JOURNAL OF RADAR
Year:2021 | Volume:9 | Issue:1|Papers Count:12

In this paper, phased multiple-input-multiple-output radars (known as PMRs) that transmit frequency diverse orthogonal signals with full overlapped sub-arrays are studied. At first, the optimal detector of PMR is designed by assuming heterogeneous clutter and random target scattering coefficients. Then, for the optimal detector, the closed-form detection probability and false-alarm rate are computed. At the end, the power assigned to the orthogonal signals is optimized analytically based on the convex optimization framework to maximize the detection probability. The numerical simulations show that the optimal detector is a joint spatial-temporal filter that attenuates the clutters considerably by effectively combining orthogonal signals in order to to improve the PMR detection probability in comparison with the phased radar (PR). Furthermore, simulation results illustrate that optimal power assignment in the form of orthogonal waves, based on the statistics of the target scatterings and that of the clutter, improves the detection performance of the PMR in comparison with the conventional equal power assignment methods.

Numerous researches have been performed on the reflector antenna for realizing beam-shaping using level-shaping. However, little study has been done for realizing the shaped beam through the multi-feed approach. The main goal of this paper is to provide a synthesis procedure for realizing the flat-topped pattern in reflector antennas using the multi-feed approach. In this way, based on the genetic algorithm (GA) and utilizing the physical optic (PO) method, the excitation coefficient of the feeding array is synthesized to achieve the desired pattern. Furthermore, in this paper, an efficient method for reducing the computational time of PO integrals is introduced. In this way, the 3D PO integrals are mapped to 2D integrals; which results in about 30% computational time reduction. The proposed procedure is employed to realize a flat-topped pattern in the angular scope of-20o to +20o and the radiation characteristics are compared with those presented through the shaped reflector method in the literature. Results show that the multi-feed approach obtains the desired beam more accurately.

In this paper, the effect of errors in the Euler angles on the performance of the LEO single-satellite LOS geolocation method is analyzed. In the LEO single-satellite LOS geolocation method, the aim is the estimation of the terrestrial target location by finding the intersection of the two direction vectors and the ground. In the presence of errors in the measured values, the target position estimate deviates from its true value and it is required to analyze the effects of this deviation. To this end, first, by expressing the problem in the ECEF coordinate system and transferring the origin to the satellite position by using the latitude and longitude of the satellite and the state vector, it is tried to determine the intersection of the LOS from the satellite to the target and the earth’ s surface as the target location. Then, the effect of the error in Euler angles on the performance of the LOS method is theoretically analyzed and its covariance matrix is derived by the perturbation method. In addition, the CRLB for the LOS method due to the error in Euler angles is presented. According to the simulation results, in order to achieve an RMSE of less than 1500 meters in the considered scenario, the angle errors in the attitude vector should be less than 0. 1 degrees.

In this paper, the physical characteristics of a plasma reflector are investigated. It is observed that the frequency and angle of the incident electromagnetic waves and also the physical parameters of the plasma affect the characteristics of the plasma reflector. The analytical analysis show that a plasma reflector behaves like a high-pass filter whose cut-off frequency is a function of the plasma frequency and the angle of the incident electromagnetic wave. The amount of loss in this filter can be controlled by the plasma pressure and also the thickness of the reflector. It is possible to turn this filter on and off by energizing/de-energizing the plasma. In the case of the de-energized filter, the electromagnetic waves pass through it with a partial loss. In this research commercial off-the-shelf dielectric tubes which are cheap and available are used to implement the concept, and various feasible arrangements, for the implemetation of the reflectors with cylindrical dielectric tubes (equivalent to commercial plasma containers) are investigated. The simulation results show that using two tublar layers perpendicular to each other, is the most efficient structure for the plasma reflector.

As underground hidden facilities are used for various applications, imaging systems are required for the detection and recognition of these facilities. In this paper, imaging by mechanical wave propagation in the soil is investigated. Most underground facilities can be considered as air chambers located in the middle of the soil. Air and soil have a large difference in acoustic impedance, so underground facilities can produce a large reflective signal because the amplitude of the reflected signal depends on the difference in impedance of the two materials. Seismic and non-destructive concrete testing systems also use the process of propagation of mechanical waves in the material. Although seismic systems have been successful in the detection issue, they require several meters of space for equipment layout, and transportation complexity is also one of their problems. They are unsuitable for urban space because they are inherently designed to detect water sources at depths of several hundred meters. On the other hand, while the non-destructive concrete testing system equipment have suitable dimensions, they have low penetration depth which is impractical for this purpose. Seismic and non-destructive testing systems of concrete operate in the range of subsonic and ultrasonic waves, respectively. This research project proposes the idea that by choosing an operating frequency between the two mentioned ranges, it is possible to obtain equipment with the appropriate dimensions for imaging underground facilities. In this project we managed to image an underground constructed cylindrical cavity with the diameter of 1 meter and the depth of 4 meters. The accuracy of this method depends on the sound propagation speed in the material. Since there are accurate relationships for the propagation speed of sound in air, the diameter of the cylinder was estimated with an accuracy of about 4%, but with the measurement of propagation speed being infeasible in this project, leading to the ambiguity in the value of propagation speed of sound in soil, the values cited in several reference sites were used, giving the accuracy of 4 to 20%.

In this paper, the scattering of long wavelength electromagnetic waves from a warm plasma column with an elliptical cross section is investigated. We assume that the incident wavelength is much larger than the cross-sectional area of the elliptical column and enter the thermal effects into the calculations using the Boehm-Gross equation. Using suitable boundary conditions, we calculate the electric potential as well as the electric field at the points inside and outside a plasma column with an elliptical cross section. Then we obtain the dispersion equation in this case and prove that in the limit state, this equation becomes the dispersion equation in a plasma column with a circular cross section. Considering the plasma resonance condition in an elliptical cross-section plasma column, we calculate the resonant frequency in this configuration. Finally, we plot the graphs of potential amplitude at the inside and outside points. Note that using the resonant frequency, we can calculate the characteristics of the plasma antenna under study, such as the plasma density.

Radar network deception through phantom track generation using cooperative unmanned aerial vehicles (UAVs) is an effective way of encountering sophisticated radar networks. In previous studies a method based on virtual motion camouflage (VMC) and path control parameter (PCP) has been developed to design the trajectory of cooperative UAVs during the phantom track generation mission. In these studies, the radar locations are assumed to be known. In real situations, the knowledge of radar locations has an inaccuracy. The radar position inaccuracy leads to an incoherent phantom track. The radar network can recognize the phantom track according to the distance between the false targets created by each UAV. In this paper, the effect of the inaccuracies of the radar position on the generated phantom track is considered. By adding a constraint that limits the flyable range of UAVs, the phantom track is generated such that the probability of the radar network detecting the deception is minimized. The mentioned constraint is specified based on the maximum radar position inaccuracy, the radar error, and the false target trajectory. The simulation results show that using this constraint in the trajectory design for UAVs, reduces effectively the recognition rate of the phantom track for various ranges of inaccuracies.

This paper presents the design of a high-isolation power divider based on the groove gap waveguide. The proposed structure is similar to a rectangular waveguide Magic-T when its difference port is terminated using a waveguide match-load. Wideband impedance matching and high-isolation of the structure are obtained by placing some PEC steped cones inside the structure. First, a 1×2-way power divider is designed such that by combining a specific number of it, power dividers with more outputs can be acheived and to demonstrate this idea a 1×4-way power divider is assembled. The results of simulating the proposed power divider show that the structure has 33% frequency bandwidth covering from 42 GHz to 59 GHz. The structure reflection coefficient is below-15 dB, the insertion loss is lower than 0. 12 dB and the isolation is better than 18 dB in the whole frequency bandwidth and the simulation results prove that the proposed power divider is an excellent candidate for millimeter-wave applications.

The phased array radars are a favourable type in the group of radars due to their agility in scanning the space and their highly flexible radiation patterns. However, due to their dependence on the phase to frequency shifters, these radars suffer from “ beam squint” , which limits the radar bandwidth. Using the true time delay (TTD) technique is one of the suggested solutions to this problem. Due to their unique features, the optical circuits have been widely used for the implementation of the TTD method but these circuits have problems such as high complexity, high cost, and the large size of structures. For example, fiber delay lines can only generate a certain and limited amount of delay, they are difficult to maintain, and they take up a lot of space. Conversely, the delay lines based on ring resonators create continuous delay and occupy little volume. However, because of the very small size of the rings, these lines face the challenge of complexity in construction. In this paper, a delay line based on ring resonators and microcomb laser source, with a new structure is presented that while enjoying the conventional advantages of these rings, is simpler in structure and requires fewer rings than other conventional configurations.

In a location estimation system, the deployment of reference nodes significantly affects the accuracy of estimating the location of the desired points. In this paper, it is assumed that the location system is equipped with a number of reference nodes in a specified arrangement, and the goal is to add a number of new reference nodes to improve the location estimation accuracy of a desired emitting node. In this network, the location of an emitting node is estimated by measuring the distances to the reference nodes. An algorithm is proposed to find the optimal place of the new added reference nodes using the frame theory. The basis of this algorithm is to arrange the new reference nodes without changing the location of the present reference nodes in the system in such a way that the determinant of the Fisher information matrix is maximized. The simulation results verify the efficiency of the proposed algorithm in the optimal deployment of new reference nodes.

The synthetic aperture radar is an imaging radar that has a high resolution. The synthetic aperture radar image may be degraded by the interference of radio frequencies and an incomprehensible image may be created. Interferences in the synthetic aperture radars are divided into the three categories of, , and, which represent radio frequency noise interference, narrow band interference and wideband interference, respectively. To effectively reduce the interference in synthetic aperture radar images, first the presence of interference and its type should be asserted and then the interference reduction algorithms should be calculated according to interference type. In this paper an algorithm for the detection of interference and its type in the synthetic aperture radar images is presented. Whilst in the previous articles the SSD method is used for interference detection, in this paper we have used the Faster RCNN method based on neural network convolutional which has a higher speed and accuracy than the SSD method. In this method, first a neural network is trained with the ability of multiple classification. Then the Faster RCNN is constructed with the neural network and and is trained by 25 time-frequency images from the artificial aperture radar signal. The trained network is able to detect any interference in the radar signal of a synthetic window with 99% accuracy. After detecting the interference by the proposed algorithm, the normalized least mean square filter is able to reduce the interference and improve the radar image. This filter operates similarly in decreasing all three types of interference.

In this paper a modified Gaussian pulse stimulus is employed to improve the accuracy of tumor detection inside breast phantom for 2D reconstructed image results in cylindrical setup of the microwave imaging system. This pulse shaping puts more energy at higher frequencies in contrast with conventional Gaussian pulse shaping in the impulse radar. Hence a wider bandwidth is available to achieve higher accuracy for precise spatial localization. In the present article a simulated cylindrical setup of the microwave imaging system with a modified stimulated pulse is generated. The main purpose of this paper is employing a new stimulating pulse to detect a tumor from a biological phantom for 2D visualization of time-domain results. In order to achieve the goal, the advantages of generating a novel confocal image-reconstructing algorithm based on back-projection method is employed. The advantage conferred by “ high resolution imaging” is that more energy is used at reflected signal than with conventional confocal imaging, and subsequently a relatively lower spatial resolution in identifying the reflected signal is achieved. Simulated results are presented to validate the effectiveness of the proposed method for precisely calculating the time-dependent location of targets.