Two band single element short wave antenna - acts as half wave surface wave dipole and twice five eighths lambda directional antenna with third harmonic excitation

摘要

In the HF range, a half wave antenna for surface wave resonance at the fundamental (e.g. 7 MHz) must be extended by about 3.5 percent to resonate precisely at the third harmonic (21 MHZ). Thus two one-eighth lambda coaxial conductive loops with air dielectrics are replaced by coaxial cable lengths with a specific dielectric. With surface wave resonance excitation the lambda over eight elements reach their predetermined electric wavelength of twice 45 deg. and supply the five-eights lambda elements in correct phase and impedance. The geometric spacing of the colinear radiation elements is reduced from 90 deg. to 70 deg. If the antenna is excited as a half wave dipole the outer conductor of the coaxial cable is part of the length of the half-wave surface wave dipole. ADVANTAGE - Improves transmission either in VHF/UHF or Hf regions with one-element antenna at fundamental and third harmonic.