RF Signal Processing Research Articles

Acoustoelectric amplification of Rayleigh waves in low sheet density AlGaN/GaN heterostructures on sapphire

This letter demonstrates amplification of surface acoustic waves through the application of dc electric fields in low sheet density heterostructures of AlxGa1−xN barrier layers over GaN grown by metal organic chemical vapor deposition on a sapphire substrate. The use of the GaN material offers a convenient platform to study acoustoelectric (AE) effects, due to its piezoelectricity and the ability to support a two-dimensional electron gas at the interface with the barrier. In this work, low Al molar fractions (between 6% and 10%) in the barrier layer are investigated to tune the sheet resistivity, which is a key aspect to realizing appreciable AE gains. Rayleigh waves in GaN at 920 MHz exhibit non-reciprocity (defined as the contrast in the peak amplitude of the amplified forward traveling wave and the attenuated reverse traveling wave) of up to 6.5 dB/mm under the influence of dc bias fields applied to a 24 nm Al0.07Ga0.93N barrier over GaN on sapphire. Gain dependence on the sheet resistance is also observed, consistent with the AE effect. This work demonstrates an approach to counteract acoustic propagation losses in GaN, which can be implemented in long delay lines for RF signal processing, in addition to other applications.

Microwave Photonic Channelizer Based on Polarization Multiplexing and Photonic Dual Output Image Reject Mixer

Microwave photonic channelizer based on coherent frequency combs (OFCs) enables processing of ultra-wideband RF signals using low-frequency components. The channel number usually equals to the comb line number of the OFCs and the bandwidth for the microwave input is determined by the frequency spacing of the OFCs. However, the generation of coherent OFCs with large comb lines and large frequency spacing is extremely challenging, limiting greatly the potential of the OFC-based channelizer. In this paper, a microwave photonic channelizer based on polarization multiplexing and photonic dual output image reject mixing is proposed and demonstrated. A broadband signal can be divided into 8 channels using only one optical carrier and a pair of dual-polarization local oscillators (DP-LOs). Each DP-LO has only 2 spectral lines with orthogonal polarization states. In addition, by introducing a pair of OFCs with $N$ comb lines, $8N$ channels can be output. The requirement of the comb line number is efficiently reduced, and the in-band interference is greatly suppressed by introducing the polarization multiplexing and the photonic dual-output image-reject mixing. A proof-of-concept experiment is carried out. An RF signal with 9.6-GHz bandwidth centered at 14 GHz is successfully divided into 8 channels with 1.2-GHz bandwidth, and the in-band interference is effectively suppressed for each channel. In addition, RF signals with 2.4-GHz bandwidth centered at 24.8 and 30.8 GHz are also successfully channelized, respectively.

Implementation of the modeling and simulation software of search and rescue system based Korea navigation satellite system

This paper describes the development of M&S (Modeling and Simulation) system based COSPAS-SARSAT SAR (Search and Rescue) system. SAR system transmits a distress signal to the terminal and transmits it to the satellite network or the terrestrial network. It recognized distress incident from anywhere in the world. The M&S system is designed to analyze the accuracy, reliability, and availability of the SAR (Search and Rescue) system. It is also designed to simulate the actual distress beacons of a distress situation. It was developed to enable performance analysis. We will verify the validity of the implemented results, applying the RF signal processing based on KNSS.

A Discrete-Time RF Signal-Processing Technique for Blocker-Tolerant Receivers With Wide Instantaneous Bandwidth

A new signal-processing approach aimed at improving the intermodulation performance of wideband receivers implemented in CMOS technologies is described. The receiver operates by downconverting an input signal to $N$ decimated baseband signals. The local oscillator signals used in this process are each a different phase of a pseudo-random bit sequence of length $N$ . The baseband signals are amplified and digitized before the original RF signal is reconstructed in the digital domain. The operating principles of the system are described and the performance specifications of this system are studied using a combination of analytical and numerical techniques. A prototype integrated circuit has been designed and fabricated using a 130-nm CMOS process. Detailed measurements demonstrating the narrowband and wideband operation of the system are presented and compared to theory. The measured in-band $IIP3$ has been found to be greater than 5.7 dBm from 40 to 300 MHz. The blocker tolerance of the circuit has also been characterized and it was found that a 10-MS/s −50-dBm 16-QAM signal could be received with nearly constant error-vector magnitude as the power of an in-band blocker signal was swept from −20 to −7 dBm.

Introduction to the Special Issue on Emerging Areas in Integrated Photonics

This special issue combines 13 invited and 35 contributed papers, offering a unique perspective on the most recent developments in integrated photonics over the last few years. The invited papers, authored by world-renowned research groups and promising scientists from all over the world, present extended reviews on recent progresses and significant perspectives on future research directions. Heterogeneous integration of dissimilar materials for integrated photonics remains one of the most active and promising areas of research, with both traditional semiconductor materials such as amorphous Si, germanium, and III-V quantum dots on silicon, as well as emerging materials such as thin film lithium niobate, nitride, silicon carbide, diamond, etc. Device structures are being explored for new functional applications, from traditional Datacom/telecom to optical, RF and nonlinear signal processing, nonreciprocal optics, midwave infrared sensing, etc. Integration schemes and system architecutures are being pursued for quantum computing, signal processing, machine learning, energy efficient neuromorphic computing, etc.

Credit-card sized field and benchtop NMR relaxometers using field programmable gate arrays

The tools for developing systems for NMR improve each year. Some firmware based designs based on Field Programmable Gate Arrays (FPGAs) have been developed to implement both the core and peripheral apparatus for NMR Relaxometers and NMR Cryoporometers. Hand held in size they are particularly suitable for desktop, mobile and field use.Software tools now enable the writing of firmware that enable the rapid design of digital and digitised R.F. data and control systems. This firmware can then be loaded into and run on hardware that often is only the size of a credit-card. These devices can include a single-chip Linux computer with an FPGA capable of processing digital RF on the same chip. These can generate RF signals digitally, process RF signals for up- and down-conversion, and can provide an on chip NMR pulse sequencer.An extremely well tested NMR digital transmitter has been upgraded to use the latest surface-mount Bipolar and Field Effect Transistors. The circuitry is now the size of a book of matches, and interfaces to credit-card sized FPGA modules for RF generation, phase shifting and drive signals. This NMR transmitter design uses digital logic principles rather than conventional tuned R.F. techniques Offering both active-damping and active-quench, a very square R.F. Pulse with fast turn off is achieved, with Mark 1 giving 2.6 μs π/2 and 4.8 μs π pulses into a 5 mm diameter NMR sample (2.7 mT B1) at 20 MHz for Protons. T1ρ pulses are stable and consistent.

Continuously tunable orthogonally polarized RF optical single sideband generator based on micro-ring resonators

We demonstrate a continuously RF tunable orthogonally polarized optical single sideband (OP-OSSB) generator based on dual cascaded micro-ring resonators (MRRs). By splitting the input double sideband signal into an orthogonally polarized carrier and lower sideband via TE- and TM-polarized MRRs, an OP-OSSB signal is generated. A large tuning range of the optical carrier to sideband ratio of up to 57.3 dB is achieved by adjusting the polarization angle of the input light. The operation RF frequency of the OP-OSSB generator can be continuously tuned with a 21.4 GHz range via independent thermal control of the two MRRs. Our device represents a competitive approach towards OP-OSSB generation with wideband tunable RF operation, and is promising for photonic RF signal transmission and processing in radar and communication systems.

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

The creation of high-performance narrowband filters is of great interest for many RF-signal processing applications. To this end, numerous schemes for electronic, MEMS-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 GHz-widths and often have large RF insertion losses, posing challenges for integration into high-fidelity radiofrequency circuits. In this article, 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, a RF signal encoded on a guided optical wave is transduced onto a GHz-frequency acoustic wave, where it may be filtered through shaping of acoustic transfer functions before being re-encoded onto a spatially separate optical probe. This emit-receive functionality, realized in an integrated silicon waveguide, produces MHz-bandwidth band-pass 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.

Artificial bee colony algorithm for energy efficiency optimisation in massive MIMO system

This paper deals with antenna selection for multi-user massive MIMO systems with the aim of maximising energy efficiency. Massive MIMO technology, by employing a large number of antennas at base station, provides huge improvements in throughput and energy efficiency. The increased number of antennas leads to additional energy consumption due to RF chains and signal processing circuit. The main purpose of the paper is to determine the optimal subset of antennas at the base station that should be activated to serve a given number of active user equipment. This idea is implemented using artificial bee colony algorithm which has proven it efficiency by specifying the best control parameters.

Artificial bee colony algorithm for energy efficiency optimisation in massive MIMO system

This paper deals with antenna selection for multi-user massive MIMO systems with the aim of maximising energy efficiency. Massive MIMO technology, by employing a large number of antennas at base station, provides huge improvements in throughput and energy efficiency. The increased number of antennas leads to additional energy consumption due to RF chains and signal processing circuit. The main purpose of the paper is to determine the optimal subset of antennas at the base station that should be activated to serve a given number of active user equipment. This idea is implemented using artificial bee colony algorithm which has proven it efficiency by specifying the best control parameters.

Tunable Multiband Microwave Photonic Filters

The increasing demand for multifunctional devices, the use of cognitive wireless technology to solve the frequency resource shortage problem, as well as the capabilities and operational flexibility necessary to meet ever-changing environment result in an urgent need of multiband wireless communications. Spectral filter is an essential part of any communication systems, and in the case of multiband wireless communications, tunable multiband RF filters are required for channel selection, noise/interference removal, and RF signal processing. Unfortunately, it is difficult for RF electronics to achieve both tunable and multiband spectral filtering. Recent advancements of microwave photonics have proven itself to be a promising candidate to solve various challenges in RF electronics including spectral filtering, however, the development of multiband microwave photonic filtering still faces lots of difficulties, due to the limited scalability and tunability of existing microwave photonic schemes. In this review paper, we first discuss the challenges that were facing by multiband microwave photonic filter, then we review recent techniques that have been developed to tackle the challenge and lead to promising developments of tunable microwave photonic multiband filters. The successful design and implementation of tunable microwave photonic multiband filter facilitate the vision of dynamic multiband wireless communications and radio frequency signal processing for commercial, defense, and civilian applications.

High-resolution, on-chip RF photonic signal processor using Brillouin gain shaping and RF interference

Integrated microwave photonics has strongly emerged as a next-generation technology to address limitations of conventional RF electronics for wireless communications. High-resolution RF signal processing still remains a challenge due to limitations in technology that offer sub-GHz spectral resolution, in particular at high carrier frequencies. In this paper, we present an on-chip high-resolution RF signal processor, capable of providing high-suppression spectral filtering, large phase shifts and ns-scale time delays. This was achieved through tailoring of the Brillouin gain profiles using Stokes and anti-Stokes resonances combined with RF interferometry on a low-loss photonic chip with strong opto-acoustic interactions. Using an optical power of <40 mW, reconfigurable filters with a bandwidth of ~20 MHz and an extinction ratio in excess of 30 dB are synthesized. Through the concept of vector addition of RF signals we demonstrate, almost an order of magnitude amplification in the phase and delay compared to devices purely based upon the slow-light effect of Brillouin scattering. This concept allows for versatile and power-efficient manipulation of the amplitude and phase of RF signals on a photonic chip for applications in wireless communications including software defined radios and beam forming.

Spatial-spectral holographic real-time correlative optical processor with >100 Gb/s throughput.

The demonstration of an all-optical, ultra-high-speed, time-domain signal correlator based on spatial-spectral holographic (SSH) technology is described. The fully programmable signal correlator demonstration operates asynchronously and continuously on signals with up to 32 GHz of bandwidth and correlative filter length exceeding a time-bandwidth product of 104, for the equivalent of teraflop-scale processing. Experimental demonstrations are presented that show both digital and analog correlation capability using phase-shift keyed modulation formats to search plain text ASCII data sources for arbitrary phrases at continuous line rate throughputs up to 200 Gbps with minimal latency. These high-bandwidth demonstrations were enabled by improvements in the photonic supporting components and cryogenic SSH for RF and microwave signal processing methods. Potential application of the SSH real-time correlator for high-bandwidth analog or multi-level format signals is discussed.

Mathematical analysis of RF imaging techniques and signal processing using wavelets

Non-linear optics plays an important role in the imaging. In this paper using non-linearity, we have derived three different techniques for imaging. In the first technique, an algorithm is developed for the scattering of electromagnetic waves from the medium, which gives higher-order harmonics of the EM wave. Here, the linear and non-linear interactions of molecules with the applied electromagnetic waves play an important role in target detection. We assume the material is inhomogeneous and represented by its susceptibility tensor. Second technique for detection of non-linearity or higher-order harmonic is using anharmonic oscillator model where the perturbation due to non-linearity in the electron moment is derived and mapped to the second harmonic generation of electromagnetic waves. Third technique is applied using Gaussian monopulse where the non-linear interaction of wave with the matter makes the phase change of the wave. When wavelet transforms with dilations and translation are applied to these non-linear waveforms, we get the details of region of interest in terms of wavelet coefficients. The region of interest may be 1-dimensional, 2-dimensional or 3-dimensional. These methods can be used in biomedical applications and other areas where target is in the near-field range.

Mathematical analysis of RF imaging techniques and signal processing using wavelets

Non-linear optics plays an important role in the imaging. In this paper using non-linearity, we have derived three different techniques for imaging. In the first technique, an algorithm is developed for the scattering of electromagnetic waves from the medium, which gives higher-order harmonics of the EM wave. Here, the linear and non-linear interactions of molecules with the applied electromagnetic waves play an important role in target detection. We assume the material is inhomogeneous and represented by its susceptibility tensor. Second technique for detection of non-linearity or higher-order harmonic is using anharmonic oscillator model where the perturbation due to non-linearity in the electron moment is derived and mapped to the second harmonic generation of electromagnetic waves. Third technique is applied using Gaussian monopulse where the non-linear interaction of wave with the matter makes the phase change of the wave. When wavelet transforms with dilations and translation are applied to these non-linear waveforms, we get the details of region of interest in terms of wavelet coefficients. The region of interest may be 1-dimensional, 2-dimensional or 3-dimensional. These methods can be used in biomedical applications and other areas where target is in the near-field range.

All-fiber radio frequency-modulated pulsed laser based on frequency-shift feedback loop

Lidar-radar by using an radio frequency modulated (RF-modulated) laser transmitter is a powerful technique for applications involving remote sensing. The method is based on the use of an optically carried RF signal in order to acquire the merits of both the directivity of the optical beam (lidar) and the accuracy of RF signal processing (radar). Compared with single-frequency coherent lidars, lidar-radars are less sensitive to atmospheric turbulence and the speckle noise induced by target roughness. For long range detection, pulsed operation is usually required because of the high peak power. In order to meet the requirement for long range detection, an RF-modulated pulse train based on an all-fiber frequency shifted feedback loop is proposed in this paper. A continuous-wave single-frequency fiber laser (seed laser) is coupled into a fiber link and an acousto-optic chopper is used as a frequency shifter and beam chopper. A Yb3+-doped fiber amplifier is used to compensate for the loss of the signal in the fiber loop. The pulse duration is determined by the open time of acousto-optic chopper, which is fixed at 110 ns. A square wave generated by an arbitrary waveform generator is used as a trigger signal of the acousto-optic chopper. The RF within the pulse results from the interference of frequency shifed pulse with the seed laser. By inserting a 10 km fiber in the loop and accurately controlling the trigger cycle of the acousto-optic chopper equal to the roundtrip time of the loop, the pulse train generated by acousto-optic chopper can circulate in the loop, leading to the generation of RF-modulated pulse with about 20 kHz repetition rate and 110 ns width. The gain provided by fiber amplifier in the loop partially compensates for the loss. By adjusting the gain of fiber amplifier, the modulation depth of RF within the pulse can be continuously adjusted and the maximum modulation depth is 0.67. We also present an time-delayed scalar interference model which includes the loop length, trigger cycle, frequency-shift, and the gain. According to the theoretical model, the RF-modulated pulse affected by trigger cycle and fiber amplifier is numerically simulated. The experimental results accord well with theoritical predictions. The RF-modulated pulse has the advantage of high pulse-to-pulse coherence, which provides potential applications in lidar-radar detection. Besides, with an additional frequency doubling stage one can obtain a source for underwater detections and communications. Extension of the scheme to the 1.5 μm telecommunication window is straightforwardfor various radio-over-fiber applications.

Low Power Synthesis and Validation of an Embedded Multiplier for FPGA Based Wireless Communication Systems

The advancement in wireless telecommunication technologies like 3G, 4G and now 5G enrich the demand of high performance portable devices, operating at high frequencies i.e. from few hundred MHz to several GHz. High performance can only be achieved at the cost of high power dissipation. Nowadays, the use of FPGAs is rapidly increasing due to its low cost and smaller time to market. Today’s high end FPGAs are capable of implementing high performance designs such as transceivers for RF application, signal processing and image processing applications etc. This is only possible due to their complex designs that includes on chip dedicated multipliers, Dual RAM blocks, Ethernet and DCMs etc. Since FPGAs consume large amount of power, it becomes a challenge for the designers to implement low power battery operated communication systems. Several power estimation models are available in literature for early stage power estimation of FPGAs in the synthesis design flow but they provide less accuracy (high percentage error) for the designs incorporated with low power reduction technique. This paper presents the limitation of existing power estimation model proposed by Deng. The given model is converted into a script using MATLAB. The power values estimated from the power model (script) are compared with the high level synthesis tool: Xpower Analyzer targeted to Virtex FPGA. For estimation of power values, an embedded multiplier is synthesized for two different configurations: one with ‘CE’ (low power) and another without ‘CE’ for different I/O vector length. The results suggested that the given low level power estimation models provide less accuracy (high % error) for the designs incorporated with low power reduction technique i.e. with ‘CE’. Further, there is a scope of remodel the existing model for the observed shortcoming.

단일채널 모노펄스시스템의 구현 및 성능 검증

본 논문에서는 일반적인 3채널 구조의 모노펄스수신기와 대비해서 비용, 크기, 무게 및 소모전력 측면에서 유리한 단일채널 구조의 모노펄스수신기를 적용한 추적시스템에 관한 연구를 진행하였다. 안테나, 모노펄스수신기, 구동체, RF 신호처리기 및 전원분배기를 제작 및 통합하여 단일채널 모노펄스시스템을 구현한 후, 지향오차각 산출정확도와 포인팅 손실을 측정하여 기본 추적성능을 확인하였다. 그리고 야외환경에서 실제 이동하는 목표물에 대한 추적성능을 검증하였다. 시험결과 분석을 통해 단일채널 모노펄스시스템이 일반적인 3 채널 모노펄스시스템과 동등 이상의 추적성능을 가지면서 시스템의 구현측면에서 이점이 있음을 확인하였다. 또한, 이 연구로 향후 모노펄스 추적시스템 개발 시 제작비용 및 제품 소형화에 유리한 단일채널 모노펄스수신기 적용이 가능함을 확인하였다. In this paper, we have studied the tracking system with a single channel monopulse receiver that has a comparative advantage of costs, size, weight, and power consumption over the general 3-channel monopulse receivers. After the single channel monopulse system was composed of an antenna, a monopulse receiver, a servo unit, a RF signal processor unit and a power supply unit, we analyzed the basic tracking performance of the tracking error angle and the pointing loss. And we proved the tracking performance to a moving target in the outdoor environment. On the Analysis of the tracking test results, the single channel monopulse system shows a equal or higher performance over the general 3-channel monopulse system and also has advantages of the system implementation. Also, it is concluded that this study is useful to apply a single channel monopulse receiver with benefits of production price and miniaturization when the monopulse tracking systems will be developed in the future.

Ultra-high frequency, high Q/volume micromechanical resonators in a planar AlN phononic crystal

This paper presents the first design and experimental demonstration of an ultrahigh frequency complete phononic crystal (PnC) bandgap aluminum nitride (AlN)/air structure operating in the GHz range. A complete phononic bandgap of this design is used to efficiently and simultaneously confine elastic vibrations in a resonator. The PnC structure is fabricated by etching a square array of air holes in an AlN slab. The fabricated PnC resonator resonates at 1.117 GHz, which corresponds to an out-of-plane mode. The measured bandgap and resonance frequencies are in very good agreement with the eigen-frequency and frequency-domain finite element analyses. As a result, a quality factor/volume of 7.6 × 1017/m3 for the confined resonance mode was obtained that is the largest value reported for this type of PnC resonator to date. These results are an important step forward in achieving possible applications of PnCs for RF communication and signal processing with smaller dimensions.

Weighted-Polarization Wearable MIMO Antenna with Three Orthogonally Arranged Dipoles Based on RF Signal Processing

Weighted-Polarization Wearable MIMO Antenna with Three Orthogonally Arranged Dipoles Based on RF Signal Processing