فصلنامه رادار
سال پنجم شماره 1 (پیاپی 15، بهار 1396)

Surface distortions on the main reflector change the radiation pattern of the reflector antenna and degrade their radiation characteristics. There are different methods to compensate the undesired effects of the main reflector’s surface distortion. in the present study, it has been shown that by using a shaped sub-reflector, one can compensate the effects of the main reflector’s distortions. Based on the variational mathematics, the radiation pattern has been linearized and reformulated in the matrix form. The reverse problem has been solved using the Singular Value Decomposition (SVD), and it is shown that for a dual-reflector antenna, the proposed method can be used to design a compensator shaped sub-reflector. Results show that if the amplitude of the distortion on the main reflector is less than quarter wavelength, the proposed algorithm can converge to the solution very fast.

Navigation and localization are two key issues for many modern mobile applications. Navigation data can be gathered either passively (i.e. by means of INS) or actively (e.g. GPS, Loran). the passive navigation data Usually degrade through the time. On the other hand, the active methods are prune to interference and jamming. In this paper, the passive navigation method is aided by the measured angle of arrival from emitting objects (i.e. radars) at known locations. The results show that in the proposed method in contradiction to many other passive methods, while maintaining the passiveness of the system, using AoA measurement, the quality of navigation data is preserved or even improved through the time.

The most common radar EP technique to prevent effects of impulsive interferences is SLB. In classical SLB structure, an auxiliary antenna and receiver channel are employed to discriminate between the main beam signal and the unwanted signals entering through the sidelobes of the main antenna. In this paper, we have proposed a new SLB structure which utilizes multiple auxiliary antennas. Then, by using an envelope-detection based demodulation, we have presented a group of processing logics including AND, OR and SUM to control the switch. Additionally, we have suggested a new method for setting the detection and blanking thresholds. Simulation results show that the proposed methods using multiple auxiliary antennas, outperform the conventional structure in terms of reducing the number of false target blips on radar PPI.

In this paper, closed-loop phase calibration for coherent aperture radars has been investigated. The idea of using multiple coherent radars is known as the next generation radar. In this method, the signal to noise ratio could be improved by N2 where N is the number of coherent radars; however, achieving this coherency is not feasible unless a phase calibration procedure is conducted. In this paper, utilizing the main target as the calibration target has been modeled and simulated. Simulation results have been employed to investigate the phase error associated with the closed-loop calibration method.

The advantage of hardware and pattern recognition techniques along with the wide applications of Remote Sensing (RS) satellites have caused the development of Automatic Target Detection (ATR) systems. Especially, the automatic airport detection is a necessary task due to its important strategy. In this study, a new method is proposed for the automatic airport detection and extraction in the single Synthetic Aperture RADAR (SAR) imagery. For this purpose, an Unmanned Aerial Vehicle SAR (UAVSAR) imagery acquired in L band from Okaloosa in Florida is used. Overally, the proposed method contains the combination of Hough transform for the airport runway detection, and an object based classification stage for the airport’s area extraction. Experimental results demonstrated the perfect performance and efficiency of the proposed method for the automatic airport detection and extraction.

In this paper, a method is provided for suppressing FM noise jammer signal with polynomial-phase in pulsed radar based on the discrete polynomial-phase transform. In the first step, DPT transform is used to estimate polynomial-phase coefficients and amplitude of jammer signal. In the second step, the jammer signal has been reconstructed using the estimated amplitude and phase of the jammer signal, Then, jamming is suppressed efficiently by subtracting the reconstructed jammer signal from the received signal. Mean square error and CRLB for polynomial coefficients and amplitude of jammer signal in presence of combined target signals and the receiver noise, are calculated theoretically for the case of linear frequency modulation, and then are compared with simulations. The detection performance of the proposed method is also shown.