JOURNAL OF RADAR
Year:2020 | Volume:7 | Issue:2 (SERIAL No. 22)|Papers Count:12

Antenna positioning is very important in synthetic aperture radar systems and it is necessary in the design of a navigation subsystem to account for different sources of error and their effects on the accuracy of navigation results. According to the error behavior of inertial and satellite navigation systems, integration of inertial sensors with satellite positioning systems is a common method to achieve high accuracy navigation results. However, synthetic aperture radar considerations, lead to some problems in the utilization of integrated navigation results in the imaging period. Therefore, only the inertial navigation results are used in the imaging period, and integrated navigation results are used just as the initial conditions for the algorithm. This paper studies the estimation of these initial conditions and predicts the navigation error growth caused by them. Since the extended Kalman filter is the most common tool for the integration of inertial sensors and satellite data, the elements of the corresponding state covariance matrix represent the accuracy of integrated navigation results. In this study for a synthetic aperture radar flight scenario, in which the nominal path is a straight path with a constant velocity, the state covariance matrix is calculated analytically both in the steady-state conditions and after the GNSS data outage. These analytical results are verified with simulations. Specifically, the estimation accuracy of antenna position, velocity and attitude are calculated with respect to the noise level of inertial sensors and GNSS data. Results can be used in the design and/or selection of a proper navigation system in synthetic aperture radar applications.

Cooperative positioning utilizes information received from all the nodes in a network to estimate the position of a target node. This requires high amount of data exchange and data processing in high density networks. This paper proposes a low computational complexity algorithm to select a number of nodes among all possible nodes to cooperate in position finding. Position of nodes are estimated using both the distances between the target node and its cooperated nodes and also the information shared by these nodes. The nodes selection algorithm is proposed according to the Cramer-Rao Lower Bound, which considers the precision of distance measurements, the geometry of nodes and the uncertainty in the information shared by nodes. This fast computing algorithm reduces required computations without significantly decreasing the position estimation performance.

Estimating RCS by near field methods has achieved great significance because of noticeable cost reductions. In this research we pursue RCS reconstruction by near field imaging with small processing load in laboratory conditions. A 10×10 cm meta surface lens in the 10-12 GHz frequency is designed and simulated for estimation of RCS, using near field imaging method which obtains the aperture efficiency and-1dB bandwidth of 32% and 7% respectively. This microwave lens is able to reduce the beam width by half. In this method, we ignore the image reconstruction step and use the obtained fields directly on a plane to estimate the RCS, causing a reduction in the volume of processing. The results show improvement in the estimated RCS, in addition to reducing the experiment distance, thus ensuring the possibility of implementation in the laboratory.

In this article, a low-phase noise microwave S-Band oscillator using a pentagonal shaped SIW resonator is presented. The resonator is designed on a 20 mil RO4003 substrate and is simulated in Ansys HFSS. The loaded quality factor of the resonator is obtained to be 72. The oscillator is simulated and designed using Agilent ADS. Our measurement results show that the phase noise is better than – 140 dBc/Hz at 1MHz frequency deviation. The oscillation frequency is 3. 16 GHz, the output power is 9. 1 dBm, and the harmonic rejection is better than 40 dBc. The fabricated oscillator is suitable for low-cost high-frequency systems.

In this paper a miniaturized diplexer for WLAN and WiMAX applications is presented, based on half-mode substrate integrated waveguide (HMSIW) technology by loading a novel metamaterial unit-cell. The proposed metamaterial unit-cells are called fractal open complementary split-ring resonators (FCSRRs). The proposed FCSRRs behave as electric dipoles if appropriately stimulated, and are able to generate a forward-wave passband region below the cutoff frequency of the waveguide structure. The electrical size of the proposed FCSRRs unit-cell is smaller than the conventional CSRRs unit-cell. Therefore, the FCSRR unit-cell is a good candidate to miniaturize the SIW structure. The proposed diplexer has been designed by cascading two bandpass filters with different center frequencies. The HMSIW bandpass filters are implemented by etching two FCSRR unit-cells with different sizes. The design procedure is based on the theory of evanescent mode propagation in which the FCSRR unit-cells behave as electric dipoles. A forward-wave passband below the intrinsic cutoff frequency of the HMSIW structure has been achieved by loading the FCSRR unit-cells on the metal surface of the HMSIW structure. This proposed diplexer displays high selectivity and compact size by using sub-wavelength resonators. The designed diplexer has been fabricated and experimental verifications have been provided. The measured results are in a good agreement with the simulated ones. The total size of the proposed diplexer is about 0. 30 λ g × 0. 09 λ g. The proposed diplexer shows significant advantages in terms of size reduction, low loss, high selectivity, high Q-factor, easy bandpass frequency shifting, easy fabrication and easy integration with other planar microwave circuits.

The importance of reducing the oscillator phase noise in most radio equipment, including communication systems, radio sensors and radar, has led to many solutions, one of which is the activation of resonator in the oscillator structure. In this paper, by presentation and analysis of x cases it is shown that the correction of the phase noise by activation of the resonator depends on the model of the resonator and its position in the oscillator and does not happen in all cases. It is also, shown that designing oscillators using extra active feedback loop is not always effective in reducing phase noise. Resonators whose equivalent resistance is in the path of the oscillator loop, do not require an extra active feedback loop in order to obtain the desired phase noise, and the losses are fully compensated by the amplifier which also plays the circuit oscillation role. Two oscillator structures; a series RLC resonator and an RLC resonator with resistor in parallel to capacitor, are compared and the results show that the phase noise is not changed by the extra active feedback loop in the first case but it is decreased by 18 dB in the second one.

Detection and direction of arrival (DOA) estimation is a signal processing challenge for wideband signals like LPI radar signals. Modern radars change theirs signal waveforms from pulse to pulse and distribute the signal in the time or frequency domain. Traditional direction finders usually use a narrowband channel to maximize sensitivity and detection range. Increasing the signal bandwidth decreases the SNR and the probability of intercept (POI). In this paper we proposed a new method for the direction finding of LPI radars, which increases the POI. In the proposed method we used two rotating antennas, one antenna used as a matched filter to the other one, in order to increase the processing gain. The proposed method despite traditional direction-finding methods, is able to detect and analyze pseudo noise and spread spectrum radar signals, without any theoretical limitation on signal frequency bandwidth. In this paper we used two antennas and proposed a new method with cross correlation technic for direction finding such as the method used in Monopulse tracking radars and compared it with other methods. Simulations shows good detection specifications for low SNR and we could reach about 25dB processing gain in wideband radar signals like LPI Radars or LFM Modulated radar signals.

Passive radar research has many applications in military and commercial fields. In this paper, we investigate the scenarios of surveillance signal processing in multi-transmitter and multireceiver passive radar. These scenarios include centralized processing of the received signals reflected from the target at the central sensor and decentralized processing of the reflected signals at the receiving sensors. Different types of possible measurements including time difference of arrival (TDOA), gain ratio of arrival (GROA), angle of arrival (AOA), and their combinations are presented under different scenarios. To calculate TDOA and GROA measurements, the centralized processing and for calculation of AOA measurements, the decentralized processing of surveillance signals are performed. The impact of different signal processing scenarios and types of measurements on the efficiency of target location estimation has been investigated by the CRLB. As shown in the simulation results, the combined use of the measurements is always better than their individual employment and, the far-field placement of receiving sensors, significantly improves the efficiency.

Today, plasma technology has found significant applications in various industries including telecommunications. The high-ionization limit of plasma has made it a good conductor and a substitute for metal structures in high frequencies. In recent years, the plasma environment for the design of reconfigurable antenna structures, waveguides, and frequency-selective surfaces (FSS) has received more attention by scientific societies, especially space and military centers. This is because of the specific characteristics of the plasma environment that can be used to control and adapt the antenna for different purposes. The effects of plasma usage on the antennas include: improved sensitivity and directivity, low radar cross section (RCS), radiation pattern scanning, antenna array coupling and frequency tuning. Plasma can be created by many different ways such as surface wave driven excitation and direct or alternating current excitation. The purpose of this study has been to investigate the effect of alternating current excitation with different frequencies and waveforms on U-shaped monopole plasma antenna parameters including reflection coefficient, resonance frequencies and bandwidth. The results indicate that, in addition to its much lower power consumption, this type of excitation increases the bandwidth of the U-shaped antenna and its operating frequency up to 2 GHz. The plasma antenna sent or received signals, are applied to, or received by, a capacitive coupler. Also, various effects on antenna parameters including reflection coefficient reduction, central frequency shift and bandwidth variations were observed and measured, by changing the frequency and waveform (square, triangular, sinusoidal) of the plasma excitation current.

The adaptive block quantization approach, or BAQ, is a common approach to compress synthetic aperture radar raw data. Radar imaging systems, especially spaceborne SAR system, exploit large bandwidths and high sampling rates, resulting in large bitstreams to be handled. This leads to a large volume of data obtained for each area being imaged, and storing or sending these raw data through a data link is a major challenge. Therefore, by using “ raw data compression” , data link bandwidth and the needed memory space can be reduced effectively. In the course of developing the technical knowledge of spaceborne SAR systems in the country, the design and implementation of SAR raw data compression algorithms have been developed in the Institute of Mechanics. In order to evaluate and analyze the efficiency of these methods, the raw data of ISRCSAR; a SAR system developed by the Institute of Mechanics are used. One of the most important issues discussed in this paper is the adaptive selection of the BAQ rate in the raw data compression as well as the effect of this bit rate selection on the quality of the image which is formed by the compressed data. To compare the resulting images from different BAQ bit rates, the PSNR criterion and visual evaluations of the resulting images are used. The results of this comparison indicate the high performance of the proposed approach.

In this paper, the compressive sensing (CS) method is used in the through the wall radar imaging (TWRI) to reduce the measurement points and data acquisition time, consequently. In fact, the large required amount of measurement points is considered as one of the main challenges in TWRI which can be mitigated by this proposed method. The diffraction tomography (DT) method is the most efficient conventional method used in TWRI process. By exploiting the advantages of the CS and non-uniform fast Fourier transform (NUFFT), the effectiveness and speediness of the DT method is significantly increased. Simulations and the results of experiments have verified the validity of the proposed imaging method.

In this study, the design and simulation of a DRFM jammer system as an active radar decoy carried by an unmanned surface vessel (USV) for the protection of a ship from an anti-ship cruise missile equipped with radar seeker are presented. In this operational scenario, it is assumed that some critical parameters of the threat (missile radar) signals, are extracted by the ship ESM on time and are transmitted by a data link to the USV and jammer. By recording and altering the received signals of the threat in the radar jammer and pre-determined maneuvering schemes of the USV, the missile is prevented from hitting the target. The result shows that separating the jammer location from the target ship and mounting it on USV, can increase the effectiveness of the warfare techniques and decrease the chances of the missile hitting the target ship, through angle deception of the angle tracking radar antenna of the missile so that the target ship would be out of the missile field of view (FOV). In spite of the USV limitations, in volume, weight and maneuvering capability, outfitting it with a radar jammer can be effective for the deceiving some types of anti-ship cruise missiles equipped with tracking radar.