Multiband AntennasSeptember 19th Fact-of-the-Day
The frequency range over which an antenna can be used effectively depends on more than maintaining a satisfactory impedance match. Optimum radiation characteristics for HF paths between distant points vary on different frequencies. Multipath propagation due to multiple hops and the use of multiple ionosphere layers at different heights often causes selective fading and severe modulated signal distortion. Horizontal and vertical directivity of both transmitting and receiving antennas can discriminate between multipath signals and greatly reduce that problem. Unfortunately, multiband antennas rarely have ideal directivities on multiple bands. ©2004 Martek International All rights reserved.
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