V.A. Nicolaev, A.S. Smirnov, V.A. Yatskevich

The resonant phenomenon originating in the log-periodic dipole antenna (LPDA) under condition of some asymmetry in its design or in its environment is investigated. This phenomenon leads to resonant rise of side radiation and variations of an input impedance and an antenna gain across the antenna operating band. This phenomenon hinder with application LPDA in phased arrays scanning in a E-plane. Besides, the difficulties arise when one produce the log-periodic antenna consisting of vertically oriented dipoles above metal shield or above an earth surface. In this case there are some resonant frequencies at which the antenna performance become unacceptable. In spite of the fact that this phenomenon is known more than thirty years, it is not offered an effective method of struggle against it till now. In the present paper the easily realizable method of suppression of the indicated resonances is offered. The method is based on introduction the additional steel wire in the antenna to absorb the power of inphase waves, originating at a resonance. This wire does not influence on basic, an antiphase wave. Computer simulation and measurings have shown, that it is possible to improve essentially the performances of log-periodic antenna located above the shield.