نشریه پژوهش های نوین در سامانه های دفاع الکترونیکی
سال دوم شماره 3 (پاییز 1402)

This article, we have designed and simulated an omnidirectional antenna with horizontal polarization. The idea used in this antenna is to use cylindrical metasurfaces to rotate the vertical to horizontal polarization. Using this method will provide the ability to design omnidirectional antennas with horizontal polarization and high gain. This antenna is designed for the working frequency of 5.8GHz, which is a point-to-point or point-to-multipoint communication frequency. The designed antenna achieves a maximum gain of more than 4dB and a return loss less than -15dB.This article, we have designed and simulated an omnidirectional antenna with horizontal polarization. The idea used in this antenna is to use cylindrical metasurfaces to rotate the vertical to horizontal polarization. Using this method will provide the ability to design omnidirectional antennas with horizontal polarization and high gain. This antenna is designed for the working frequency of 5.8GHz, which is a point-to-point or point-to-multipoint communication frequency. The designed antenna achieves a maximum gain of more than 4dB and a return loss less than -15dB.

This paper deals with the design and simulation of a wideband and low loss coaxial line to groove gap waveguide transition for millimeter-wave applications. The proposed transition structure is optimized to work at Ka-band to transform coaxial mode into the groove gap waveguide mode by means of a wideband slot-line. The simulation results of bacj to back structure show a maximum insertion loss of 0.5 dB and a return loss better than 20 dB over 42% relative bandwidth from 26 to 40 GHz. The obtained results can be valuable for the design and integration of gap waveguide structures for different microwave and millimeter-wave applications.This paper deals with the design and simulation of a wideband and low loss coaxial line to groove gap waveguide transition for millimeter-wave applications. The proposed transition structure is optimized to work at Ka-band to transform coaxial mode into the groove gap waveguide mode by means of a wideband slot-line. The simulation results of bacj to back structure show a maximum insertion loss of 0.5 dB and a return loss better than 20 dB over 42% relative bandwidth from 26 to 40 GHz. The obtained results can be valuable for the design and integration of gap waveguide structures for different microwave and millimeter-wave applications.

In this article, the effective parameters in detecting and identifying buried targets have been investigated. These parameters affect the electrical permittivity of the soil and can determine the penetration depth of the waves in the soil. Knowing the type of soil and the electrical conductivity of the soil, as well as the penetration depth of electromagnetic waves in it, can help us choose the appropriate frequency, antenna type, and transmission power, and in general, optimize the radar parameters. This can prevent resource waste and reduce search time to an acceptable level, and increase the efficiency of the radar system. The effect of physical and environmental parameters on 7 soil samples has been investigated, and the electrical permittivity coefficient and the depth of wave penetration in them have been calculated. In the next stage of simulation, loamy clay & sand soil is used as a reference soil and changes in compression, temperature, and humidity are applied to it, and according to each stage, the electrical permittivity coefficient and the penetration depth of wave are calculated. In the final stage of the simulation, the detection process of a buried metal target has been simulated in CST software according to the available detection depth in the previous stages. The biggest effect on electrical permittivity is related to changes in soil moisture. The maximum penetration depth of waves in dry soil with a frequency of 100 MHz is about 23 meters, and with the increase in soil moisture, the penetration depth of waves decreases to 1 meter.

Today, the security of information in communication channels is of great importance, and the higher the classification of information, the higher the importance of security. From a long time ago, various encryption algorithms were proposed to ensure communication security, and different organizations use different encryption algorithms based on the sensitivity of the information. Information can be classified into different types, textual information is one of the most diverse types of information, which becomes more important if there is a classification. In this article, based on the 28-character alphabet, a new encryption method is presented, which has high security and speed, and is resistant to attacks based on the frequency of letters. Laboratory results show a very high resistance of this method against a comprehensive attack. The attacker's need for a lot of memory, which is practically inaccessible, that is another reason for the robustness of this algorithm. Given the key generation algorithm in this method, it can be ensured that this algorithm is also very resistant to attack in the middle.

Corner reflectors are used as a standard target for imaging, evaluating and adjusting radar systems. The radar cross-section variation of these reflectors is large for the changes in their angles in relation to the radar direction. Therefore, when conducting radar tests, when the reflectors are rotating, the test becomes complicated or impossible in many cases. In this article, by adding narrow dihedral reflectors to the end part of three-sided reflectors, an all-directional reflector set with low RCS variation at different angles is presented. According to the simulations and measurements, the presented reflector has a 42% improvement in the RCS variation compared to other reflector structures. Also, in order to carry out further investigations in this field, by applying changes to the structure parameters of the presented reflector, a suitable compromise between some physical and electromagnetic parameters of this reflector such as weight, dimensions, uniformity of the RCS and the RCS value has been done. Finally, a sample of the designed reflector was built, and the measured RCS results confirmed the results of the simulations.

Localization algorithms are traditionally developed to minimize the impact of observation errors on accurate positioning by considering the errors in observations obtained from the target. When dealing with a moving sensor, navigation systems provide reports on the sensor's locations. Consequently, the localization methods in this approach need to be modified to incorporate the navigation errors along with the erroneous target observations in the equations, with the aim of reducing the impact of these errors on positioning accuracy. This paper focuses on utilizing passive positioning methods with moving sensors and presents an analysis and design of a method to enhance the speed and accuracy of positioning algorithms, while also updating the error estimates in observations and navigation reports. Simulation results demonstrate that the single-stage generalized least squares algorithm consistently yields the most accurate results across all scenarios and is suitable for real-world conditions. Additionally, an algorithm based on adaptive filters has been devised to expedite convergence speed. Moreover, the factors influencing convergence speed have been analyzed, and a solution to enhance convergence speed has been proposed. By examining Kramer Rao's bound in various methods, a novel framework has been developed. In this article, the intersection and rotation algorithm is employed to combine orientation-based and time-based energy transmission methods. These algorithms are characterized by their high accuracy, low computational overhead, and resilience to measurement noise. Simulation-based evaluations have been conducted, demonstrating the superior performance of the proposed method compared to existing approaches in terms of quality and effectiveness.