Need help on LNA design using microstrip for 12GHz

[Murlix]

hi, i am new to LNA design. I am doing a 12GHz LNA for my final year undergraduate project. i am using ATF-36077 HEMT(avago) and Er=10.2 microstrip(rogers 3010) for my design.My design objectives are nf<1dB and gain=10dB or more. I have done the schematic and simulation using ADS2005A. i got nf of around 1dB but gain only 6dB. I don't know wat is the problem? I am also not sure of the biasing required for the design? i used λ/4 microstrip line(both sides of the transistor) as the rf choke but i am not sure it is done the right way?

i have attached the datasheet for atf-36077 and schematic before optimization in ads.
i hope u guys can help me out with the problem. thanks

 

[Element_115]

The Device should meet your requirements with no problem.
Did you draw the noise circles and match the I/P and O/P ports?

See Pozar (Chapter 11 in the 2nd Edition)

 

[toonafishy]

You have no negative bias on the gate. The gate needs to be ~0.2 V negative referenced to the source. In your schematic, the gate and source are DC shorted together.
I put a blocking capacitor between TL2 and the gate. I then injected a MINUS 0.2 VDC onto the gate thorugh an ideal 1 nH inductor. Gain went from 5 to 10.5 dB. You will have to optimize the DC value and doit in a practical way but that will get you started.

 

[Murlix]

thanks toonafishy. I tried what u advised and the gain improved like u said. My problem is :
1) I dont know how to optimize the dc biasing for the design and the gate negative biasing that u told to add

2) I dont know how to convert the decoupling capacitors and the ideal inductor in the design into microstrip parameters

3) i m also not sure if the 9V DC with series 750ohm biasing is suitable? i juz calculated it using the datasheet values and a random resistor value

 

[toonafishy]

Search at:

www.avagotech.com

There are two app notes for a ATF-36077 2 and 5 GHz amplifier (old Agilent app note numbers 1129 and 1133). You can see the bias methods commonly used. You will need to scale them to 12 GHz.

good luck