فصلنامه رادار
سال چهارم شماره 4 (پیاپی 14، زمستان 1395)

Radar cross section (RCS) calculation is an important issue of objects stealth and identification. It is necessary to design the RCS software because of the high cost of RCS measurements in practice. In this paper, designing of efficient software using physical optics theorem for radar cross section calculation of the complex perfect electric conductors or complex dielectric objects for high frequencies is investigated. In this method, first the object will be meshed in Abaqus Software. Then the obtained data of every mesh is transferred to MATLAB Software and, after that, the physical optics theorem is applied for every mesh, with considering the summation of electric fields that is seen from each mesh. As the result, the radar cross section of total object will be obtained. Simulations results show the proposed method has good agreement with CST-MS results and determines the RCS of the objects with lower complexity in the lower time consuming.

This paper presents a new design for a microstrip dual-band band-pass Microstrip filter (BPF) with suitable isolation between two passbands. In this design, a basic structure is used to achieve a desirable frequency characteristic in the passband. In this regard, Defected Ground Structure (DGS) is implemented to reach optimum parameters of the filter such as bandwidth, return loss, insertion loss. The special features of the filter are the compact size, dual-band design and suitable isolation between two passbands. Variation of the filter characteristics is compared in a table before and after applying DGS. Simulation results are at frequency of 4.84GHz and 3.8GHz. Return loss of -20dB and - 25dB and insertion loss of -0.5dB and -0.9dB are the results of the mentioned frequency, respectively. Also the bandwidth of 87 MHz is achieved for both simulation frequencies. Simulation results are well-matched to the characteristics of the fabricated filter.

In recent years, synthetic aperture radar (SAR) images have played an important role in the detection and monitoring of ground targets because of their advantages such as independence from climatic conditions and sensitivity to the target geometry. The complexity of SAR imaging sensors, especially in the conversion process from raw data to image, has made it difficult to interpret the behavior of sensors and their images. Hence, using the simulation of SAR images can be effective in resolving this problem. In this regard, SAR image simulation of three-dimensional objects is an essential step. In this paper, a method is presented to simulate SAR images of three-dimensional targets and, thus, the polarimetric scattering matrix for pure and distributed targets is developed. Also, the effects of sensor parameters and the geometry of target are investigated in simulating the SAR images of 3D targets.

For naval radars, the concept of “the sea state” is very important. In this article, the sea wave equation and its shape of movement have been determined. Then, the waveforms of the sea waves have been reconstructed using the Feko software. After that, the RCS resulting from the impact of radar waves (with high range resolution radar) to sea level has been calculated in order to acquire returned signals from sea waves in antenna input. Subsequent to determining returned signals in the time domain and receiving these signals by the radar receiver, its first to forth moments are calculated. On the following, the feature space is formed and by using it sea waves are classified in four different modes. And finally, the precision of this suggested method has been measured by adding noise to returned signals from the sea level.

Extended Interaction Oscillators (EIO) are vacuum electronic sources of microwave, millimeterwave and terahertz radiations. In this paper, EIO is investigated by using a circuit model. The value of the coupling element in the model is evaluated from the near band-edge dispersion characteristics of the RF structure. The end external loading of the interaction structure is equivalently modeled by a distributed loss along the circuit which simplifies the external loading calculations in the circuit approach. A W-band (94 GHz) EIO is simulated by using the mentioned circuit approach and also by a three-dimensional particle-in-cell (PIC) solver and the results are compared.

In this paper, by considering a squint angle for synthetic aperture radar in the strip-map mode, a method is proposed for estimating parameters of a fixed acceleration moving target. Non-zero Doppler centroid and range-azimuth coupling in the squint mode add complexity to estimation equations of moving target parameters and cause Doppler ambiguity. This, in turn, causes to lose the efficiency of using the keystone transform. Furthermore, Radon transform in the squint mode will not give accurate results in determining the unambiguous Doppler centroid. Hence, in this paper, by using a Geometry-based Doppler centroid estimator, an approach is proposed to improve the precision of Radon transform which is capable to correct linear range migration. Finally, by employing local polynomial Fourier transform, Doppler parameters of order two and three are obtained. By estimating Doppler bandwidth, the target synthetic aperture time is then obtained. The accuracy of our derived equations is examined and verified by simulation just using a single antenna.