You may find useful things both on simulation hints and practice at these links:
**broken link removed**
http://www.hp.woodshot.com/hprfhelp///4_downld/lit/diodelit/an1048.pdf
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For your desired 5.4-6Ghz band you have to choose a suitable present day pin diode type which is characterised with all its nonlinear and linear parameters from the manufacturer to be able to include it into a simulator software.
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See this Forum here too:
Also see this article in Microwave Journal: **broken link removed**