How to decrease the NF in ku-band LNB?

[littlemmx]

cdma_lna_design.pdf

hello everyone,i'm a new comer.
i have a question about LNA of ku-band LNB,usually the noise figure is very low,i want to consult anybody who is good at LNA,how can i decrease the NF in ku-band.

 

[godz]

Re: question:ku-band LNB

hello everyone,i'm a new comer.
i have a question about LNA of ku-band LNB,usually the noise figure is very low,i want to consult anybody who is good at LNA,how can i decrease the NF in ku-band.

hi littlemax,
can u give me more details please? do u want to design an RFIC or a discrete design? what are the key design parameters in your hand (current, matching netwok,etc), whether discrete or RFIC, each has its own design aspects for NF optimizatiom.

 

[littlemmx]

thanks for your reply.
i just found that the noise figure of ku-band LNB is very low,in 14ghz,the noise figure is 0.8~1dB(typ).
so i want to design a lna like that,but i don't know the important that affect the noise figure of lna.
does anybody can help me?

 

[godz]

Re: question:ku-band LNB

Hi,
Well assuming you are designing a discrete LNA, the main keys controling the NF of the LNA is the choice of the active device, the number of passive resistors, and the DC current consumped.
You need only one transistor as the active part of the LNA, choosing the transistor is a critical issue at this frequency, for instance philips semiconductos has the BFG series with low noise charateristics and high Ft, of course high Ft means better noise figure and gain, passive resistors are used for biasing and feedback, yet careful choice of their values is necessay due to their thermal noise contribution, DC current influences both minimum noise figure and gain of LNA.
The following URL contains a very useful paper on Discrete LNA design, though for 1.9GHz applications, not in the Ku band, but provides useful general design methodology for Discrete LNA design.
**broken link removed**
don't hesitate for any questions.
regards,