Phased array is widely used in radar systems with its beam steering fixed in one direction for all ranges. Therefore, the range of a target cannot be determined within a single pulse when range ambiguity exists. In this paper, an unambiguous approach for joint range and angle estimation is devised for multiple-input multiple-output (MIMO) radar with frequency diverse array (FDA). Unlike the traditional phased array, FDA is capable of employing a small frequency increment across the array elements. Because of the frequency increment, the transmit steering vector of the FDA-MIMO radar is a function of both range and angle. As a result, the FDA-MIMO radar is able to utilize degrees-of-freedom in the range-angle domains to jointly determine the range and angle parameters of the target. In addition, the Cramér-Rao bounds for range and angle are derived, and the coupling between these two parameters is analyzed. Numerical results are presented to validate the effectiveness of the proposed approach.

To improve the effectiveness of limited spectral resources, an adaptive orthogonal frequency division multiplexing integrated radar and communications waveform design method is proposed. First, the conditional mutual information (MI) between the random target impulse response and the received signal, and the data information rate (DIR) of frequency selective fading channel are formulated. Then, with the constraint on the total power, the optimization problem, which simultaneously considers the conditional MI for radar and DIR for communications, is devised, and the analytic solution is derived. With low transmit power, the designed integrated waveform outperforms the fixed waveform (i.e., equal power allocation). Finally, several simulated experiments are provided to verify the effectiveness of the designed waveform.

Suppression of radar-to-radar jammers, especially the mainbeam jammers, has been an urgent demand in vehicular sensing systems with the expected increased number of vehicles equipped with radar systems. This paper deals with the suppression of mainbeam deceptive jammers with frequency diverse array (FDA)-multiple-input multiple-output (MIMO) radar, utilizing its extra degrees-of-freedom (DOFS) in the range domain. At the modelling stage, false targets, which lag several pulses behind the true target, are considered as a typical form of mainbeam jammers. To this end the data-independent beamforming is performed to suppress false targets by nulling at the equivalent transmit beampattern with an appropriate frequency increment. However, the suppression performance degrades in the presence of transmit spatial frequency mismatch, which could be induced by quantization errors, angle estimation errors and frequency increment errors. To solve this problem, a preset broadened nulling beamformer (PBN-BF) is proposed by placing artificial interferences with appropriate powers around the nulls of the equivalent transmit beampattern. In such a way, effective suppression of deceptive jammer can be guaranteed owing to the broadened notches. At the analysis stage, numerical results in a scenario with multiple unmanned aerial vehicles (UAVs) are provided to illustrate the effectiveness of the devised data-independent BF, and the signal-to-interference-plus-noise ratio is improved compared with the conventional data-independent BF.

This paper deals with the problem of adaptive target detection in the presence of homogeneous Gaussian interference with frequency diverse array multiple-input multiple-output (FDA-MIMO) radar. Adaptive detectors are devised according to the generalized likelihood ratio test (GLRT) criterion, where the position of the target within each range cell is assumed unknown. To obtain the maximum likelihood (ML) estimate of the target incremental range under the H1 hypothesis, three different optimization strategies are pursued. They are respectively based on Semi-definite programming (SDP), discrete grid search, and Newton-method. At the analysis stage, a detection performance comparison is carried on among the new proposed adaptive detectors, benchmark and mismatched receivers. Numerical results corroborate the effectiveness of the developed receivers.

Airborne radar arrays oriented toward any direction other than sidelooking cause the range dependence of clutter. It is difficult to handle this range dependence problem in the presence of range ambiguity. Frequency diverse array (FDA) employs a small frequency increment across the array elements, which induces the spatial frequency variant with respect to slant range. Thus, it provides extra degrees-of-freedom in range domain. In this paper, a novel framework of space-time adaptive processing (STAP) radar is established with FDA as the transmit array. In the FDA-STAP radar, the range ambiguous clutter can be discriminated in spatial frequency domain. This is due to the fact that the spatial frequencies of the clutters from different slant ranges are distinguishable even though the range ambiguous clutter is within the same range bin. Simultaneously, the FDA-STAP radar induces secondary range dependence of clutter. To alleviate the secondary range dependence of clutter, a secondary range dependence compensation (SRDC) method is proposed for two cases: 1) the target is assumed in the unambiguous range region and 2) the target is assumed in the ambiguous range region. After the range ambiguous clutter is separated in the spatial frequency domain by using the proposed SRDC method, the traditional clutter compensation approach is applied to further align the spectrum distribution of clutter. Our simulation results demonstrate the superiority of the proposed approach in clutter suppression under range ambiguous clutter scenarios.