Investigations of a compact vertically polarized backfire high frequency traveling wave antenna

An antenna whose current and voltage distribution can be represented by one or more traveling waves, usually in the same direction, is referred to as a traveling wave antenna. There are various examples of traveling wave antennas, most of which are suitable for microwave frequencies. In conventional designs, quarter wavelength vertical monopoles over the ground are used to reduce the height, and, in log periodic form, to increase the bandwidth. However, at the lower end of the 3-6 MHz band, the free space wavelength, /spl lambda//sub 0/, is 100 m, and a quarter wave monopole is 25 m long, making the antenna height excessively large. The paper presents a novel design of a traveling wave vertically polarized backfire compact antenna for operation in the 3-6 MHz frequency band, with a specific requirement of keeping its height to one eighth of the free space wavelength (/spl lambda//sub 0//8). In addition, because this antenna may find applications in radar communication, it is desirable to have a good forward gain, and good front-to-back ratio. Simulations were generated using numerical electromagnetic code. It is concluded that it is possible to reduce the overall height of the antenna to merely /spl lambda//sub 0//8. The designs presented are newly invented and are not only quasi-fractal in nature but also log-periodic.