To: File hfssnotes.wpd

From: Jon Hagen

Date: Jan 22, 2004

Subject: Port distances from internal structures in waveguide components

HFSS was used to

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hfss notes:

Jan 23, 04

Analyze wg transition, WG is 12.875 deep x 21" wide x 10.5 high. Probe is centered on top broad wall and is 5.5" behine the flange. Probe has 2" da. inner contuctor in a 4" jacket. The 2" rod extends 5" down into the WG and the coax (probe + outer conductor) extends 5" above the WG. (See dwg trans.fc7.)

The transition is not particulary good at 430 - return loss about 9.2 dB. But purpose is to check higher modes. HFSS is told that port 2, the WG port, has 3 modes. Let the coax port be port 1 and the WG modes be ports 2,3,and 4. At 430 MHz, S12 is about -.6dB while S13 and S14 are around -50 dB. But HFSS gives something like -20dB for S22, rather than 0dB, which would indicate total

reflection of this mode that is beyond cutoff.

Try running the analysis at 250 MHz (below the 281 MHz cutoff of the WG). Result: S11 =0dB (total reflection, as expected), but S22 = -21, S33 = -41dB, S44 = -43dB. What do these latter

number signify? These waveguide modes are all cut off, so why aren't their Snn parameters all 0dB?

Transmission results are S12 = -9 dB, S13 = -68dB, and S14=-69 dB. S12 must be that large because the probe is do close to the port. At 100 MHz, S12 goes down to -28 d B .

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