Radio Frequency Input Research Articles

Multiband asymmetric radio frequency to direct current converter circuit for wireless power transfer

AbstractThis article presents the multiband asymmetric radio frequency (RF) to direct current (DC) converter circuit for the wireless power transfer (WPT) applications. The proposed circuit is composed of a power divider, novel asymmetric multiband matching circuit and RF Schottky diode quadrupler voltage rectifier circuit. Unlike the conventional narrow band quadrupler using two Greinacher cells with opposite polarities, the proposed circuit aims to cover the multifrequency bands, which are the cell phone 1.8–2.1 GHz, the industrial, scientific, and medical (ISM) bands 2.4–2.5 GHz and 5.725–5.875 GHz. The interested RF input power range of −10 to 20 dBm for the WPT application is focused. The measured RF‐to‐DC conversion efficiency (η) of 50–65% at 1.8–2.1 GHz, 65% at 2.45 GHz and 16% at 5.8 GHz are obtained at 10 dBm optimal input power.

Electron population properties with different energies in a helicon plasma source

The characteristics of electrons play a dominant role in determining the ionization and acceleration processes of plasmas. Compared with electrostatic diagnostics, the optical method is independent of the radio frequency (RF) noise, magnetic field, and electric field. In this paper, an optical emission spectroscope was used to determine the plasma emission spectra, electron excitation energy population distributions (EEEPDs), growth rates of low-energy and high-energy electrons, and their intensity jumps with input powers. The 56 emission lines with the highest signal-to-noise ratio and their corresponding electron excitation energy were used for the translation of the spectrum into EEEPD. One discrete EEEPD has two clear different regions, namely the low-energy electron excitation region (neutral lines with threshold energy of 13–15 eV) and the high-energy electron excitation region (ionic lines with threshold energy ≥19 eV). The EEEPD variations with different diameters of discharge tubes (20 mm, 40 mm, and 60 mm) and different input RF powers (200–1800 W) were investigated. By normalized intensity comparison of the ionic and neutral lines, the growth rate of the ionic population was higher than the neutral one, especially when the tube diameter was less than 40 mm and the input power was higher than 1000 W. Moreover, we found that the intensities of low-energy electrons and high-energy electrons jump at different input powers from inductively coupled (H) mode to helicon (W) mode; therefore, the determination of W mode needs to be carefully considered.

Investigation Into Self Actuation Limitation and Current Carrying Capacity of Chalcogenide Phase Change GeTe-Based RF Switches

This article reports investigation of self-actuation in phase change material (PCM) germanium telluride (GeTe)-based radio frequency (RF) switches as a limitation to RF power handling. PCM switches are fabricated in-house with multiple design dimensions for evaluation and testing under various RF power levels. RF power handling capability and maximum dc current carrying capacity in the ON-state of the switches is studied for four different device layouts. Self-actuation in the OFF-state is reported at varying input RF power and dc voltage levels. A tradeoff between RF power handling capacity and device performance is discussed, establishing a correlation between design parameters and the power handling. The improved PCM switches exhibit a record high continuous wave (CW) RF power handling capability ranging from +35.5 to +39.2 dBm.

Plasma-based isotropic etching polishing of synthetic quartz

Abstract To efficiently eliminate the surface defects and subsurface damage layer of synthetic quartz introduced by grinding, a plasma-based isotropic etching polishing (plasma-IEP) technique is proposed in this study. The smoothing of synthetic quartz by plasma-IEP is attributed to the formation, overlapping and merging of numerous and ultra-smooth etch pits formed by isotropic etching of SiO2 using inductively coupled plasma. Plasma diagnostics have revealed the existence of large amounts of etching radicals. The input radio frequency power and CF4 flow rate have been proved to be the two determinant factors of the material removal rate (MRR) of plasma-IEP. Under the optimized conditions, a maximum MRR of 5.62 μm/min of a 2-inch wafer has been achieved which is much higher than that of the conventional CMP process. After plasma-IEP for 30 min, the Sa roughness of the ground synthetic quartz decreases from 270.6 nm to 17.4 nm and the inner surface of the isotropic etch pits is smooth at the atomic level. The results presented in this paper demonstrate that plasma-IEP is a promising approach for the highly efficient and damage-free semi-finishing of synthetic quartz.

MPPT integrated DC–DC boost converter for RF energy harvester

This study proposes a design of a maximum power point tracking (MPPT)-based DC–DC boost converter for an radio frequency (RF) energy harvester. The MPPT technique has been implemented in the converter using an adaptable load tracking mechanism with variable input RF power to meet the supply voltage tolerance limits. The proposed MPPT scheme is implemented using a sample-and-hold circuit in the tracking loop of the DC–DC boost converter. The complete energy harvester system prototype has been realised in a 130 nm standard complementary metal-oxide-semiconductor (CMOS) process. The footprint of the proposed converter circuit is much smaller compared to similar designs reported in the literature making it applicable for wearable and implantable biomedical applications.

A 35‐GHz high image rejection resistive mixer using a tunable resonator and a narrowband bandpass filter

AbstractA 35‐GHz high image rejection resistive mixer (IRM) is implemented using a tunable resonator and a narrowband bandpass filter (BPF). To obtain a high image rejection ratio (IRR) of more than 40 dB, a tunable resonator, which consists of inductive lines and varactors, is integrated inside a mixer. It can not only mitigate the mismatch of the resonating frequency through process variation and the parasitic effect but also be used as a radio frequency input matching circuit. A narrowband BPF based on coupled slow‐wave resonators is inserted before a mixer. The proposed IRM is fabricated by a commercial 0.15 μm gallium arsenide (GaAs) pseudo high electron mobility transistor (pHEMT) monolithic microwave integrated circuit process. The proposed IRM represents 42.2 dB IRR, a conversion loss of 11.6 dB, an input 1‐dB compression point (P−1dB) of more than 8 dBm, and a 35 dB local oscillator‐radio frequency isolation at 35 GHz.

Compact Dual-Band Rectenna Based on Dual-Mode Metal-Rimmed Antenna

This paper proposes the design of a dual-band integrated rectenna. The rectenna has compact size of 0.4 × 0.3 × 0.25 cm3 and operates at 925 MHz and 2450 MHz bands. In general, the rectenna consists of two main parts, the metal-rimmed dual-band antenna used for harvesting the radio frequency (RF) signals from the environment and the rectifier circuit to convert these receiving powers to the direct current (DC). Because of the dual resonant structure of the antenna, the rectifier circuit can be optimized in terms of size and the frequency bandwidth, while the conversion efficiencies are always obtained 60% at the RF input power −2.5 dBm and −1 dBm for the lower band and the higher band, respectively. Measured results show that the metal-rimmed antenna exhibits −10 dB reflection coefficient in both desired frequency bands. Moreover, the antenna achieves 47% and 89% of total efficiency respectively at 925 MHz and 2450 MHz, which confirms that the proposed rectenna is well applicable in most of the miniaturized wireless sensor networks and IoT systems.

Low-Frequency Nonresonant Rectification in Spin Diodes

Spin-diodes are usually resonant in nature (GHz frequency) and tuneable by magnetic field and bias current with performances, in terms of sensitivity and minimum detectable power, overcoming the semiconductor counterpart, i.e. Schottky diodes. Recently, spin diodes characterized by a low frequency detection (MHz frequency) have been proposed. Here, we show a strategy to design low frequency detectors based on magnetic tunnel junctions having the interfacial perpendicular anisotropy of the same order of the demagnetizing field out-of-plane component. Micromagnetic calculations show that to reach this detection regime a threshold input power has to be overcome and the phase shift between the oscillation magnetoresistive signal and the input radiofrequency current plays the key role in determining the value of the rectification voltage.

Beam Plasma Characteristics of a Helicon Plasma Source Measured by a Spatially Resolved Optical Emission Spectroscope

Beam plasma directly forms the thrust of single-stage helicon plasma thrusters and its properties are the input parameters of the two-stage helicon thruster. Therefore, the spatial distribution of the beam plasma is vital for both single-stage and two-stage helicon thrusters. Using an optical emission spectroscope with a radial resolution of 5 mm, the spatial distribution of the beam plasma parameters and its variation with different input radio frequency (RF) powers (100–1000 W) and diameters of the discharge tube (20–60 mm) was investigated. Results show that the electron density decreases with both axial and radial distances, but the electron temperature remains nearly constant. The electron density increases with increasing input RF powers because of an increase of power deposition when the electron temperature remains constant. The radial profiles of electron density are flat, and the maximum electron densities located in the center line decrease with increasing diameters of the discharge tube, which is due to the decrease in the power density.

Sub-Nyquist Ultra-Wideband Sparse Signal Reception via Variable Frequency Comb

We demonstrate a new class of ultra-wideband (UWB) sparse radio frequency (RF) signal receiver relying on direct sub-sampling in frequency domain and compressive sensing (CS) techniques. The sampling process is realized with a hybrid RF-photonic architecture for discrete Fourier transform (DFT) on broadband RF signals using a variable-pitch frequency comb. Sub-sampled DFT coefficients are used to recover the input RF signal which is sparse in a chosen domain. Instead of digitizing signals with a full-rate analog to digital converter (ADC), the new approach requires sub-rate quantization, reducing hardware complexity via sub-sampling in frequency domain. Both simulated and experimental verifications were achieved by high-fidelity reception of various sparse signals within 3 GHz to 7.9 GHz band.

Radio-frequency-to-optical conversion using acoustic and optical whispering-gallery modes

Whispering gallery modes (WGMs), circulating modes near the surface of a spheroidal material, have been known to exhibit high quality factors for both acoustic and electromagnetic waves. Here, we report an electro-optomechanical system, where the overlapping WGMs of acoustic and optical waves along the equator of a dielectric sphere strongly couple to each other. The triple-resonance phase-matching condition provides a large enhancement of the Brillouin scattering only in a single sideband, and conversion from the input radio-frequency signal exciting the acoustic mode to the output optical signal is observed.

Sub-nanosecond-speed frequency-reconfigurable photonic radio frequency switch using a silicon modulator

Radio frequency (RF) switches are essential for implementing routing of RF signals. However, the increasing demand for RF signal frequency and bandwidth is posing a challenge of switching speed to the conventional solutions, i.e., the capability of operating at a sub-nanosecond speed or faster. In addition, signal frequency reconfigurability is also a desirable feature to facilitate new innovations of flexible system functions. Utilizing microwave photonics as an alternative path, we present here a photonic implementation of an RF switch providing not only the capability of switching at a sub-nanosecond speed but also options of frequency doubling of the input RF signals, allowing for flexible output waveforms. The core device is a traveling-wave silicon modulator with a device size of 0.2 mm × 1.8 mm and a modulation bandwidth of 10 GHz. Using microwave frequencies, i.e., 15 GHz and 20 GHz, as two simultaneous RF input signals, we experimentally demonstrated their amplitude and frequency switching as well as that of the doubled frequencies, i.e., 30 GHz and 40 GHz, at a switching frequency of 5 GHz. The results of this work point to a solution for creating high-speed RF switches with high compactness and flexibility.

Switched Capacitor Based High Bandwidth Envelope Tracking Power Supply

The envelope tracking (ET) power supply can output a variable voltage which tracks the envelope of the radio frequency input signal to the power amplifier (PA), and the system efficiency can be significantly improved. To achieve a high tracking bandwidth, the switching frequency of the ET power supply is usually too high. The pulse edge independent distribution (PEID) method has been proposed to reduce the switching frequency to 1/n (n ϵ N) of the tracking bandwidth, but a large number of isolated voltage sources are needed, leading to increased power stage and system complexity. In this letter, a switched capacitor based high bandwidth ET power supply is proposed, which employs optimized charging topologies and mechanisms to stabilize the voltages across the switched capacitors, and thus they can fully replace the isolated voltage sources. Since the proposed configuration is derived from the PEID method, all the features of PEID method are retained. A prototype with 6-26-V output voltage and 20-W peak output power is fabricated and tested with a 1-MHz sine wave and a 5-MHz bandwidth communication envelope. The experimental results validate the proposed configuration.

Dynamic range improvement of six-port receiver through analysis of output DC offset

In this paper, we improved the error vector magnitude (EVM) performance of six-port receiver using a low noise amplifier (LNA) bias control algorithm based on analyzing the correlation between normalized output DC offset voltage and EVM relative to input radio frequency (RF) power variation. In contrast to the other works published in the literature, we consider test setup through which the software impairments of six-port receiver blocks are considered. Therefore, in this work to substantiate the EVM improvement, a designed 26–30 GHz CMOS six-port receiver is used which consists of LNA, coupled line bandpass filter, six-port correlator, diode power detectors and two instrumentation amplifiers for recovering the baseband I/Q data. The EVM improvement process is assessed in terms of 64QAM modulation, and according to obtained results, EVM is reduced from 61% when using constant DC bias to 22% achieved with an LNA bias control algorithm for low input power (− 60 dBm) at the center frequency of 28 GHz. Moreover, the EVM is become less sensitive to input RF power, and also the dynamic range is improved more than 20 dB.

Design and Experimental Measurement of Input and Output Couplers for a 6–18-GHz High-Power Helix Traveling Wave Tube Amplifier

In this article, two types of compact and effective input and output couplers for a 6–18 GHz 5-kW-level helix traveling wave tube (TWT) are designed, fabricated, and cold- tested. The input coupler section includes an impedance transformer, a conical coaxial window, and a transition to a subminiature version A (SMA) connector for a radio frequency (RF) input. For achieving a high-power output, a new type of double-ridged waveguide window is used in the output coupling section. The output coupling structure consists of a standard double-ridged waveguide (WRD650), an impedance transformer, a square sapphire window, and a coaxial to double-ridged waveguide transition. The commercially available 3-D electromagnetic simulation software package CST is used to further optimize these structures, including couplers terminated with an actual complex helix slow-wave structure (SWS). According to the simulation results, the input and output couplers are fabricated and tested. The experimental results of the optimized coupled structures are presented, and both couplers show excellent transmission performance for a 6–18-GHz high-power helix TWT.

Frequency-Domain Analysis of Single-Surface Multipactor Discharge With Single- and Dual-Tone RF Electric Fields

This article presents the frequency-domain analysis of multipactor discharge on a single dielectric surface. We employ the multiparticle Monte Carlo simulation model in one dimension with adaptive time steps to obtain the temporal profiles of the normal electric field, which is due to surface charging that corresponds to the multipactor strength, induced by single- or dual-tone radio frequency (RF) electric fields acting parallel to the surface. We apply a discrete Fourier transform (DFT) to obtain the amplitude spectrum of the normal electric fields. It is found that for the single-tone RF operation, the normal electric field consists of pronounced even harmonics of the driving RF frequency. The strength of a harmonic component in the normal electric field depends on its frequency and the incident RF amplitude. An empirical relation between the strength and frequency of the harmonics and the input RF amplitude has been proposed. For dual-tone RF operation, spectral peaks are observed in the amplitude spectrum of the normal electric field at various frequencies of intermodulation product of the RF carrier frequencies. Pronounced peaks are observed at the sum and difference frequencies of the carrier frequencies, at multiples of those frequencies, and at multiples of the carrier frequencies. Empirical relations between the heights of different spectral peaks and the input RF amplitudes have been proposed.

Tunable Matching Networks Based on Phase-Switched Impedance Modulation1

The ability to provide accurate, rapid, and dynamically controlled impedance matching offers significant advantages to a wide range of present and emerging radio-frequency (RF) power applications. This article develops a new type of tunable matching network (TMN) that enables a combination of much faster and more accurate impedance matching than is available with conventional techniques and is suitable for use at high power levels. This implementation is based on a narrow-band technique, termed here phase-switched impedance modulation (PSIM), which entails the switching of passive elements at the RF operating frequency, effectively modulating their impedances. The proposed approach provides absorption of device parasitics and zero-voltage switching (ZVS) of the active devices, and we introduce control techniques that enable ZVS operation to be maintained across operating conditions. A prototype PSIM-based TMN is developed that provides a 50-Ω match over a load impedance range suitable for inductively coupled plasma processes. The prototype TMN operates at frequencies centered around 13.56 MHz at input RF power levels of up to 200 W.

Angling for angles

Researchers from Australia have presented their novel technique to estimate incoming radio-frequency (RF) signal angles of arrival (AOA), irrespective of the RF signal amplitude. Experimental results show that the AOA measurement can be achieved between 0°–63° with less than 3° of errors for a 15 GHz signal at varying power levels. Identifying the location of an object is extremely important for a number of different applications, including navigation, wireless communication and electronic warfare. The process of identifying an object involves a transmitter, for example a mobile phone or a radar unit, that transmits an RF signal, and a detector device to measure the RF signal. The RF signal reflects off an object and towards the detector. The detector unit can identify the difference in time or phase for the arriving RF signal to when it was transmitted – the angle of arrival. The AOA can then be used to identify the object's location. Chan (left) and Chen (right), authors of the published submission. Correlation between estimated (Y) and actual (X) AOA. The deviation above 60° can clearly be seen. Schematic of the proposed system. Using microwave photonics, the AOA of high-frequency RF signals can be determined, with a reduction in electromagnetic interference as well as system size, weight and power consumption. There are drawbacks to using microwave photonics, however, in that a calibration process involving measuring either system output power at a 0° AOA, or measuring the incoming RF signal amplitude, is necessary to eliminate the RF signal amplitude dependence in the system output prior to measuring the AOA. The work of Chan and Chen is useful because it allows for a measurement of the AOA without the need for measuring the incoming RF signal amplitude, simplifying the process. The new technique works by using a continuously laser-generated wave of light, which is split equally between two modules. Each module comprises one dual-drive Mach Zehnder modulator, an optical bandpass filter and a photodetector. After some phase shifting, the photodetectors eventually generate two DC photocurrents, which can be used to calculate a K value which is a function of the RF signal phase difference. K can then be used to derive the AOA without the need for information about the input RF signal amplitude. Further experiments were carried out using the system. An RF signal of 15 GHz was generated by a microwave signal generator, producing two RF signals with 3.2 dBm power level after the initial splitting between the two modules. It was found that the methodology performed well when the actual AOA was between 0° and ∼60°. The experiment was also repeated with different signal powers of −0.3 dBm and −3.6 dBm, with accurate results being obtained, proving that the AOA can be estimated independent of the RF signal amplitude. With a larger optical carrier suppression, it should be possible to accurately measure the RF signal AOA beyond 60°.

A High-Efficiency and Wide-Input Range RF Energy Harvester Using Multiple Rectenna and Adaptive Matching

In this paper, a Radio Frequency (RF) energy harvester (EH) system for Internet of Things (IoT)-related applications is presented. The proposed EH architecture operates at 5.2 GHz band and utilizes multiple rectenna. This approach enhances the efficiency of the whole system over a wide dynamic RF input range. In the presented circuit, configuration of the rectenna is controlled by Field-Programmable Gate Array (FPGA) with respect to the input power level of the received RF input signal. In addition, an automatic adaptive matching based on the configuration of the rectenna, level of the received signal, and load current adjusts the matching network. The rectenna is realized through the Radio Frequency-Direct Current (RF-DC) converter composed of two Schottky diodes and generates the output DC voltage. Finally, a buck-boost converter provides the flattened and fixed voltage for the IoT and wearable devices. The 5.2 GHz band reconfigurable system demonstrates 67% high efficiency and 6.1 V output DC voltage where the power level of RF input is +20 dBm. The main application of the proposed structure is for charging wearable smart devices such as a smart watch and bracelet.

An X‐band high‐efficiency GaN load modulated balanced amplifier MMIC

AbstractAn X‐band high‐efficiency GaN load modulated balanced amplifier monolithic microwave integrated circuit (MMIC) composed of 90° Lange Couplers at radio frequency (RF) input and output, a pair of balanced power amplifier (BPA) and a control signal (CS) PA is presented in this article. The impedance of the BPA is modulated by varying the amplitude and phase of the injected CS at same frequency. The prototype has a peak continuous wave output power of 42.5 dBm, with efficiency of 45% to 55% at peak power and 40% to 45% at 6 dB output back‐off over 8 to 11 GHz. The average efficiency for the 37.2 dBm output power is 40%, with adjacent channel leakage ratio of −32 dBc without digital predistortion at 10 GHz center frequency.