Log periodic monopole array

Abstract

This paper describes a vertically-polarized, unidirectional, frequency-independent antenna that utilizes its image to reduce its maximum height to 1/4 wavelength at its lowest operating frequency rather than the 1/2-wavelength dimension that has been necessary in other types of log periodic antennas. This relatively small dimension makes this antenna particularly desirable for use in the lower portion of the h-f spectrum as well as in other frequency ranges where frequency-independent operation must be coupled with small size. The frequency-independent properties of the antenna are produced by a unique arrangement of reactive elements which introduce additional degress of freedom in the design. Radiation pattern and phase center data are given as a function of the usual log periodic parameters. In addition, design data is given that allows the designer to control the antenna characteristic impedance and vswr by adjusting the additional parameters. Techniques that are necessary to ensure proper operation are discussed. Finally, the measured vswr of an antenna designed to operate from 4 to 20 mc is presented.