HELICAL ANTENNA ARRAY FOR HIGH POWER BEAMING

Abstract

Helical antenna array is an array of helical antennas. A helical antenna is a type of antenna which consist of a conducting wire which is wound in the shape of a helical structure. Generally,the helical antennas are affixed over a ground plane. The bottom of the helix is connected with the ground plane with a feed line that lies in between them. The two principal modes of operation of Helical antenna are normal mode or axial mode. The dimensions of the helix (the diameter and the pitch) are small compared with the wavelength in the normal mode or broadside helical antenna. The antenna acts similarly to an electrically short dipolar monopole, and the radiation pattern, is omnidirectional as similar to these antennas and the maximum radiation will be at right angles to the helix axis. The radiation is parallel to the helix axis and is linearly polarised. These are used for compact antennas for man-portable and mobile two-way radios, and for UHF television broadcasting antennas. The dimensions of the helix are comparable to a wavelength, in the case of an axial mode or end-fire helical antenna. In this case the antenna radiates a beam off the ends of the helix and functions as a directional antenna, the beam is along the antenna’s axis. Circularly polarised radio waves are radiated by it, which are then used for satellite communication. A hybrid of two simple radiating elements forms a helical antenna, which consist of the dipole and loop antennas. When the diameter approaches zero or pitch angle increases to 90 degrees a helix then becomes a linear antenna. Whereas, when the spacing between the turns vanishes then a helix of fixed diameter can be observed as a loop antenna . With advancement of information technology, due to its convenience the land mobile satellite communication is becoming increasingly popular among the masses. Moreover, the provisioning of communications at high speed data rate to moving vehicles is presently a considerable interest. The L-Band INMARSAT Broadband Global Area Network (BGAN) systems are being used to satisfy a large number of current requirements. Cost-effective low profile and high gain antennas are being looked into to best utilize the L-Band broadband communications in mobile environments, that are being i sought for in both commercial and military systems integrators. Circularly polarized (CP) antennas provide better mobility and weather penetration than the linearly polarized antennas and are thus widely used in satellite communication. In the past few years, a number of CP antennas have been developed for INMARSAT application due to their distinct advantages of low cost, low profile, ease of fabrication and their being compatible with integrated circuit technology. Therefore Microstrip antenna is one of the most widely used. However, since axial-mode helix antennas can provide circular polarization radiation over a wide bandwidth without the need for a polarizer therefore they are widely used in satellites and radars. Even in the past the axial-mode helix antennas continued to be developed into new designs and also being included in various research papers. The primary focus of modifications is on optimization of the pitch angle, length or radius of the helix antenna so as to attain a good radiation performance. The dissertation topic would ensure design and development of a six element Helical Antenna Array for use in specific defence applications.