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This paper describes a concept of the circulating codes covering the whole class of the space-time codes. The circulating codes do not narrow the radiated pattern of the antenna array, thus providing a wide angular coverage, possibly tunable. In turn, the beam-forming on transmit is achievable by means of the signal processing in one (or each) rece...
Citations
... It can be noted that the time diverse array can be applied to the frequency scanning mode. Babur et al. propose the space-time coding array (STCA) to fulfill the time diversity and combine it with the MIMO radar [25][26][27]. The simulation results verify that the transmitted beam of the STCA has a beam scanning effect and tunable angular coverage capability, and constant high gain of the coverage area can be further achieved. ...
... The space-time coding array automatically realizes beam scanning in space by transmitting the same waveform with a small relative delay from each array element, thus providing a consistent high gain over the available coverage area [25]. In this section, considering that each sensor of the STCA transmits the chirp signal that is commonly used in SAR systems, the synthetic antenna pattern is derived, which varies with the signal frequency and the direction. ...
... where ε is an integer, the amplitude function reaches its maximum value and the antenna pattern reaches its peak here. The relationship between the beam pointing angle β and the time t can be obtained by substituting the expression of λ(t) into Equation (25) and deducing the outcome. The pencil beam scans to angle β after a period of time t: ...
The F-SCAN principle is a better alternative to the scan-on-receive technique (SCORE) based on digital beamforming (DBF), which can avoid low gain caused by a conventional broad beam in the case of a wide swath. In F-SCAN SAR, a pencil beam scans the entire target area from far to near, providing high energy independent of the position and ensuring a low range ambiguity-to-signal ratio (RASR). Moreover, echo compression can be achieved via appropriate system parameter configuration, significantly shortening the receive window and reducing the amount of data. A wider range swath can, therefore, be achieved. However, for this novel F-SCAN SAR working mode, signal modeling and imaging processing are key issues that needed to be addressed. In this paper, the far-field synthetic antenna pattern of the space–time coding array (STCA) is first derived and analyzed, based on which the signal modeling of the F-SCAN SAR is carried out. Then, according to the signal model and echo characteristics, a novel imaging processing method based on the hybrid correlation algorithm is presented for the F-SCAN SAR. First, the dechirp operation is performed to compensate for the quadratic phase of the range time. The range compressed result is obtained after a range Fourier transform, where different range targets are successfully separated and range aliasing is avoided. Then, the modified azimuth reference function is correlated with the echo at each range cell to complete range cell migration correction (RCMC) and azimuth compensation. The received signal parameters and the Doppler parameters of each range cell are derived to update the azimuth reference function. Finally, accurate focused results are obtained in the range-frequency, azimuth-time domain. The simulation results indicate that the signal model based on the STCA can satisfy the requirements of the F-SCAN principle, and the proposed imaging algorithm can complete the precise focusing processing of the F-SCAN SAR echo.
... Recent studies on waveform diversity array and space-time coding technologies have attempted to address the aforementioned issues in wide-spatial surveillance [22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Among these studies, the FDA radar has garnered considerable attention due to its beam agility, computational convenience, and additional DOF in transmission. ...
... Requirements in detection, including P d , P f a . Radar system parameters in (23). Required beampattern gain G id (Ω ROI ) or detectable range extension R id (Ω ROI ). ...
... In the following simulation, the idealized range extensions ∆R = R id − R l in ROI are set as 2, 4, 6, and 8 km. According to (23), the required additional beampattern gain ∆G = G id (Ω ROI ) − G l is s 2.44, 4.58, 6.49, and 8.22 dB, respectively. Another example may be presented by setting ∆R 1 = 8 km in [−20 • , 0 • ] and ∆R 2 = 2 km in [30 • , 50 • ], which demonstrates the ability to synthesize different beampattern gain in different ROI. ...
Wide-spatial radar surveillance missions are challenging tasks, requiring an increased power budget and agility in transmission aimed at extracting information from multiple targets in different environments. These requirements necessitate high transmitting degrees of freedom (DOF) to achieve the objective of multiscale observation for specific tasks in specialized regions of interest. Herein, we exploit the multiscale observation ability in wide-spatial radar surveillance based on frequency diverse array (FDA) radar. The proposed method facilitates spatial anisotropic control of multiple radar resources, including the transmitting waveforms, beampattern, and bandwidth. By utilizing a coherent FDA radar, we offer principles for the selection of baseband waveforms, in addition to the quantitative design of the beampattern gain and optimal bandwidth from the perspective of detection. The feasibility of the proposed method is validated through numerical experiments, thus indicating the potential in wide-spatial radar surveillance. Moreover, this work can be regarded as a preliminary attempt to gauge the efficacy of the computational array, a novel academic concept.
... Notice that the proposed time offset methods differ from the space-time coding array (STCA). In STCA, the time offsets act on both rectangular window rectð•Þ and baseband waveform xðtÞ [30]. It means that the pulse duration of each element is different, and each transmitted waveform is the same [31]. ...
Frequency diversity array (FDA) radar can provide full spatial coverage with stable gains within a pulse duration. Based on the FDA, the integrated radar‐communication system can perform multi‐directional communication and whole‐space detection. However, the embedded communication bits disrupt the correlation of the transmitting waveform of each element. Correspondingly, the range sidelobe level (SLL) of the multi‐dimensional ambiguity function increases significantly. To address this issue, a low‐sidelobe waveform for integrated radar‐communication systems based on the FDA was designed. Two techniques based on the subarray time delay are employed to reduce the SLL in range dimension. Both methods, however, lower the angular resolution. Thus, a tangent FM signal as the baseband waveform to improve the angular resolution was selected. Simultaneously, the received signal processing methods of radar and communication was designed. The performances of the designed waveform are verified by analysing the multi‐dimensional ambiguity function and the bit error rate. The simulation results reveal that the proposed method can maintain a good radar target detection capability and satisfy the communication function.
... As a start, it is assumed that azimuth beamsteering is implemented using a horizontal linear array. The coherent signal is circulated from one antenna element to another with a relatively small time-delay difference ( t), made possible by circulating codes (CC) [32], [33], [39]. Hence the transmit signal from the p-th element for a transmit antenna array with an odd number of elements, N t , can be written as: ...
... Circulating code in MIMO radar using LFM signals has been implemented for beamforming at transmit [32], [39]. The multiple antenna elements in a linear array with equal element spacing transmit coherent signals having small time-delay difference, t, between successive elements. ...
A conventional phased array radar provides a high gain by transmitting coherent signals over a large number of antenna elements. However, it does not provide a full time-on-target because it produces a beam that scans the whole angular view of the radar. This paper describes an implementation of circulating codes (CC) in azimuth scanning MIMO radar that adopts OFDM waveform. The CC MIMO technique can produce a beam toward a certain angle by applying an appropriate delay difference between the MIMO antennas that transmit the same waveform across the azimuth. The adoption of OFDM waveform in the CC MIMO radar, gives the possibility to apply the phase difference for beamforming in the frequency domain of the OFDM signals. CC-OFDM MIMO with spectrum division into sub-bands and use of orthogonal codes, allow for simultaneous transmission of orthogonal OFDM symbols that generate orthogonal beams toward different angles. This strategy makes it possible for the radar system to have multiple and simultaneous beamforming to provide a full-time coverage. Furthermore, the transmission of a series of orthogonal OFDM symbols in each beam enables the detection of long-range targets. By taking as an example the design of long-range surveillance radar, the paper discusses further issues pertinent to the implementation of the CC OFDM MIMO radar, including the beam squinting problem and its remedy, arrangement of the multiple beams, the radar system structure, use of Golay codes for orthogonalization and PAPR mitigation, use of software-defined radar that eliminates the need of amplitude and phase control in each transmitter, transmit scheduling for multi-beam long-range target detection, and multidimensional ambiguity function analysis. The latter indicates that the CC OFDM MIMO radar can achieve a high resolution in angle, range, and velocity, with beam isolation of −30 dB for neighboring beams and co-channel beams.
... However, TSPW also requires a sampling rate much larger than the signal bandwidth, which will limit its application in ultrawideband cases. In Ref. [12], another single receive channel DBF method was developed based on the circulating time-delay coded array (CTDCA) [13]- [15]. Compared to the method proposed in Ref. [7], this CTDCA-based method also introduces an increasing time delay across the array elements through TTD lines. ...
In this paper, we present a space code agility-based single receive channel digital beamforming (DBF) method for ultra-wideband radar. The proposed single channel DBF method outperforms the existing single channel DBF method with a space-time coded array architecture regarding both the angular and the range sidelobe levels by integrating multiple pulses modulated by irrelevant space codes. A frequency-domain equivalent DBF algorithm is also developed. This algorithm is immune to the mismatch between the sampling rate of the recorded signal and the space-time response function of the space-time coded array under ultra-wideband circumstances, in which cases the existing space-time coded array DBF methods will suffer. Moreover, the target motion over multiple pulse repetition intervals (PRIs) is taken into account in the development of the frequency-domain DBF algorithm. Therefore, performance degradation due to target motion is avoided. Numerical simulations verify the effectiveness of the proposed method.
... Let us consider this ambiguity function for "circulating codes", which are a good example of such space-time coding, with nice properties as detailed in [3] and [10]. Circulating codes are generated, as shown in Fig. 7, by the same waveform (e.g., a chirp) "circulating" with a relative time shift δt through N transmitter channels. ...
... Circulating codes for space-time coding (from[10]). s i (t) = s[t − (i − 1) t] is the signal sent through the ith transmitting element. ...
When designing a new radar system, standard resolution trade-offs play a major role, providing the basic parameters of the radar, such as size, update rate, and range. Besides, diversity has long been used for mitigating fading effects due to the fluctuation of targets and clutter.
However, with the arrival of more flexible systems, using multiple parallel channels on transmit and receive, and wider instantaneous bandwidths, these standard trade-offs are becoming less simple—and more flexible. In this communication, we will analyse the benefits of diversity and its relations with range, Doppler, and angle, for detection and location of moving targets with wideband/wide-beam radar systems. The idea is to contribute to a better understanding of the real benefits of agile transmissions for detection/localization of moving targets, focusing on range, velocity, and angular measurement improvements, as well as on the benefits for detection of moving targets.
Special attention will be given to the quality of the different wideband wide-beam sensor modes for long-range surveillance, and new results on detection of moving targets in clutter will be provided to demonstrate the effectiveness of these new architectures for small target detection at long range, in difficult environments.
... Circulating space-time coding array (CSTCA) as a simple transmission diversity technique has drawn tremendous attention from researchers recently [1][2][3][4][5][6]. Unlike traditional colocated MIMO radar [7][8][9][10], CSTCA transmits a single waveform with a tiny time shift across array elements to acquire full spatial illumination. ...
... The impact of mutual coupling on MIMO radar with space-time coding was investigated in [4], and a calibration procedure for the transmit beamforming was presented. Particularly, the concept of circulating space-time coding was proposed in [1]. As a special type of coherent colocated MIMO radar [16], CSTCA is simple to be implemented in engineering [17,18]. ...
As a special type of coherent collocated Multiple-Input Multiple-Output (MIMO) radar, a circulating space-time coding array (CSTCA) transmits an identical waveform with a tiny time shift. It provides a simple way to achieve a full angular coverage with a stable gain and a low sidelobe level (SLL) in the range domain. In this paper, we address the problem of direction-of-arrival (DOA) estimation in CSTCA. Firstly, we design a novel two-dimensional space-time matched filter on receiver. It jointly performs equivalent transmit beamforming in the angle domain and waveform matching in the fast time domain. Multi-beams can be formed to acquire controllable transmit freedoms. Then, we propose a beamspace multiple signal classification (MUSIC) algorithm applicable in case of small training samples. Next, since targets at the same range cell show characteristics of coherence, we devise a transformation matrix to restore the rotational invariance property (RIP) of the receive array. Afterwards, we perform spatial smoothing in element domain based on the transformation. In addition, the closed-form expression of Cramer-Rao lower bound (CRLB) for angle estimation is derived. Theoretical performance analysis and numerical simulations are presented to demonstrate the effectiveness of proposed approaches.
... In fact, dynamic range is another constraint to be carefully considered in addition to eclipsing losses, to coding accuracy, and so on. The interest in the AF has reoccurred in the 1990s and 2000s with the studies of multiple transmitters and multiple receivers' radar as a multiple input multiple output (MIMO) system [13][14][15][16], often named netted, multistatic, or multisite, as well as with studies of integration of telecommunication capabilities in radars [17]. These systems call for waveforms designed and optimized in order to get a low Peak Side-Lobe Ratio (PSLR), good orthogonality properties, and a low degradation in the mainlobe, that is, low SNR loss (typically 1-2 dB, depending on the weighting function used). ...
... Sidelobe suppression of both the autocorrelation and cross- correlation function of a set of M waveforms (with M > 1 and of the order of a few units or a few tens) is a relevant problem in a MIMO radar, whose receivers have to discriminate, after each matched filter, the mth signal among the others. So, M "orthogonal" waveforms are required [13] for MIMO radar and for space-time coding or "colored" transmission [16]. ...
... The same waveform is emitted by multiple transmitters (array elements) on the same carrier frequency and highly overlapped in time. A relative time offset, from antenna element to antenna element, δt = 1/ΔF inversely proportional to the bandwidth ΔF of the sounding signal, is introduced into the sounding signal components according to the circulating signal principle [22]. Some examples of circulating codes can also be found in [10,[23][24][25], when s(t) is a linear-frequency modulated signal. ...
... On this basis the analysis of the standard (range-Doppler) AFs [9,10,29,30] is not sufficient. Therefore, we employ the multi-dimensional AF [3,9,10,22,31] for our analysis. The examples of the transmit AF presented in this paper provide insight in the resolution capability for both time (range) and angular domains. ...
... Fig. 5 evidences that all four considered signals provide the same range resolution (main peak width of the range profiles), defined by the sounding signal bandwidth. Hence, we can state that the hybrid codes do not have the main disadvantage proper for their predecessorscirculating codes [22]. The price for that is some sidelobes (see the zoomed areas in Figs. ...
Simple transmit diversity technique for phased array radar
ISSN 1751-8784
Accepted on 22nd November 2015
doi: 10.1049/iet-rsn.2015.0311
www.ietdl.org
Galina Babur, Pascal Aubry, Francois Le Chevalier
Abstract: This study presents a simple yet ingenious transmit diversity technique (so-called hybrid codes) for phased array radar. Its main property is the capability of digital beamforming on transmit just like with a set of orthogonal signals employed by coherent multiple-input–multiple-output radar and simplicity (only one waveform has to be generated in time). The performance of the hybrid codes is examined by analysing the transmit ambiguity functions containing beampatterns and range profile for all angular directions of interest.
... For this comparison, we will focus here on circulating codes [8][9][10], which exhibit very basic properties of the ambiguity function. Circulating codes are generated by the same waveform ...
Active antennas and modular generation and reception opens the way to radar systems where different waveforms are simultaneously transmitted and received through multiple channels (MIMO radars). Such an increase in the degrees of freedom is shown to allow improvements in angular resolution compared to standard wide beam. It can also be used to optimize the trade-offs between angular and range resolution and sidelobes. In this paper, the basic properties are analyzed on a new class of space-time circulating codes adapted to 2D antennas, and the benefits are demonstrated through fair comparisons of transmit/receive ambiguity functions.
