K. K. Belostotskaya - Ph.D. (Eng.), Leading Research Scientist, JSC Special Research Bureau of Moscow Power Engineering Institute E-mail: dpeshkova@yandex.ru M. D. Duplenkova - Ph.D. (Eng.), Leading Research Scientist, JSC Special Research Bureau of Moscow Power Engineering Institute E-mail: duplenkova@okbmei.ru

The present article describes the problem of near-omnidirectional wideband antennas designing. As a basis we took conical dipole above the screen. At low frequencies such antenna has a radiation pattern almost independent from frequency which is equal to a radiation pattern of a short vertical dipole. The radiation pattern deformation is inadmissible starting with some frequency which is possible to assume as a high boundary frequency. On the other hand such antenna has well matching at high frequencies. When frequency is decreased a reflection coefficient has increased and become unacceptable high from some frequency, which lets assume as a down frequency boundary. An operating frequency band is an interval between these boundary frequencies. There are practical recommendations about the choice of the optimal angle correspondence in cone vertex and wave impedance coaxial. The additional condition in the problem statement is severe limitation on space for antenna or antenna device. The admissible volume is given by semi-cylinder for the definiteness. The main purpose of studies is to look for opportunities of natural operating frequency band expansion both to a range of low frequencies and to a range of high frequencies. Usually a conical dipole is cut off by the plane, perpendicular to the cone axis. This paper suggests the original way to cut a cone by the cylindrical surface, which is almost equal to the surface of limited volume. As a result a form of antenna has become slightly elongated (that is why we call such antenna - a small boat - Lodochka?). The maximum length of generatrix of "Lodochka" is increased compared to the length of generatrix of the initial symmetrical cone. Taking into account shunting [1], installed in the minimum cross-section of "Lodochka", the lowest operating frequency is significantly decreased. The loss of symmetry of radiator results to the additional non-uniformities in a radiation pattern. Based on a thorough analysis of cal-culated radiation patterns it can be argued that the additional non-uniformities are acceptable for technical application. Using of the original way of cutting off the cone didn-t increase the height of antenna, so higher operating frequency stayed where it was. Expansion of an operating range was achieved by admissible non-uniformities in a radiation pattern. Expansion of an operating range into a range of higher frequency with only one antenna is impossible. However the design of "Lodochka" allows placing the second wideband antenna of smaller size in allowed volume. That is how we can get an additional length of an operating range in a range of higher frequency. So we get not antenna but the antenna system what we mentioned in the name of the present article. A coaxial cable of the second antenna goes through one of shunts of "Lodochka". It absolutely has not an influence on the antenna system. Unfortunately, an expansion of an operating range into a range of higher frequency is not continuously. This paper considers the problem of addition of frequency spacing for specific navigation systems GLONASS and GPS. The present paper is a result of massive calculations. We have used complex programs for getting data about matching antennas. We have also made a combined antenna model and got the experimental data about reflection coefficient. The calculating data and the experimental data were coincided exactly. Calculations about radiation patterns were made under such condition that perfect conducting screen has endless size. Only under this condition we could estimate the level of non-uniformity as a result of "Lodochka" form.

 

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