Calculating radar cross section (RCS) of complex conductive targets is of great significance to design highly precise radar system, recognize targets and so on. This paper simulates complex objects with a periodic array of cylinders, and mainly focuses researches on the impacts on RCS by number, spacing and size of cylinders. The experimental results show that the biggest backward scattering RCSs of two-body to five-body cylinders were 0.0334sm, 0.0750sm, 0.1334sm and 0.2084 sm.
We present a system to measure objective backscattering properties at 2.52 terahertz (THz). The optical setup combining 90° off-axis parabolic mirrors with 15° off-axis parabolic mirror decreases the size of the system and then realizes its compact structure. The calibration object, a conducting sphere with a diameter of 50 mm, was introduced to eliminate the influence of the instability of THz radiation and the background noise on measurement results. The lock-in amplifier was adopted to enhance the signal-to-noise ratio (SNR) and then make it possible to observe delicate backscattering behaviors on the surface of the object. Backscattering properties of four scale models were measured in this paper. Experimental results indicate that the maximal error of our system is less than 1 dB, paving the way for practical measurements of objective backscattering properties at THz frequencies.
Conventional strapdown gyrocompass alignment methods are based on the assumption that the fiber-optic-gyro inertial navigation system has a small azimuth misalignment angle. A large azimuth misalignment angle would lead to an extension of the alignment duration. A time-varying gyrocompass alignment method to solve this problem is provided. An appropriate parameter setting is given for the gyrocompass alignment with a large misalignment angle. Also, a proper protocol for a parametric switch is derived. Simulation and trail results show that the proposed method has better alignment performance than conventional ones, as the system has large misalignment angles.
This paper aims to propose a new strapdown fiber optic gyrocompass (strapdown FOGC) using adaptive network-based fuzzy inference system (ANFIS). The strapdown FOGC is based on the principle of strapdown inertial navigation system and utilizes electromagnetic log (EM log) and damping equalizer to bound oscillatory errors existing in attitude and heading. As the introduction of damping technique, extra errors are aroused by EM log errors. To decrease the extra errors, ANFIS is utilized to adjust the damping ratio automatically in terms of the ship maneuver conditions. The simulation and trial results indicate that, compared with the conventional gyrocompass scheme, the proposed one can reduce the attitude and heading errors and improve the system performance effectively.