International Journal of
Microwave and Wireless
Technologies
cambridge.org/mrf
Research Paper
Cite this article: Mu T, Song Y (2019). Target
range–angle estimation based on time reversal
FDA-MIMO radar. International Journal of
Microwave and Wireless Technologies 1–9.
https://doi.org/10.1017/S1759078719001351
Received: 12 June 2019
Revised: 14 September 2019
Accepted: 17 September 2019
Key words:
Multiple-input and multiple-output; frequency
diverse array; time reversal; range-angle
estimation
Author for correspondence:
Yaoliang Song, E-mail: ylsong@njust.edu.cn
© Cambridge University Press and the
European Microwave Association 2019
Target range–angle estimation based on time
reversal FDA-MIMO radar
Tong Mu and Yaoliang Song
School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, China
Abstract
Different from traditional multiple-input and multiple-output (MIMO) radar, the frequency
diverse array MIMO (FDA-MIMO) radar generates beampattern that is dependent on both
range and angle, making it applicable for joint range–angle estimation of targets. In this
paper, we propose a novel time reversal based FDA-MIMO (TR-FDA-MIMO) approach
for target detection. Based on the time reversal theory, the TR-FDA-MIMO signal model is
established, the TR transmitting–receiving and signal processing procedure are analyzed,
and the resulting range–angle spectra for targets imaging are acquired by utilizing the multiple
signal classification algorithm. Numerical simulations are carried out for both single and mul-
tiple targets cases. The imaging resolution and robustness to the noise of the proposed
approach are investigated and results are compared with conventional FDA-MIMO radar.
It turned out that by cooperating with TR, the performance of FDA-MIMO radar for target
range–angle estimation is effectively enhanced, consequently improving its applicability in
practical target-detecting cases.
Introduction
The flexibility of multiple-input and multiple-output (MIMO) radar in signal waveform and
array structure brings increased degrees-of-freedom (DoFs) and spatial diversity gain, leading
to enhancement of target detecting accuracy and resolution. MIMO radar has gained wide atten-
tion in recent years due to its promising advantages [1–3]. However, the beampattern of trad-
itional MIMO radar only depends on the angle, which results in difficulty in distinguishing
targets and suppressing interferences located in the same direction but different ranges.
The frequency diverse array (FDA) provides new ideas for radar system design by introdu-
cing a tiny frequency increment among array elements. The main difference between FDA and
phased array (PA) is that the transmit beampattern of FDA changes as a function of range,
angle, and time, which is favorable for locating targets and suppressing range-dependent inter-
ferences. Thus, FDA has been extensively investigated since it was proposed in 2006 [4–6]. The
periodic modulation properties of FDA were studied in [7]. A logarithmically increasing fre-
quency offset was introduced in [8] to decouple the beampattern, but it causes reduced
range–angle resolution and increased sidelobes. In [9], time-modulated frequency offset was
proposed to solve the time-variance problem in FDA, and some other studies concerning
the same issue were presented in [10–13]. However, FDA cannot be directly used as a receiving
array for target localization due to the range–angle coupling. Naturally, advantages of FDA in
range-dependent beampattern and MIMO in increased DoFs are combined to realize unam-
biguous target range–angle estimation. Joint parameters estimation based on FDA-MIMO was
proposed in [14], and suppressing range-dependent interferences using FDA-MIMO was pre-
sented in [15]. The Cramer–Rao lower bound, mean square error, and resolution performance
of FDA-MIMO radar were derived in [16].
The time reversal (TR) technique exploits the invariance of wave equation in lossless and
time-invariant media to implement the reversion, retransmission, and focusing of signals [17 ].
Recently, TR has been widely utilized in radar applications for its temporal-spatial focusing
characteristic and statistical stability [ 18–20]. In [21], TR was combined with MIMO to
improve radar performance in multipath rich cases. In [22], a TR-MIMO algorithm was pro-
posed for direction of arrival (DOA) estimation, and the multi-target signal model for
TR-MIMO radar was analyzed in [23]. The method proposed in [24] applies the compressive
sensing and TR to MIMO radar for target detection in a rich clutter environment. However,
existing studies mainly focus on the angle acquirement of target, while the problem of range
parameter estimation and range-dependent interferences mitigation cannot be solved effect-
ively, limiting the potential of TR-MIMO radar.
In this paper, we introduce time reversal to FDA-MIMO radar and propose a new
TR-based FDA-MIMO (TR-FDA-MIMO) scheme for enhanced target detection.
Orthogonal signals with a small frequency increment are used for transmission, which
makes the transmit beampattern or steering vector dependent on both range and angle.
https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1759078719001351
Downloaded from https://www.cambridge.org/core. University of Massachusetts Amherst, on 21 Oct 2019 at 12:50:38, subject to the Cambridge Core terms of use, available at