Physics Help Forum Waveguides & PCB vias

 Electricity and Magnetism Electricity and Magnetism Physics Help Forum

 Jan 9th 2018, 07:58 AM #1 Junior Member   Join Date: Jan 2018 Location: Malage, Spain Posts: 1 Waveguides & PCB vias If anyone can de-confuse my brain, I'll have a nice day. This is my thought process: If I think of a waveguide with a large flange at each end, an incident em wave at one end can only pass through the waveguide if its frequency is above the waveguide cut-off frequency. My proposition is as follows: An incident em wave below the cut-off frequency will induce currents on the surface of the flange, but the current cannot flow through the waveguide & so do not appear on the outer surface of the flange at the opposite end. If current did flow through, then it would re-radiate from the flange at the opposite end, which contravenes the first statement. Applying this idea to a printed circuit board with a large copper plane on one side & a similar copper plane on the opposite: This printed circuit board has a single plated through hole connecting the two outer surfaces. By analogy to the waveguide, current flowing on the outer surface of one copper plane cannot, therefore, flow through the inside surface of the plated through hole, unless its frequency is above the waveguide cut-off. The current can of course take the long way round, but it's the flow through the inside surface of the plated through hole that's bugging me. What's the flaw in this thought process, or am I correct (although I think not)?

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