[SI-LIST] : Merits of low dielectric constant

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From: Hassan Ali (hali@nortelnetworks.com)
Date: Fri Jun 23 2000 - 06:36:41 PDT


I attended a presentation by a high-frequency (1GHz < f < 65GHz) coaxial
cable vendor, and the presenter claimed that their cables use a material
with a very low dielectric constant and therefore are ideal for high-speed
application as they give rise to low capacitive loading. He gave a formula
showing the capacitance (I think per unit length) decreasing as you decrease
dielectric constant. This claim, however, perplexed me as I don't know how a
cable's capacitance per unit length would give rise to a capacitive loading.
All I know from my transmission line classes, a lossless transmission line
with Z0 = sqrt(L/C) would transmit signals exactly the same way regardless
of the value of the p.u.l. capacitance C as long as the ratio L/C is
maintained. Am I missing something here?

Thanks.

Hassan.
 

--
Hassan Ali <hali@nortelnetworks.com>
Equipment & Network Interconnect, Nortel Networks
2 Brewer Hunt Way, Kanata ON, K2K 2B5 Canada
Tel: 613-765-1410 (ESN 395) Fax: 613-765-5512 (ESN 395)

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