| 摘要 |
PURPOSE:To maintain a constant antenna radiation pattern over a wide frequency band by providing a radio wave absorber which shows resonance absorbance characteristics at frequencies lower than the 1/2-wavelength resonance frequency of a cavity on the internal bottom surface of the cavity. CONSTITUTION:The internal wall of the cavity 2 provided in combination with an antenna electrode 1 is a good conductor and the radio wave absorber, preferably, a magnetism absorber type resonance absorber 4 is mounted on the bottom surface in this cavity 2. Here, the resonance absorption frequency of the absorber 4 is set to a frequency a little bit lower than the 1/2-wavelength resonance frequency of the cavity 2. Consequently, the antenna radiation characteristics are obtained which maintain the nearly constant antenna radiation pattern over the wide frequency range and has small variation in the radiation pattern and is made unidirectional.
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