Radio Frequency Signal Processing Research Articles

Liver tissue changes during and post 6-month spaceflight as measured by ultrasound radio frequency signal processing.

Analysis of ultrasound radio frequency (RF) signals allows for the determination of the index of reflectivity (IR), which is a new measure that is dependent on tissue properties. Previous work has shown differences in the IR of the carotid artery wall with long-duration spaceflight; therefore, it was hypothesized that liver tissue would also show differences in this measure with spaceflight. The RF signal of a liver tissue region of interest (ROI) was displayed and processed along six different lines covering a surface of approximately 2cm × 2cm. The IR was calculated as the energy backscattered by the liver ROI divided by the total energy returned to the ultrasound probe. Seven astronauts were investigated preflight, inflight on day 150, and postflight 4days and 6months after rerunning to Earth. Compared to preflight (63% ± 18%), the liver tissue ROI IR was significantly lower on flight day 150 (46% ± 14%; p = 0.027) and 4days postflight (46% ± 19%; p = 0.025). At 6months postflight, the IR returned to preflight values (59% ± 13%; p = 0.919). The significant decrease in the coefficient of reflectivity inflight and 4days postflight indicates an alteration in the liver tissue that reduces the reflection of ultrasound waves. This change in tissue properties could either be due to the addition of particles that do not reflect ultrasound waves or structural or cellular changes that alter the reflectivity of the tissue.

A mixer architecture using GaN-based split-gate nanowire transistor

Frequency mixer is an essential block in radio-frequency signal processing for frequency translation and phase comparison. The most common mixers are fabricated using passive elements which suffer from significant conversion loss and low isolation. Mixers using active devices are used less frequently and rather less matured on GaN technology. Here, we demonstrate a mixer based on GaN split-gate nanowire transistor, allowing low conversion loss and high isolation. A constriction is formed by electrostatic modulation of the effective gate width. The threshold voltage of the transistor is modified by one of the gate voltages through the width variation, while the other gate voltage biases the transistor in the saturation region. The nonlinear dependency of the transistor characteristics on the two gate voltages facilitates frequency translation. The mixing characteristics of this architecture are verified both experimentally and theoretically. The output power spectral density peaks at the difference frequency with a minimal conversion loss. Extremely high isolation is measured using three-port S-parameter measurements. The proposed architecture shows multiple benefits, additionally facilitating monolithic mixers on the GaN platform.

The Optimization Research on RF Chip Signal Processing Based on Deep Learning Algorithms

With the rapid development of wireless communication technology, radio frequency (RF) chips, as the core components of communication systems, directly influence the overall system performance through their signal processing capabilities. Traditional signal processing methods often struggle to achieve optimal results in the face of complex and variable communication environments. In recent years, deep learning technology, due to its powerful feature learning and pattern recognition capabilities, has shown tremendous potential in various fields. This paper addresses the signal processing issues of RF chips and proposes an optimization method based on deep learning algorithms. Firstly, the status and challenges of RF chip signal processing are analyzed, followed by the design of a deep learning model suitable for RF signal processing. Through data pre-processing and feature extraction, the generalization ability of the model is enhanced. Experimental results demonstrate that the proposed method outperforms traditional methods in signal noise suppression, interference cancellation, and signal distortion compensation, significantly improving the signal processing performance of RF chips. This research provides new ideas and methods for the application of deep learning in the field of RF chip signal processing and holds significant theoretical and practical importance for the future development of wireless communication systems.

Non‐Hermitian Broadside Coupled Split Ring Resonators with Directional Sensitivity

AbstractDirectional radiofrequency (RF) sensing, also known as radio direction finding, is essential in various applications that involve localizing RF sources. However, existing RF sensing technologies face challenges due to their large antenna sizes and complex RF signal processing circuits, which hinder the realization of miniaturized subwavelength direction sensors. In this article, a non‐Hermitian broadside coupled split ring resonators (BC‐SRRs) are presented, which can identify the direction of an incident RF signal with angles ranging from 0° to 180°. The non‐Hermitian Hamiltonian of the system, which can be interpreted by the temporal coupled mode theory, gives rise to asymmetric resonant modes of the BC‐SRRs. The asymmetry allows the direct measurement of RF wave incident angle by probing the resonant strength of the two BC‐SRRs. For the proof of concept, a one‐stage Dickson voltage multiplier is employed to rectify the RF signals and demonstrate angle sensing ability by relating the rectified voltage to the incident angle. The results showcase the potential of the proposed technique using non‐Hermitian BC‐SRRs as a pathway toward subwavelength antenna‐based radio direction finding.

Strain-enhanced dynamic ranges in two-dimensional MoS2 and MoTe2 nanomechanical resonators

Two-dimensional (2D) materials are promising for atomic-scale, ultralow-power, and highly tunable resonant nanoelectromechanical systems (NEMS) in sensing, communications, and computing. Toward these applications, a broad and controllable linear dynamic range (DR) is desirable for increasing the signal-to-noise ratio (SNR) and reliability. Here, we develop a comprehensive strain-enhanced DR model for 2D NEMS resonators, which is experimentally verified through the tuning of DRs in 2D molybdenum disulfide (MoS2) and molybdenum ditelluride (MoTe2) NEMS resonators using gate-induced strain. We find that the resonance frequency, quality factor, and nonlinear coefficient are all tuned by the gate voltage, which enhance the DR together. Through the guidance of the DR tuning model, we demonstrate DR enhancement by up to 26.9 dB (from 69.5 to 96.4 dB) in a 2D MoS2 NEMS resonator by properly tuning the gate voltage, leading to a theoretical mass resolution of 26 yg (1 yg = 10−24 g). To accurately extract the DR, we further differentiate the quality factors for thermomechanical resonances and for resonances at the largest linear amplitude. This gate-enhanced DR model is also verified using a MoTe2 resonator, with DR enhancement of 7 dB (91.2 to 98.2 dB). The results provide a promising pathway for accurately predicting and optimizing the DRs in NEMS resonators, toward enhanced sensitivity and SNR in mass sensing, radio frequency signal processing, memory, and computing applications.

Low-Loss GHz Frequency Phononic Integrated Circuits in Gallium Nitride for Compact Radio Frequency Acoustic Wave Devices.

Guiding and manipulating GHz frequency acoustic waves in [Formula: see text]-scale waveguides and resonators open up new degrees of freedom to manipulate radio frequency (RF) signals in chip-scale platforms. A critical requirement for enabling high-performance devices is the demonstration of low acoustic dissipation in these highly confined geometries. In this work, we show that gallium nitride (GaN) on silicon carbide (SiC) supports low-loss acoustics by demonstrating acoustic microring resonators with frequency-quality factor ( fQ ) products approaching 1013 Hz at 3.4 GHz. The low dissipation measured exceeds the fQ bound set by the simplified isotropic Akhiezer material damping limit of GaN. We use this low-loss acoustics platform to demonstrate spiral delay lines with on-chip RF delays exceeding [Formula: see text], corresponding to an equivalent electromagnetic delay of ≈ 750 m. Given GaN is a well-established semiconductor with high electron mobility, this work opens up the prospect of engineering traveling wave acoustoelectric interactions in [Formula: see text]-scale waveguide geometries, with associated implications for chip-scale RF signal processing.

Integrated microwave photonic notch filter using a heterogeneously integrated Brillouin and active-silicon photonic circuit

Microwave photonics (MWP) has unlocked a new paradigm for Radio Frequency (RF) signal processing by harnessing the inherent broadband and tunable nature of photonic components. Despite numerous efforts made to implement integrated MWP filters, a key RF processing functionality, it remains a long-standing challenge to achieve a fully integrated photonic circuit that can merge the megahertz-level spectral resolution required for RF applications with key electro-optic components. Here, we overcome this challenge by introducing a compact 5 mm × 5 mm chip-scale MWP filter with active E-O components, demonstrating 37 MHz spectral resolution. We achieved this device by heterogeneously integrating chalcogenide waveguides, which provide Brillouin gain, in a complementary metal-oxide-semiconductor (CMOS) foundry-manufactured silicon photonic chip containing integrated modulators and photodetectors. This work paves the way towards a new generation of compact, high-resolution RF photonic filters with wideband frequency tunability demanded by future applications, such as air and spaceborne RF communication payloads.

Partially Etched Piezoelectric Film Filled with SiO2 Structure Applied to A1 Mode Resonators for Transverse Modes Suppression.

With the arrival of the Fifth Generation (5G) communication era, there has been an urgent demand for acoustic filters with a high frequency and ultrawide bandwidth used in radio-frequency (RF) front-ends filtering and signal processing. First-order antisymmetric (A1) lamb mode resonators based on LiNbO3 film have attracted wide attention due to their scalable, high operating frequency and large electromechanical coupling coefficients (K2), making them promising candidates for sub-6 GHz wideband filters. However, A1 mode resonators suffer from the occurrence of transverse modes, which should be addressed to make these devices suitable for applications. In this work, theoretical analysis is performed by finite element method (FEM), and the admittance characteristics of an A1 mode resonator and displacement of transverse modes near the resonant frequency (fr) are investigated. We propose a novel Dielectric-Embedded Piston Mode (DEPM) structure, achieved by partially etching a piezoelectric film filled with SiO2, which can almost suppress the transverse modes between the resonant frequency (fr) and anti-resonant frequency (fa) when applied on ZY-cut LiNbO3-based A1 mode resonators. This indicates that compared with Broadband Piston Mode (BPM), Filled-broadband Piston Mode (FPM) and standard structures, the DEPM structure is superior. Furthermore, the design parameters of the resonator are optimized by adjusting the width, depth and filled materials in the etched window of the DEPM structure to obtain a better suppression of transverse modes. The optimized A1 mode resonator using a DEPM structure exhibits a transverse-free response with a high fr of 3.22 GHz and a large K2 of ~30%, which promotes the application of A1 mode devices for use in 5G RF front-ends.

High-resolution reconfigurable RF signal spectral processor.

Recent developments in microwave photonic filters (MPFs) offer superior properties for radio frequency (RF) signal processing, such as large instantaneous bandwidth, high resolution and multifunctional shapes. However, it is quite challenging to realize two or more characteristics simultaneously to meet the diverse needs in complex electromagnetic environment. In this paper, we propose a reconfigurable RF signal spectral processor with both large instantaneous bandwidth and high resolution. In the proposed spectral processor, sufficient taps supplied by an optical frequency comb (OFC) offer a large instantaneous bandwidth to process broadband RF signals. Flexible tap coefficients can be obtained by manipulating an optical spectral shaper (OSS), which provides excellent reconfigurability. This tap-by-tap manipulation is realized with a high resolution of hundreds of megahertz, allowing precise shape configuration of the response. In the experiment, we demonstrate a flat-top response with a wide bandwidth of 7.1 GHz. Reconfigurable features such as tunable bandwidth, adjustable center frequency and diverse shapes are also shown. In particular, the measured frequency resolution of 96.5 MHz demonstrates the ability for precise configuration.

From fiber Bragg gratings to coaxial cable Bragg gratings: One-dimensional microwave quasi-periodic photonic crystals

Coaxial cables and optical fibers are two types of cylindrical waveguides used in telecommunications. Fiber Bragg gratings (FBGs) have found successful applications in various fields, such as optical communications, fiber lasers, and fiber-optic sensing. In this paper, we propose and numerically investigate the implementations of various fiber Bragg configurations, including uniform, chirped, apodized, and phase-shifted configurations, on coaxial cables to generate the corresponding special types of coaxial cable Bragg gratings (CCBGs). The simulation results of different CCBGs match well with the well-known FBG theories. It is demonstrated that the reflection spectrum of a CCBG can be flexibly tailored by introducing various quasi-periodic perturbations in the permittivity of the dielectric layer along the coaxial cable. The proposed special types of CCBGs with unique characteristics could find potential applications in radio frequency signal processing, communication, and sensing fields.

Design of a 240 GHz on-chip dual-polarization receiver for SIS mixer arrays

We report the design of a compact dual-polarization on-chip superconductor–insulator–superconductor receiver for array applications. The planar-circuit receiver chip is comprised of the entire radio frequency (RF) signal processing chain with three main circuit components alongside some auxiliary circuits: (1) a polarization splitting 4-probe orthomode transducer (OMT) that couples the RF and local oscillator signal from free space to the chip via a drilled feedhorn; (2) two hybrids that recombine the power of each polarization from the two sets of orthogonal OMT probes; and (3) twin-junction Nb/AlOx/Nb mixers that downconvert the recombined signals to the intermediate frequency. We ensure that the four side walls of each pixel are free from obscuration, using only the top and bottom of the pixel for various connections. Consequently, the design is extendable to a large format array. In this paper, we present the detailed design of the on-chip receiver, including extensive heterodyne simulations and its potential extension into a large format array.

A Novel Design of Hilbert Huang Based All Digital Phase Locked Loop Using FPGA

Many applications for digital processing are steadily increasing in radio frequency signal processing from analog to digital. ADPLL plays a vital role in digital signal processing. Several ADPLL models were introduced in the past. However, in those models, the power dissipation gets increased due to the delay in the lock state. Due to the generated digital noise, the system leads the output signal with inherent phase noise and does not undergo the frequency division process. Therefore, a novel Hilbert-Huang based All Digital Phase Locked Loop (HH-ADPLL) was proposed to make the ADPLL into the locked state. The input reference signal is initially entered in the Hilbert-Huang transform to extract the analytic component and generate the up and down signals. By eliminating the higher frequency part from these signals, the up/down counter produces borrow and carry signals. The carry and borrow signals are fed into the increment decrement counter to produce the output signal. At last, input and output signal matching is carried out in the phase detector module, and ADPLL enters a locked state. The presented HH-ADPLL is implemented in Artix-7 FPGA, and the efficiency is validated in terms of stability, phase error, power dissipation, combinational delay, and performance improvement computed.

EVALUATION OF RADIO PATH PARAMETERS OF INFOCOMMUNICATION SYSTEMS 5G/6G

A study of the parameters of the radio path was carried out to substantiate the possibility of expanding the integrated multi-level spectrum of 5G/6G and increasing the efficiency of the station equipment of the next generation information communication systems. The paper presents the results of research into the bandwidth of the transmission channel in the THz range, taking into account the transmission power and noise of the components of modern telecommunication systems, as well as the influence of atmospheric attenuation. The idea of ​​a new spectrum, possibilities and problems of using the THz range for both communication and scanning were presented. It also describes the process of modeling and measuring new channels along high-frequency bands, for scenarios with large aperture arrays, non-terrestrial networks, and scanning in millimeter and THz bands. Improved methods for solving technical problems identified in 5G systems, such as mobility and coverage, as well as implementation problems of telecommunications equipment, are identified. In particular, to facilitate the optimal design of radio technologies in 6G systems, it is necessary to model transmission channels with higher accuracy. In addition, to improve the transmission characteristics of millimeter waves, improvements are needed in the radio signal beamforming technology, in particular in beamforming during the scanning process. It is determined that the use of the millimeter range spectrum will be significantly improved due to the improvement of technologies related to materials, radio frequency components and signal processing. Thus, it becomes possible to achieve ultra-high data transfer speed and high-precision scanning resolution. A study of the theoretical foundations of the creation of new devices, the design of electronic, photonic and hybrid receivers, large-sized antenna arrays, gratings on a common crystal or case, and new technologies for the formation of materials for the manufacture of gratings, which ensure the rapid development of communication technologies in the THz range, was carried out. time identified the need for further research in the field of designing powerful high-frequency devices, new materials for antennas and RF transistors, receiver architecture, channel modeling, grating signal processing, and energy efficiency issues. The 6G radio path has been studied, which will contain new capabilities and provide new services using new wireless technologies. It is determined that the 6G system will include many new elements, such as new spectrum, new channels, new materials, new antennas, new computing technologies and new end devices. THz spectrometry at 6G has been found to have many potential applications in health care, industry, food quality control, and the environment, as the vibrational and rotational frequencies of most molecules lie in the THz range. THz spectrometry is of considerable interest due to its ability to provide continuous real-time information through dynamic, non-invasive, passive and non-contact measurements. Of particular note is that THz spectrometry provides results comparable to professional CT or MRI machines, but with a much safer and more portable functional process.

Analog-to-spike encoding and time-efficient RF signal processing with photonic neurons.

The radio-frequency (RF) signal processing in real time is indispensable for advanced information systems, such as radar and communications. However, the latency performance of conventional processing paradigm is worsened by high-speed analog-to-digital conversion (ADC) generating massive data, and computation-intensive digital processing. Here, we propose to encode and process RF signals harnessing photonic spiking response in fully-analog domain. The dependence of photonic analog-to-spike encoding on threshold level and time constant is theoretically and experimentally investigated. For two classes of waveforms from real RF devices, the photonic spiking neuron exhibits distinct distributions of encoded spike numbers. In a waveform classification task, the photonic-spiking-based scheme achieves an accuracy of 92%, comparable to the K-nearest neighbor (KNN) digital algorithm for 94%, and the processing latency is reduced approximately from 0.7 s (code running time on a CPU platform) to 80 ns (light transmission delay) by more than one million times. It is anticipated that the asynchronous-encoding, and binary-output nature of photonic spiking response could pave the way to real-time RF signal processing.

Quantum Microwave Photonics

By combing photonics and radiofrequency (RF) engineering, microwave photonics has been widely studied in the past few decades for the generation, processing, control and distribution of microwave and RF signals using photonic techniques. In parallel with the continuous hot research on classic microwave photonic systems, cross research between microwave photonics and other disciplines is also a promising research spot for scientists in this area. Here we review emerging advances in recent years in cross research between microwave photonics and quantum technology, i.e., quantum microwave photonics that harnessing quantum technology to achieve features or functions that are very complex or even not possible using traditional microwave photonic technology and vice versa. Key motivations of quantum microwave photonics are discussed. The basic operation principle of the quantum single-photon detection scheme, which is the main building block of current quantum microwave photonic systems, is provided. Selected recent advances, including weak microwave signal detection, microwave photonic phase shifting and filtering, nonlocal frequency-to-time mapping, RF compressed sensing, and quantum key distribution, are summarized. Challenges and future prospects of quantum microwave photonics are also discussed.

Multi-delay photonic correlator for wideband RF signal processing

Correlation of radio-frequency (RF) signals is a fundamental operation in many fields such as information processing, detection, and imaging techniques at large. Because of the intrinsic limitations of electronic techniques, standard digital correlators, which rely on the acquisition of signals and their processing, become very complex to implement for the real-time analysis of signals whose bandwidth exceeds a few hundred MHz. On the other hand, analog correlators are limited by the performances of RF components. In this paper, we report the proof-of-concept of a correlator architecture based on a simple photonic platform, suitable for analog wideband RF signal processing. The concept, based on multi-heterodyne interferometry, gives access in real time to the entire correlation function of two signals by computing the cross correlation coefficients for 200 values of their relative delay simultaneously. The time-delay step can be adjusted from a few ns down to a few ps, enabling us to process signals with MHz to multi-GHz bandwidth. We have applied this architecture to the localization of RF transmitters by time difference of arrival (TDoA) and obtained a precision close to 10 ps for a 100 ms integration time. This concept is expected to find practical applications in various domains, from radar and electronic warfare to telecommunications, imaging, and radio-astronomy.

Radio Frequency and Microwave Photonic Signal Processing and Generation Based on Optical Kerr Micro-Combs

Radio Frequency and Microwave Photonic Signal Processing and Generation Based on Optical Kerr Micro-Combs

Integral order photonic RF signal processors based on a soliton crystal micro-comb source

Soliton crystal micro-combs are powerful tools as sources of multiple wavelength channels for radio frequency (RF) signal processing. They offer a compact device footprint, a large number of wavelengths, very high versatility, and wide Nyquist bandwidths. Here, we demonstrate integral order RF signal processing functions based on a soliton crystal micro-comb, including a Hilbert transformer and first, second and third-order differentiators. We compare and contrast the results and the trade-offs involved with varying the comb spacing, and tap design and shaping methods.

Ultrahigh spectral resolution single passband microwave photonic filter.

Microwave photonic filters (MPFs) with only one ultra-narrow passband are able to provide high frequency selectivity and wide spectral range, and they are of great importance in radio-frequency (RF) signal processing. However, currently all MPFs are limited by trade-offs between key parameters such as spectral resolution and range, tunability, and stability. Here, we report the first demonstration of a single passband MPF with unprecedented performance including ultrahigh spectral resolution of 650 kHz, 0-40 GHz spectral range, and high stability of center frequency drifting within ±50 kHz. This record performance is accomplished by breaking the amplitude equality of a phase-modulated signal via a Brillouin dynamic grating (BDG) which has an ultra-narrow reflection spectrum of sub-MHz. The results point to new ways of creating high performance microwave photonic systems, such as satellite and mobile communications, radars, and remote-sensing systems.

A readout system for microwave kinetic inductance detectors using software defined radios

Microwave kinetic inductance detectors (MKIDs) are typically readout using custom high-speed electronics and firmware, a challenging and time-intensive undertaking. We have developed a readout system for these devices using a software defined radio (SDR), a software implementation of radiofrequency signal processing. The SDR allows use of pre-existing software libraries and minimizes specialized firmware coding, a significant reduction in effort. We customized our SDR to readout mm and optical band MKIDs with resonant frequencies of 1.8-2 GHz and 2-2.2 GHz respectively. We used this readout system to measure the sensitivity of our MKIDs devices to visible light. We show that SDRs are a good candidate for small pixel count MKIDs readout systems, and make recommendations for readout systems for larger Pixel count arrays.