INTERNATIONAL JOURNAL OF INFORMATION TECHNOLOGY - volume 5 issue 6, Aug-Sep

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Dynamic RCS Prediction of Rapidly Blooming Chaff Cloud and its Validation using Measurement on Scaled-down

Author: Verandra Kumar, Ajit Kumar Singh, Prashant Vasistha* and Ravindra Kumar

Category: Microwave Measurements

Abstract:

In modern warfare scenario, chaff cloud consisting of millions of small individual microwave scatterers, is used as a passive electronic countermeasure to rapidly create a false target having Radar Cross Section (RCS) more than a real target. RCS prediction of chaff cloud by modeling and simulation is a complex phenomenon as each scatterer has different resonating length, oriented randomly and interact with each other in a complex form. Monostatic RCS measurement of the chaff cloud in the real scenario is also difficult as the target size is quite big and shape and size are changing with time. In the present paper, the dynamic RCS prediction of chaff cloud has been carried out by modeling and simulation using the in-house developed software in MATLAB. Various regular shapes like a plume, sphere, cylindrical and cubical have been presumed and interaction of each scatterer has been analytically evaluated based on screening effect. RCS response of chaff clouds of different shapes and sizes were predicted. To validate the predicted RCS values, miniaturized models of different shapes and sizes are prepared to simulate scale down dynamic chaff cloud blooming. Their monostatic RCS responses were measured in the anechoic chamber for 8-18 GHz. A good agreement is observed in measurement and predicted values

Keywords: RCS, chaff, dipole, polarization

DOI: 10.32452/IJAMT.2018.170175

DOI URL: http://dx.doi.org/10.32452/IJAMT.2018.170175

Full Text:

Chaff cloud consisting of millions of small individual microwave dipoles resonating at specified frequencies suspended randomly in the space, is used to create a false target having RCS more than real target [1] to confuse or deceive hostile seekers. The chaff cloud shape and size are changing rapidly when ejected under the combined effect of the dispensing platform and the surrounding atmospheric conditions. As the RCS strongly depends upon shape, size and orientation of the individual dipoles, the rapid change in the cloud give rise to dynamic RCS behaviour. The dynamic RCS prediction and measurement of the chaff cloud is an important parameter for the effective functioning of chaff as a passive electronic countermeasure. The overall dynamic RCS response of chaff cloud depends upon a number of parameters of chaff material, radar polarization, kinetics of chaff cloud blooming, environmental conditions etc. Considering all these parameters, the prediction of dynamic RCS response of blooming chaff cloud is a complex phenomenon. Several models have been proposed in the literature for the dipole behaviour in free space [1?8]. The efficiency of chaff cloud jamming, when deployed as corridor tactic, has been given in [2]. The scattering properties of individual chaff dipoles and their bi-static RCS behaviour has been discussed in [3] and [4]. The jamming effect of chaff to radar along with the introduction to RCS of chaff cloud reference has been described in [5]. Aerodynamics properties of chaff fiber and cloud along with the probability distribution of chaff fibers and RCS density within the chaff cloud have been elaborated in [6]. The chaff dipole by treating it as a wire scatterer has been analytically explained in [7]. Chaff interference based on polarization parameter measurement has been explained in [8]. The study of the spectral behaviour of chaff dipoles in terms of radar echoes is given in [9]?[11] explained the chaff cloud behaviour by considering the randomly distributed dipoles and evaluating the backscattering from it. Theoretical discussions on the dynamic RCS behaviour of the chaff cloud based on screening effect have been provided in [12]. The dynamic RCS has been formulated for the chaff cloud distributed randomly in a spherical volume. No reference is available in the literature for dynamic RCS prediction of realistic chaff cloud shapes and validation of predicted values by experimental measurement. In the present paper, an attempt has been made, using in-house developed software, to predict real-time dynamic RCS response of blooming chaff cloud by modeling various regular shapes like sphere, cylindrical, cubical and plume shape. Also, the predicted RCS values have been validated by preparing scale-down models of chaff cloud of different shapes and sizes and measurement of their RCS responses in the anechoic chamber in the frequency range of 8-18 GHz. 2. The backscattering of microwave with randomly distributed dipoles in the chaff cloud The chaff cloud may expand in any irregular shape depending upon local environmental conditions and turbulence of aircraft. As any irregular shape can be constructed by integrating infinitesimal volume elements of regular shapes, backscattering based on screening effect from dipoles present in the infinitesimal volume elements has been analyzed and integrated to get the overall RCS response of whole chaff cloud. 2.1. Backscattering model of spherical cloud The backscattering of spherical chaff cloud based on screening effect has been discussed in [12]. He analyzed the screening effect for the random distribution of dipoles in the spherical shaped cloud as shown in Figure 1. The incident power is given by P, reflected power P1 and transmitted power as P2.

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