Hi John. I dug out a textbook I had in school titled "Microwave
Engineering and Applications" by Om P. Gandhi which shows in Figure 12 a
wide strip (w/h > 0.1) and narrow strip (w/h < 0.1) plots of characteristic
impedance, with multiple plots of varying dielectric constants
(epsilon-sub-r) from 1 through 90. Table 3.1 in the same book gives
dielectric constants for various substrate materials. I hope this can be
of some help.
Rob Shapiro - ND3A
Potomac Valley Radio Club
> From: John Brosnahan <email@example.com>
> To: firstname.lastname@example.org
> Subject: [TowerTalk] microstrip transmission lines
> Date: Thursday, February 12, 1998 9:16 PM
> I am looking for a formula for calculating the impedance of
> a microstrip transmission line in an arrangement that does
> not seem to be covered by any of my references.
> I only need moderate accuracy through the VHF bands so
> some of the more esoteric terms are probably not required.
> The configuration is that of a single sided (ie, no pcb ground
> plane) G-10 circuit board with the transmission line trace
> etched on the side towards the grounded chassis and with
> an air gap between the trace and the chassis ("ground").
> Primary variables are of course the 1) trace width and
> 2) the height above the ground plane with air for the dielectric
> on one side and 3) the thickness of the G-10 pcb on the
> "back side" (and then more air), and 4) the copper trace
> If anyone has any good references on this configuration
> or a formula I would certainly appreciate it.
> Thanks in advance for any help.
> John Brosnahan W0UN
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