How to make a X-band VCO that works in few hundred MHz?

[yykk]

Hi, all

I need to make a x-band VCO, I have made one, but the tunning rang only has 5 MHz, How can I obtain a few hundred Mhz ??? Help me please !!!

 

[vfone]

Re: X-band VCO

X-band frequency range is from 8GHz to 12GHz.
For me is hard to believe that can be a VCO for this band, with only 5MHz tuning range (~0.01%)
I think somewhere is a mistake.

The following parameters affect the VCO Frequency Range:

TUNING VOLTAGE
-An increase in tuning voltage range widens frequency range.
TUNING SENSITIVITY
-Lower sensitivity means a narrower frequency range for a given range of tuning voltage.
PUSHING
-Increased pushing causes decreased effective frequency range.
PULLING
-Increased pulling causes decreased effective frequency range.
TEMPERATURE
-An increase in the range of the ambient operating temperature causes a decrease in the VCO’s frequency range and vice-versa.

 

[DJ]

Re: X-band VCO

Generaly speaking if the varactor is located at the E (or S), you can get wide tuning range.
If you got only 5MHz it means the varactor location is wrong or the varactor value. If you locate the varactor around low impedance then you short it. Also if the varactor has high capacitance compared for example to a siries low value capacitance then it has no influence etc.

 

[yykk]

Re: X-band VCO

Thanks for DJ and Vfone reply. I put the varactor in the gate pin of the FET device. My designed tunning rang is 0-3V. Do you have any suggestions or which configurations should I use to obtain more tunning range. Thanks a again !!!!

 

[vfone]

Re: X-band VCO

A higher value of the coupling capacitor will allow a larger tuning variation, but will pull down the center frequency.
Therefore, the tuning range depends mostly on the amount of the supply voltage.
Take a look to this document:
**broken link removed**

regards

 

[DJ]

Re: X-band VCO

Varactor might be located at the Source instead and load the gate with an inductor.

 

[yykk]

Re: X-band VCO

Hi all,


I have try to put the varactor in the Source, but the result are the same. Also my tunning range only at 0-3V.

 

[DJ]

Re: X-band VCO

If the oscillator works and the mode sense is too low it might be a wronge choce of varactor value.

 

[yykk]

Re: X-band VCO

Thanks all to reply, I get some idea to re-design it....

 

[somf0872]

Re: X-band VCO

Take a look to this stuff!