BROADBAND ARRAYS OF HELICAL DIPOLES
Final technical rept. (Part 2), 1 Jun 1962-31 Aug 1963
ILLINOIS UNIV AT URBANA ANTENNA LAB
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The report deals with the problem of reducing the resonant length of radiating elements of log-periodic dipole antenna arrays by the use of helical dipole elements. Some consideration is given also to the problem of boom length shortening. Reduced size log-periodic arrays are required to make practical shipborne applications in the high frequency band at frequencies as low as 8 MHz. Several reduced scale models were built using helical dipole elements and compared with similar designs using linear dipole elements. Directive gains and impedance characteristics were compared. An element shortening factor of 0.54 was used. Some mixed dipole arrays, where only the longer low frequency elements were shortened, also were tested. Conclusions are that helical dipoles are useful and practical size-reduced elements for log-periodic arrays. However, boom length is increased by dipole length shortening and antenna performance somewhat impaired. The most practical design is a log-periodic mixed dipole array. Measurement techniques are treated in an appendix.
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