Front end receiver characterization
a. Three stage LNA at 14.5GHz with a gain of 30dB(fabricated on 10mil alumina)
b. A single balanced mixer(schottky diode based) with a imgae reject filter ahead( image rejection ~-20dB) with IF at 594 MHz.
c. A filter at 594MHz is required at the output of IF port of the mixer.
d. LO port of the mixer at 13.9GHz consist of a doubler with a driver amplifier, required to generate power to drive the mixer.
The following doubts i want to clear before realizing the front end package:
i) Since all other circuits were realized in 10 mil alumina substrate, is it good to realize 594MHz filter in 10 mil alumina substrate or in a more thick substrate! Plz suggest !
ii) How to determine the combined noise temperature of the front end ( analytically) at the output of the IF stage.?
What does it mean realize 594MHz filter? I hope you do not intend to make it printed it will be huge.... If you use a filter from vendor you have two options depending on its footprint... if Input/output pads are small you can use your 10mil substrate... if not and if hopefully you on multilayer PCB make "windows" at layers
No we want to fabricate it by own( RESONATOR TYPE),can we use 25 mil instead of 10 mil or even higher value?
- - - Updated - - -
what is basic rule for the selection of substrate ( such as 10 mil , 25 mil or even higher)? suppose if we want to design at higher frequency what will be the substrate height? how the dielectric constant of the substrate helps?
Since this 594MHz filter what will be best substrate height? since we have to integrate it with other circuits of the front (they are at 10 mil alumina substrate).
- - - Updated - - -
Can u plz suggest me how to calculate the noise figure of the front end at the end of the first down converter( considering the effect of LO).
@abhijitrc: there is a cascaded noise factor (F) rule, please look it up. Doesn't matter how many stage you have you can calculate the total , F for the whole chain, but you need to know (must) NF for each individual blocks.