A Log-Periodic Array of Monopole-Slot Elements,
HUGHES AIRCRAFT CO EL SEGUNDO CA TECHNOLOGY DIV
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In feeding a log-periodic monopole or slot array, excess line must be used between radiating elements to achieve proper phasing for backfire radiation. Discontinuities presented by the radiating elements, which are approximately one-half wavelength apart on a series feedline, cause additive reflections on the line. There is, therefore, a region on the log-periodic array which behaves simiilarly to a periodically loaded transmission line operating in a stopband. Reflections occuring in this region inhibit propagation of energy down the feedline. To obtain a frequency-stable impedance, these structural stopband regions should be reduced. One technique that can be used to minimize the stopband region on a series feedline is to reduce the reactive nature of the non-radiating elments using the principle of complementarity. A two-port monopole-slot antenna has been previously shown to have a relatively constant image impedance below its first resonance.
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