Monopulse Ratio Research Articles

Dual-mode Antenna Tracking System for Rocket Launch Applications

Rocket launches are complex events that require tracking antennas to maintain a communication link. This study introduces a hybrid tracking strategy that combines manual and program modes by utilizing a predetermined trajectory of the rocket. Automatic switching between tracking modes ensures ongoing monitoring, even during unexpected trajectory changes with the monopulse approach. The dual parabolic antenna arrangement enables this switching. The system estimates the monopulse ratio from the signal strength of each antenna, allowing automatic program tracking to shift to manual mode when reception concerns arise. Performance evaluations included manual, programmable, and dual-mode tests. The system responded to human input and automatically aligned the antenna with slight elevation errors during the initial phase. Adjusting the initial elevation reduced the error. The mode transition was examined by measuring the antenna radiation patterns and monopulse ratio. The system’s performance was evaluated in rocket launches, with the rocket trajectory input into the graphical user interface. The antenna exhibited an azimuthal movement of up to 10 °, and the ratio fluctuation values remained within the antenna’s field of view. After 8.8 seconds, the mode switched from program to manual, indicating that the functioning of the system’s functioning was stable.

A Study of Direction-of-Arrival Estimation with an Improved Monopulse Ratio Curve Using Beamforming for an Active Phased Array Antenna System

When constructing a wireless communication network, the line of sight of radio waves is limited by the terrain features in a ground communication network. Also, satellite communication networks face capacity limitations and are vulnerable to jamming. Aviation communication networks can solve the above-mentioned problems. To construct seamless aviation communication networks, fast counterpart location estimation and efficient beam steering performance are essential. Among various techniques used for searching the counterpart’s location, the monopulse technique has the advantage of quickly estimating the location through a simplified procedure. However, the nonlinear characteristics of the monopulse ratio curve, which are inevitably caused by the general antenna beam shape, both limit the location estimation range and reduce the estimated location accuracy. To overcome these limitations, a method that improves the estimation accuracy and extends the range by correcting the sum and difference patterns using the beamforming technique of active phased array antennas was proposed. An antenna system model suitable for aviation communication networks was presented, and the proposed model was experimentally proven to be effective. An average angle error of 0.021° was observed in the estimation of the accuracy of the antenna location.

Unambiguous Direction Estimation and Localization of Two Unresolved Targets via Monopulse Radar

Traditional monopulse radar cannot resolve two closely spaced targets present in one resolution cell (range and Doppler) by means of the monopulse ratio. This study presents a closed-form solution to resolve the directions of arrival of two unresolved targets using a single snapshot of four independent channels in phase comparison monopulse radar. If both targets have the same elevation or same azimuth direction, the proposed scheme cannot estimate their directions. To estimate the direction of such targets, an extra antenna is required. The impact of input noise power, the targets’ direction, and phase difference of the targets’ signal on the accuracy of angle estimation are also explained. The numerical simulation result validates the effectiveness of the presented scheme.

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.

Hybrid Continuous-Wave and Self-Injection-Locking Monopulse Radar for Posture and Fall Detection

This article presents a novel monopulse radar that combines high-sensitivity continuous-wave (CW) and self-injection-locking (SIL) receivers to detect and localize the movements in a human body. The proposed radar utilizes a CW sum pattern and an SIL difference pattern to process the echo signal from the target, so it can produce a monopulse ratio to estimate the angle of arrival (AoA) of the echo signal. With this capability, the radar can localize the movements on the target’s chest that are caused by vital signs such as respiration and heartbeat for posture classification. In addition, the radar can be used in a fall alarm as it can detect a change of posture during a fall. As a proof of concept, a 2.4-GHz prototype radar was experimentally implemented to validate the robustness of detecting falls regardless of their direction.

Method for Robust Ground Ranging Using Monopulse Radar in Heterogeneous Clutter Environment

Aircraft radar has special function which is ranging from aircraft to ground of antenna boresight. Because ranging information is used to calibrate altitude of aircraft or to drop a conventional bomb, the measuring have to be precise and robust. Therefore, we propose a simple and efficient method using monopulse radar for ground ranging. Proposed method calculates balancing weight according to linearity of monopulse ratio and mixes two ranging measurements in proportional to the weight. By exploiting balancing weight, radar is able to react to various environment as monopulse ratio contains characteristics of clutter environment. As a result, robust ranging information can be achieved. We use DEM(Digital Elevation Model) in order to simulate heterogeneous environment. In experimental result, it is shown that proposed method shows better accuracy and precision in any environment.

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.

Target detection and localization method for distributed monopulse arrays in the presence of mainlobe jamming

In this paper, we propose a target detection and localization method on distributed monopulse arrays for tracking radar. An optimized mainlobe jamming (MLJ) cancellation filter was designed by maximizing the power ratio of the received siackgnal to the jamming-plus-noise. By exploiting the different correlation characteristics between the target echo and MLJ on distributed antennas, the designed filter is able to cancel MLJ and maintain the target echo. By applying the identical filter on sum-difference beams, MLJ can be cancelled, and the monopulse ratio can be maintained simultaneously. Hence, we simply detect and locate the target on the filtering output of sum-difference beams according to the monopulse principle. Monte Carlo simulations demonstrated that the proposed filter outperforms the conventional algorithms.

Hybrid Precoding Based on Monopulse Ratio for Millimeter Wave Systems With Limited Feedback

Multiuser hybrid precoding in 5G NR mmWave communication system faces significant challenges such as establishing accurate directional radio links and maintaining links for mobile stations (MSs) moving in outdoor environments. A conventional solution relies on finite codebook-based beam sweeping for initial first-stage beam acquisition and subsequent second-stage beam tracking by sweeping adjacent beam pairs. However, such a conventional solution has inevitable residual AoA/AoD errors even after the best beam pair is established in the first stage and incurs nonnegligible overheads to sound adjacent beam pairs for maintaining the best beam pair in the second stage. To overcome these problems, a novel codebook-based two-stage solution that combines a novel beam tracking protocol with a low sounding overhead, a unique receiver structure employing a beam scheduler and a beam tester, and a fine accuracy residual AoA/AoD error estimation algorithm based on the monopulse ratio concept is proposed. The solution is unique because of the receiver structure for the residual AoA/AoD error estimation that exploits the cyclic prefix in OFDM systems, inspired by the monopulse ratio in radar systems. Moreover, it can be applied to MSs with a single RF chain. This solution, using the proposed receiver structure and algorithm, can establish a more accurate directional beam pair right after the initial beam sweeping in the first stage. For beam tracking in the second stage, it estimates the residual AoA/AoD errors of the current best beam pair rather than sweeping adjacent beam pairs, thereby reducing beam tracking overheads. Numerical evaluation and computer simulations show that the proposed solution offers more accurate beam acquisition (i.e., average array gain improvement of several dB) and costs considerably reduced beam sounding overheads compared to the conventional solution. Lastly, a ray-tracing tool is used to demonstrate that our solution is effective in practical channel parameters for outdoor environments.

Robust adaptive beamforming with mainlobe maintenance of monopulse beams

Adaptive monopulse approaches for angularly localising a main-beam target in jamming are usually based on variations of the concept of optimising the sum (Σ) beam via standard adaptation and then optimising the delta (Δ) beam subject to maintain the monopulse slope. These methods have some deficiencies: they do not address target self-nulling issues; they lack tapering, leading to high sidelobes; they introduce multiple point constraints, which may result in target leakage; and they assume linearity of the monopulse ratio curve, something valid only in a small region close to the beam steering direction. The method of this study addresses these and other concerns by maintaining tapered Σ and Δ beams and fully preserving their mainlobes while adaptively suppressing jammers. This approach provides the added bonus of enabling operating in the monopulse curve's non-linear region at wider beamwidths, hence also increasing the efficiency of radar searching and tracking functions. It is shown that such approach is extremely robust and flexible, as it avoids target self-nulling effects due to beam mispointing, it is immune to target and interference dithering effects, and it can be easily extended for super-resolving multiple main-beam targets.

Ground moving target detection algorithm for monopulse‐SAR based on complex monopulse ratio

Monopulse processing has been proved to be an effective way for airborne synthetic aperture radar (SAR)/ground moving target indication. In the monopulse-SAR system, moving target detection is applied to a complex ratio diagram, referred to as a complex monopulse ratio diagram (CMRD), generated through a pixel-by-pixel comparison between the range-Doppler (RD) spectra obtained from the difference and sum channels. This study examines the statistics of complex monopulse ratio (CMR) in the Gaussian background. Based on the statistics, a new random variable termed normalised CMR (NCMR) is derived by a linear transform to CMR. It is demonstrated that the conditional probability density function of NCMR, under the null hypothesis ( H 0 ), is independent of the clutter-plus-noise environment. Motivated by this characteristic, a constant false alarm rate detector using the modulus of NCMR as the test statistic is proposed to detect moving targets. The detection performance is evaluated with a closed-form expression of the probability of false alarm ( P FA ) derived. Moreover, the construction of the detector is extended to a so-called multi-CMRD form to accommodate even higher detection performance. Experimental results from two groups of real data are displayed to validate the statistical analysis and verify the detection performance.

Combined Constrained Adaptive Sum and Difference Beamforming in Monopulse Angle Estimation

Motivated by beam distortions in multiple interferences environment, we propose a novel combined constrained method for adaptive sum and difference beamforming in monopulse angle estimation. By optimizing the adaptive weights of sum and difference beams jointly, the restriction on the degree of freedom to determine the adaptive sum or difference weight is evenly distributed to all weights. The constraints of array gain and monopulse ratio curve are utilized to avoid beam distortion while nulling the interferences. Simulations of the proposed algorithm have been provided, which show a significant improvement in beamforming and angle estimation performance compared with the conventional constrained adaptive monopulse algorithm.

MIMO–monopulse target localisation for automotive radar

In this study, the authors propose a novel direction of arrival (DoA) estimation algorithm called ‘multiple-input–multiple-output (MIMO)–monopulse’ by combining the monopulse approach with MIMO radar. Monopulse is fast and accurate angle estimation algorithm, which has been well developed for tracking radar. The application of the monopulse technique on MIMO radar is not much considered before, especially for automotive-radar application, and will be discussed in this study. Conventional methods of monopulse DoA estimation include amplitude and phase comparison monopulse. In this study, to improve the performance of monopulse, they utilise Chebyshev and Zolotarev weighting to synthesise sum and difference patterns. A new visualisation method for monopulse ratio is discussed. Finally, they demonstrate the success of the proposed algorithm by processing real data from a 79 GHz frequency-modulated continuous-wave automotive radar.

Adaptive Monopulse Approach With Joint Linear Constraints for Planar Array at Subarray Level

This paper investigates the problem of angle measuring of the target in the presence of jammings with planar arrays. The relationship between the quiescent monopulse ratios and azimuth/elevation is first studied. On this basis, the distortion of the surface of the conventional minimum variance distortionless response monopulse ratio is analyzed. In order to avoid such distortion and approximate the adaptive monopulse ratio surface to the quiescent one, an adaptive monopulse approach with joint linear constraints on both the azimuth and elevation is proposed. Simulation results demonstrate that the proposed approach is capable of attaining a high angle measuring accuracy in the presence of mainlobe jammer.

다변수 모노펄스 추적 시스템에서 유전 알고리즘 기반 선형구간 확장

In this paper, we consider a single-channel amplitude comparison monopulse system(SCACMS). The monopulse ratio curve(MR-C) of the SCACMS can be controlled by an amplitude difference between sum and different signal, a phase difference and the coefficient of the signal processor. We first propose the SCACMS with multiple variables, and then apply a genetic algorithm to optimize the multiple variables in terms of minimizing a root mean square error. The simulation results show that when three variables of the SCACMS are jointly optimized, the linear region of the MR-C can be extended approximately 187 % compared to that of two variables.

Effects of Compound K-Distributed Sea Clutter on Angle Measurement of Wideband Monopulse Radar

The effects of compound K-distributed sea clutter on angle measurement of wideband monopulse radar are investigated in this paper. We apply the conditional probability density function (pdf) of monopulse ratio (MR) error to analyze these effects. Based on the angle measurement procedure of the wideband monopulse radar, this conditional pdf is first deduced in detail for the case of compound K-distributed sea clutter plus noise. Herein, the spatial correlation of the texture components for each channel clutter and the correlation of the texture components between the sum and difference channel clutters are considered, and two extreme situations for each of them are tackled. Referring to the measured sea clutter data, angle measurement performances in various K-distributed sea clutter plus noise circumstances are simulated, and the effects of compound K-distributed sea clutter on angle measurement are discussed.

Symmetrical difference pattern monopulse for low-angle tracking with array radar

Tracking low-elevation targets over a smooth surface is challenging because of the multipath effect. The symmetrical difference pattern monopulse is proposed for low-angle tracking with array radar. At first, the optimal symmetrical difference pattern is designed. The proposed monopulse is implemented using symmetrical sum and difference patterns by digital beam forming. The monopulse ratio derived from the symmetrical sum and difference patterns is not affected by the multipath effect. Then, the performance of the symmetrical difference pattern monopulse is evaluated by simulations in terms of the signal-to-noise ratio, target elevation, and complex reflection coefficient. Field data sets acquired from a VHF array radar are used for validation. It is found that the measurement error is still less than 1/30th of a beamwidth when the target elevation is less than a quarter of a beamwidth. The proposed monopulse scheme is suitable for VHF array radar, for which the multipath effect is serious.

An Efficient Adaptive Monopulse Estimation Algorithm Based on MPASTd Approach

In this paper, an improved adaptive monopulse scheme based on modified projection approximation subspace tracking deflation (MPASTd) approach is proposed. Owing to the fast convergence speed of MPASTd for recursively estimating the interference subspace, the proposed algorithm can obtain the formula for adaptive monopulse ratio calculation by a subspace projection. Therefore, it is able to accurately estimate the source location using less training data and reduce the computational complexity significantly. The effectiveness and fast convergence speed of the proposed method is verified by simulation results.

Joint-Bin Monopulse Processing of Rayleigh Targets

Amplitude comparison monopulse systems provide precision angle localization of a target. In practice, the in-phase part of the monopulse ratio is commonly used for direction-of-arrival (DOA) estimation due to simplicity and computational speed, but it suffers poor performance for off-boresight and/or low signal-to-noise ratio (SNR) targets. Target energy is typically assumed to be contained in a single range bin, while in practice the matched filter sampling process often results in multiple adjacent matched filter samples with target energy. In the traditional radar literature, this is called bin straddling and is typically treated as a nuisance—an undesired loss of signal energy. Recent literature has addressed bin straddling for DOA and range estimation for the case of multiple unresolved targets. However, error variance reports on those target estimates, which are required by target tracking algorithms, are not provided. Furthermore, target strength is assumed to be a known parameter, which is often not valid in practice. Here, we explicitly incorporate sampling into the statistical model for sum and difference channel signal samples, and derive estimators for the unknown range and unknown DOA of a single Rayleigh target. Closed-form Cramer-Rao lower bounds (CRLBs) on those estimators are provided. Furthermore, we propose the generalized CRLB (GCRLB) as an error variance report, and SNRs required for statistical efficiency and variance consistency are provided.

Difference beam aided target detection in monopulse radar

The classical detection step in a monopulse radar system is based on the sum beam only, the performance of which is not optimal when target is not at the beam center. Target detection aided by the difference beam can improve the performance at this case. However, the existing difference beam aided target detectors have the problem of performance deterioration at the beam center, which has limited their application in real systems. To solve this problem, two detectors are proposed in this paper. Assuming the monopulse ratio is known, a generalized likelihood ratio test (GLRT) detector is derived, which can be used when targeting information on target direction is available. A practical dual-stage detector is proposed for the case that the monopulse ratio is unknown. Simulation results show that performances of the proposed detectors are superior to that of the classical detector.