Monopulse System Research Articles

Arc-Scanning Synthetic Aperture Radar for Accurate Location of Targets

The purpose of this article is to present the advantages that the use of arc-scanning synthetic aperture radar (Arc-SAR) would provide for accurate location of target to the weapon systems. Arc-SAR systems have an extraordinary capacity of angular discrimination of the targets, this fact make possible they can be used for the precise location of targets by replacing the large antennas required by the monopulse systems, used in this kind of applications, with a small rotating antenna. However, to carry out the real-time location of targets with the current processors a much more complex signal processing is needed. A simulator has been developed in this work, which allows the comparison of the theoretical and experimental results obtained by the classical systems against those obtained with the proposed Arc-SAR system working in the millimeter frequency bands. The results obtained demonstrate the ability of the proposed technique to accurately locate targets. This confirms that the obtained precisions allow the use the presented system in some important applications as Sense & Avoid (S&A) and weapon-pointing systems. Finally, possible applications of these techniques are described, especially useful is onboard sensors, because of the small size and weight of the antenna needed to implement an Arc-SAR system.

Design of Vivaldi array antenna with low sidelobe for Monopulse tracking application

The article will present the array antenna system for Monopulse tracking application. The Antenna includes 3 parts: monopulse comparator, unequal power divider, and antenna array. The monopulse comparator and unequal power divider are designed by microstrip line on PCB. Antenna array consists of 244 Vivaldi elements. Conducted simulation of the antenna system and obtained the following results: The bandwidth of the antenna system is greater than 10% with Voltage Standing Wave Ratio smaller than 1.6 (VSWR ≤1.6); Realized gain of the sum beam (radiation pattern) at the central frequency reaches 26.2 dBi; Sidelobe level of sum beam is less than -20dB in the whole frequency range; The peak and null of two difference beams are smaller than 20dB. With the results obtained, the Antenna Monopulse system is mentioned as completely suitable for use for tracking applications and arrangement in narrow space locations with compact size.

Geometric Arithmetic Mean Method for Low Altitude Target Elevation Angle Tracking

In tracking operation, the signal reflected from the target comes to the antenna in two paths. The first is the direct path, from the target to the antenna, and the second is the indirect path, due to the multipath phenomenon, from the target to the surface then to the antenna. In a low altitude situation, the indirect path can cause severe errors in tracking operation as it enters the antenna main beam and combines with the direct path signal. In such a scenario, the antenna fails to track the elevation angle by the target's image located under the ground. A significant challenge in tracking systems is to mitigate the multipath effect. To do so, we extended the elevation geometric mean method and presented the target and image elevation angles separation method. Two monopulse equations are proposed to calculate the target elevation angle. The proposed method offers low computational load and can be implemented on monopulse system. The complete noise analysis is derived for the method. It is shown that the error of the proposed method reaches the Carmer Rao Lower Bound by proper selection of frequencies. Simulation results show accurate target tracking in a multipath environment.

Design of a Single Circular Radiator With Multiple Patterns for a UWB Three-Axis Monopulse System

Design of a Single Circular Radiator With Multiple Patterns for a UWB Three-Axis Monopulse System

Time modulation based unconventional phased antenna arrays for monopulse and multifunction radar systems

AbstractThe development of novel and innovative phased array designs toward affordable and performance‐oriented solutions has become the dire need of modern‐age wireless communication technologies. This paper proposed an unconventional method to design phased array antennas by eliminating the need of phase shifters. A cost‐effective alternative is presented by using “time‐modulation” based arrays capable of beam steering and electronic scanning. Controlling the high‐speed absorptive switches connected with each radiating elements in a periodic manner to generate the desired amplitude and phase tapering is the main purpose of these time‐domain arrays. So, the need for expensive phase shifters and erroneous attenuators can be avoided. This article explored the idea of “time‐modulation” to design innovative and efficient phased arrays for monopulse and multifunction radar systems. Suitable switching sequences are designed to produce simultaneous sum‐difference radiation patterns for monopulse tracking radars, and simultaneous scanned beam patterns for multifunction radars. To achieve the desired objectives, time‐modulated linear arrays of 10, 20, and 30 elements are proposed with appropriate switching sequences. The parameters of the arrays such as switch‐ON instants, switch‐ON periods, and switch‐OFF instants are controlled by employing the crow search optimization (CSO) algorithm. Representative results for both the applications are elaborated and compared with recently published counterpart designs to present the potentialities of the proposed concept for electronic steering and beam scanning applications.

Research on Mono-Pulse Beam Angle Tracking Algorithm of Phased Array Antenna Based on CKF

Phased array antenna beam tracking and communication system based on mono-pulse system is an alternative satellite-to-earth communication technology solution for future planetary spacecraft, which meets the mission requirements of agile scanning, multimode, wide field of view, and small size. This paper firstly outlines the technical scheme of mono-pulse angle tracking based on the planar phased array antenna. A simplified mathematical model of angle measurement is summarized. Secondly, the beam pointing of the spacecraft communication antenna is frequently affected by the attitude and presents a nonlinear dynamic change. A robust two-dimensional angular tracking filtering algorithm based on cubature Kalman filter (CKF) is proposed, in order to solve this complex high-order nonlinear dynamic estimation problem. Finally, the comprehensive performance of the proposed algorithm is simulated and analyzed under two conditions of stable flight and high dynamic flight of the spacecraft. When the angular velocity is within 4°/s, the tracking accuracy can be better than 0.65°, and the tracking accuracy will be better than 1° when the angular velocity is within 8°/s. Compared with the basic CKF algorithm, the robust CKF tracking accuracy is significantly improved, while the resource consumption is slightly reduced. The research results can provide reference for the engineering implementation of related fields in the future.

Synthesis of Simultaneous Sum and Difference Patterns in Single-Channel 1-Bit Time-Modulated Array

In this letter, a novel synthetic approach for simultaneous sum and difference patterns based on a single-channel 1-bit time-modulated array (TMA) is proposed. A series of asymmetric 1-bit modulating waveforms suited for monopulse systems is generated by theoretically analyzing the formation circumstances of simultaneous sum and difference patterns. The designed sum and difference patterns have equivalent radiated power as compared to the state-of-the-art approaches, and the TMA has a good power conversion efficiency. Furthermore, because the sum and difference patterns are synthesized at the first positive and negative sidebands, respectively, the signal allowed transmission bandwidth is enhanced when the switching speed is taking into account. Modulation schemes for different scenarios are provided to show the feasibility and effectiveness.

The deception effect of FDA counteracting amplitude-comparison monopulse reconnaissance

Conventional phased array radar can direct the high-gain beam, resulting in high visibility under the reconnaissance system and even direct exposure to the enemy. As an amplitude-based direction-finding system, the amplitude monopulse system can recognize the traditional radar signals. However, there are still some issues with the countermeasures of the monopulse system, so it is necessary to find better styles of jamming. Since the beam of the frequency diverse array (FDA) signal at a certain angle varies with the range, we studied the deception effect of the FDA against the amplitude-comparison monopulse direction-finding system. By analyzing the established FDA-based direction-of-arrival location deception model against the amplitude-comparison monopulse system, we found that the introduction of the frequency increment might cause the FDA signals to deceit the monopulse system in principle. Then, to indicate the superiority of our deception method, we obtain the instantaneous signal-to-noise ratio, Cramér–Rao lower bound, root-means-square error, and variation. Numerical simulation results demonstrate that the FDA can generate deceptive signals to counteract the amplitude-comparison monopulse direction-finding system.

Dual‐interference filtering method for the main lobe based on polarimetric monopulse radar

In the field of target tracking, monopulse radar is widely used to obtain the positions of radar targets. The achieved angle measurement performance is greatly weakened when barrage interference is contained in the main lobe of the receiving antenna. Interference signals can be easily filtered by the conventional polarization filtering (PF) method. However, the conventional PF method is unable to address situations in which two barrage interferences with different polarization states are contained in the main lobe, because the polarizations of both interferences become complex. To filter dual-interference sources in the main lobe, a novel polarimetric filtering method is proposed in this letter. This novel method is based on polarization selection, which is implemented to suppress one of the dual-interference sources. The appropriate polarimetric parameters are first selected by a monopulse ratio constraint condition. Then, the spatial location of the other interference source can be measured. After searching the whole polarimetric domain, the spatial parameters of the two interference sources can be acquired by the polarimetric monopulse system. Finally, the waveforms of the interference signals can also be estimated during the filtering process. The results of a microwave chamber experiment demonstrate that this novel filtering method is effective.

Design of a High-Gain Single Circular Patch Radiator With a Cavity-Backed Structure Using Multiple SIW Feeders for Monopulse DF-Applications

This paper proposes the design of a gain enhanced single circular patch radiator (SCPR) with a cavity-backed structure using multiple substrate integrated waveguide (SIW) feeders for monopulse systems. We derive the equations of a radiation pattern for the multi-feed SCPR and compare it with the full EM simulation results. Based on the theoretical results, the proposed SCPR with multiple feeds is designed by adding the cavity-backed structure to obtain high gain characteristics. In the feeding network, four SIW structures are designed and circularly arranged, which can reduce loss and mutual coupling. Each pair of the SIW feeders can provide sum ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Sigma$ </tex-math></inline-formula> ) and difference ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta$ </tex-math></inline-formula> ) patterns to achieve the monopulse direction finding (DF) properties in both elevation and azimuth directions. To verify the feasibility, the proposed antenna is fabricated, and the antenna characteristics are measured. The measured reflection coefficient is −14.5 dB at 5.8 GHz, and the maximum gains are 4.9 dBi and 4.8 dBi in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">zy</i> -plane. To observe the monopulse DF, the estimated direction of arrival (DOA) results are examined in both elevation and azimuth directions. In the whole estimated angle range, the estimation error is lower than 0.49, and the average error is 0.26.

How Radar Technology Changed the Course of the World after World War II - Science and Technology

After the independent invention of radar in the early 1930s, the development of radar went rapidly during World War II (1939-1945) when both Axis and Allied forces relied on the system to get an edge over the other. Ever since the war, radar technology has substantially increased in its innovation and capability throughout the years. This paper examines the progress of radar technology following World War II (1939-1945) with an aim to provide a landscape of the prevalent radar system during the war which was mono-pulse tracking radar systems and moving-target indication (MTI) system. After a thorough background study of the past radar system, the paper highlights application of the newer developed Phased Array Radar System which was formulated out through the implementation of the improved capabilities of both prevalent systems. Moreover, the paper provides a brief overview of the modular system and formulates a time frame relating to the development of radar research. Thus, the paper, later on, foresees the prominent future where phased array systems could be expanded to civilian and non-civilian technological research by providing thorough research and comparative analysis. Phased array systems are found to a prominent possible cheaper alternative for the civilian and non-civilian system. It shows prominence to be an effective useful tool for radar systems.

Метод определения направления на цель цифровой антенной решеткой моноимпульсной радиолокационной станции

On the basis of the analysis of the errors of the monopulse method of direction finding of the target of a radar station with a digital antenna array, a group of errors associated with fluctuations of the equisignal direction when scanning the beam of the antenna system, as well as with the non-identical shape of the generated beams of the monopulse group, was separated into a special cluster. This circumstance is especially critical for large-aperture radars with phased array with electric scanning, where the number of formed receiving beams is significant, in addition, the coordinates of the target usually do not coincide with the coordinate planes along which the coordinates are measured. The nonlinearity of this problem requires unique approaches and solutions. The classical formulation of the problem is associated with obtaining an estimate of the radiation vector of the entire antenna array from the known measured vector of complex signals at the output of the antenna array at a fixed time. To solve this problem and determine the decision rule, a neural network approach was used, while the neural network was trained according to the criterion of the minimum of the selected objective function. The substantiation of increasing the accuracy of measurements of angular coordinates in monopulse systems with scanning digital phased antenna arrays based on the use of neural networks in the process of radar data processing without the formation of direction finding characteristics is given. The results of modeling the characteristics of the antenna array (using the example of a flat antenna array with a dimension of 30 by 30 emitters) under the conditions adopted in the model of the antenna array of assumptions when implementing the classical and original methods are shown using examples of the surfaces of the variances of errors in measuring angular coordinates by the monopulse method in a rectangular spatial domain, which showed reduction of error and expansion of the measurement area. In the future, the practical implementation of this approach is assumed using FPGA in the receiving paths of the frequency-dependent part of the radio direction finder.

Monopulse-Radar Angle Estimation of Multiple Targets Using Multiple Observations

Amplitude comparison monopulse systems encounter the target resolution problem when multiple targets occupy the same range-azimuth cell. To solve this problem, a new angle estimation approach is proposed. The traditional range-cell-based signal processing is improved by modeling the signal in the frequency domain. Thus, the range straddling loss and the range migration problem can be avoided. The closely spaced targets in the same range-azimuth cell can be well resolved by the jointly maximum likelihood estimation of the range and velocity of the targets. Then, the angle estimates are extracted by using the monopulse ratio technique with the estimated parameters of the resolved targets in the two channels. Furthermore, the RELAX algorithm is utilized to reduce the computational burden of the proposed approach. The performance of the proposed estimator is evaluated using Monte Carlo simulation.

Low sidelobe level circularly polarised monopulse slot waveguide antenna array for Ka‐band application

A circularly polarised (CP) monopulse waveguide antenna array for Ka-band wireless communication is proposed. The antenna structure can be divided into six layers from top to bottom, including radiating layer, aperture layer, cavity layer, aperture layer, feeding layer and monopulse comparator. The upper radiating layer allows two transmission modes of the transverse electric (TE) wave and the transverse magnetic (TM) wave to pass through. The 90° phase difference can be obtained by adjusting the horizontal and vertical angles of the horn radiator, which realises the CP radiation pattern. Besides, the 0° or180° phase difference produced by the monopulse comparator enables the antenna to obtain a monopulse radiation mode. In order to obtain the low sidelobe characteristics, the coupling parameters of the coupling layer are weighted by the Taylor distribution. The overall size of the antenna is 194 × 25 × 31 mm3. The slot waveguide antenna is fabricated and measured to validate the proposed design. The measured results show that the monopulse system can achieve an impedance bandwidth of 3.7% (34.5–35.8 GHz) in the Ka-band at the centre frequency of 35 GHz. The sum-pattern maximum gain and radiation efficiency are 23.3 dBic and 75% at 35 GHz, and the gain of the whole bandwidth is >20 dBic. The axial ratio and the sidelobe level is less than 1.2 and −28 dB, respectively. The difference-pattern amplitude imbalance is <0.2 dB and the null-depth lower than −30 dB. Also, the isolation is better than 30 dB. Besides, the pure metal structure of waveguide has incomparable advantages in a harsh environment.

Design of a Monopulse System Using a Single Patch Radiator with a Simple Multi-Mode Substrate Integrated Waveguide Feeding Network

This paper proposes the design of a single radiator monopulse antenna with a substrate integrated waveguide (SIW) multi-mode feeding system to reduce the aperture size and simplify the feeding structure. The proposed antenna can effectively reduce the overall system size by using a single patch radiator, compared to conventional systems that require multiple radiators. In addition, to simplify the structure of the pattern comparator we use a SIW multi-mode feeding system with TE10 and TE20 modes. To verify the feasibility, the patch antenna with the SIW multi-mode feed is fabricated, and its antenna characteristics of reflection coefficients, mutual coupling, and radiation patterns are measured in a full anechoic chamber. The accuracy of the direction of arrival (DOA) estimation is further improved by applying the derived calibration factor to the resulting sum and difference ratio. The results demonstrate that the proposed antenna is suitable for compact and lightweight monopulse systems with the single radiator and the simple multi-mode feeding network.

A compact substrate‐integrated‐waveguide monopulse slot antenna array with TE 20 mode

A compact substrate-integrated-waveguide (SIW) monopulse slot antenna array with TE20 mode is proposed, manufactured, and tested in this communication. The TE20 mode electric field distribution is used in this antenna design. The phase difference required by the monopulse system is constructed by changing the orientation of the end of the top microstrip feed line. The microstrip line implements not only the feed function, but also the function of a monopulse comparator. The design greatly reduces the size of the monopulse comparator and the feed network, and improves the aperture efficiency of the antenna. Our measurement shows that the operating frequency of the antenna is 10.4 GHz, and the maximum gain of the sum beam is 13.7 dBi, and the difference beam null depth is −26 dB. The antenna has the advantages of simple structure, small size, and easy integration of planar circuits. This proposed idea can open new ways for monopulse antenna design.

ACCURACY OF BEARING DETERMINATION IN A THREE-CHANNEL MONOPULSE AMPLITUDE CORRELATION DIRECTION FINDER

In the work, the study of the achievable accuracy of determining the coordinates of the radiating in the radio range of spacecraft using a three‑element amplitude correlation direction finder has been performed. The proposed scheme makes it possible to select single and group low‑power complex signals and simultaneously determine the bearings of several sources, the signals of which can be separated in time‑frequency‑code space. As an example, the radiation pattern of a three‑element antenna system with an orthogonal arrangement of partial diagrams with respect to the equal‑signal direction is considered. The results of statistical modeling of the correlation processing algorithm obtained for a three‑channel monopulse system with a 3.7° pattern width and estimates of the potential accuracy of determining the bearing are presented. Simulation results are given to evaluate the instrumental accuracy of the direction finder. The proposed method of direction finding provides the ability to determine the geodetic coordinates of aerospace objects using the station electronic reconnaissance.

Multi‐beam monopulse substrate integrated waveguide slot array antenna

A multi-beam slot array antenna is proposed in the 10-GHz band for a monopulse tracking system with resolution enhancement techniques. The antenna architecture combines a four-subarray substrate integrated waveguide (SIW) slot antenna, a multi-beam-forming network of microstrip Rotman lens array, and a SIW comparator of four-quadrant monopulse technique. A method to form difference patterns in both E-plane and H-plane for mutibeams is presented, and the method can improve the accuracy of angle detection for all beams. The key point of the method is to compensate the phase difference caused by the beam deflection between the two subarrays (quadrants) by constraining input delay lines of the Rotman lens array. To validate the proposed concepts, an antenna prototype is realized and measured. The experimental results demonstrate a scanning range of ±36° with -5 dB crossover level between two adjacent sum beams in the E-plane. The corresponding difference patterns are generated in both E-plane and H-plane via the monopulse comparator. The multi-beam monopulse system can achieve gains between 21.7 and 23.5 dBi for all sum beams at the center frequency of 10 GHz. This multi-beam monopulse slot antenna can be applied in radars and communication systems requiring beam-scanning capabilities and target tracking.

Adaptive hybrid method for low‐angle target tracking in multipath

Tracking low-angle targets is a serious problem in radar systems because of the multipath phenomenon. When a signal is reflected from the ground surface, due to the low altitude of the target, it enters the radar main beam and seriously reduces its performance. The authors propose a novel adaptive hybrid method based on the complex angle (CA) method and the array monopulse system. They present a way to reduce the ambiguity of the CA method, and then, eliminate the multipath effect by using beamforming and provide an accurate estimate of the elevation angle. The simulation results show the performance of this method in tracking low-angle targets.

Wideband dual‐polarised SAW spiral antenna for monopulse system

This study proposes a new technique for generating dual polarisation in spiral antennas. The proposed antenna is achieved by creating stair discontinuities in spiral antenna arms, entitled stair arm width (SAW) spiral antenna. Commonly, the spiral antenna is activated in direction finding systems, especially in wideband monopulse systems. Capability of generating sum and difference beams over a wide bandwidth is another feature of the proposed antenna. Radiation characteristics and generated modes of a wideband dual polarised four-arm SAW antenna in comparison with the modulated arm width (MAW) and conventional spiral antennas are presented. The cross-polarisation gain of SAW antenna, compared to MAW antenna, is decreased in difference pattern, which improves the antenna circular polarisation purity. Moreover, the input impedance of the proposed antenna with high n s is more stable than MAW antenna over a wide bandwidth due to gradual discontinuities. Finally, a prototype four-arm SAW spiral antenna is built and evaluated with an available beamformer for 5.8-10 GHz frequency bandwidth. Simulated and measured radiation characteristics proved dual circularly polarised and wideband properties of the antenna.