Effect of the tank main gun on the radiation pattern of the monopole antenna

Abstract

For telecommunication purposes, a monopole antenna is usually positioned on the tank turret. At low frequencies the whole tank has to be treated as a part of the antenna system. In this paper a method for electromagnetic modeling of metallic structures is presented and applied to the analysis of radiation of a tank monopole antenna. Radiation simulations are performed at the frequency range from 1MHz to 30MHz. A special attention is given to the analysis of the effects of increased elevation of the tank main gun to the radiation pattern of the antenna. The analysis of the radiation of the tank monopole is performed with and without the presence of conducting ground. It is shown that the increase in the main gun elevation at certain frequencies can lead to degradation of uniformity of radiation in the horizontal plane. Introduction Informational technologies and reliable and secure communications are an important part of a modern military doctrine. Regarding telecommunications, armored vehicles and tanks in particular present a specific problem. In this paper, a theoretical basis of the electromagnetic analysis of metallic structures and a modeling technique will be presented. The effect of the tank on the radiation pattern will be investigated both for a tank in free space and above the conducting ground. Method of moments The method of moments (MoM) is a method for an approximate solution of integral equations. This section presents the fundamentals of the MoM and the higher-order quadrilaterals as the basic elements used for geometry modeling. The currents in our method are approximated using high-order two-dimensional polynomials. Modeling of the tank geometry The tank is modeled using only 28 elements, out of which 10 bilinear quadrilaterals and 18 second-order surfaces. The monopole antenna is modeled using one straight wire segment. Results The use of the polynomial current approximation yields a reduction in the number of unknowns required for the analysis, compared to classical methods that use linear current distribution defined on small triangles. The analysis of the tank from 1MHz to 30MHz, with a 1MHz step, requires from 130 to 337 unknowns and about one minute of the CPU time on a Dell Vostro 1015 laptop computer. Tank in free space At low frequencies, the monopole-tank system acts as a dipole antenna and the computed directivity is 1.76dBi, almost equal to that of a short dipole. The elevation of the tank main gun does not influence the radiation pattern much at low frequencies. In the resonant range, the effect of the main gun elevation is much more pronounced. At 17MHz, the difference between the minimum and the maximum of radiation in the horizontal plane is 1.22dB, 1.90dB, and 2.33dB for the main gun elevation of 0°, 13°, and 20°, respectively. The effect of conducting ground The effect of the conducting ground (in this paper we assume the ground is perfectly conducting) is taken into account using the image theory. Since the original currents and their images are electrically close at low frequencies (their distance is small compared to the wavelength), their mutual coupling cannot be neglected. Once again, at low frequencies the whole structure acts as a short dipole antenna and the computed directivity is 4.76dBi; at the same time, the radiation pattern in the horizontal plane is almost uniform. At the frequency of 13MHz, however, the difference between the minimum and the maximum of the radiation in the horizontal plane is almost 8dB for the main gun elevation of 20°. Conclusion This paper presented an electromagnetic modeling and an analysis of the monopole antenna positioned on the tank turret. The antenna was analyzed at frequencies from 1MHz to 30MHz, and the effect of the main gun elevation on the antenna radiation pattern was studied. It was determined that at low frequencies the elevation of the gun does not influence the radiation pattern much, but at higher frequencies, where the tank can be considered as a resonant structure, the detrimental effect on the radiation pattern can be quite substantial. At the frequency of 13MHz, the range of communication in the horizontal plane can be almost cut in half for certain directions if the elevation of the main gun is 20°.