As the complexity of the battlefield electromagnetic environment has increased, it has become challenging to identify radiation sources using traditional radar emitter identification technology in low signal-to-noise ratio (SNR) environments. We propose a method of radar emitter recognition based on the scale-invariant feature transform (SIFT) position and scale features. The proposed method first uses time-frequency analysis to analyze the radar emitter signal, and the obtained three-dimensional time-frequency image is normalized into a two-dimensional gray image. Next, the Gaussian difference pyramid of the gray image is established, and the SIFT scale features and position features of the image are extracted based on the Gaussian difference pyramid. The extracted noise feature points are suppressed based on the scale features. Finally, a support vector machine is used for the automatic identification of radiation sources based on the SIFT position features. The simulation results show that the proposed method performs well in a low-SNR environment.

As the use of radar and radar jammers increases, a radar device is likely to face interference from jammers or other radar devices. Traditional phase-coded pulse compression radar devices are widely used, but these tools struggle to overcome jamming and mutual interference. To solve this problem, we propose a novel chaotic-encrypted pulse compression radar signal based on radar identity (ID). Each radar has its own ID, which is encrypted with different chaotic binary sequences in every pulse period. The ambiguity function calculated for the coded radar signal is thumbtack-shaped, indicating that the signal has a good resolution. The received signal is used to range and decrypt in two channels: the range channel and the radar ID channel. The signals of the two channels are analyzed separately. Analyses of anti-barrage jamming and anti-mutual interference show that both channels perform well in terms of antijamming, while the antijamming ability is influenced by the processing gain, bit error rate (BER) and correlation function. In addition, the dual-channel antijamming method further improves the radar antijamming ability. The simulation result verifies the strong antijamming ability and high range resolution of the proposed radar signal, and the proposed antijamming method performs much better than the traditional phase-coded pulse compression radar signal in the antijamming scenario.

Currently, frequency-modulated continuous-wave (FMCW) proximity sensors are widely used. However, they suffer from a serious sweep jamming problem, which significantly reduces the ranging performance. To improve its anti-jamming capability, this paper analyzed the response mechanism of a proximity sensor with the existence of real target echo signals and sweep jamming, respectively. Then, a multi-channel harmonic timing sequence detection method, using the spectrum components’ distribution difference between the real echo signals and sweep jamming, is proposed. Moreover, a novel fast Fourier transform (FFT)-based implementation was employed to extract multi-channel harmonic information. Compared with the traditional band-pass filter (BPF) implementation, this novel realization scheme only computes FFT once, in each transmission cycle, which significantly reduced hardware resource consumption and improved the real-time performance of the proximity sensors. The proposed method was implemented and proved to be feasible through the numerical simulations and prototype experiments. The results showed that the proximity sensor utilizing the proposed method had better anti-sweep jamming capability and ranging performance.

The mechanism of resonant perfect optical absorbers is quantitatively revealed by the coupled mode method for the air/grating/dielectric film/air four region system. The sufficient and necessary conditions of the perfect optical absorption are derived from the interface scattering coefficients analyses. The coupling of the Fabry-Perot modes in the grating slits and non-zero order quasi waveguide modes in the dielectric film play a key role for the perfect optical absorption when the light is incident from the grating side. The analytical sufficient and necessary conditions of the perfect optical absorption provide an efficient tool towards geometry design for the perfect optical absorption at the specific wavelengths. The advantages of a widely tunable perfect optical absorption wavelength, a high Q factor and the confined energy loss on metal surfaces make the air/grating/film/air structures promising for applications in sensing, modulation and detection.