Center of Excellence on Applied Electromagnetic Systems, School of ECE, College of Engineering, Univ. of Tehran, P. O. Box 14395-515, Tehran, Iran.
Department of Electrical and Electronics Engineering, Malek Ashtar University, P. O. Box 1774-15875, Tehran, Iran.
It is known that if a conductor resides in the neighboring of an antenna with a small distance relative to the wavelength, it induces a reverse current on the conductor. This paper involves the unavoidable coupling effects on some common types of LF antennas, due to the large wavelength in this frequency band. In particular, after some discussions about top-loaded antennas, the coupling effect of wire supports is studied for these antennas. In addition, the effect of support masts on the radiation resistance is shown for three kinds of Loran transmitter antennas with four masts. Furthermore, some formulas for the impedance of small monopole antennas with neighboring masts are proposed and some simulation results of practical antennas are reported. Finally it is indicated that the coupling effect is more destructive for sectional Loran transmitter antenna compared with square top loaded antenna.