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Photonic architecture for remote multi-parameter measurement and transmission of microwave signals
Optics Express
Abstract
A photonic architecture for remote multi-parameter measurement and transmission of microwave signals is proposed and demonstrated, which utilizes a dual-parallel dual-drive Mach-Zehnder modulator (DP-DDMZM) in the antenna unit and a dual-drive Mach-Zehnder modulator (DDMZM) in the processing unit. Doppler frequency shift (DFS) and angle of arrival (AOA) can be determined by analyzing the down-converted intermediate frequency signals. Introducing a reference signal in the processing unit ensures DFS measurement without directional ambiguity. The proposed architecture can also be applied for instantaneous frequency measurement based on down-conversion. Due to the use of optical single sideband modulation, long-distance transmission of radio frequency (RF) signals without dispersion-induced power fading can be achieved. Experiments for accurate and stable DFS and AOA measurement as well as long-distance RF signal transmission with dispersion-induced power fading are presented. The approach avoids the use of optical filters and polarization-related devices, facilitating wideband and stable operation, which is highly desirable. The proposed architecture is a potential solution for microwave photonic antenna remoting, offering support for both remote transmission and multi-parameter measurement.
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This work proposes compact multimode Multiple-Input Multiple-Output (MIMO) antennas for Angle of Arrival (AoA) estimation in miniaturized Internet of Things (IoT) systems. The method excites different orthogonal radiating modes (TM
$_{21}$
, TM
$_{02}$
, and TM
$_{31}$
modes) for beamforming capabilities, and the AoA performance is investigated using the MUltiple SIgnal Classification (MUSIC) algorithm, executed using numerical and experimental data. The technique is tested at
$2.238 \,\mathrm{GHz}$
, while using an antenna diameter
$< 7.5 \,\mathrm{cm}$
. Overall, an Envelope Correlation Coefficient (ECC)
$< 0.01$
is realized between all antenna ports, and a
$360^{\circ }$
field of view AoA estimation is demonstrated across the entire azimuthal plane with mean absolute errors smaller than
$0.098^{\circ }$
. Furthermore, it is shown that the capability of separating multiple simultaneous impinging signals is comparable to that of state-of-the-art circular arrays with similar number of RF transceivers, while offering respectively up to
$35\%$
and
$71\%$
antenna diameter and height miniaturization.
This paper presents an angle-of-arrival (AOA) measurement system based on microwave photonic frequency down conversion. It has the novelty of no LO is needed for the frequency conversion process. Instead, a ramp waveform is used to shift the frequency of an optical carrier, which is phase modulated by a microwave signal in the subsequent stage. Two low-frequency IF signals are generated after photodetection. The AOA of the incoming microwave signal can be determined by measuring the phase difference of the two IF signals. Comparing with the previously reported frequency converter based AOA measurement systems, the proposed structure does not need a high-frequency tunable LO source and high-frequency electrical components. Expensive and bulky equipment such as an electrical spectrum analyser are not required in the proposed AOA measurement system. Experimental results show AOA measurement of different-frequency and different-power microwave signals, with small measurement errors.
This paper describes the implementation of a Doppler spectrum measurement platform for narrowband frequency-dispersive vehicle-to-vehicle (V2V) channels. The platform is based on a continuous-wave (CW) channel sounding approach widely used for path-loss and large-scale fading measurements, but whose effectiveness to measure the Doppler spectrum of V2V channels is not equally known. This channel sounding method is implemented using general-purpose hardware in a configuration that is easy to replicate and that enables a partial characterization of frequency-dispersive V2V channels at a fraction of the cost of a dedicated channel sounder. The platform was assessed in a series of field experiments that collected empirical data of the instantaneous Doppler spectrum, the mean Doppler shift, the Doppler spread, the path-loss profile, and the large-scale fading distribution of V2V channels under realistic driving conditions. These experiments were conducted in a highway scenario near San Luis Potosí, México, at two different carrier frequencies, one at 760MHz and the other at 2,500MHz. The transmitting and receiving vehicles were moving in the same direction at varying speeds, ranging from 20 to 130km/h and dictated by the unpredictable traffic conditions. The obtained results demonstrate that the presented measurement platform enables the spectral characterization of narrowband V2V channels and the identification of their Doppler signatures in relevant road-safety scenarios, such as those involving overtaking maneuvers and rapid vehicles approaching the transmitter and receiver in the opposite direction.
A simple and all-optical Doppler frequency shift (DFS) measurement system is presented. It is based on a dual-drive Mach Zehnder modulator (DDMZM) driven by a transmitted signal and an echo signal received by an antenna. A low-frequency sawtooth wave is applied to the DDMZM DC port to frequency shift the carrier and sidebands generated by the transmitted signal. Beating of a frequency-shifted transmitted signal sideband and an echo signal sideband at the photodetector produces a low-frequency electrical signal. The DFS, and consequently the speed and moving direction of a target, can be obtained from the frequency of this low-frequency electrical signal. The DDMZM used in the proposed DFS measurement system does not need to be operated at a specific point in the transfer function and hence it has no bias drift problem. The proposed DFS measurement technique can be used in both CW and pulsed radar systems. Experimental results demonstrate the proposed DFS measurement system has a wide operating frequency range of 10 GHz to 19.95 GHz, small DFS measurement error of less than ±0.6 Hz and long-term stable performance. Results also demonstrate, for the first time, DFS measurement of a pulsed signal using a microwave photonic technique.
A photonic scheme that can simultaneously estimate the microwave Doppler-frequency shift (DFS) and angle-of-arrive (AOA) is demonstrated. In the proposed system, the transmitted signal is independently mixed with two echo signals by a dual-channel microwave photonic mixer. By measuring the frequency of the intermediate frequency (IF) signal output from the two channels and the phase difference between them, the DFS (with direction identification) and AOA parameters can be obtained. In a proof-of-concept experiment, the errors are less than ${{\pm}}\;{0.08}\;{\rm{Hz}}$ ± 0.08 H z for the DFS measurement within a range of ${\rm{\pm 100}}\;{\rm{kHz}}$ ± 100 k H z and less than ${\rm{\pm 1}.{3}}\deg$ ± 1 . 3 deg for the AOA measurement ranging from 0° to 90°, respectively.
Phased array radars have remarkable advantages over radars with single-element antenna in terms of agility, flexibility, robustness, and reconfigurability. Current pure-electronic phased array radars face challenges when operating with a large frequency tunable range and/or with broad instantaneous bandwidth. Microwave photonics, which allows wide bandwidth, flat frequency response, low transmission loss, and immunity to electromagnetic interference, is a promising solution to cope with issues faced by pure electronics. In this paper, we introduce a general architecture of microwave photonic array radar systems and review the recent advancement of optical beamforming networks. The key elements for modelling the response of the true time delay (TTD) and/or phase-shifting unit are presented and discussed. Two typical array antenna structures are introduced, i.e., microwave photonic phase shifter based array and optical true time delay based array, of which the principle and typical implementations are described. High-resolution inverse synthetic aperture radar (ISAR) imaging is also realized based on a microwave photonic array radar. The possibility of on-chip integration of the microwave photonic array radar is discussed.
A simple approach to estimating microwave Doppler frequency shift (DFS) based on a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is capable of estimating both the value and direction of the DFS simultaneously and precisely owing to the introduction of the reference signal. In the proposed approach, the transmitted signal (microwave carrier) and the reference signal are loaded on the upper branch of the DP-QPSK modulator to generate carrier suppression double-sideband signals, respectively, while the echo signal is loaded on the lower branch of the DP-QPSK modulator to perform carrier suppression single-sideband modulation. Then optical sidebands of two branches are combined and sent to a low-speed photodetector to heterodyne. The value of the DFS is equivalent to the frequency of the beat signal between the transmitted and reference signals; meanwhile, the direction can be distinguished by comparing the frequency of the beat signal between the transmitted and reference signals with the frequency of the beat signal between the echo and reference signals. In the experiment, the accurate measurement of DFSs from $ - {100}\;{\rm kHz}$ − 100 k H z to $ + {100}\;{\rm kHz}$ + 100 k H z at the carrier frequencies of 15, 20, 35, and 39 GHz is implemented with errors less than $ \pm {10}\;{\rm Hz}$ ± 10 H z .
A novel Doppler frequency shift (DFS) measurement system based on a cascaded modulator topology is presented. It is capable to measure both the object speed and moving direction on an electrical spectrum analyser with the use of a fixed low-frequency reference signal. It has a simple single-laser and single-photodetector structure, a robust performance and a wide operating frequency range, which is only limited by the optical modulator bandwidth. Experimental results are presented that demonstrate DFS ranging from -100 kHz to +100 kHz with an error of less than ±10.1 Hz at different microwave signal frequencies. Over 35 dB suppression in unwanted frequency components present at the system output is also demonstrated.
A photonic method used to simultaneously measure the Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) of microwave signals is proposed and experimentally demonstrated. At the remote antenna unit (RAU), the local oscillator (LO) signal and two echo signals are applied to a phase modulator (PM) and a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM), respectively. After transmission over a fiber link, the DFS and AOA parameters can be obtained by processing the two low-frequency electrical signals at the central office (CO). Experimental results show that the DFS between ± 100-kHz with < ± 5 × 10⁻³-Hz error and the AOA from 1.82° to 90° with <0.85° error at 10 GHz are obtained over a 10-km single mode fiber (SMF) transmission. Moreover, the DFS direction can also be distinguished by comparing the phase difference of two electrical signals.
An improved sensitivity Doppler frequency measurement system based on microwave photonics technology was demonstrated practically. The system employs a four-wave mixing effect to achieve broad radio-frequency (RF) frequency measurement. In addition, a lock-in amplification technique was utilized to achieve high-measurement sensitivity. The system is, thus, capable of Doppler frequency estimation of radar echoes with a carrier frequency up to 40 GHz and a power level as low as $-$35 dBm.
Many conventional Doppler analysis techniques for radar sensors suffer from velocity ambiguity when confronted with targets that are moving at speeds higher than the Nyquist velocity. The present paper proposes a signal processing method for estimating accurately the Doppler velocity of targets from such sub-Nyquist radar data. The hypothesis tested in the paper is the possibility of circumventing the velocity ambiguity by exploiting the high range resolution of ultra-wideband radar sensors, more specifically incorporating the texture method applied to the signal envelope intensity profile. We employ a millimeter-wave radar sensor operating at 60 GHz to measure a rotating cylinder and a walking human to investigate the applicability of the proposed approach. The experimental results indicate that the proposed method can estimate the Doppler velocity accurately without aliasing from sub-Nyquist data, demonstrating that the use of the texture method is promising for resolving the ambiguity caused by sub-Nyquist sampling. The advantage of the proposed method is that the ambiguity can be resolved simply with the signal processing technique, and the approach does not require any custom hardware such as nonuniform samplers. An important future study based on the current paper is the application of the proposed approach to develop a low-cost radar system with a low sampling rate that can measure fast-moving targets.
A photonic approach for both wideband Doppler frequency shift (DFS) measurement and direction ambiguity resolution is proposed and experimentally demonstrated. In the proposed approach, a light wave from a laser diode is split into two paths. In one path, the DFS information is converted into an optical sideband close to the optical carrier by using two cascaded electro-optic modulators, while in the other path, the optical carrier is up-shifted by a specific value (e.g., from several MHz to hundreds of MHz) using an optical-frequency shift module. Then the optical signals from the two paths are combined and detected by a low-speed photodetector (PD), generating a low-frequency electronic signal. Through a subtraction between the specific optical frequency shift and the measured frequency of the low-frequency signal, the value of DFS is estimated from the derived absolute value, and the direction ambiguity is resolved from the derived sign (i.e., + or −). In the proof-of-concept experiments, DFSs from − 90 to 90 kHz are successfully estimated for microwave signals at 10, 15, and 20 GHz, where the estimation errors are lower than ± 60 Hz . The estimation errors can be further reduced via the use of a more stable optical frequency shift module.
The Angle of Arrival (AoA) is an important factor in the localization of a wireless sensor network. This paper deals with AoA measurement using omnidirectional antennas. In our case microstrip monopole antennas are used which have radiation patterns with two sharp minimums. Therefore, an algorithm based on an approach where an AoA is obtained along a direction where the measured received strength signal indicator (RSSI) is minimal. Multiple stationary microstrip antennas are placed on a printed circuit–board and no moving parts are needed for measurement. In comparison with rotating antennas this simple method has lower resolution. We show that the resolution can be improved using interpolations and approximations. When using the proposed algorithm, the experimental results for the outdoor measurements reached a root-mean-square error (RMSE) of less than 10 • , and an indoor environment of less than 25 •. Index Terms—Angle of Arrival (AoA), Omnidirectional Antenna , Received Signal Strength Indicator (RSSI), Wireless Sensor Network (WSN).
High-resolution Doppler frequency shift (DFS) estimation in a wide frequency range is essential for radar, microwave/millimeter-wave, and communication systems. In this paper, a photonic approach to DFS estimation is proposed and experimentally demonstrated, providing a high-resolution and frequency-independent solution. In the proposed approach, the DFS between the transmitted microwave signal and the received echo signal is mapped into a doubled frequency spacing between two target optical sidebands by using two cascaded electrooptic modulators. Subsequently, the DFS is then estimated through the spectrum analysis of a low-frequency electrical signal generated from the frequency beating of the two target sidebands with an improved resolution by a factor of 2. In the experiments, DFSs from ${-}{hbox{90}}$ to 90 kHz are successfully estimated for microwave/millimeter-wave signals at 10, 15, and 30 GHz, where the estimation errors are lower than $pm {hbox{5}} times {hbox{10}}^{-10}$ Hz. For radial velocity measurement, these results reveal a range from 0 to 900 m/s and a resolution of ${hbox{1}} times {hbox{10}}^{-11}$ m/s at 15-GHz frequency band, or a range from 0 to 450 m/s and a resolution of ${hbox{5}} times {hbox{10}}^{-12}$ m/s at 30-GHz band. To eliminate the estimation ambiguity, a reference branch is introduced for generating an indicator frequency to discriminate the sign of DFS and the direction of radial velocity for approaching or receding motion. In addition, extended discussions on the signal-to-noise ratio, the minimum measurable DFS, and other detection features of the proposed approach are presented.
An optical wireless location (OWL) system is introduced for indoor positioning. The OWL system makes use of a mobile photoreceiver that facilitates triangulation by measuring angle-of-arrival (AOA) bearings from LEDs in an optical beacon grid. The photoreceiver has three photodiodes (PDs), arranged in a corner-cube, to facilitate differential photocurrent sensing of the incident light AOA, by way of azimuthal ϕand polar θ angles. The AOA error for indoor positioning is characterized empirically. Optical AOA positioning is shown to have a fundamental advantage over known optical received signal strength (RSS) positioning, as AOA estimation is insensitive to power and alignment imbalances of the optical beacon grid. The OWL system is built, and a performance comparison is carried out between optical AOA and RSS positioning. It is shown that optical AOA positioning can achieve a mean 3-D positioning error of only 5 cm. Experimental design and future prospects of optical AOA positioning are discussed.
We experimentally demonstrate a widely tunable opto-electronic oscillator (TOEO) based on a tunable optical resonant filter and a wideband phase modulator. The oscillator can be tuned in the range of 2-15 GHz, limited by the bandwidth of the RF components utilized in the loop, with a tuning speed greater than 1 GHz/μs. The TOEO, with 220 m fiber link used as the high Q element, is characterized with phase noise less than -100 dBc measured at 10 kHz frequency offset. The agile tunable optical filter in the TOEO is a whispering gallery mode resonator made of lithium tantalate crystal. We develop a theoretical model for the TOEO and find a good agreement between the measurement results and the theoretical predictions.
A photonic-assisted microwave channelizer with improved
channel characteristics based on spectrum-controlled stimulated
Brillouin scattering (SBS) is proposed and experimentally
demonstrated. In the proposed system, lightwaves from a laser
array are multiplexed and then split into two paths. In the upper
path, the lightwaves are modulated by a microwave signal with its
frequency to be measured. In the lower path, for each lightwave,
the wavelength is shifted to a specific shorter wavelength via carrier-
suppressed single-sideband modulation and the spectrum is
then shaped. The wavelength-shifted and spectrum-shaped lightwaves
are used to pump a single-mode fiber to trigger SBS. Thanks
to the SBS effect, multiple gain channels at the wavelengths are
generated. The channel profile of each channel, determined by the
designed spectral shape of the pump source, is improved with a flat
top and a reduced shape factor. The characteristics including the
bandwidth, channel spacing, and channel profile can be controlled
by adjusting the spectral shape of the pump source.Aproof-of-concept
experiment is performed. A microwave channelizer with a
shape factor less than 2, a tunable channel bandwidth of 40, 60,
or 90 MHz, and a tunable channel spacing of 50, 70, or 80 MHz, is
demonstrated.
We demonstrate a 60 GHz broadband picocellular Radio-over-Fiber network architecture that enables seamless con-nectivity for highly mobile end-users. Its seamless communication capabilities arise by the supported handover scheme that relies on a novel Moving Extended Cell (MEC) concept. MEC exploits user-centric virtual groups of adjacent cells that transmit the same data content to the user and utilizes a switch mechanism for restructuring the virtual multi-cell area according to the user's mobility pattern, so that a virtual antenna group moves together with the mobile user. We present the theoretical formulation for MEC and show that it can provide zero packet loss and call dropping probability values in high-rate wireless services for a broad range of mobile speeds up to 40 m/sec, independently of the fiber link distances. We also demonstrate the physical layer network architecture and switch mechanism both for a RoF network with a single 60 GHz radio frequency (RF) over each wavelength, as well as for a RoF configuration supporting simultaneous multi-RF channel transmission over each optical wavelength. The performance of the multi-RF-over-network implementation is evaluated via simulations showing successful 100 Mb/s radio signal transmission over fiber links longer than 30 km. To this end, MEC can enable seamless connectivity and bandwidth guarantees in 60 GHz picocellular RoF networks being also capable of serving multiple users over the same wavelength in a RF frequency-division-multiplexed (FDM) approach.
Broadband and low loss capability of photonics has led to an ever-increasing interest in its use for the generation, processing, control and distribution of microwave and millimeter-wave signals for applications such as broadband wireless access networks, sensor networks, radar, satellite communitarians, instrumentation and warfare systems. In this tutorial, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion. Challenges in system implementation for practical applications and new areas of research in microwave photonics are also discussed.
When, in addition to the constant Doppler frequency shift induced by the bulk motion of a radar target, the target or any structure on the target undergoes micro-motion dynamics, such as mechanical vibrations or rotations, the micro-motion dynamics induce Doppler modulations on the returned signal, referred to as the micro-Doppler effect. We introduce the micro-Doppler phenomenon in radar, develop a model of Doppler modulations, derive formulas of micro-Doppler induced by targets with vibration, rotation, tumbling and coning motions, and verify them by simulation studies, analyze time-varying micro-Doppler features using high-resolution time-frequency transforms, and demonstrate the micro-Doppler effect observed in real radar data.
A simplified Doppler frequency shift (DFS) measurement approach based on Serrodyne optical frequency translation is reported. A sawtooth wave with high amplitude is sent to one phase modulation arm of a Mach-Zehnder modulator in conjunction with the transmitted signal to implement the Serrodyne optical frequency translation, as well as the optical phase modulation of the transmitted signal on the frequency-shifted optical carrier. The echo signal is applied to the other arm of the modulator. The lower first-order optical sidebands from the modulator are selected by an optical bandpass filter and detected in a photodetector. By measuring the frequency of the output low-frequency signal, the value and direction of the DFS can be determined. DFS from -100 to 100 kHz is measured for 6- to 17-GHz microwave signals with a measurement error of ±0.03 Hz and a measurement stability of ±0.015 Hz in 30 min when a 500-kHz sawtooth wave is used.
We report a novel simple photonic approach for measuring the Doppler frequency shift (DFS) and the angle of arrival (AOA) of a microwave signal in a radar detection system. The echo signals combined with a reference signal are applied to a dual-polarization Mach-Zehnder modulator (DPol-MZM), and a low-frequency electrical signal is generated after beating between the two signals in a low-speed photodetector. The DFS without direction ambiguity can be calculated by the value of the low-frequency signal. A phase difference is introduced between two echo signals which are sent to two sub-MZMs of the DPol-MZM respectively. The AOA is determined by the peak power of the down-convert signals, and a simple calibration is used to remove the amplitude of the echo signals and the reference signal by switching the output polarization states of the system. Compared with previously reported works, the proposed method carries out a comprehensive and multifunction measurement system based on a filterless and simple structure. Experimental results demonstrate the DFS errors within ± 0.5 Hz for a 15 GHz echo signal with a frequency offset of ± 100 kHz, and AOA measurement errors are within ± 1° for a range of 16° – 82°.
A dual channel system based on a dual-parallel Mach-Zehnder modulator (DPMZM) is proposed for simultaneous measurement of angle of arrival (AOA) and Doppler frequency shift (DFS). The echo signals are received by two antennas and sent into two sub modulators (sub-MZMs) of the DPMZM respectively. The transmitted signal is fed into one of the sub-MZMs to act as a local oscillator signal. The upper and the lower sidebands of the output signal from the DPMZM are separated by a wavelength-division multiplexer (WDM) to form two channels. By measuring the power of the beating signal of the two channels, the AOA can be measured and the phase measurement error is less than 3.4° in the range of about 300° (The AOA is measured from ±10° to ±90°). Moreover, the system can measure DFS with the measurement error less than 0.07 Hz and determine the DFS direction by comparing the phase relationship between the two channels. The system structure is simple and compact, which is a simple and effective solution for modern radar and electronic warfare receiver.
A filter-free photonic approach for measuring microwave Doppler frequency shift (DFS) based on two cascaded electro-optic modulators (EOMs) and a fixed low-frequency reference signal is proposed. An optical carrier is carrier-suppressed single-sideband modulated by the transmitted signal and the reference signal at EOM-I. The output from EOM-I is then single-sideband modulated by the echo signal at EOM-II. Subsequently, the output from EOM-II is injected into a photodetector to implement optical-to-electrical conversion. Both the value and direction of the DFS can be obtained by analyzing the frequency of the generated low-frequency electrical signal. The proposed approach has a compact structure and no optical filtering is needed. An experiment is performed to verify the proposed approach. For different microwave frequencies from 7 to 16 GHz, DFS from -100 kHz to 100 kHz is measured, with a measurement error of less than ± 0.05 Hz. The stability of the system is also verified. Within 30 minutes, the change of measurement error is less than ± 0.05 Hz.
A novel photonic approach for wideband Doppler frequency Shift (DFS) measurement and direction discrimination based on phase modulators (PMs) and optical frequency shift module is proposed and experimentally demonstrated. In the proposed scheme, a light emitted from the laser is split into two paths, one of which is modulated by the transmitted signal through the first PM and the other of which passes through the carrier frequency shifter and then is modulated by the echo signal through the second PM. After combining two optical signals and filtering out the negative sidebands, the value and direction of DFS can be obtained by comparing two peak frequencies in the low-frequency electrical signals generated by a low-speed photodetector. Proof-of-concept experiments with DFSs from -1 MHz to 1 MHz at an optical carrier frequency shift of 40 MHz are implemented, where the measurement errors are kept within ±0.7 Hz.
A new photonics-based microwave angle of arrival (AOA) measurement system is presented. It is based on a single-laser, single dual-drive Mach Zehnder modulator (DDMZM) and single-photodetector structure. The AOA of a microwave signal can be determined by simply measuring the system output DC voltage. The proposed system is suitable for determining the AOA of a microwave signal with a single frequency or a band of frequencies, and has a wide AOA measurement range. Experimental results are presented that demonstrate an AOA measurement range of 0° to 76.8° and 12.6° to 90° without and with introducing a time delay to one of the DDMZM input RF ports respectively, and measurement errors of less than 2°. Results also demonstrate an AOA measurement for a pseudorandom binary sequence signal upconverted into a microwave frequency.
In this paper, we introduce a novel concept for frequency-modulated continuous-wave radar. The approach is based on an interlaced chirp sequence waveform, which is controlled by phase-locked loops (PLLs). The use of PLLs improves frequency chirp linearity and reduces phase noise compared with open-loop voltage-controlled oscillators commonly used to generate the fast chirps. In contrast to basic range–Doppler processing, it enables higher target velocities to be detected unambiguously at the same resolution, which makes it suitable for automotive applications. Separate frequency synthesizers generate the interlaced ramps in the system. An RF switch combines these two signals to suppress transients caused by oscillator overshoot and to avoid incoherencies due to programming times of the PLL ICs. We built a prototype radar system in K-band. The test results are promising and bode well for other applications.
As an emerging topic, photonic-assisted microwave measurements with distinct features such as wide frequency coverage, large instantaneous bandwidth, low frequency-dependent loss, and immunity to electromagnetic interference, have been studied extensively recently. In this article, we provide a comprehensive overview of the latest advances in photonic microwave measurements, including microwave spectrum analysis, instantaneous frequency measurement, microwave channelization, Doppler frequency shift measurement, angle-of-arrival detection, time-frequency analysis, compressive sensing, and phase noise measurement. A photonic microwave radar, as a functional measurement system, is also reviewed. The performance of the photonic measurement solutions is evaluated and compared with the electronic solutions. Future prospects using photonic integrated circuits and software-defined architectures to further improve the measurement performance are also discussed.
A standalone microwave photonics system for Doppler frequency measurement purposes is conceived and demonstrated practically. The system exhibits a maximum of 1.61% relative error in Doppler frequency estimation at the worst case. Utilization of all optical mixing has enabled RF frequency independent operation. The system is thus capable of operating at any radar carrier frequency up to 40 GHz. This makes it a perfect candidate for various types of photonic-based radars and frequency agility systems.
A novel parallel optical delay detector is proposed for angle-of-arrival (AOA) measurement of a microwave signal with accuracy monitoring. A theoretical model is built up to analyze the proposed system, including measurement accuracy monitoring. The measurements of AOA are then experimentally investigated with monitored measurement accuracy.
Microwave photonics, which brings together the worlds of radiofrequency engineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years and is set to have a bright future. The technology makes it possible to have functions in microwave systems that are complex or even not directly possible in the radiofrequency domain and also creates new opportunities for telecommunication networks. Here we introduce the technology to the photonics community and summarize recent research and important applications.
A Ti:NiNbO<sub>3</sub> serrodyne optical frequency shifter with
40-dB overall sideband suppression has been demonstrated. This
performance can be achieved using either a laser diode or a broadband
superluminescent diode as an optical source. The device utilizes a
single-polarization waveguide design and a specialized sawtooth drive
circuit
A general derivation of the optical modulation process in a
dual-drive Mach-Zehnder modulator (DD-MZM) is introduced. The
expressions include all harmonics and are entirely general in terms of
bias point. Chromatic dispersion is also included allowing the
prediction of a number of important phenomena in photonic signal
transmission. Examples of special cases of these general equations are
then presented. Similar expressions are introduced for harmonic optical
up-conversion through a photonic mixer based on a DD-MZM covering any
bias point or phase shift between DD-MZM drives