range-Doppler Resolution Research Articles

Multi-passive coherent location radar system for detection range and range-doppler resolution in Tarakan

The presence of many radio frequency illuminators in an area provides an opportunity to be used as a transmission source for a passive radar system called a passive coherent locator (PCL). Unlike the active radar, the passive radar provides advantages such as low cost without an active transmitter, potential for broad range measurements, portable in construction, anti-detectable by active radar or electronic counter measures (ECM), etc. Just like other areas where there are many PCL in Tarakan such as FM radio transmission (RRI), many base-stations (BTS) from 4G-LTE network, digital TV transmission, access-point (AP) from wireless fidelity (WiFi), and so on. This paper will present and analyze all of these PCLs which include predictions of performance and ambiguity function (AF). Performance prediction is related to range detection which provides information about target detection range, radar cross section, and range-velocity resolution. While AF analyzes the transmit waveform of all PCL which gives a limit of resolution to the range and Doppler of adjacent targets. The results of the evaluation and analysis of performance predictions show that FM radio transmission (RRI) has a range and velocity resolution of 1 km and 12 m/s, respectively and the detection range at a maximum SNR of 15 dB is around 4 km. While the results of the AF evaluation on the PCL obtained range and Doppler resolution of around 2.73 km and 500 Hz, respectively.

Photonic joint radar and communication system using a chirp-polarity coded LFM waveform

A photonic joint radar and communication system using a frequency improved, bandwidth doubled, chirp-polarity coded linear frequency modulation (LFM) waveform is proposed and demonstrated. In the scheme, a dual-polarization modulator is driven by a repetitive LFM waveform and an RF signal to generate different optical sidebands in two orthogonal polarization directions. Then, the orthogonally polarized optical sidebands are filtered and polarization modulated to achieve chirp-polarity coding. The generated signal is employed to simultaneously perform dual functions. Both the radar echo and the communication reception are processed based on optical de-chirping. The approach is demonstrated by simulation. A chirp-polarity coded LFM waveform with central frequency of 24 GHz, bandwidth of 8 GHz, bit rate of 10 Mbit/s is generated and processed for dual functions. The radar range resolution, unambiguous range, and range-Doppler resolution are investigated. The optical demodulation of the communication is verified, and the speed improvement of communication is discussed.

Multiband dual- and cross-LFM waveform generation using a dual-drive Mach–Zehnder​ modulator

Linear frequency modulation (LFM) signals are widely used in modern radar systems owing to their intrinsic pulse compression capability but are restricted due to a limited range-Doppler resolution. On the other hand, dual- or cross-LFM signals have complementary LFM waveforms at the same time instant that reduces the range-Doppler coupling and thus improving range-Doppler resolution. We propose a simple microwave-photonic-based approach to generate multiband dual- and cross-LFM waveforms using only a single dual-drive Mach–Zehnder modulator (DDMZM). A theoretical analysis is carried out, which is modeled and verified through experiments. Dual- and cross-LFM waveforms at a carrier frequency of 6 GHz and 18 GHz with a bandwidth of 2 GHz is generated by controlling the DC and RF bias of the DDMZM. The tunability of the carrier frequency from 3 GHz to 9 GHz is also verified. A range resolution of 6.3 cm for dual- and cross-LFM waveforms, is obtained with a time-bandwidth-product (TBWP) of 20,000. The proposed technique is a promising solution for dual- and cross-LFM waveform generation in two-band multipurpose radar systems.

Photonic Generation of a Tunable Dual-Chirp Microwave Waveform

A photonic-assisted tunable dual-chirp microwave waveform generator based on optical heterodyne detection is proposed and experimentally demonstrated. In the proposed scheme, a three-electrode distributed Bragg reflector laser diode (DBR-LD) is used to generate a broadband frequency-chirped optical pulse. A stable optical fiber laser and a Mach-Zehnder modulator (MZM) are used to perform a double-sideband suppressed carrier (DSB-SC) signal. The frequency difference between the two sidebands of the DSB-SC signal is larger than the frequency chirp range of the optical pulse. By tuning the center frequency of the optical pulse equals that of the DSB-SC signal and beating the optical pulse and the DSB-SC signal at a photodetector (PD), a dual-chirp microwave waveform is generated. The center frequency of the generated waveform is tuned by adjusting the modulated frequency of the DSB-SC signal. The tunability of the bandwidth and the temporal duration are achieved by tuning the optical pulse. Experimental results show that the center frequency, the bandwidth, and the temporal duration have tuning ranges from 7 to 13 GHz, 13 to 17 GHz, and 500 ns to 50 μs, respectively. Chirp rates up to ±26 GHz/μs for the up- and down-chirp waveforms are measured in the experimental demonstration, respectively. The demonstration shows new avenues to implement high-performance dual-chirp microwave waveform generators for applications in modern radar systems with improved range-Doppler resolution.

Joint range-Doppler resolution limit for multi-pulse radar based on scattering information

Resolution limits are essential tools in the evaluation of parameter system performance. However, there is very limited literature that deals with the resolution limit for joint estimation of multi-parameters. In this paper, we employ thoughts of information theory to propose a joint resolution limit (JRL) for range and Doppler shift estimation in multi-pulse radar. Based on the general multi-pulse radar model, the closed-form expression of scattering information is derived for two targets with complex Gaussian scattering properties. A critical state is selected where the quadrature component of the scattering information is 1 bit and corresponding intervals of range and Doppler shift are defined as the JRL. Under the assumption of adjacent targets, the closed-form approximation for the JRL is obtained by a second-order Taylor series, which illustrates that there exists interference between range and Doppler shift. In addition, explicit range resolution limit and explicit Doppler shift resolution limit are derived as special cases of the explicit JRL. These resolution limits are general and are not based on any specific resolution method. Numerical simulations are performed to validate the validity of the proposed resolution limits.

Flexible Multi-band Dual-chirped Microwave Waveforms Generation with Double Bandwidth

ABSTRACT A multi-band dual-chirp linearly frequency modulated (LFM) signal-generation scheme with doubled chirp bandwidth and flexible center frequency and band numbers is proposed. In the scheme, the polarization multiplexed multi-tone optical signals with chirped phases are generated via a dual-polarization dual-parallel Mach–Zehnder modulator (DPMZM) cascaded with a polarization modulator. The two polarization multiplexed lightwaves are recombined as two linearly polarized beams by a polarization beam splitter and are detected by a balanced photodiode with a photocurrent that includes the multi-band dual-chirp LFM signal with doubled bandwidth and multiplied central frequencies but does not have a dc component. Since the orders and numbers of the generated optical sidebands are changed by adjusting the bias voltages of a DPMZM, we can obtain the multi-band dual-chirp LFM signal flexibly. Based on simulation, four-band, six-band and two seven-band dual-chirp LFM signals are generated with four groups of bias voltage configurations. For each case, every dual-chirp LFM signal of the generated multi-band dual-chirp LFM signal has a 5-GHz bandwidth and a time-bandwidth product of 512. The auto-correlations and ambiguity function of the generated LFM signal show good performance of pulse compression and range-Doppler resolution.

Generation and anti-dispersion transmission of quadrupling-bandwidth dual-chirp microwave waveform based on a polarization-division multiplexing Mach–Zehnder modulator

We propose and demonstrate a photonic approach to generate and transmit a quadrupling-bandwidth dual-chirp microwave waveform with anti-dispersion transmission. Commonly, dual-chirp microwave waveforms are generated by double-sideband modulation, which brings severe chromatic-dispersion-induced power fading (CDIP) over fiber transmission. In this scheme, we perform optical carrier suppression via a polarization controller based on an integrated polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) to eliminate the CDIP. Moreover, by properly adjusting two bias voltages of PDM-MZM, we find that the bandwidth of the generated dual-chirp microwave signal is quadrupled. It is worth mentioning that we just need to operate in the central office to realize the above-mentioned functions and no optical filters are needed, which significantly improves the limitation of the devices. The method is analyzed theoretically and proved experimentally, which is of great significance for improving range-Doppler resolution and the detection capability of radars for one-to-multi base stations over fiber transmission.

Photonics-Assisted Multi-Band Dual Linear/Nonlinear Chirp Waveform Generation Based on Optical Phase Modulation

A novel photonic scheme for generating multi-band dual-chirp waveforms with linear or nonlinear chirp rates is proposed via two cascaded polarization modulators (PolMs) paralleled with a phase modulator (PM). The cascaded PolMs produce a flat optical frequency comb (OFC) as a multi-frequency reference light, while the PM is driven by the power-function-type baseband signals to obtain the lightwave with different order phase chirp. The phase-chirped lightwave and the multi-frequency reference lightwave are orthogonally coupled by a polarization beam combiner (PBC) and then recombined via a polarization beam splitter (PBS) to make them in-phase in one output port of the PBS and anti-phase in the other. The two recombined lightwaves are detected by a balanced photodetector (BPD), and the different order dual-chirp signals, covering six bands, can be generated in their differential photocurrent without interference components. Compared with the single-chirp signal of the knife-edge-type ambiguity function, the dual-chirp signal with the peak-saliency-type ambiguity function significantly suppresses sidelobe and shows better range-Doppler resolution performance. With the 1GHz-bandwidth and 102.4ns-duration quadratic baseband driving signal, six-band linear dual-chirp signal, centered at 10, 30, 50, 70, 90 and 110GHz, are generated by simulation, and each linear dual-chirp signal has a bandwidth of 4.1GHz, the pulse compression ratio of 465.45 and the peak-to-sidelobe ratio (PSLR) of 12.8dB. As baseband driving signal has higher (3rd) order power, the six-band nonlinear dual-chirp signals with the same central frequencies can also be generated but with increased bandwidth (6.3GHz) and the improved PSLR (15.51dB). Their autocorrelation functions show that compared with the linear chirp signal, the nonlinear chirp signal has better sidelobe suppression capability, which is improve as the degree of nonlinearity increase.

Polarization Manipulated Fourier Domain Mode-Locked Optoelectronic Oscillator

We report a polarization manipulated Fourier domain mode-locked optoelectronic oscillator (FDML-OEO) using a polarization modulator (PolM). Frequency and bandwidth doubling linearly chirped microwave waveforms (LCMWs) are generated from a PolM-based FDML-OEO. The multiplying operation is capable of increasing the frequency and bandwidth of LCMWs, which doubles the time-bandwidth product of the LCMWs and makes it possible to increase the center frequency of the LCMWs beyond the bandwidth of the optical modulator. Moreover, by simply adding the other laser diode, it is also possible to generate a dual-chirp LCMW. The polarization manipulated of two optical signals avoids the undesired beating signals from optical carriers. Thus, an electrical bandpass filter which is essential in previous work is no longer required. To the best of our knowledge, this is the first time that polarization manipulation is used in FDML-OEO, which can further satisfy the demands of modern radars in terms of improved range-Doppler resolution, higher carrier frequency, and larger bandwidth.

Dual-chirp waveform generation and its TBWP improvement based on polarization modulation and phase coding

A photonics approach to generate a phase-coded dual-chirp waveform with reconfigurable time duration, arbitrary large TBWP, flexible tuning frequency and bandwidth is proposed and demonstrated. In the scheme, one polarization modulator (PolM) is applied to modulate a repetitive parabolic waveform with an dual-wavelength optical signal, while another PolM is utilized to achieve phase coding with a Pseudorandom (PN) sequence. After balanced detection, a phase-coded dual-chirp signal with improved time-bandwidth product (TBWP) can be generated. The approach is verified by simulation. Basis dual-chirp waveforms with tunable central frequency of 20 to 30 GHz, tunable bandwidth of 1.25 to 5 GHz but fixed TBWP of 16 are generated. Then, 30-GHz central frequency, 2.5-GHz bandwidth phase-coded dual-chirp signals with phase shift of π, TBWP of 240, 1008 and 2032 are obtained. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution.

Dual-chirp Fourier domain mode-locked optoelectronic oscillator.

Optoelectronic oscillators (OEOs) have been widely investigated to generate ultra-pure single-frequency microwave signals. Here, we propose and experimentally demonstrate a dual-chirp Fourier domain mode-locked (FDML) OEO to generate dual-chip microwave waveforms. In the proposed FDML OEO, a frequency-scanning dual-passband microwave photonics filter based on phase-modulation-to-intensity-modulation conversion using an optical notch filter and two laser diodes is incorporated into the OEO cavity. Fourier domain mode-locking operation is achieved by synchronizing the scanning period of the filter to the cavity round-trip time. Tunable dual-chirp microwave waveforms with a large time-bandwidth product are generated directly from the FDML OEO cavity in the experiment, which can be used in modern radar systems to improve its range-Doppler resolution.

Chromatic-dispersion-induced power-fading suppression technique for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission.

We report a technique to overcome chromatic-dispersion-induced power fading (CDIP) for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission. Normally, dual-chirp microwave signals are generated using double-sideband (DSB) modulation. However, DSB modulation suffers from CDIP significantly. We propose a carrier-frequency shift method to suppress the CDIP based on a dual-polarization dual-parallel Mach-Zehnder modulator. In addition, the bandwidth of the dual-chirp signal can be quadrupled by properly setting the biases of the modulator. The proposed technique is theoretically analyzed and experimentally verified. Our technique is promising for improving the range-Doppler resolution of radars for one-to-multi base stations transmission.

Photonic approach to dual-band dual-chirp microwave waveform generation with multiplying central frequency and bandwidth

Abstract A novel photonic approach to generate frequency and bandwidth multiplying dual-chirp microwave for application in dual-band radar system is proposed using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. The proposed approach is based on optical frequency multiplying and polarization selection. In the approach, the baseband signal and RF signal are injected into the DP-QPSK modulator to generate optical broad spectra and sidebands respectively. By adjusting the bias points of the DP-QPSK modulator, after polarization selection and optical to electrical conversion, frequency-quadrupling bandwidth-octupling and frequency-double bandwidth-quadrupling or frequency-tripling bandwidth-sextupling and frequency-fundamental bandwidth-doubling dual-chirp signals can be generated in the single structure respectively. The proposed approach is verified by simulations. Dual-chirp microwaves with central frequency–bandwidth of 32 GHz-8 GHz, 16 GHz-4 GHz or 24 GHz-6 GHz, 8 GHz-2 GHz are generated in the two ports respectively. Their autocorrelation results manifest good pulse compression capabilities. The central frequency, bandwidth, chirp rate and time duration can be tuned independently. The generated dual-chirp signals show good performance on the range-Doppler coupling and can significantly improve the range-Doppler resolution in dual-band radar system.

A New Proposed Scheme to Generate Arbitrary Microwave Waveform by Using Four C-Bands Laser

Abstract A completely photonic approach to generate a arbitrary microwave waveform having chirp nature is proposed and experimentally demonstrated. A chirp signal may be defined as the signal whose frequency increases or decreases with respect time. Signal may have arbitrary shape, it may be sinusoidal wave, triangular wave, or may have some other wave shape. Chirp signal is used to identify the pattern of moving signal having deterministic nature. In this paper an arbitrary chirped microwave waveform has been generated experimentally by using four c-band lased schemes. The chirp microwave waveform can be used in Radar system to improve its range Doppler resolution. The paper give the specific details about various performance parameters like input signal frequency and power, output signal parameters viz output frequency, chirp rate, chirp bandwidth, time bandwidth product (TBWP), etc. The overall model and its performance parameters are computed through experimental setup.

A novel approach to generate a chirp microwave waveform using temporal pulse shaping technique applicable in remote sensing application

ABSTRACTMicrowave photonics is a prominent field in which photonic technologies are used to empower and extend the functionalities of microwave system which is a very tough exercise to fulfil directly in microwave domain. A photonic technique to generate a high chirp rate arbitrary microwave waveform using dual-drive LiNbO3 has been put forward and demonstrated experimentally in this paper. Nowadays in order to increase the Range-Doppler resolution of radar, the chirp microwave waveform is widely used. The Mach-Zehnder modulator (MZM) performs the intensity modulation techniques which can operate on the principle of electro-optic effect. In this paper, the authors used a very simple and straightforward method of producing chirped arbitrary millimetre waveform by change in phase at the two arms of dual-drive LiNbO3 MZM. The generated waveform has the 3 dB bandwidth of 12.6 GHz which exists in extremely high-frequency band applicable in high-frequency microwave radio relay, microwave remote sensing, radar range resolution and millimetre wave scanner. The proposed design is simpler, cost-effective and compact than the previously proposed model of chirped waveform generation using MZM and fibre Bragg grating.

Photonic Generation of Frequency and Bandwidth Multiplying Dual-Chirp Microwave Waveform

A photonic approach to generate a frequency and bandwidth multiplying dual-chirp microwave waveform using a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and demonstrated. In the proposed scheme, an RF carrier is applied to one QPSK modulator and a baseband single-chirp waveform is applied to another. By setting the driving signals applied to the modulator and adjusting the dc bias phases in the modulator, high-order optical sidebands can be obtained with the optical carrier suppressed. After optical to electrical conversion, a frequency-doubling and bandwidth-quadrupling, or frequency-quadrupling and bandwidth-octupling dual-chirp microwave can be generated. The approach is verified by simulation. Dual-chirp microwave waveforms with 16-GHz central frequency, 2048-MHz bandwidth and 32-GHz central frequency, 4096-MHz bandwidth are generated through an 8-GHz RF carrier and 512-MHz bandwidth baseband signal. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution.

Effect of Laser Modulation on Dispersion Induced Chirp Microwave Signal Generation by Using Temporal Pulse Shaping Technique

A photonic approach for generating an arbitrary chirp microwave waveform using optical coupler of different length is proposed and experimentally demonstrated. The chirp microwave waveform can be used in Radar system to improve its range Doppler resolution. The paper give the specific details about various performance parameters like input signal frequency and power, output signal parameters viz output frequency, chirp rate, chirp bandwidth and time bandwidth product etc. In this proposed approach two single mode optical fibers of different lengths are used to create the phase variation of the light coming from the continuous wave laser. The overall model and its performance parameters are computed on optiwave software and compared with experimental results carried out in lab which shows the validity of our experimental setup.

Compressive sensing applied to radar systems: an overview

Modern radar systems tend to utilize high bandwidth, which requires high sampling rate, and in many cases, these systems involve phased array configurations with a large number of transmit–receive elements. In contrast, the ultimate goal of a radar system is often to estimate only a limited number of target parameters. Thus, there is a pursuit to find better means to perform the radar signal acquisition as well as processing with much reduced amount of data and power requirement. Recently, there has been a great interest to consider compressive sensing (CS) for radar system design; CS is a novel technique which offers the framework for sparse signal detection and estimation for optimized data handling. In radars, CS enables the achievement of better range-Doppler resolution in comparison with the traditional techniques. However, CS requires the selection of suitable (sparse) signal model, the design of measurement system as well as the implementation of appropriate signal recovery method. This work attempts to present an overview of these CS aspects, particularly when CS is applied in monostatic pulse-Doppler and MIMO type of radars. Some of the associated challenges, e.g., grid mismatch and detector design issues, are also discussed.

Dual-Chirp Microwave Waveform Generation Using a Dual-Parallel Mach-Zehnder Modulator

A photonic approach to generating a dual-chirp microwave waveform using a single dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. A dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution. In the proposed approach, a baseband single-chirp waveform is applied to one sub-Mach-Zehnder modulator (sub-MZM) in the DPMZM and a microwave carrier is applied to the other sub-MZM. By biasing the two sub-MZMs at the minimum transmission point to suppress the optical carrier, a dual-chirp microwave waveform with a central frequency upconverted to the frequency of the microwave carrier is generated. A theoretical analysis is performed, which is then verified by a proof-of-concept experiment. A dual-chirp microwave waveform at 6 GHz with a tunable bandwidth at 200 MHz and 2 GHz is generated.

Range-Doppler Resolution of the Linear-FM Noise Radar Waveform

This research considers the linear-FM (LFM) of a noise radar waveform for resolving targets when channel noise and four popular radar sidelobe weighting functions are considered. By using large time-bandwidth products and systematically varying the phase scaling factor κ, results from the digital matched filter output provide evidence that the LFM noise waveform 1) has range-Doppler resolution similar to conventional chirp waveforms and 2) has a low probability of intercept (LPI) similar to random noise waveforms. We acquire the results using a computer-based simulation and verify the location of target peaks using the chirp waveform output for both stationary and moving target cases.