Showing papers on "Pulse repetition frequency published in 2015"
TL;DR: In this paper, a frequency diverse array (FDA) radar with uniform interelement frequency offset has been proposed and investigated and a transmitter for the proposed radar system has been described and analyzed mathematically.
Abstract: In recent years, frequency diverse array (FDA) radar with uniform interelement frequency offset has been proposed and investigated. It has been shown that the beampattern of this form of radar is range-angle-dependent, and it exhibits maxima at multiple range values. Due to the multiple maxima, a number of reflectors located at any of the maxima can interfere the target-return, thus deteriorating signal-to-interference-plus-noise ratio (SINR). In this letter, we have proposed FDA with logarithmically increasing frequency offset to achieve a beampattern with a single maximum at the target location. A transmitter for the proposed radar system has been described and analyzed mathematically. Furthermore, the transmit beampattern has been derived and plotted and compared to that of phased-array radar (PAR) and the existing forms of FDA employing uniform frequency offset.
246 citations
10 May 2015
TL;DR: A new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using sidelobe control in tandem with waveform diversity to operate in multiple-input multiple-output (MIMO) mode is developed.
Abstract: In this paper, we develop a new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using sidelobe control in tandem with waveform diversity. A set of Q orthogonal waveforms is exploited to embed a sequence of Q bits during each radar pulse. All waveforms are transmitted simultaneously where one bit is embedded in each waveform. We design two transmit weight vectors to achieve two distinct transmit power distribution patterns which share the same main radar beam but have different sidelobe levels towards the communication direction. The receiver interprets the bit associated with a certain waveform as binary information based on whether that waveform is radiated over the transmit beam associated with the first or the second weight vector. The proposed technique enables information delivering to a single or multiple communication directions located outside the mainlobe of the radar. The communication message has low probability of intercept from directions other than the preassigned communication directions. Additionally, the waveform diversity enables the radar to operate in multiple-input multiple-output (MIMO) mode. The performance of the proposed technique is investigated in terms of the bit error rate (BER).
91 citations
TL;DR: The proposed chirp z-transform (CZT)-based algorithm for frequency-modulated continuous wave (FMCW) radar applications is optimized for real-time implementation in field-programmable gate arrays and nearly matches the theoretically predicted mean standard deviation.
Abstract: In this paper, a chirp $z$ -transform (CZT)-based algorithm for frequency-modulated continuous wave (FMCW) radar applications is presented. The proposed algorithm is optimized for real-time implementation in field-programmable gate arrays. To achieve a very high accuracy, the FMCW radar uses an additional phase evaluation. Therefore, a phase calculation based on the CZT algorithm is derived and compared with a correlation based algorithm. For a better classification of the algorithm, the respective Cramer–Rao bounds are calculated. The performance of the algorithm is shown by the evaluation of different radar measurements with a K-band radar. In the measurements, an accuracy of $5~\mu $ m with a mean standard deviation of 774 nm is achieved, which nearly matches the theoretically predicted mean standard deviation of 160 nm.
83 citations
28 Dec 2015
TL;DR: A new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using phase-rotational invariance and is inherently secure against interception from directions other than the desired communication direction.
Abstract: In this paper, we develop a new technique for dual-function radar-communications in a transmit multi-sensor array where information embedding is achieved using phase-rotational invariance. A sequence of Q bits is first mapped into a dictionary of 2Q phase rotations. Then, one pair of transmit orthogonal waveforms is used in tandem with 2Q pairs of transmit beamforming weight vectors for embedding a certain entry of the phase-rotation dictionary during each radar pulse. The same pair of waveforms is used during all pulses while the pair of transmit beamforming weight vectors changes from pulse to pulse based on which entry of the phase-rotation dictionary is embedded. During each pulse, the receiver detects the embedded phase rotation and employ it to decipher the transmitted bit sequence. The proposed information embedding technique is angle-dependant and, therefore, the communication process is inherently secure against interception from directions other than the desired communication direction. The performance of the proposed technique is investigated in terms of the bit error rate (BER).
74 citations
TL;DR: In this article, stable 30 fs pulses centered at 1068 nm (less than 10 optical cycles) were demonstrated in a diode pumped Yb:CaYAlO4 laser by using high-quality chemical vapor deposited monolayer graphene as the saturable absorber.
Abstract: Stable 30 fs pulses centered at 1068 nm (less than 10 optical cycles) are demonstrated in a diode pumped Yb:CaYAlO4 laser by using high-quality chemical vapor deposited monolayer graphene as the saturable absorber. The mode locked 8.43 optical-cycle pulses have a spectral bandwidth of ~ 50 nm and a pulse repetition frequency of ~ 113.5 MHz. To our knowledge, this is the shortest pulse ever reported for graphene mode-locked lasers and mode-locked Yb-doped bulk lasers. Our experimental results demonstrate that graphene mode locking is a very promising practical technique to generate few-cycle optical pulses directly from a laser oscillator.
63 citations
TL;DR: This work introduces an artificial on-chip target (OCT) to mitigate the SR leakage, based on the cross-correlation properties of the residual phase noise in the intermediate frequency (IF) domain, and shows that a gain in sensitivity is achieved, compensating for the performance degradation caused by theSR leakage.
Abstract: A major drawback of frequency modulated continuous-wave (FMCW) radar systems is the permanent leakage from the transmit into the receive path. Besides leakage within the radar device itself, signal reflections from a fixed object in front of the antennas additionally introduce so-called short-range (SR) leakage. It causes a strong degradation of detection sensitivity due to the unpreventable phase noise of the transmit oscillator. In this work, we introduce an artificial on-chip target (OCT) to mitigate the SR leakage. The OCT consists of a delay line whose time delay is significantly smaller than the round-trip delay time of the SR leakage. This is motivated by the fact that in integrated circuits for automotive radar applications operating at 77 GHz delay lines in the range of only a few picoseconds can be realized with a reasonable amount of circuitry. Despite this constraint, we show that the proposed method achieves almost perfect cancelation of the SR leakage. The concept is based on the cross-correlation properties of the residual phase noise in the intermediate frequency (IF) domain. Further, the effectiveness of the proposed method is verified in an FMCW radar system simulation. It almost perfectly shows that a gain in sensitivity of approximately 6 dB is achieved, compensating for the performance degradation caused by the SR leakage. The novel leakage cancelation concept is carried out mainly in the digital domain enabling high flexibility and adaptivity.
55 citations
10 May 2015
TL;DR: This paper develops a cognitive radar tracking system based on the Maximum a Posteriori Penalty Function (MAP-PF) tracking methodology, which allows us to cognitively control both the radar sensor and the processor.
Abstract: Most radar systems employ a feed-forward processing chain in which they first perform some low-level processing of received sensor data to obtain target detections and then pass the processed data on to some higher-level processor such as a tracker. Cognitive radar systems use adaptation between the information extracted from the sensor/processor and the design and transmission of subsequent illuminating waveforms. In this paper, we develop a cognitive radar tracking system based on the Maximum a Posteriori Penalty Function (MAP-PF) tracking methodology, which allows us to cognitively control both the radar sensor and the processor. We demonstrate performance for a pulse-Doppler radar system in which the pulse repetition frequency is adjusted to optimize tracking performance, while keeping the target from being Doppler-aliased and away from the zero-Doppler clutter. Results are shown on experimentally collected data using a software defined radar system.
48 citations
TL;DR: An efficient actively Q-switched Tm3+-doped single-oscillator fiber laser based on a silica polarization-maintaining (PM) double-clad fiber provided average powers of 23 W at pulse widths of 65 ns at 40 kHz pulse repetition frequency.
Abstract: An efficient actively Q-switched Tm3+-doped single-oscillator fiber laser based on a silica polarization-maintaining (PM) double-clad fiber provided average powers of 23 W at pulse widths of 65 ns at 40 kHz pulse repetition frequency It was used to directly pump a ZnGeP2 optical parametric oscillator (OPO) Up to 65 W were generated in mid-IR wavelength range
47 citations
TL;DR: This letter addresses and quantifies the effects caused by the transmit pulse length (here denoted as pulse extension loss) through a rigorous analysis, with the purpose of introducing an important SAR performance figure.
Abstract: One of the benefits of synthetic aperture radar (SAR) systems utilizing digital beamforming is the ability to increase the receive power. The relevant SAR technique is known as SCan-On-REceive (SCORE), which steers the receive antenna beam such that it follows the radar pulse echo traversing the ground. This allows the use of a narrow receive beam in elevation, and therefore, the height of the receive antenna can be increased, resulting in a higher gain, which explains the higher receive power. Although advantageous, this technique has some pitfalls, which impose an upper limit on the antenna size and constrain the selection of SAR operation parameters. These limitations (which are often neglected in the system conception) are caused by the pulse extent on the ground and the way it is modulated by the receive antenna pattern. This letter addresses and quantifies the effects caused by the transmit pulse length (here denoted as pulse extension loss) through a rigorous analysis, with the purpose of introducing an important SAR performance figure. Closed expressions are derived for the simplified case of a uniform linear antenna array.
43 citations
TL;DR: The article presents some possibilities of same type radar copies identification with the use of graphical representation based on transformation and analysis of basic parameters distribution which are measured by the radar signal especially Pulse Repetition Interval.
Abstract: The article presents some possibilities of same type radar copies identification with the use of graphical representation. The procedure described by the authors is based on transformation and analysis of basic parameters distribution which are measured by the radar signal especially Pulse Repetition Interval. A radar intercept receiver passively collects incoming pulse samples from a number of unknown emitters. Information such as Pulse Repetition Interval, Angle of Arrival, Pulse Width, Radio Frequency and Doppler shifts are not usable. The most important objectives are to determine the number of emitters present and classify incoming pulses according to emitters. To classify radar emitters and precisely identification the copy of the same type of an emitter source in surrounding environment, we need to explore the detailed structure i.e. intra-pulse information, unintentional radiated electromagnetic emission and fractal features of a radar signal. An emitter has its own signal structure. This part of radar signal analysis is called Specific Emitter Identification. Utilization of some specific properties of electronic devices can cause heightening probability of a correct identification.
40 citations
17 May 2015
TL;DR: The design of a stepped frequency continuous wave (SFCW) radar is discussed, which transmits long duration pulses with higher average power and much narrower instantaneous bandwidth than UWB waveforms, to facilitate comparable signal resolution.
Abstract: In this paper, we discuss the design of a stepped frequency continuous wave (SFCW) radar, which transmits long duration pulses with higher average power and much narrower instantaneous bandwidth than UWB waveforms, to facilitate comparable signal resolution. FFT spectrograms, typically used in the extraction of vital signs from radar measurements, produce several spurious peaks at harmonics and intermodulation frequencies of respiration and heart rates, thereby increasing the uncertainty of these estimates, especially the heart rate. We apply a signal processing algorithm based on the state-space method for the extraction of cardiac and respiration rates from the data measured on a human subject using SFCW radar. Results show that accurate estimates of vital signs (heart rate < 1.2% in static mode and < 5.7% in motion) can be obtained without producing inter-modulation products that plague signal resolution in FFT spectrograms.
TL;DR: In this article, an approach to improve the range resolution of a 24 GHz industrial, scientific, and medical (ISM) band pulse radar is presented for the automotive short-range radars.
Abstract: An approach to improve the range resolution of a 24-GHz industrial, scientific, and medical (ISM) band pulse radar is presented for the automotive short-range radars. The resolution of the range profile was improved by applying the regularized least squares method to a discrete baseband signal at the receiver. For a 24-GHz ISM band pulse radar adopting a regularized least square method, a triangular pulse was identified as the optimal pulse shape under the regulations and in terms of cost effectiveness. To resolve multiple adjacent pulses with a constant false alarm rate, MATLAB simulations based on the least absolute shrinkage and selection operator (LASSO) algorithm were used to derive additional threshold values for output signals after the LASSO operation and the required signal-to-noise ratio (SNR). The simulated and measured values of the required SNR were 20.5 and 21.1 dB, respectively, for the two-target detection with a range resolution of 30 cm, at the detection and false alarm probabilities of 0.9 and $10^{-3}$ , respectively.
TL;DR: A probabilistic analysis is addressed to derive mathematical expressions for the signal-to-noise ratios, the peak- to-sidelobe ratios and the signal -to-interference ratios (due to ambiguous targets) throughout a typical receiver processing chain of a pulsed FM noise radar.
Abstract: Noise radars are electromagnetic systems that use random signals for detecting and locating reflecting objects. Besides high performance against external interferences (intentional or not), the stochastic nature of the transmitted waveforms may lead to the suppression of range ambiguity in the detection of targets and low range sidelobes, if systems parameters are properly chosen. This paper addresses a probabilistic analysis to derive mathematical expressions for the signal-to-noise ratios, the peak-to-sidelobe ratios and the signal-to-interference ratios (due to ambiguous targets) throughout a typical receiver processing chain of a pulsed FM noise radar. A receiver that employs matched filtering and pulse integration prior to detection was considered. Pulse compression and integration gains (in signal-to-noise and signal-to-interference, due to ambiguous targets, ratios) are also derived. The analysis provides closed-form expressions relating the precise dependence of sidelobe levels as well as interference levels due to ambiguous targets to the integration time, the transmit signal bandwidth, and the number of integrated pulses.
TL;DR: In this article, an experimental and computer studies of the CuBr laser with periodic-pulse pumping are performed with and without addition of HBr. The analysis based on the numerical simulation reveals how additions improve the lasing characteristics of this laser at both typical (10 to 20 kHz) and higher (up to 100 kHz) excitation pulse repetition frequencies during the operation with a low energy deposition in the discharge.
Abstract: Experimental and computer studies of the CuBr laser with periodic-pulse pumping are performed with and without addition of HBr. The analysis based on the numerical simulation reveals how additions improve the lasing characteristics of this laser at both typical (10 to 20 kHz) and higher (up to 100 kHz) excitation pulse repetition frequencies during the operation with a low energy deposition in the discharge. This allows the lasing pulse repetition frequency to be increased in the experiment to 750 kHz, which does not seem to be a limit as yet.
Patent•
28 Aug 2015TL;DR: In this article, a radar device mounted in a moving object includes a radar transmitter and a radar receiver, with a plurality of antenna brunch processors that perform correlation processing of the received returning signals and the radar transmission signal.
Abstract: A radar device mounted in a moving object includes a radar transmitter and a radar receiver. The radar receiver includes a plurality of antenna brunch processors that perform correlation processing of the received returning signals and the radar transmission signal, and generate respective correlation signals each including arrival delay information of each of the received returning signals, an electric power profile generator that generates an electric power profiles for each arrival direction of the received returning signals and Doppler frequency component, using the generated correlation signals, and a stationary object group distribution generator that, based on the generated electric power profiles, obtains a first distribution of a Doppler frequency components of a stationary object group including a plurality of stationary objects as the plurality of targets in the perimeter of the moving object, for each azimuth angle.
10 May 2015
TL;DR: In this paper, the authors investigated cooperative in-band radar and communications signaling for frequency-modulated continuous-wave (FMCW) radar and Doppler estimation and derived a joint performance bound in terms of the communications rate and the target delay estimation rate of the system for pulsed waveforms.
Abstract: We investigate cooperative in-band radar and communications signaling for frequency-modulated continuous-wave (FMCW) radar and Doppler estimation. While each system typically considers the other system a source of interference, by considering the radar and communications operations to be a single system, joint performance bounds can be formulated. We extend previous work where a novel estimation and information theoretic bound formulation was constructed for a receiver that observes communications and radar returns in the same frequency allocation. While the previous work derived a joint performance bound in terms of the communications rate and the target delay estimation rate of the system for pulsed waveforms, we derive a similar bound for FMCW radar and include Doppler estimation. This extension is important given the rise of popularity of FMCW radars, and since the continuous signaling brings them closer to how communications systems operate.
TL;DR: A wide altitude range is attained by employing an optical delay in the path of transmission to reduce the dynamic range of the altitude being measured and by improving the sweep linearity using a direct digital synthesizer and minimizing phase noise.
Abstract: This paper presents the design of a frequency-modulated continuous-wave radar altimeter with wide altitude range and low measurement error. A wide altitude range is attained by employing an optical delay in the path of transmission to reduce the dynamic range of the altitude being measured. The transmitter power and receiver gain are also controlled to facilitate a reduction in the dynamic range of the received power. In addition, low measurement error was obtained by improving the sweep linearity using a direct digital synthesizer and minimizing phase noise by employing a phase-locked loop with the offset frequency driven by a reference clock (Ref_CLK). The performance of the radar altimeter was experimentally verified using an optical-delay simulator, which provided a delay time corresponding to a 200-m radar distance. To assess the performance of the system in a realistic setting, the radar altimeter was tested using a crane setup. The crane test demonstrated that the design described in this paper resulted in a reduced measurement-error rate.
TL;DR: The results of testing a high voltage pulse generator based on parallel gyromagnetic nonlinear transmission lines filled with saturable ferrite capable of producing almost identical stable rf-modulated nanosecond high voltage pulses in each of the two, or four, parallel output channels.
Abstract: This paper presents the results of testing a high voltage pulse generator based on parallel gyromagnetic nonlinear transmission lines filled with saturable ferrite. The generator is capable of producing almost identical stable rf-modulated nanosecond high voltage pulses in each of the two, or four, parallel output channels. The output voltage amplitude in each channel can reach −285 or −180 kV, respectively, with a rf modulation depth of up to 60%. Drive pulses were produced as the packets of duration 1–5 s at a pulse repetition frequency of 800 Hz using a driver equipped with all-solid-state switches. Splitting the driver pulse provided electric field strengths in the channels which were below the breakdown field strength of the transmission lines. As a result, the use of nonlinear transmission lines of reduced diameter made it possible to increase the center frequency of the excited rf oscillations to ∼2 GHz.
TL;DR: Passive Q-switching of a compact Tm:KLu(WO(4))(2) microchip laser diode pumped at 805 nm is demonstrated with a polycrystalline Cr(2+):ZnS saturable absorber.
Abstract: Passive Q-switching of a compact Tm:KLu(WO(4))(2) microchip laser diode pumped at 805 nm is demonstrated with a polycrystalline Cr(2+):ZnS saturable absorber. This laser generates subnanosecond (780 ps) pulses with a pulse repetition frequency of 5.6 kHz at 1846.6 nm, the shortest pulse duration ever achieved by Q-switching of ~2 μm lasers. The maximum average output power is 146 mW with a slope efficiency of 21% with respect to the absorbed power. This corresponds to a pulse energy of 25.6 μJ and a peak power of 32.8 kW.
TL;DR: A pulse picking technique based on a travelling-wave-type acousto-optic modulator having the AOM carrier frequency synchronized to the repetition rate of the original pulse train is introduced, rendering this technique suitable for applications requiring carrier-envelope phase stabilization.
Abstract: We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.
10 May 2015
TL;DR: A new approach for detecting a particular class of moving targets that exploits characteristics of specific non-linear targets to both eliminate moving objects that are not of interest and suppress stationary clutter is presented.
Abstract: A new approach for detecting a particular class of moving targets is presented. This method exploits characteristics of specific non-linear targets to both eliminate moving objects that are not of interest and suppress stationary clutter. Details of the underlying physical phenomena are discussed, and the signal processing procedures leveraged by the non-linear radar system are outlined in detail.
11 May 2015
TL;DR: The proposed spectrum-sharing algorithm causes minimum loss in radar performance by selecting the best interference channel that does not cause interference to the ith LTE base station due to the radar signal.
Abstract: In this paper, we present our spectrum sharing algorithm between a multi-input multi-output (MIMO) radar and Long Term Evolution (LTE) cellular system with multiple base stations (BS)s We analyze the performance of MIMO radars in detecting the angle of arrival, propagation delay and Doppler angular frequency by projecting orthogonal waveforms onto the null-space of interference channel matrix We compare and analyze the radar's detectable target parameters in the case of the original radar waveform and the case of null-projected radar waveform Our proposed spectrum-sharing algorithm causes minimum loss in radar performance by selecting the best interference channel that does not cause interference to the $i^{th}$ LTE base station due to the radar signal We show through our analytical and simulation results that the loss in the radar performance in detecting the target parameters is minimal when our proposed spectrum sharing algorithm is used to select the best channel onto which radar signals are projected
02 Apr 2015
TL;DR: SDR based FMCW radar for target detection and air traffic control radar application is implemented in real time using open source software and hardware.
Abstract: Nowadays, FMCW (Frequency Modulated Continuous Wave) radar is widely adapted due to the use of solid state microwave amplifier to generate signal source. The FMCW radar can be implemented and analyzed at low cost and less complexity by using Software Defined Radio (SDR). In this paper, SDR based FMCW radar for target detection and air traffic control radar application is implemented in real time. The FMCW radar model is implemented using open source software and hardware. GNU Radio is utilized for software part of the radar and USRP (Universal Software Radio Peripheral) N210 for hardware part. Log-periodic antenna operating at 1GHZ frequency is used for transmission and reception of radar signals. From the beat signal obtained at receiver end and range resolution of signal, target is detected. Further low pass filtering followed by Fast Fourier Transform (FFT) is performed to reduce computational complexity.
TL;DR: A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency and achieved high output power and efficiency for Nm-polarized laser output.
Abstract: A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8 W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at a pulse repetition frequency of 62 MHz. For Np polarization, 143 fs pulses with pulse energy of 139 nJ and average output power of up to 8.6 W with optical-to-optical efficiency of 31% were generated.
TL;DR: A new architecture for an integrated fully coherent radar-lidar system based on a single mode-locked laser is proposed and demonstrated, allowing a dynamic tradeoff among robustness and sensitivity of measurements.
Abstract: A new architecture for an integrated fully coherent radar–lidar system based on a single mode-locked laser is proposed and demonstrated. The lidar exploits a multi-frequency optical signal with tunable tones separation allowing a dynamic tradeoff among robustness and sensitivity of measurements. The radar that is based on photonics technologies employs the mode-locked laser for generating the radio frequency signals in the X-band and Ku-band, simultaneously with the lidar. Velocity measurements for different tones separation are demonstrated with good agreement among the values measured with the lidar and radar.
TL;DR: A new BWE technique based on matched filtering (MF) is formulated and it is shown that the proposed approach allows the range depth of interest (RDOI) to be as large as the radar unambiguous distance.
Abstract: Existing bandwidth extrapolation (BWE) techniques developed for wideband radar systems use stretch processing. A major drawback of these BWE techniques is that the range depth of interest (RDOI) can only be a small fraction of the radar unambiguous distance. This drawback restricts existing BWE techniques from being applied to narrowband radar systems where the RDOI can extend to a significant fraction of the radar unambiguous distance. To address this problem, we formulate a new BWE technique based on matched filtering (MF) and show that the proposed approach allows the RDOI to be as large as the radar unambiguous distance. We demonstrate the capability of the proposed method using both simulated data and real data collected from an over-the-horizon (OTH) radar system. We show that the proposed technique successfully resolves closely spaced targets where conventional range-Doppler (RD) processing technique has failed and is capable of improving the range resolution in the presence of stationary clutter that is 20–50 dB stronger than the targets. In addition to range resolution improvement, we observe that the proposed technique also improves the signal-to-noise ratio (SNR) of the targets.
TL;DR: In this paper, the authors investigate the dynamics of a semiconductor laser with an active cavity coupled to an external passive cavity and show that the output field intensity sensitively depends on the relative position of the frequency combs of the two cavities giving rise to a resonant behavior.
Abstract: Using a delay differential equation model with two time delays, we investigate the dynamics of a semiconductor laser with an active cavity coupled to an external passive cavity. Our numerical simulations indicate that when the coupling between the two cavities is strong enough and the round-trip time of the active cavity is an integer multiple of the round-trip time of the external passive cavity, a harmonic mode-locking regime can develop in the laser with the pulse repetition period close to the passive cavity round-trip time. We also demonstrate that the output field intensity sensitively depends on the relative position of the frequency combs of the two cavities giving rise to a resonant behavior. The period and width of the resonances depend on the ratio of the round-trip times to the coupling between the two cavities. We show that the coupled cavity system under consideration can demonstrate a bistability between different regimes of generation.
10 Aug 2015
TL;DR: A new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD), is introduced.
Abstract: Frequency modulated continuous wave (FMCW) radar is widely adopted solution for low-cost, short to medium range sensing applications. However, a multistatic FMCW architecture suitable for meeting the low-cost requirement has yet to be developed. This paper introduces a new FMCW radar architecture that implements a novel technique of synchronizing nodes in a multistatic system, known as over-the-air deramping (OTAD). The architecture uses a dual-frequency design to simultaneously broadcast an FMCW waveform on a lower frequency channel directly to a receiver as a reference synchronization signal, and a higher frequency channel to illuminate the measurement scene. The target echo is deramped in hardware with the synchronization signal. OTAD allows for low-cost multistatic systems with fine range-resolution, and low peak power and sampling rate requirements. Furthermore, the approach avoids problems with direct signal interference. OTAD is shown to be a compelling solution for low-cost multistatic radar systems through the experimental measurements using a newly developed OTAD radar system.
TL;DR: A double pulse multiple input multiple output–frequency diverse array (MIMO–FDA) radar to improve the range-angle localization of the target is proposed and derived and compared with the double pulse FDA radar.
Abstract: In this paper, we have proposed a double pulse multiple input multiple output---frequency diverse array (MIMO---FDA) radar to improve the range-angle localization of the target. Although frequency diverse array (FDA) radar has been widely used to generate both range and angle dependent beamforming, however, it is difficult for FDA to localize the target in both dimensions due to strong coupling of range and angle dimension. To overcome this inability of FDA radar, a double pulse based MIMO---FDA has been presented here. MIMO---FDA can be obtained by partitioning of FDA transmit array into subarrays and then transmit a unique waveform from each subarray. The resultant MIMO---FDA radar will send a pulse with zero frequency increment to locate the target in angle dimension, which is followed by a pulse with suitable frequency increment to locate the target in range dimension. Using the MIMO---FDA radar with double pulse method has improved the range-angle localization of the target. Simulations and results have verified the effectiveness of the proposed radar. The Cramer Rao lower bound for the proposed radar has also been derived and compared with the double pulse FDA radar.
TL;DR: This work shows how to adapt standard clutter rejection techniques to work directly on the sub-Nyquist samples, allowing to preserve high detection rates even in the presence of strong clutter, while avoiding the need to first interpolate the samples to the Nyquist grid.
Abstract: Recently, a new approach to sub-Nyquist sampling and processing in pulse-Doppler radar was introduced, based on the Xampling approach to reduced-rate sampling combined with Doppler focusing performed on the low-rate samples. This method imposes no restrictions on the transmitter, reduces both the sam- pling and processing rates and exhibits linear signal-to-noise ratio improvement with the number of pulses. Here we extend previous work on sub-Nyquist pulse-Doppler radar by incorporating a clutter removal algorithm operating on the sub-Nyquist samples, allowing to reject clutter modeled as a colored Gaussian random process. In particular, we show how to adapt standard clutter rejection techniques to work directly on the sub-Nyquist samples, allowing to preserve high detection rates even in the presence of strong clutter, while avoiding the need to first interpolate the samples to the Nyquist grid.