Instantaneous Frequency Measurement Research Articles

Photonic Microwave Frequency Measurement With High Accuracy and Sub-MHz Resolution

A dynamic photonic instantaneous microwave frequency measurement approach is reported based on frequency-to-time mapping and filtering using an integrated ring resonator, a local oscillator for heterodyne detection, and an electrical bandpass filter. The unknown signal is time-swept through the narrow linewidth of the ring resonator, realized on a silicon nitride platform. A shifted local oscillator at a fixed frequency difference from the center of the ring resonator defines an intermediate frequency for heterodyne detection. After conversion to the electrical domain using a photodiode, this intermediate frequency is filtered by a narrowband electrical bandpass filter. The proposed system demonstrates a resolution of less than 1 MHz and a measurement accuracy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.4 MHz over a frequency range of 10 GHz, only limited by the used experimental components. To the best of our knowledge, this is the highest accuracy and resolution shown so far for photonic microwave frequency measurement systems. Since the method can be easily integrated on any photonic platform, it might become an integral part of future wireless devices.

Design and Evaluation of a Low-Cost SAW Resonator Read-Out System at 2.4 GHz

The functionality of using surface acoustic wave (SAW) resonators in wireless sensing applications has been demonstrated in many publications. When used, their resonance frequency has to be determined with a precision of up to 10 ppm with measurement periods in the microsecond range. For this purpose, the so-called instantaneous frequency measurement (IFM) can be used, which uses a six-port receiver to measure a frequency-dependent phase delay. This work presents a system that incorporates an alternative low-cost circuitry that multiplexes the four six-port outputs on only one detection circuitry with the help of an RF switch. This reduces the system cost and eliminates the measurement errors otherwise caused by differing gain and group delay values in the baseband filters. Based on this idea, a complete SAW readout system is presented and experimentally evaluated, which also can be used as a sensor node as it incorporates a Bluetooth interface. The shown measurement results demonstrate that the system can achieve a precision of 7.9 ppm concerning frequency measurement at an update rate of 41.7 Hz, demonstrating the feasibility of the alternative detection circuit.

Photon-assisted Instantaneous Frequency Measurement Scheme Based on Stimulated Brillouin Scattering

Photon-assisted Instantaneous Frequency Measurement Scheme Based on Stimulated Brillouin Scattering

A Scheme of Instantaneous Frequency Measurement with High Precision Assisted by Photonics

In modern complex battlefield environment, it is important to obtain the frequency spectrum precisely. We propose an operational method of instantaneous frequency measurement (IFM) assisted by photonics, which can achieve high precision based on stimulated Brillouin scattering (SBS), giving the credit to the narrow linewidth of gain spectrum of SBS. We use MZM and DPMZM cascade to generate a tunable continuous optical signal and modulate the measured signal to the continuous

Generalized Analysis of Dual-Output Mach-Zehnder Modulator With Applications to Photonic-Assisted Instantaneous Frequency Measurement

We propose a general and exact analytical model forintensity modulation and direct detection (IM/DD) fiber optic links using dual-output dual-drive Mach-Zehnder modulator (DO-MZM). This model extends previously published results relying on the small-signal approximation and infinite extinction ratio at the modulator outputs. In our treatment the output optical powers are calculated through analytical expressions taking into account the modulator electronic driver and directional coupler characteristics. Closed-form expressions, explicitly displaying the dependence of the link output power on the directional coupler transmission coefficients, optical modulation depth, and bias point, are obtained for output optical power, frequency chirp, extinction ratio and static characteristic MZM curves. We also propose an equivalent interferometric representation of each DO-MZM output in terms of virtual dual-drive Mach-Zehnder modulators (DD-MZMs) and show that each modulator output has distinct characteristic curves. The model is applied to a photonic-assisted instantaneous frequency measurement (IFM) based on frequency-to-power mapping, in which an amplitude comparison function (ACF) is generated by the power fading functions. We have obtained a generalized ACF through which both the frequency and amplitude of the input RF signal can be determined by a search procedure.

Switchable instantaneous frequency measurement by optical power monitoring based on DP-QPSK modulator

We propose and analyze an instantaneous frequency measurement system by using optical power monitoring technique with improved resolution. The primary component adopted in the proposal is a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which is used to modulate the microwave signal that has a designed time delay and phase shifting. The generated optical signal is sent to polarization beam splitter (PBS) in DP-QPSK modulator. Owing to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted into the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal can be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the direct current (DC) biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range, and the influence of imperfection devices. The proposed scheme is wavelength-independent and its measurement range is switchable, which can avoid the laser wavelength drifting problem and thus greatly increasing the system flexibility.

2.45 GHz Band Quadrature Microwave Frequency Discriminators with Integrated Correlators Based on Power Dividers and Rat-Race Hybrids

Instantaneous frequency measurement devices are useful for conducting extremely fast measurements of the current frequency value of microwave signals, even if their duration is extremely short. This paper presents the principle of determination of temporary values of the microwave signal phase and frequency using interferometer techniques, based on passive microwave components. Additionally, the structures and results of measurements of two novel versions of integrated microwave correlators for microwave frequency discriminators, made on a single printed circuit board, are shown. Three Wilkinson-type, single-stage power dividers, and two rat-race hybrids create the developed correlators. The developed devices were designed to work over a wide frequency range, i.e., of 1.6–3.1 GHz, and can be used to monitor Wi-Fi devices as well as pulse and CW radar systems operating in the S band. They can also be applied in passive radars and active Doppler radars. The view of the printed circuits boards and results of measurements are presented. Recommendations for improving the accuracy of measurement are proposed.

Broadband Instantaneous Multi-Frequency Measurement Based on a Fourier Domain Mode-Locked Laser

Broadband instantaneous multi-frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked (FDML) laser source is proposed and experimentally demonstrated. An electrically controlled silicon microdisk resonator (MDR) with an ultra-narrow linewidth of 60 pm (~7.5 GHz) functioning as a fast tunable optical filter is used to implement the FDML to generate a linearly chirped optical waveform (LCOW) with a wide frequency-sweeping range of 0.5 nm. The LCOW is then mixed at a modulator with a microwave signal with its frequency to be measured, detected at a low-speed photodetector (PD) and sent to a narrow bandpass filter (BPF). When the difference between the instantaneous frequency of the LCOW and that of the signal to be measured is equal to the center frequency of the BPF, a short-duration temporal signal is produced, and the time location of the temporal signal represents the frequency of the signal to be measured. A proof-of-concept experiment is carried out. Both single and multi-tone microwave frequency measurements are experimentally demonstrated. The measurement range is as large as 20 GHz with a measurement resolution of 200 MHz and an accuracy better than ±100 MHz. The proposed method showcases a new method for instantaneous frequency measurement (IFM) with high performance in terms of multi-frequency identification, real-time measurement, and high measurement speed compared with traditional approaches, which is attractive for applications in modern radar, electronic warfare, communication, and cognitive radio systems.

Photonic instantaneous frequency measurement using a dense wavelength-division multiplexer.

A photonic instantaneous frequency measurement receiver based on frequency to optical power mapping is proposed and experimentally demonstrated. One channel of a dense wavelength-division multiplexer (DWDM) is used as an optical filter to establish a power ratio function related to the frequency of the microwave signal. Different from most optical filters, the DWDM filter features smooth and quasilinear roll-off over a wide bandwidth. With the help of a laser of good wavelength stability and a bias controller, large measurement range and high accuracy are simultaneously achieved without multi-step operation. The instanstaneous frequency measurement receiver can measure the frequency with an accuracy of 0.2% of the signal frequency in the range of 1-40 GHz over 1.5 h in the experiment.

Utilization of slow light enhancement of four-wave mixing within a silicon photonic crystal for microwave frequency measurement purposes

We report the demonstration of an instantaneous frequency measurement system based on the four-wave mixing (FWM) effect in short dispersion engineered slow-light silicon photonic crystal waveguides for RF frequency measurement purposes within a range of 10 MHz to 80 GHz. Three nonlinear media were investigated including 3 mm ridge waveguide, 80 µm nanowire, and 80 µm photonic crystal (PhC). The system size could thus be decreased, and as a result system integration would become possible. We have shown that the optical power required to excite FWM is low enough to remove any need for optical amplification, and hence the system noise floor will be kept low. Issues due to the amplifier saturation will also be resolved this way. As a result, no noise reduction system, like lock-in amplification, would be required. A better system latency will also be achieved accordingly. The system dynamic range would also be improved in two ways. First, due to the low noise floor, and second, because of removing any optical amplifier that possibly could become saturated at higher power levels. All three media behaviors were simulated by the split step Fourier method, and the results showed that the best medium to be used is PhC.

Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

A scheme for instantaneous frequency measurement (IFM) using two parallel I/Q modulators based on optical power monitoring is proposed. The amplitude comparison function (ACF) can be constructed to establish the relationship between the frequency of radio frequency (RF) signal and the power ratio of two optical signals output by two I/Q modulators. The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators. The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line. The feasibility of the scheme is verified, and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given. Compared with previous IFM schemes, the structure of this scheme is simple. Polarization devices, a photodetector and an electrical power meter are not used, which reduces the impact of the environmental disturbance on the system and the cost of the system. In simulation, the measurement range can reach 0 GHz–24.5 GHz by adjusting the delay amount of the electrical delay line τ = 20 ps. The measurement error of the scheme is better at low frequency, and the measurement error of low frequency 0 GHz–9.6 GHz can reach –0.1 GHz to +0.05 GHz.

Instantaneous microwave-photonic spatial-spectral channelization via k-space imaging

The ability to both spatially and spectrally demultiplex wireless transmitters enables communication networks with higher spectral and energy efficiency. In practice, demultiplexing requires sub-millisecond latency to map the dynamics of the user space in real-time. Here, we present a system architecture, referred to as k-space imaging, which channelizes the radio frequency signals both spatially and spectrally through optical beamforming, where the latency is limited only by the speed of light traversing the optical components of the receiver. In this architecture, a phased antenna array samples radio signals, which are then coupled into electro-optic modulators (EOM) that coherently up-convert these signals to the optical domain, preserving their relative phases. The received signals, now optical sidebands, are transmitted in optical fibers of varying path lengths, which act as true time delays that yield frequency-dependent optical phases. The output facets of the optical fibers form a two-dimensional optical phased array in an arrangement preserving the phases generated by the angle of arrival (AoA) and the time-delay phases. Directing the beams emanating from the fibers through an optical lens produces a two-dimensional Fourier transform of the optical field at the fiber array. Accordingly, the optical beam formed at the back focal plane of the lens is steered based upon the phases, providing the angle of arrival and instantaneous frequency measurement (IFM), with latency determined by the speed of light over the optical path length. We present a numerical evaluation and experimental demonstration of this passive AoA- and frequency-detection capability.

A Multiple Baseline Interferometric Radar for Multiple Target Angular Velocity Measurement

We present a novel technique for directly estimating the angular velocities of multiple targets using multi-baseline millimeter-wave interferometric radar to significantly reduce nonlinear signal distortion caused when multiple targets are present. We show that through the multiplication of the normalized instantaneous frequency measurements across different baselines, nonlinear intermodulation products resulting from dual-antenna interferometric angular velocity measurements can be mitigated, producing only the terms corresponding to the angular velocity of the targets in the scene. To validate this, simulations were performed demonstrating the close agreement between the proposed method and an ideal correlation (without intermodulation distortion). Near-field errors resulting from far-field approximations are analyzed. Finally, experimental results of a three-antenna, three-baseline 38-GHz interferometric radar are presented that demonstrate the recovery of the motion of two oscillating pendulums of differing angular frequencies.

A wideband mono-bit digital receiver circuit using InP/CMOS 3D heterogeneous integration

A mono-bit digital receiver circuit for instantaneous frequency measurement is presented. The circuit is co-designed with Indium Phosphide Double Heterojunction Bipolar Transistor and complementary metal oxide semiconductor (CMOS) devices. The chip is fabricated by InP/CMOS three-dimensional (3D) heterogeneous integration using the wafer-level bonding technique. The measurable signal frequency within + 15 to − 25 dBm power is up to 7.5 GHz with a 14-GHz clock. Compared to an integrated circuit (IC) with a traditional InP or CMOS technologies, the proposed chip could benefit from both InP and CMOS technology. In the heterogeneous integration, InP devices provide high operating frequency, broad signal bandwidth, and large input signal dynamic range, while CMOS devices achieve complex function with low power consumption. In this way, the system FoM is improved for a mono-bit digital receiver while the system power consumption is kept the same. This work also shows the great potential of the 3D heterogeneous integration for the high-performance mixed-signal and multifunction radio-frequency ICs.

The Art of Piecewise Linear Approximation in MMSE Estimator for Most Accurate and Fast Frequency Extraction in DIFM Receivers

Detection of wideband passive radar signals, accomplished by instantaneous frequency measurement (IFM) systems, is crucial for gaining a profound knowledge of environmental circumstances. The need for fast pulse detection has hindered the investigation of frequency extraction with higher accuracy in IFM receivers. A noteworthy research in recent years shows that fast and reliable frequency extraction in high bit-count (HBC) IFMs while attaining a better frequency accuracy [called intelligent, reliable, and design-independent (InReDI)] is feasible. In addition, some investigated process-intensive algorithms like the minimum mean squared error (MMSE) estimator promise excellent frequency accuracy. In this work, we present a new method of MMSE algorithm modified by a piecewise linear approximation [named linear approximation of MMSE (LAMMSE)]. By utilizing the InReDI methodology and the novel LAMMSE algorithm, we propose a new architecture for a fast, accurate, and reliable frequency extraction (FAREx) in HBC digital IFMs (DIFM) receivers. The proposed FAREx architecture resolves the compromise challenge between frequency accuracy and extraction speed that has been long lingered in DIFM receivers. We have implemented the new architecture using Xilinx field-programmable gate array (FPGA) on a fabricated 15 bit, 2–4 GHz, and 70 dB dynamic range IFM receiver. The measurement results show an average frequency rms error of 1.43 MHz for a CW signal, 2.49 MHz average rms error for a 50 ns pulsed input signal, and 2.7 MP/s detection speed, representing a state-of-the-art receiver and a breakthrough compared to the latest works.

МОДЕЛЬ ПРИЕМНИКА ОПЕРАТИВНОГО ИЗМЕРЕНИЯ ЧАСТОТЫ С ПРЕДВАРИТЕЛЬНЫМ УМНОЖЕНИЕМ ЧАСТОТЫ И ДОПОЛНИТЕЛЬНЫМ КАНАЛОМ НА ОСНОВЕ НЕЛИНЕЙНЫХ ПАРАМЕТРОВ РАССЕЯНИЯ

The article deals with instantaneous frequency measurement (IFM) receiver model. Proposed receiver exploits preliminary frequency multiplication of input signal and auxiliary microwave detector channel. Article goal is investigation of microwave transfer coefficient irregularity compensation method. Another goal is investigation and reduction of measurement error sources. Research goals are reached by mathematical model construction and it further investigation. Mathematical model is based on the nonlinear large signal scattering parameters. Model demonstrates that preliminary frequency multiplication allows reduction of required group delay time of delay line. It is showed that measurement result affected by transfer coefficient irregularity, transfer coefficient instability of receiver chain elements and multiply reflected from irregularities waves. Auxiliary measurement channel and measurement function in the form of voltage ratio at basic channel detector and auxiliary channel detector provide a way to reduce influence of input signal amplitude, instabilities and irregularities of transfer coefficient on the frequency measurement result. It is showed that full reduction of aforementioned factors prevented by parasitic harmonics and multiply reflected waves. Required suppression level of parasitic harmonic are presented. Obtained results can find applications in sphere of electronic warfare and measurement theory and techniques.

Chip-scale Brillouin instantaneous frequency measurement by use of one-shot frequency-to-power mapping based on lock-in amplification

We demonstrate a chip-scale scheme of Brillouin instantaneous frequency measurement (IFM) in a CMOS-compatible doped silica waveguide chip. In the chip-scale Brillouin IFM scheme, the frequency-to-power mapping process is achieved by one-shot detection without additional time averaging and implemented by lock-in amplification, which successfully detects the Brillouin gain of the doped silica waveguide chip in the time domain. A Costas frequency modulated signal ranging from 8 GHz to 9 GHz is experimentally measured, and the frequency measurement errors are maintained within 58 MHz.

Measurement and Analysis of Instantaneous Microwave Frequency Based on Bisymmetric Stimulated Brillouin Scattering Effect

Measurement and Analysis of Instantaneous Microwave Frequency Based on Bisymmetric Stimulated Brillouin Scattering Effect

Wind-Induced Displacement Analysis for a Traffic Light Structure Based on a Low-Cost Doppler Radar Array

This study is concerned with the analysis of the displacement measurements simultaneously retrieved from multiple Doppler radars placed at different positions of a traffic light's mast. Currently, the structural health monitoring (SHM) works based on portable Doppler radars consider primarily methods for the extraction of displacement measurements. However, other measurements in the form of instantaneous natural frequencies and mode shapes can also be calculated with the use of Doppler radars arranged as an array. In this article, the wind-induced vibration displacement analysis based on a low-cost Doppler radar array is proposed. The sensitivity of the proposed array to changes in the instantaneous natural frequencies is evaluated. In addition, the structural modal analysis based on a Doppler radar array operating in the passive backscattering mode is demonstrated. The accuracy of the measurements obtained from the radars' demodulated data is compared with the accelerometer-based measurements. The ability of the proposed array to provide instantaneous natural frequency measurements and structural modal analysis is validated by the experimental results.

Microwave Instantaneous Frequency Measurement Based on Single Lightpath Polarization Multiplexing

Microwave Instantaneous Frequency Measurement Based on Single Lightpath Polarization Multiplexing