable, making MoS2 atomristors suitable as energy-efficient radio-frequency (RF) switches. MoS2 RF switches afford zero-hold voltage, hence, zero-static power dissipation, overcoming the limitation of transistor and mechanical switches. Furthermore, MoS2 switches are fully electronic and can be integrated on arbitrary substrates unlike phase-change RF switches. High-frequency results reveal that a key figure of merit, the cutoff frequency (fc), is about 10 THz for sub-μm2 switches with favorable scaling that can afford fc above 100 THz for nanoscale devices, exceeding the performance of contemporary switches that suffer from an area-invariant scaling. These results indicate a new electronic application of TMDs as non-volatile switches for communication platforms, including mobile systems, low-power internet-of-things, and THz beam steering.

Broadband RF Channelizer Based on an Integrated Optical Frequency Kerr Comb Source

Abstract: We report a broadband RF channelizer based on an integrated optical frequency Kerr micro-comb source, with an RF channelizing bandwidth of 90 GHz, a high RF spectral slice resolution of 1.04 GHz, and experimentally verify the RF performance up to 19 GHz. This approach of realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

Multiband Ambient RF Energy Harvesting Circuit Design for Enabling Batteryless Sensors and IoT

Abstract: Ambient radio frequency (RF) energy harvesting (RF-EH) allows powering low-power electronic devices without wires, batteries, and dedicated energy sources. Current RF-EH circuit designs for ambient RF harvesting are optimized and fabricated for a predetermined frequency band. Thus, a single circuit is tuned for a given band with simple extensions to multiple circuits operating individually in distinct bands. Our approach is different in the sense that it designs and implements a common circuit design that can operate on multiple different RF cellular and ISM bands. This paper makes two contributions. First, it presents a study of ambient RF signal strength distribution conducted in Boston, MA, USA, indicating locations and associated RF bands that can point toward the practicality of ambient RF-EH. Second, it demonstrates an adjustable circuit for harvesting from LTE 700-MHz, GSM 850-MHz, and ISM 900-MHz bands with one single circuit. Our circuit design is fabricated on printed circuit board with comprehensive evaluations at each associated frequency to test the power conversion efficiency (PCE). In addition, we characterize the charging performance, and feasibility of powering sensors outdoors such as TI eZ430-RF2500. Results reveal more than 45% PCE for our prototype.

Spectrum Allocation for Noncooperative Radar Coexistence

Abstract: Access to the electromagnetic spectrum is an ever-growing challenge for radar. Future radar will be required to mitigate RF interference from other RF sources, relocate to new frequency bands while maintaining quality of service, and share frequency bands with other RF systems. The spectrum sensing, multioptimization (SS-MO) technique was recently investigated as a possible solution to these challenges. Prior results have indicated significant improvement in the signal-to-interference plus noise ratio at the cost of a high computational complexity. However, the optimization computational cost must be manageable in real time to address the dynamically changing spectral environment. In this paper, a bioinspired filtering technique is investigated to reduce the computational complexity of SS-MO. The proposed technique is analogous to the processing of the thalamus in the human brain in that the number of samples input to SS-MO is significantly decreased, thus, resulting in a reduction in computational complexity. The performance and computational complexity of SS-MO and the proposed technique are investigated. Both techniques are used to process a variety of measured spectral data. The results indicate a significant decrease in computational complexity for the proposed approach while maintaining performance of the SS-MO technique.

On-chip intercalated-graphene inductors for next-generation radio frequency electronics

Abstract: On-chip metal inductors that revolutionized radio frequency electronics in the 1990s suffer from an inherent limitation in their scalability in state-of-the-art radio frequency integrated circuits. This is because the inductance density values for conventional metal inductors, which result from magnetic inductance alone, are limited by the laws of electromagnetic induction. Here, we report inductors made of intercalated graphene that uniquely exploit the relatively large kinetic inductance and high conductivity of the material to achieve both small form-factors and high inductance values, a combination that has proved difficult to attain so far. Our two-turn spiral inductors based on bromine-intercalated multilayer graphene exhibit a 1.5-fold higher inductance density, leading to a one-third area reduction, compared to conventional inductors, while providing undiminished Q-factors of up to 12. This purely material-enabled technique provides an attractive solution to the longstanding scaling problem of on-chip inductors and opens an unconventional path for the development of ultra-compact wireless communication systems.

Biological and medical aspects of electromagnetic fields

Abstract: Effects of Radiofrequency and Extremely Low-Frequency Electromagnetic Field Radiation on Cells of the Immune System T. Paunesku and G.E. Woloschak Evaluation of the Toxicity and Potential Oncogenicity of Extremely Low-Frequency Magnetic Fields in Experimental Animal Model Systems D.L. McCormick Interaction of Nonmodulated and Pulse-Modulated Radio Frequency Fields with Living Matter: Experimental Results S.M. Michaelson, E.C. Elson, and L.E. Anderson Behavioral and Cognitive Effects of Electromagnetic Field Exposures S.A. Johnston and J.A. D'Andrea Thermoregulation in the Presence of Radio Frequency Fields D. Black Epidemiologic Studies of Extremely Low-Frequency Electromagnetic Field L. Kheifets and R. Shimkhada Epidemiological Studies of Radio Frequency Fields M. Feychting EMF Standards for Human Health E. van Deventer, D. Simunic, and M.Repacholi Electroporation J.C. Weaver and Y. Chizmadzhev Electrical Shock Trauma R.C. Lee, E. Bodnar, P. Betala, and S. Blom-Eberwein Mechanisms and Therapeutic Applications of Time-Varying and Static Magnetic Fields A.A. Pilla Therapeutic Heating Applications of Radio Frequency Energy C-K. Chou

Scalable high performance radio frequency electronics based on large domain bilayer MoS 2 .

Abstract: Atomically-thin layered molybdenum disulfide (MoS2) has attracted tremendous research attention for their potential applications in high performance DC and radio frequency electronics, especially for flexible electronics. Bilayer MoS2 is expected to have higher electron mobility and higher density of states with higher performance compared with single layer MoS2. Here, we systematically investigate the synthesis of high quality bilayer MoS2 by chemical vapor deposition on molten glass with increasing domain sizes up to 200 μm. High performance transistors with optimized high-κ dielectrics deliver ON-current of 427 μA μm−1 at 300 K and a record high ON-current of 1.52 mA μm−1 at 4.3 K. Moreover, radio frequency transistors are demonstrated with an extrinsic high cut-off frequency of 7.2 GHz and record high extrinsic maximum frequency of oscillation of 23 GHz, together with gigahertz MoS2 mixers on flexible polyimide substrate, showing the great potential for future high performance DC and high-frequency electronics. Large area two-dimensional materials show promise for applications in DC and RF flexible electronics. Here, the authors report RF transistors based on chemical vapor deposited bilayer MoS2 with 23 GHz extrinsic maximum oscillation frequency, and gigahertz mixers on flexible polyimide substrates.

Sensitive and Nonlinear Far-Field RF Energy Harvesting in Wireless Communications

Abstract: This paper studies both limited sensitivity and nonlinearity of far field RF energy harvesting observed in reality and quantifies their effect, attempting to fill a major hole in the simultaneous wireless information and power transfer (SWIPT) literature. RF harvested power is modeled as an arbitrary nonlinear, continuous, and non-decreasing function of received power, by considering limited sensitivity and saturation effects. RF harvester’s sensitivity may be several dBs worse than communications receiver’s sensitivity, potentially rendering RF information signals useless for energy harvesting purposes. Given finite number of datapoint pairs of harvested (output) power and corresponding input power, a piecewise linear approximation is applied and the statistics of the harvested power are offered, as a function of the wireless channel fading statistics. Limited number of datapoints is needed and accuracy analysis is also provided. Case studies include duty-cycled (non-continuous), as well as continuous SWIPT, comparing with industry-level, RF harvesting. The proposed approximation, even though simple, offers accurate performance for all studied metrics. On the other hand, linear models or nonlinear-unlimited sensitivity harvesting models deviate from reality, especially in the low-input-power regime. The proposed methodology can be utilized in the current and future SWIPT research.

Long-distance telecom-fiber transfer of a radio-frequency reference for radio astronomy

Abstract: Very-long-baseline interferometry (VLBI) for high-resolution astronomical imaging requires phase-stable frequency references at widely separated radio-telescope antennas. For the first time to our knowledge, we have disseminated a suitable radio-frequency (RF) reference for VLBI over a “real-world” telecom optical-fiber link between radio telescopes that are >100 km apart, by means of an innovative phase-conjugation technique. Bidirectional optical amplification is used in parallel with live traffic, and phase perturbations in the effective optical-fiber path length are compensated. This RF-over-fiber approach obviates the need for separate hydrogen masers at each antenna, offering significant advantages for radio-astronomy facilities such as the Square Kilometer Array.

Stepped-Carrier OFDM-Radar Processing Scheme to Retrieve High-Resolution Range-Velocity Profile at Low Sampling Rate

Abstract: Recent publications show that the potential of using orthogonal frequency division multiplexing waveforms as radar signals. Since the range resolution is proportional to the RF bandwidth, the major obstacle that obstructs the practical use in automotive and other low-cost radars is the requirement to sample the received signal at sampling rates that span the whole RF signal bandwidth requiring ADCs with sampling rates in the order of GHz. This paper presents a method to achieve the high range resolution induced by a large RF bandwidth, but with a much lower baseband bandwidth, consequently requiring a much slower ADC while at the same time delivering a velocity profile for each subcarrier. In addition, the processing scheme induces a range migration compensation, independent of the number of targets. This is achieved with barely increased computational effort. The scheme is verified with simulations and measurements at 77 GHz.

Fiber-coupled vapor cell for a portable Rydberg atom-based radio frequency electric field sensor.

Abstract: We demonstrate a movable, Rydberg atom-based radio frequency (RF) electric (E) field probe. The technique is based on electromagnetically induced transparency and Autler–Townes splitting. Two fibers attached to a 10 mm cubic Cs133 vapor cell are used to couple counter-propagating probe and control lasers through the cell. This all-dielectric fiber-coupled sensor can be moved from the optics table to locations more suitable for RF (gigahertz to sub-terahertz) E-field measurements and calibrations.

Revisiting Orbital Angular Momentum Beams: Fundamentals, Reflectarray Generation, and Novel Antenna Applications

Abstract: Inspired by the unique and compelling traits of orbital angular momentum (OAM) laser beams, such as the twisted wavefront and annular-shaped intensity pattern, we use this work to design antennas generating OAM beams at radio frequency (RF) and, especially, to tailor the antennas' far-field characteristics. We demonstrate that the reflectarray antenna is an efficient apparatus to generate and manipulate OAMcarrying beams at RF.

Helicon high-density plasma sources: physics and applications

Abstract: Helicon high-density (up to ~1013 cm−3) plasma sources using a radio frequency wave in the presence of a magnetic field under a low pressure are very promising for various application fields owing ...

A Radiating Near-Field Patch Rectenna for Wireless Power Transfer to Medical Implants at 2.4 GHz

Abstract: A radiating near-field method of recharging and activating medical implants using a 2.4-GHz rectifying patch antenna (rectenna) is designed and tested. Traditional near-field charging uses magnetically coupled coils, but these are highly sensitive to misalignments between the transmitter and receiver. In contrast, the proposed design employs the principles of wireless power transfer using radiating antennas. These antennas provide a misalignment-insensitive power delivery method, even when the receive antenna footprint is small (27.5 mm × 19.75 mm). A misalignment analysis is performed up to 15 cm, showing a maximum loss of 7.5 dB. As a proof-of-concept demonstration, a rectenna receiver was fabricated consisting of a patch antenna attached to a radio frequency (RF) rectifier. This integrated rectifier is a voltage quadrupling circuit that provides RF–DC rectification with efficiency of 40% at 0 dBm. For validation, a real-time actuation of a medical drug pump is demonstrated using only wirelessly transmitted power with no additional power storage elements.

Inherent Self-Interference Cancellation for In-Band Full-Duplex Single-Antenna Systems

Abstract: We propose a new analog self-interference cancellation (SIC) technique for in-band full-duplex transmission in single-antenna systems. We use an RF circulator to separate transmitted (Tx) and received (Rx) signals. Instead of estimating the SI signals and subtracting them from the Rx signals, we use the inherent secondary SI signals at the circulator, reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port. We modified the frequency response of the secondary SI signals using a reconfigurable impedance mismatched terminal (IMT) circuit, which consists of two varactor diodes at the antenna port. We can also adjust the frequency band and the bandwidth by controlling the varactor diodes bias voltages. The IMT adjustability makes it robust to antenna input impedance variations and fabrication errors. We analyze and fabricate a prototype of the proposed technique at 2.45 GHz. We achieved more than 40-dB cancellation over 65 MHz of bandwidth. Our technique is independent of the RF circulator and antenna type and it can be applied to any frequency band. It is also very relevant to small mobile devices because it provides a simple and low-power and low-cost adjustable analog SIC technique.

Compact Multiband Wireless Energy Harvesting Based Battery-Free Body Area Networks Sensor for Mobile Healthcare

Abstract: This paper demonstrates a prototype of a self-sustained body area networks (BAN) sensor, which consists of the electrically small triple-band rectenna, the direct current (dc) energy management and storage module, the microcontroller, and the sensing and communication module. The proposed antenna is composed of corrugated metal-insulator-metal plasmonic structures, which covers triple frequency bands, including GSM-900, UTMS-2100, and TD-LTE bands. Its electrical size is only ${\text{0.21}}\,\lambda \times {\text{0.2}}\,\lambda $ at 900 MHz. The gains reach 1 dBi, 2.64 dBi, and −0.19 dBi at 0.9 GHz, 2.025 GHz, and 2.36 GHz, respectively. A triple-band rectifier for low power application is designed to convert the harvested radio frequency (RF) power into dc power. The maximum RF to dc conversion efficiency of the rectifier reaches 59% when the input power is −10 dBm. The proposed compact BAN sensor based on multiband wireless energy harvesting is suitable for human body self-monitoring and mobile healthcare.

RF-Photonic Filters via On-Chip Photonic–Phononic Emit–Receive Operations

Abstract: The creation of high-performance narrow-band filters is of great interest for many radio frequency (RF) signal processing applications. To this end, numerous schemes for electronic, microelectromechanical systems-based, and microwave photonic filters have been demonstrated. Filtering schemes based on microwave photonic systems offer superior flexibility and tunability to traditional RF filters. However, these optical-based filters are typically limited to gigahertz (GHz) widths and often have large RF insertion losses, posing challenges for integration into high-fidelity RF circuits. In this paper, we demonstrate a novel type of microwave filter that combines the attractive features of microwave photonic filters with high- Q phononic signal processing using a photonic–phononic emit–receive process. Through this process, an RF signal, which is encoded on a guided optical wave, is converted into a GHz-frequency acoustic wave, where it is filtered through shaping of acoustic transfer functions before being converted back to the optical domain. In contrast to prior phononic filters that utilize gain or loss based on stimulated Brillouin scattering, optical amplification is not used to mediate signal processing. This emit–receive functionality, realized in an integrated silicon waveguide, produces megahertz-bandwidth bandpass filtering while supporting low RF insertion losses necessary for high dynamic range in a microwave photonic link. We also demonstrate record-high internal efficiency for emit–receive operations of this type, and show that the emit–receive operation is uniquely suitable for the creation of serial filter banks with minimal loss of fidelity. This photonic–phononic emitter–receiver represents a new method for low-distortion signal processing in an integrated all-silicon device.

Three-dimensional radio-frequency transformers based on a self-rolled-up membrane platform

Abstract: Radio-frequency (RF) integrated circuits are used for wireless communications and require transformers capable of transferring electrical energy at RF/microwave frequencies. Traditional on-chip RF transformer designs have complex fabrication schemes and offer limited performance scalability. Here we report on-chip RF/microwave transformers that are based on a self-rolled-up membrane platform. The monolithic nature and versatility of this platform allows us to create high-performance transformers while maintaining an ultra-compact device footprint and by using only planar processing. We also show that the performance of the three-dimensional RF transformers improves with scaling, which is in contrast to conventional planar designs. In particular, we observe a continuous rate of increase in the index of performance of our RF transformers as we scale up the turns ratio. This behaviour is attributed to the almost ideal mutual magnetic coupling inherent to the self-rolled-up membrane three-dimensional architecture.

Multistatic Scatter Radio Sensor Networks for Extended Coverage

Abstract: Scatter radio, i.e., communication by means of reflection, has been recently proposed as a viable ultra-low power solution for wireless sensor networks (WSNs). This paper offers a detailed comparison between monostatic and multistatic scatter radio architectures. In monostatic architecture, the reader consists of both the illuminating transmitter and the receiver of signals scattered back from the sensors. The multistatic architecture includes several ultra-low cost illuminating carrier emitters and a single reader. Maximum-likelihood coherent and noncoherent bit error rate (BER), diversity order, average information, and energy outage probability comparison is performed, under dyadic Nakagami fading and filling a gap in the literature. It is found that: 1) diversity order, BER, and tag location-independent performance bounds of multistatic architecture outperform monostatic; 2) energy outage due to radio frequency (RF) harvesting for passive tags, is less frequent in multistatic than monostatic architecture; and 3) multistatic coverage is higher than monostatic. Furthermore, a proof-of-concept digital multistatic scatter radio WSN with a single receiver, four low-cost emitters, and multiple ambiently-powered low-bitrate tags, perhaps the first of its kind, is experimentally demonstrated (at 13 dBm transmission power), covering an area of 3500 m2. Research findings are applicable in the industries of WSNs, RF identification, and emerging Internet-of-Things.

Radio-over-fiber using an optical antenna based on Rydberg states of atoms

Abstract: We provide an experimental demonstration of a direct fiber-optic link for RF transmission (“radio-over-fiber”) using a sensitive optical antenna based on a rubidium vapor cell. The scheme relies on measuring the transmission of laser light at an electromagnetically induced transparency resonance that involves highly excited Rydberg states. By dressing pairs of Rydberg states using microwave fields that act as local oscillators, we encoded RF signals in the optical frequency domain. The light carrying the information is linked via a virtually lossless optical fiber to a photodetector where the signal is retrieved. We demonstrate a signal bandwidth in excess of 1 MHz limited by the available coupling laser power and atomic optical density. Our sensitive, non-metallic and readily scalable optical antenna for microwaves allows extremely low-levels of optical power (∼1 μW) throughput in the fiber-optic link. It offers a promising future platform for emerging wireless network infrastructures.

Dual-Band Dual-Polarized Full-Wave Rectenna Based on Differential Field Sampling

Abstract: A dual-band rectenna for radio frequency (RF) energy harvesting is presented in this letter. The proposed antenna has two concentric square patches electrically connected with a small microstrip line connection. Four ports are located in the inner patch. The configuration of the ports enables a differential field sampling scheme and dual polarization. The antenna operates for the WiFi frequency bands of 2.4 and 5.5 GHz with 7.52 and 7.26 dBi gain, respectively, for each frequency. A full-wave Greinacher voltage doubler rectifier for each polarization has been employed for RF-to-dc conversion. The proposed novel topology utilizes the differential field sampling for each polarization and quadruples the overall output voltage by the rectification process. The differential output voltage source from the rectenna can directly act as a power source as typically electronics require differential source for their operation.

Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit–Receive Systems

Abstract: This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary TX chain to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low-noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation learning rule, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear PA with memory, finite passive isolation, and a nonlinear LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the LNA input, even at very high transmit power levels and with wide transmission bandwidths. Such a novel cancellation solution can, therefore, substantially improve the TX–RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.