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Dual gate fet mixer design problem

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muheeb16

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1-I have designed an LNA amplifier at 5.5 GHz and a Dielectric Resonator at 5GHz.I was hoping to down convert the LNA output using a dual gate mixer (5.5GHz at RF and 5GHz at LO) but none of the dual gate FETs I came across operate at such high frequencies e.g BF998 2-While designing the FET mixer,can I use the S parameters for calculations?Aren't they specified for linear models while mixer is clearly non-linear.
 

I suggest use diode mixer, no oscillation problems. I googled why peoples want to use dual gate mixer, so as i understand you want to get good isolation? S-parameters still can be useful to determine stability.
 

NE25139 from NEC is a dual-gate GaAs MESFET which they claim that working at 4GHz. Might work as a mixer at 5.5 GHz, with less conversion gain.
**broken link removed**

I have used for a 5.5 GHz application HMC218BMS8GE from Hittite (ADI). The price I think is about $6. The mixer is using single ended connection for all ports, so very easy to implement into the design.
Two GaAs FETs placed in cascode configuration, and the afferent components for mixer use, it will cost you the same $.
5.5 GHz is already a microwave frequency which needs careful design.

https://www.analog.com/media/en/technical-documentation/data-sheets/HMC218B.pdf
 
Terminator3 said:
I suggest use diode mixer
Click to expand...

Diode is one port device.I will have trouble diplexing RF and LO signals.But I would appreciate if you can give me a hint on how to do diplexing.It itself becomes cumbersome.

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You mean I can use NE25139 at 5.5GHz?I don't care much about conversion gain since I have a pre amplifier.
 

muheeb16 said:
Diode is one port device.I will have trouble diplexing RF and LO signals.But I would appreciate if you can give me a hint on how to do diplexing.It itself becomes cumbersome.

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You mean I can use NE25139 at 5.5GHz?I don't care much about conversion gain since I have a pre amplifier.
Click to expand...

I am sure it can be used. They just gave s-parameters up to 4GHz. For example ne32584 fet have s-parameters only up to 18GHz, but also can be used (gain) around 25GHz, that is almost 10GHz higher than measurements from datasheet.

Also i think for 500MHz difference you can use something like rat-race microstrip mixer or single-balanced mixer. At 5GHz freq it is easy to optimize isolation, because measurement devices at this frequency easy to find.

If it is convenient to you to buy Hittite IC, it would be most simple way.
 
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