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Distinguishing multiple targets in the same resolution cell is an important and challenging task in the forward-looking imaging process of monopulse radar. Although Doppler processing can improve the recognition performance for multiple targets at high squint angles, the precise estimation of Doppler frequency remains challenging under conditions with unknown target numbers and energy leakage from strong point targets. To address these issues, this paper proposes a Fast Iterative Interpolated Beamforming (FIIB) algorithm with model order estimation and single snapshot processing for monopulse forward-looking imaging, which combines information theory to unbiasedly estimate the number of targets and Doppler frequencies. The simulation results show the superiority of the proposed FIIB algorithm over the Chirp-Z Transform (CZT) algorithm for estimating target numbers and Doppler frequencies within the same resolution cell in the presence of multiple point targets. In addition, the proposed FIIB algorithm can accurately estimate point targets beyond a ±5° azimuth angle in monopulse angle measurement tasks. Real-data experiments also reveal that FIIB-based monopulse forward-looking imaging has high focusing capability and imaging contrast and can effectively suppress background clutter.

In the terminal guidance phase of radar seeker, low signal to noise ratio (SNR) leads to the deterioration of target detection and positioning performance. Therefore, a joint detection and DOA (Direction of Arrival) estimation algorithm based on random finite set is proposed. In the framework of single target Bernoulli filter, the algorithm constructs the target observation equation for the data after low threshold decision based on the point target spread function, establishes the state variable description in the antenna and line of sight hybrid coordinate system, solves the state vector differential equation and discretizes it to obtain the discrete-time difference equation. The state transition model is obtained through state error analysis, then the particle recursion is used to realize joint detection and state estimation. Simulation results show that the algorithm is effective. Compared with the traditional DBT (Detect before Track) method, the algorithm can improve the detection performance and DOA estimation accuracy at low SNR.

Blinking jamming is an active self-screening technique performed by at least two aircraft to tackle monopulse radars and all complexity related thereto. Nowadays, the technique can be performed with digital radiofrequency memories (DRFMs), which are cumbersome, complex, expensive, need a dedicated compartment and antenna, and introduce spurs in the signals. In this paper, we propose an alternative to the implementation of blinking jamming with DRFMs, namely with reconfigurable metasurfaces. By covering the aircraft parts that most contribute to the radar cross-section (RCS), reconfigurable metasurfaces can interchangeably absorb or amplify impinging waves, making the aircraft ‘blink’ from the radar perspective. To validate the feasibility, simulations accounting for realistic phenomena are conducted. It is seen that, if the aircraft RCS can be varied in a ratio of 10:1, either with absorptive or power-amplifying metasurfaces, a performance similar to that of the DRFM is achieved. Furthermore, a ratio of 2:1 is sufficient to make the radar antenna system movements exceed the angular range of the formation. We also anticipate our work to be a starting point for completely new ways of countering radars, e.g., with countless small drones performing passive or active stand-off blinking jamming.

Abstract Monopulse radars operate with simultaneous beams and are used for tracking purposes, relying only on hardware to provide a real-time indication of the target position. A monopulse array and its feeding network is implemented and tested, in the frequency of 5.4 GHz, based on patch antennas using dieletric to provide wide bandwidth and high gain. The system field styrofoam as pattern was evaluated in two different environments, a shielded room and an indoor area. Results agreed with simulation for either individual elements as well as the final integrated monopulse array.

Monopulse technique is used in scanning radar systems to improve image quality in the forward-looking area. However, monopulse measurements fail to resolve multiple targets in the same resolution cell because of angular glint which often results to image blurring. In response to this, we propose a monopulse forward-looking imaging method utilizing Doppler estimates of sum-difference measurements. First, target multiplicity is resolved by exploiting the different Doppler shifts caused by the relative motion between the platform and the targets at different directions. High azimuthal angle measurement accuracy of the Doppler estimates is then obtained using the Sum-Difference Amplitude-Comparison (SDAC) monopulse technique. Subsequently, the intensity of the sum channel estimates is projected onto the image plane according to the range and angle measurements. To further improve the precision of angle measurements, a Chirp-Z Transform (CZT)-based algorithm is proposed for the reconstruction of the Doppler estimates of the sum-difference channels. Simulation results demonstrate the capability of the proposed methods in resolving multiple targets at high squint angles in a large scanning field. Real data experiments show significant improvement of image profiles using the CZT-based algorithm compared to that of the conventional monopulse imaging method.

To evaluate the performance of a monopulse radar system, it is necessary to accurately model radar return signals from the ground surface in a time domain. In this paper, we propose a numerical method to model these return signals including radar radio frequency specifications, such as the pulse repetition interval, frequency, and polarization, as well as the antenna geometry, the ground clutter backscattering characteristics, and so on. The Doppler effect is also incorporated into the signal generation scheme because of the dynamics of the platform/clutter and the antenna orientation. The Doppler frequency shift caused by the ground clutter is modeled by employing the time correlation of the received signals. In some scenarios, the monopulse signals are generated and numerically examined. For real radar application, the effect of the platform’s roll stabilization on the monopulse signals is investigated based on the proposed signal generation scheme.

The cross-eye method is commonly used to interfere monopulse radars. To overcome the strict tolerance and the range limitation of the traditional retrodirective cross-eye method and the multi-loop method, a novel four-element retrodirective cross-eye based on Direction of Arrival (DoA) is proposed. The mathematical model of the four-element retrodirective cross-eye jamming is derived based on the method of expansibility analysis, and the general formulas of indication angle are obtained. Based on the DoA information, the antenna layout of jamming loops is optimized, and the influence of the modulation parameters on cross-eye jamming effect are analyzed. The orthogonal four-element retrodirective cross-eye is compared with the traditional cross eye jamming, the results show that the the proposed method is superior to the traditional and the orthogonal four-element retrodirective cross-eye in terms of the jamming effect and the modulation parameter tolerance.

Monopulse is a mainstream technique used to acquire the angle information about active radar systems that are widely used in air defense warning, target tracking, and precision guidance. This study briefly reviews the development history of the monopulse theory and technology for the main-lobe multi-source condition. The importance of several key technologies within multi-source parameters estimation and multisource jamming mitigation is also summarized. Finally, the future development of monopulse technology to resolve the problem of multi-source jamming is considered.

Cross-eye jamming is an effective angular deception jamming technique used for countering monopulse radars. With the need of countermeasure against active radar seekers, the research on cross-eye jamming becomes a hot research topic in electronic war. This study overviews the cross-eye jamming with regard to jamming theories, equipment, application problems, and current research trends to offer comprehensive knowledge and future research ideas.

The design of a K-band radial leaky-wave antenna is presented for polarization diversity applications. The antenna structure is constituted by an annular, radially periodic, and metallic strip grating printed on top of a single-layer grounded dielectric slab. The integrated feeding system is defined by a 2 × 2 array of planar slot sources for cylindrical surface-wave excitation. By the addition of the grating, the surface wave is perturbed and enables cylindrical leaky-wave radiation by means of a fast n = -1 space harmonic, whose behavior is characterized through a full-wave dispersive analysis. By proper phasing and spacing of the four independent TM feeds, positioned close to the center of the annular grating and on the ground plane, we demonstrate the possibility of radiating directive broadside beams offering linear, left or right-handed circularly polarized radiation, and sum and delta patterns. Thus, we propose an original solution to flexibly control the polarization of a high-gain beam by means of a simple and low-cost feeding system, made by the minimum number of integrated array sources. To accurately assess the antenna features and performance, the role of a zeroth and first-order cylindrical leaky waves propagating along the antenna aperture is also discussed. The proposed antenna design may be of interest for direction-of-arrival estimation by means of monopulse radars, as well as for a wide class of applications where flexible control of the polarization is desired, such as satellite and terrestrial point-to-point communication systems and earth observation.

Chaff centroid jamming released by vessel causes the indicated angle of radar seeker of anti-ship missile to deviate from the target. The failure to track the target is catastrophic for the radar seeker. In this paper, the angle estimation of the target in the presence of chaff centroid jamming is investigated. In the circumstance of chaff centroid jamming, the jamming is usually in the same range and angle resolution cells as the target. Under these circumstances, the essence of this problem is to estimate two unresolved targets' angles in the main beam of the radar seeker. To this end, two alternative methods are proposed to estimate the direction of arrival of the target in this paper. First, we present a maximum likelihood (ML) method implemented by a 2-D numerical search, which has high estimation accuracy but large computational load. Subsequently, considering both the accuracy and computational load, an improved ML (IML) method is developed. Based on the ML method, the proposed IML method adopts a search optimization processing by moment estimation. Furthermore, the effects of some key factors on the estimation performance are analyzed. The accuracy of the proposed methods is compared with the existing methods and the Cramer Rao lower bound as well.

This paper presents two amplitude comparison monopulse algorithms and their covariance prediction equation. The proposed algorithms are based on the iterated least-squares estimation method and include the conventional monopulse algorithm as a special case. The proposed covariance equation is simple but predicts RMS errors very accurately. This equation quantitatively states estimation accuracy in terms of major parameters of amplitude comparison monopulse radar, and is also applicable to the conventional monopulse algorithm. The proposed algorithms and covariance prediction equations are validated by the numerical simulations with 100,000 Monte Carlo runs.

Based on ElectroMagnetic (EM) theory and the monopulse radar angle measurement principle, the formulae of angular glint for complex target are proposed and generally applied to tackling practical problems. The inherent relations among the three representations of radar angular glint, i.e. the phase-front distortion concept, the energy-flow tilt concept, and the monopulse radar angular noise concept, are clearly demonstrated. The two existing concepts of angular glint are also revised. Thus, a firm theoretical foundation for understanding, modeling, simulating and suppressing the angular glint from complex radar targets is established.

U radu je prikazan uticaj metode ometanja "Cross eye" na uspešno vođenje rakete monoimpulsnom radarskom glavom za samonavođenje. Analiza dobijenih rezultata pokazala je: da se maksimalna greška određivanja položaja cilja postiže kada ometači emituju koherentne signale čija je fazna razlika 180°, da je greška veća što je međusobno rastojanje između antena ometača veće, da je, suprotno očekivanju, efikasnost ometanja veća što je rastojanje između ometača i rakete koja se ometa manje. / This article shows the effect of the "Cross eye" jamming method on successful guidance of monopulse homing missiles. The analysis of the results has shown that the maximal tracking error is made if the jamming signals are coherent and out of phase, that a larger distance between jamming antennas causes a greater error, and that, opposite to expectations, a smaller distance between the jammer and the missile results in better jamming effects.

Development, construction and testing of a student laboratory model of the radar system that can be used for monopulse tracking is described. The laboratory model is simple and can be assembled from the existing equipment while the missing parts can be manufactured in a basically equipped RF electronics workshop. The laboratory model is used for student laboratory exercises as a part of a basic course on radar systems. The system is based on a Σ-Δ hybrid for processing signals obtained from two antennas. The composition of the model is described. Student exercises and measurements on the model are proposed. Alternative instruments which can be used in the model are considered. Possible improvements of the model are discussed.

U ovom radu razmatrane su metodologije i eksperimentalni rezultati ispitivanja uticaja oblaka smetnji na monoimpulsne nišanske radare i protivradarske rakete. Rezultati su pokazali ispravnost postavljenih teorijskih modela i izvršenih analiza primene oblaka smetnji tokom NATO agresije na Jugoslaviju 1999. godine. / This paper considers the methods and the experimental results of the analysis of the jamming cloud influence on monopulse tracking radars and antiradar missiles. The results confirmed the value of the set theoretical models and the analyses of the application of jamming clouds carried out during the NATO aggression on Yugoslavia in 1999.