To address the problem that array radar is seriously affected by complex mainlobe jamming, a method of mainlobe jamming suppression with space–time multichannel via blind source separation is proposed. First, 4 space–time sum–difference channels are constructed to enhance the discriminability of the source signals based on two-dimensional space–time information, and multiple channels are provided to suppress mainlobe jamming from multiple sources simultaneously. Then, the joint approximate diagonalization of eigenmatrices blind source separation (BSS) algorithm is used to separate the target echo signal from the mixed signal. On the basis of the pulse compression and signal phase statistics, the target distance information can be obtained. Finally, in accordance with the phase relationship between the subarray BSS results, sparse recovery is performed to obtain the target direction of arrival information. Simulation results show that the proposed method can effectively suppress interference and extract the target information in the presence of up to 3 near-mainlobe blanket jamming signals or self-defensive mainlobe deceptive jamming signals.

A novel data‐nulling superimposed pilot scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed, where the input data vector is spread over all the subcarriers by a precoding matrix and then nulled at certain subcarriers for the insertion of training pilots. This method avoids the loss of the data rate for frequency‐division multiplexed pilots, but results in the distortion of input data. To mitigate the distortion introduced by the nulling operation, a simple iterative reconstruction scheme is used to improve the detection performance.

Massive machine type communication (mMTC) is expected to support the connections of billion devices, where a sporadic short packet transmission is a key feature for mMTC applications. Conventional pilot-based coherent schemes suffer from a huge resource overhead as the pilot occupies a large portion in the short packet transmission. To avoid the overhead and latency caused by pilot symbols and mitigate the adverse effect of wireless fading, we develop a noncoherent single-input multiple-output (SIMO) framework with modulation on conjugate-reciprocal zeros (MOCZ) for short packet transmission. A novel lowcomplexity noncoherent Viterbi-like detector is proposed, which can exploit diversity of receive antennas by jointly testing the zeros of the received MOCZ symbol over independent channel realizations. Simulation results demonstrate that the proposed detector can outperform the pilot-based OFDM systems and get better performance than the direct zero-testing detector for short packet transmissions in frequency-selective fading environments.

To solve the problem that radar performance is seriously affected by mainlobe deception jamming, a jamming suppression approach using singular value decomposition (SVD) and the fractional Fourier transform (FrFT) is proposed. First, Hankel matrix rearrangement and SVD are performed for the signals in each coherent processing interval. The energy of jamming and of the radar targets is aggregated from the slow-time dimension. Ensemble learning is then used for its cognitive properties. The corresponding relationship between jamming and the singular values is judged, and the interference is initially suppressed. Finally, the FrFT is applied for each pulse signal. The linear frequency modulation signal energy is aggregated from the fast-time dimension, and jamming is suppressed a second time. The results of simulations show that the proposed approach can be used to detect targets more effectively than existing methods in scenarios involving multiple strong mainlobe deception jammers.

The magnetoelectric (ME) antennas rely on the mechanical movement of magnetic dipoles, making it possible to break the constraints on physical dimensions decided by the wavelength of the electromagnetic wavelength. The ME antennas achieve super-low frequency (SLF) communications with a smaller size to provide a novel solution for long-range, underwater, and underground communications; navigation over the horizon; and geological exploring. As a result, further theoretical research and optimization of ME antennas have been an open challenge for decades. Here, we report on minitype arrays of acoustically actuated ME antenna and their more rigorous equivalent circuits. These arrays of ME antenna adjust amplitude-frequency response through the mechanical regulation method. The mechanical parameters of ME antennas in the arrays result in regulating amplitude-frequency response, such as working frequency, fractional bandwidth, and intensity of magnetic induction. Our work provides a more accurate theoretical model and diverse array form over state-of-the-art ME antenna arrays. The frequency, fractional bandwidth, and magnetic induction strength of the ME antenna arrays were achieved to be adjustable in the ranges of 84 to 181 Hz, 3.9% to 8.3%, and two to four times, respectively. In addition, we have calculated the attenuation characteristics of ME antennas and their minitype arrays in seawater. The results show that the ME antenna array described in this manuscript is able to enhance the radiation intensity and information-loading capability, which has a positive potential for application in SLF communication systems.

Since sky wave over-the-horizon radar is seriously affected by transient interference, a transient interference suppression method based on an improved Teager-Kaiser energy operator and fuzzy reasoning is proposed. Initially, due to the extraction of the information entropy of slow time samples, the resolution ability of the energy operator to short-term fluctuation characteristics is improved and used to more accurately locate transient interference. Then, four evaluation indexes are constructed to quantify the confidence of the data reconstruction results obtained via the autoregressive, subspace and smoothing methods. Finally, Dempster and Shafer evidence theory is introduced to conduct fuzzy reasoning on the various reconstruction results, and comprehensive results are obtained. The experimental results show that our proposed method has evident advantages in locating weak interference, preventing clutter broadening and maintaining high-speed target energy.