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Resonant Wideband Antennas

February 21st Fact-of-the-Day

All resonant antennas that have good performance over wide bands of frequencies have crosswise dimensions that are relatively large compared to their lengths. A large crosswise dimension has very little effect on the radiation resistance of a halfwave dipole, but increases its capacitance and reduces its inductance. Both those effects lower the resonant Q, which is the reason the bandwidth is wide. Low-Q circuits often are thought of as having high losses, because low Q most commonly results from high inductor resistance, high inductor core loss, and/or high capacitor dielectric loss. However, it is important to note that large crosswise dimension dipole antennas have low Q's, not because of high losses, but because of lower Inductive and capacitive reactances. Their efficiencies are high, even though their bandwidths are wide. ©2005 Martek International All rights reserved.


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