s53mvvco.htm

Hello,

I would like to make a microwave VCO at 5GHz, with small tuning range and a microstrip resonator, in discrete technology. Which topologies do you suggest?

Thanks

Simple. Use BJT 681000 (of Nec)or its package or 420000 (Of Agilent).
Load the Emiter by an open stub or a capacitor. Load the base with a narrow line as an inductor ended with MaCom or Metalic or Micrometric varactor to the ground. You have to concider DC of course.

Some helpful links:

http://www.vhfcomm.co.uk/s53mvvco.htm
http://www.fbh-berlin.de/english/ver01/th2a_0401.pdf
http://www.ansoft.com/EMpower/Advanc...t_Designer.pdf

regards

DJ, looks like a neat idea. Can you tell which relative bandwidth to expect from this kind of oscillator?

You asked for a narrow band. If you make a real effort you can get 25% with still a good Phase noise.

That's the tradeoff I was thinking about too. The preference lays on low phase noise though. I'll do the design straight away. Thanks!

Around 5GHz VCO's are done generally base(gate) grounded topology to
supply rapidly high negative resistance. In this case imaginary part of resonator may be low and correspondingly real part of resonator.

That helps to obtain low phase noise.

But these strucutures doesn't provide large tuning range.

There are much trade-offs like those...