A possible solution is covering one or both of the resonator end walls
with an absorbent material. This should damp ("even-out") the
apparently strong standing waves and time delay ISI. Such material is
used in anechoic test chambers and frequently consists of
carbon-particle-loaded foam formed into spear-like projections to
gradually "match" to the space wave.
A way to model this would be to consider an oversize waveguide of
infinite extent in both directions with bidirectional excitation in
center. One would presume use of bidirectional yagi is better than
lighting-up the nearby walls as a dipole would.
If used be cautious of possible fire hazard if power is high (few 10's
of Watts or more) and other aspects of the tunnel environment .
Dan Bathker
Received on Sun Apr 09 2000 - 12:25:08 EDT
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