Radio Frequency Phase Research Articles

High-Order Electrical Spectrum Method for Measuring the Chirp of a Silicon Mach–Zehnder Modulator

The chirp parameter of a silicon optical modulator (SOM) is difficult to measure precisely because the plasma dispersion effect is due to electro-refraction and electro-absorption occurring simultaneously. A novel method for measuring the chirp parameter of a SOM is presented, which is adopted from the beat-frequency method. Firstly, based on the model of the differential driver silicon Mach-Zehnder modulator(DDSMZM), the chirp parameter of the DDSMZM is presented by mathematical derivations, and we prove that achieving the multi-order coefficients of the radio frequency phase shift is a key point for characterizing the chirp accurately. In the proposed method, a wavelength tunable laser, as a local source, is applied to mix with the chirped modulated optical signal of the DDSMZM. In this way, the multi-order electric signals of beat frequency are mapped from high-frequency to low-frequency. Meanwhile, a balanced detector with a low-speed trans-impedance amplifier(TIA) is employed for realizing photo-electric conversion, which can improve the signal-to-noise ratio of the measurement. Finally, we have examined the chirp parameter of the DDSMZM in the case of low-frequency and high-frequency modulation signal condition and the results show the beat-frequency method has a higher frequency resolution and measurement accuracy for measuring the chirp parameter of the DDSMZM compared with the optical spectrum analysis(OSA) method and the optical heterodyne method.

Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment.

Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.

Nonlinear geometric phase shifting in optically generated gigahertz radio frequency signals for microwave photonics

We present a method for predicting the geometric phase introduced by wave plates and a polarizer, wherein mathematical formulas to calculate the phase using the Mueller formalism are visualized as a triangle on the surface of the Poincare sphere. These constructions are used to describe a simple experiment with a birefringent medium in a Mach–Zehnder interferometer and polariscopic setup. A geometric radio frequency (RF) phase shifter for controlling the geometric phase introduced by the birefringent medium is also presented. The RF phase generated from orthogonally polarized light signals was shifted from 0 deg to 360 deg; this phase shift exhibited nonlinear characteristics. Thus, the proposed phase-shifter device improves phase control sensitivity in the partial region.

Radiofrequency phase resolved electron density measurements with the hairpin resonator probe

A floating hairpin resonator probe is used to measure electron density within the radiofrequency cycle of a parallel plate capacitively coupled plasma at steady state. A time resolution capable of detecting electron density oscillations within the radiofrequency cycle is demonstrated. Electron density oscillations are observed at the drive frequency over a range of operating conditions including 10–250 mTorr (1.3–33 Pa) in argon driven at 13.56 or 27.12 MHz. Localized electron density oscillation amplitudes show moderate agreement with literature and fluid simulations near the powered electrode and disagreement in the plasma bulk. The technique is useful for studying electron heating mechanisms in radiofrequency discharges due to its high time resolution.

Compressive Sensing Based Channel Estimation for Millimeter-Wave Full-Dimensional MIMO With Lens-Array

Channel estimation (CE) for millimeter-wave (mmWave) lens-array suffers from prohibitive training overhead, whereas the state-of-the-art solutions require an extra complicated radio frequency phase shift network. By contrast, lens-array using antenna switching network (ASN) simplifies the hardware, but the associated CE is a challenging task due to the constraint imposed by ASN. This paper proposes a compressive sensing (CS)-based CE solution for full-dimensional (FD) lens-array, where the mmWave channel sparsity is exploited. Specifically, we first propose an approach of pilot training under the more severe haraware constraint imposed by ASN, and formulate the associated CE of lens-array as a CS problem. Then, a redundant dictionary is tailored for FD lens-array to combat the power leakage caused by the continuous angles of multipath components. Further, we design the baseband pilot signals to minimize the total mutual coherence of the measurement matrix based on CS theory for more reliable CE performance. Our solution provides a framework for applying CS techniques to lens-array using simple and practical ASN. Simulation results demonstrate the effectiveness of the proposed scheme.

Broadly tunable and low power penalty radio frequency phase shifter using a coupled silicon microcavity.

We present a continuously tunable silicon photonics assisted radio frequency (RF) phase shifter using a coupled microring resonator. Using the coupled cavity, we demonstrate a sub-1 dB power penalty for a RF bandwidth of 34.5 GHz (9-43.5 GHz) and a phase shift of π over the reported frequency range. Rigorous optimization of the cavity design using the coupled-mode theory is carried out to realize ultranarrow resonance peaks with a low-extinction ratio and large phase shift. Thermal tuning of the cavity is used to tune the phase while all-optical tuning is exploited to achieve broadband operation. We present a detailed simulation and experimental study of the proposed configuration. The proposed device configuration exhibits a configurable resonance linewidth and extinction ratio that allows for a broad bandwidth and an extremely low power penalty microwave phase shifter. We believe the demonstration would allow better integration of the on-chip functional elements of integrated microwave photonics.

Simulation of RF Noise Propagation to Relativistic Electron Beam Properties in a Linear Accelerator

The control system of the superconducting electron linear accelerator ELBE is planned to be upgraded by a beam-based feedback. As the design of the feedback algorithm enters its preliminary stage, the problem of analyzing the contribution of various disturbances to the development of the electron beam instabilities becomes highly relevant. In this paper we exploit the radio frequency (RF) phase and amplitude noise data measured at ELBE to create a behavioral model in Simulink. By modeling the interaction between a RF electromagnetic field and an electron bunch traversing a bunch compressor we analyze how the addition of RF noise impacts the electron beam properties, such as energy, duration and arrival time.

Active cancellation of power supply ripple effects in continuous wave superconducting radio frequency cavities

Digital low-level radio-frequency (LLRF) systems are used at the compact energy recovery linac (cERL) test facility to stabilize the accelerating field inside the radio frequency (RF) cavities. Proportional and integral feedback controllers are implemented in the LLRF system to suppress the various disturbances in the cavities. At cERL, the typical disturbances include microphonics detuning and high-voltage power supply (HVPS) ripples. These two types of disturbances are reflected in the sum of sinusoidal fluctuations in the RF phase. Recently, a real-time narrow-band active noise control (ANC) approach which aims to reject the microphonics detuning of less than several dozen Hz, was proved to be effective in cavity resonance control. We extend this ANC method to the LLRF field control to suppress the RF ripples caused by the HVPS. In this paper, we present our experience of applying the ANC algorithm to the LLRF system of the cERL facility at KEK. We confirmed that high frequency ripples of up to 20 kHz can be well compensated by the ANC method during the cERL beam-commissioning.

Miniaturized DC–60 GHz RF PCM GeTe-Based Monolithically Integrated Redundancy Switch Matrix Using T-Type Switching Unit Cells

This article presents an approach to monolithically implement radio-frequency (RF) phase change material (PCM) germanium telluride (GeTe) T-type switch as a switching unit cell for millimeter-wave (mmWave) redundancy switch matrix applications. The miniature T-type switch demonstrates three states of operation, including one crossover state and two turn states. A seven-layer microfabrication process, including an additional conductive layer to reduce the $RC$ time constant due to the bias network routing, is developed and optimized to fabricate the multiport RF devices. A $4 \times 6$ PCM-based redundancy switch matrix is developed by monolithically integrating four T-type switches in the cascade configuration. Thermal crosstalk in PCM switches is experimentally investigated using submicrometer spatial resolution transient thermal imaging. The presented T-type switch has the device periphery of 0.55 mm $\times \,\,0.55$ mm, while the overall integrated PCM redundancy switch matrix is fabricated with a device footprint of 0.88 mm $\times \,\,1.1$ mm. The measured results of the T-type switches demonstrate an excellent RF performance with lower than 1.6 dB insertion loss, better than 20 dB return loss, and higher than 20 dB isolation in all states from dc–67 GHz. The redundancy switch matrix exhibits an insertion loss less than 3 dB, return loss better than 14 dB, and isolation higher than 20 dB from dc–60 GHz. To the best of our knowledge, this is the first implementation of a PCM-based redundancy switch matrix.

Optically Controlled RF Phase Shifts in SOAs by Adding the XGM Response of an Optical Signal

This study focuses on the possibility to achieve optical control of the radiofrequency (RF) phase shifting in semiconductor optical amplifiers (SOA). Based on the addition of the cross-gain modulation response (XGM) of a CW signal at an SOA output, the phase shift can be independently controlled from the operating conditions of the SOA (optical input power and bias current) by varying the external CW power. The impact of the XGM response of the amplified spontaneous emission (ASE) on the signal relative phase shift has also been studied. Small-signal analysis is developed and a numerical calculation is used to analyze the controllable RF phase shift. The measurement results for several control signal powers are given.

A Platform for 4-Channel Parallel Transmission MRI at 3 T: Demonstration of Reduced Radiofrequency Heating in a Test Object Containing an Implanted Wire

To describe a platform for 4-channel parallel transmission (pTx) integrated on a 3 T MRI system; to demonstrate utility of the platform with a pTx method to reduce localized radiofrequency (RF) heating during MRI of a test object implanted with an electrically conductive wire; and to compare the pTx results with those from a standard birdcage (BC) head coil. A 4-channel pTx system with independent amplitude and phase control was added to a Siemens Prisma MRI system. Turbo spin echo pTx MRI of a homogenous tissue-mimicking head phantom, including an implanted wire to simulate a deep brain stimulation (DBS) electrode, was performed in (a) circular-polarized “quadrature” transmission mode to demonstrate localized RF heating effects, and (b) an optimized RF shim “suppression” mode to counteract RF heating at the tip of the implanted wire. Signal-to-noise ratio (SNR) and temperature results from the pTx experiment were compared with imaging using a Siemens BC head coil. The pTx platform provided effective control of RF amplitude and phase to minimize localized RF heating at the wire tip. No temperature elevation was detected for pTx in suppression mode, whereas maximum increases of 6.9 °C and 2.7 °C were observed for pTx quadrature mode and imaging using the BC head coil, respectively. The platform has been adapted to a Siemens MRI system without impacting the standard RF transmission pathway, while providing accurate RF signal modulation. Demonstration of the platform showed substantial reduction of localized RF heating in a simulated DBS implant without significant SNR loss.

A Silicon Photonic RF Phase Shifter With Linear Phase Response and Low RF Power Variation

We propose and experimentally demonstrate a microwave photonic phase shifter based on a tunable silicon photonic interleaver. This device consists of a microring resonator, a tunable interleaver, and a $2\,\times \,1$ multimode interferometer (MMI). By thermally tuning the interleaver, a linear phase shift of 188° is realized with a linearity of 0.08 and a radio-frequency (RF) power variation within 1 dB for a 40-GHz signal.

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

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.

Radiofrequency phase encoded half-pulses in simultaneous multislice ultrashort echo time imaging.

To describe a simultaneous multislice (SMS) ultrashort echo time (UTE) imaging method using radiofrequency phase encoded half-pulses in combination with power independent of number of slices (PINS) inversion recovery (IR) pulses to generate multiple-slice images with short T2 * contrasts in less than 3 min with close to an eightfold acceleration compared with a standard 2D approach. Radiofrequency phase encoding is applied in an SMS (NSMS = 4) excitation scheme using "sinc" half-pulses. With the use of coil sensitivity encoding (SENSE) and controlled aliasing in parallel imaging (CAIPI) in combination with a gradient echo 2D spiral readout trajectory and IR PINS pulses for contrast enhancement a fast UTE sequence is developed. Images are obtained using a model-based reconstruction method. Sequence details and performance tests on phantoms as well as the heads of healthy volunteers at 3T are presented. An SMS UTE sequence with an undersampling factor of 4 is developed using radiofrequency phase encoded half-pulses and PINS IR pulses which enables the acquisition of 8 slices at 0.862 mm2 resolution in less than 3-min scan time. UTE images of the head are obtained showing highlighted signal of cortical bone. Image quality and T2 contrast are comparable to the one obtained by corresponding single slice acquisitions with only minor deviations. The method combining radiofrequency phase encoded SMS half-pulses and PINS IR pulses presents a suitable approach to SMS UTE imaging. The usage of coil sensitivity information and increased sampling density by means of interleaved slice group acquisitions allows to reduce the total scan time by a factor close to 8.

Performance Analysis of Directional Modulation With Finite-Quantized RF Phase Shifters in Analog Beamforming Structure

The radio frequency (RF) phase shifter with finite quantization bits in analog beamforming (AB) structure forms quantization error (QE) and causes a performance loss of received signal to interference plus noise ratio (SINR) at the receiver (called Bob). By using the law of large numbers in probability theory, the closed-form expression of SINR performance loss is derived to be inversely proportional to the square of sinc (or sin(x)/x) function. Here, a phase alignment method is applied in directional modulation transmitter with AB structure. Also, the secrecy rate (SR) expression is derived with QE. From numerical simulation results, we find that the SINR performance loss gradually decreases as the number L of quantization bits increases. This loss is less than 0.3dB when L is larger than or equal to 3. As L exceeds 5, the SINR performance loss at Bob can be approximately trivial. Similarly, SR performance loss gradually reduces as L increases. In particular, the SR performance loss is about 0.1 bits/s/Hz for L=3 at signal-to-noise ratio of 15dB.

Phase-Aware Directional Energy Transmission Algorithm in Multiple Directional RF Energy Source Environments

Radio frequency (RF) energy harvesting technique has received high attention as a promising technology for Internet of Things (IoT) based industrial systems due to its flexibility of energy supply. When multiple IoT gateways are used as directional RF energy sources, the direction and phase of RF energy transmissions influence the RF energy transmission efficiency. In this paper, we propose a phase-aware directional energy transmission algorithm (PA-DETA) where directional RF energy sources (e.g., IoT gateways) are connected to a controller and their operation parameters (i.e., RF energy transmission direction and initial phase) are decided by the controller to maximize the total harvested energy while maintaining the energy consumption in RF energy sources and the number of discarded packets due to energy depletion of harvesting nodes below certain levels. To optimize the performance of PA-DETA, we formulate a constraint Markov decision process and the optimal policy on the direction and initial phase of RF energy transmissions is obtained by a linear programming. Evaluation results demonstrate that PA-DETA with the optimal policy outperforms the comparison schemes in terms of the total harvested energy, the energy consumption in RF energy sources, and the packet discard rate.

A Broadband Phased-Array Antenna System Employing Frequency-Upconverted Local Signals With Phase Difference

This paper proposes a novel configuration for a phased-array antenna system (PAS) that achieves ultrabroadband transmission using millimeter-wave (mm-wave) and quasi-mm-wave. Since a PAS is expected to employ an unprecedented number of antenna elements to compensate for propagation loss in high-frequency bands, the configuration must be compact and cost effective. A PAS that employs radio frequency (RF) phase shifters to control the phase of RF carriers is a promising approach for broadband transmission because it needs to control only the phase of a continuous wave signal and not that of the broadband signal. In the proposed configuration, direct digital synthesizers (DDSs) are employed to generate phase-controlled local signals with a lower frequency than the carrier frequency. The signal is upconverted to an RF carrier frequency. More specifically, a formed beam using RF radiated signals with mm-wave or quasi-mm-wave is steered by the DDS in a precise phase-controlled manner. To confirm the feasibility of the configuration, a four-branch PAS transmitter is configured and tested in a 28-GHz operating band. The results verify that the proposed configuration is applicable to a PAS that operates in a broadband at high frequency.

Gibbs-Phenomenon-Reduced Digital PWM for Power Amplifiers Using Pulse Modulation

The pulse-modulated polar transmitter (PMPT) uses radio-frequency (RF) phase modulated signal with pulse-width modulated envelope to drive a power amplifier (PA) as a switch to achieve high linearity and high efficiency. However, as the signal bandwidth increases, various non-idealities limit the performance of the PMPT architecture. In this paper, a Gibbs-phenomenon reduction filter is proposed with a partial Fourier series of digital pulse-width modulation (PWM) such that the pulsed signal is more immune to the distortion in nonlinear high-efficiency RF PAs. For validation, a prototype transmitter was tested with a 20-MHz bandwidth 256-QAM 5G new radio (NR) signal at 2.14 GHz. The proposed method achieved a drain efficiency of 28.3%, error vector magnitude (EVM) of 1.67%, and adjacent channel leakage ratio (ACLR) of -45.4 dBc at an output power of 18 dBm using the prototype transmitter. Linearity requirements for base stations were met without the use of any digital predistortion methods.

Filterless frequency octupling circuit using dual stage cascaded polarization modulators

ABSTRACTThis paper demonstrates the photonic generation of millimetre-wave carriers by frequency octupling of a radio frequency (RF) carrier using a circuit with two parallel arms each containing two polarization modulators in series. The low RF drive power required and the absence of optical filters make this architecture suitable for generating highly stable and tunable optical millimetre-waves. A transfer function representation is used to analyse the operation and a simulation using Virtual Photonic Inc. software package is presented as a proof of concept. The simulation results show very high unwanted optical and electrical side harmonic suppression ratio for a wide range of modulation index compared to the prior art. Further, considering the practical scenario, operating tolerance against the imbalances in the key parameters is established. The unwanted RF sidebands are more than 19 dB and 30 dB below the desired signal power even when a deviation of ±3° is considered in individual RF phase and polarizer angle respectively.

Tunable Silicon Photonic RF Phase Shifter With Low RF Power Variation Based on Constructive Interference of an Add-Drop Ring Resonator

We propose and experimentally demonstrate a tunable silicon photonic radio frequency (RF) phase shifter with low power variation based on constructive interference of an add-drop ring resonator. The thermal nonlinear effect of the add-drop ring resonator is used to realize a nearly 2π-phase shift, and the RF power variation is minimized by allowing two lights at the outputs of the add-drop ring resonator to combine at a directional coupler to achieve constructive interference. By thermally tuning the add-drop ring resonator, a nearly 2π-phase shift is realized and the operation is verified by an experiment. Experimental results show that a 0-5.2-rad phase-shift range with an RF power variation within 0.2 dB for a frequency range of a 40-GHz signal is achieved by thermally tuning the ring resonator. A phase shift up to 4.1 rad over a frequency range of 20-40 GHz is also realized.