In this work, an ultra-thin frequency selective surface is developed with a square unit cell loaded with three ring slot pairs. The outer ring slot pair is loaded with metal shorts It achieves one polarization-insensitive passband with sharp transition at Ka-band. The design is verified with full-wave simulated results, as well as the measured results. The fabricated FSS has a flat passband and its measured 3-dB bandwidth is from 33 GHz to 37.5 GHz. A complete angular stability study of the FSS has been conducted. Meanwhile, it can directly attach to the aperture of the horn antenna to lower the whole profile of FSS-antenna configuration. Working as a radome, this FSS can be a good candidate for radar communications and radar cross section reduction in radar stealth research area at Ka-band.

A novel algorithm is proposed for estimating the direction of arrival (DOA) of linear frequency modulated (LFM) signals for the uniform circular array (UCA). Firstly, the UCA is transformed into an equivalent virtual uniform linear array (ULA) using the mode-space algorithm. Then, the short time Fourier transform (STFT) of each element's output is worked out. We can obtain the spatial time-frequency distribution matrix of the virtual ULA by selecting the single-source time-frequency (t-f) points in the t-f plane and then get the signal subspace of the array. The characteristics nature of the Bessel function allow us to obtain the multiple invariance (MI) of the virtual ULA. So the multiple rotational invariant equation of the array can be obtained and its closed-form solution can be worked out using the multi-least-squares (MLS) criterion. Finally, the two dimensional (2-D) DOA estimation of LFM signals for UCA can be obtained. Numerical simulation results illustrate that the UCA-STFT-MI-ESPRIT algorithm proposed in this paper can improve the estimation precision greatly compared with the traditional ESPRIT-like algorithms and has much lower computational complexity than the MUSIC-like algorithms.

The airborne and spaceborne SAR system are not universal access to a large area due to its higher cost and harsh demand conditions. This paper presents a vehicle millimeter wave SAR system. According to the features and application needs of the platform, this system uses range migration algorithm (RMA). Firstly, the system uses dechirping algorithm to deal with every echo. Then, we derive the two-dimensional frequency domain expression of the echo whose residual video phase (RVP) has been compensated and then analogize it to the spatial frequency domain to calculate the spatial frequency domain expression. Finally we complete the location reconstruction of the target. Due to the fan-shaped distribution of the signal distribution in the spatial frequency domain, there will be a large error if we reconstruct the location of the target directly. In this paper, we use stolt interpolation to turn the fan-shaped distribution into a rectangular distribution and the specific interpolation step is given. We also simulate the algorithm proposed in this paper. Finally, we use the vehicle millimeter wave SAR system to image for the actual scenario and the focusing effect of the image results is good to meet the demand. So the system can be applied to a variety of areas.

With the rapid development of high-speed signal processing devices, the algorithm with large amounts of data can be implemented in real-time. This paper proposes a kind of signal processing system based on five pieces of multi-core DSP. Firstly, the interface circuit and program between FPGA and DSP, DSP and DSP, the system and computer are designed and tested. Then, this paper puts forward that the system can use Semaphore2 to schedule the task and use DDR3 as well as MSCM to share the data. Finally, the system is tested by using the imaging algorithm with a large amount of data. The time-consuming results of the system and imaging results demonstrate that this system is able to process the algorithm with a large amount of data in real-time.