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VK2ZRG > TECH 20.07.04 18:39l 27 Lines 1088 Bytes #999 (0) @ WW
BID : 808_VK2ZRG
Read: GUEST
Subj: Microstrip impedance vs frequency?
Path: DB0FHN<DB0MRW<DB0ERF<DB0FBB<DB0GOS<DB0EEO<DB0RES<ON0AR<7M3TJZ<SP7MGD<
ZL2TZE<VK5UJ<VK5BRC<VK5ATB<VK2AAB<VK2WI
Sent: 040720/1104Z @:VK2WI.#SYD.NSW.AUS.OC #:43295 [SYDNEY] FBB7 $:808_VK2ZRG
From: VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
To : TECH@WW
VK2ZRG/TPK 1.83d Msg #:808 Date:20-07-04 Time:12:03Z
Hello all techies,
I've been trying a few old BASIC programmes that calculate
Microstrip impedance. Some of the programmes just take inputs of track width,
substrate height and dielectric constant to calculate the impedance (Zo).
Other programmes also take track thickness and frequency into account in the
calculation.
I can see that track thickness will affect the Zo somewhat for very thin
tracks and also that frequency may have an effect if the substrate height is
a significant part of a wavelength.
The problem is that one programme says the Zo of a 50 ohm line on a 1.5 mm
fibreglass substrate will drop by 1 ohm at 10 GHz while another programme
says it will rise by 2.5 ohms.
For practical purposes this hardly matters but can anyone tell me which
way the Zo varies with frequency? I tend to think that it should rise. Has
anyone got an accurate formula for Microstrip?
Thanks in advance.
73s from Ralph VK2ZRG@VK2WI.#SYD.NSW.AUS.OC
/ack
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