SATELLITE ANTENNA RADIATION PROPERTIES AT VLF IN THE IONOSPHERE.
ELECTROMAGNETIC RESEARCH CORP COLLEGE PARK MD
Pagination or Media Count:
The research reported herein was directed toward the determination of the most effective antennas for maximum power radiation at VLF in the ionosphere. Because the wavelength is in the order of 10 miles, practicable forms of antennas are the dipole and loop. For the dipole, previous results were extended to allow calculation of the impedance at VLF and some numerical computations were made for certain cases of interest. By a variational technique, an optimized propagation constant for the current along the dipole was obtained, from which it is found that a short dipole is principally a capacitive reactance for angles of the dipole axis to the earths magnetic field below a critical angle theta c, while above theta c the impedance is predominantly resistive. In either case, the impedance is strongly dependent on the ionosphere parameters. The impedance of an electrically small loop in the ionosphere is obtained in closed form. The reactance is substantially the same as in free space. The radiation resistance, however, is many orders of magnitude higher than in free space and varies only a small amount with orientation. For a loop 1 meter in diameter at 18 kc the ratio of radiation resistance to that in free space is about 10 to the 8th power. For a practical case, the ratio of reactance to resistance can be made in the order of 100, so that such a loop should be easy to feed efficiently. The method of determining the radiation field at VLF is presented. Author
- Radiofrequency Wave Propagation
- Unmanned Spacecraft