Effect of inductance of the ribbon used in inter-stage connections in the Rf package

[abhijitrc]

Hi guys,

I just want to share one of the point related to the design of the microwave/Rf packages ,operating at ku-band, during the design of the rf package which consist of Rf section (three LNAs cascaded together), LO section ( Active doubler circuit, and a driver amplifier) and a down converter section( a schottky diode based mixer and an IF filter), all these sections are mounted in a common package, now my doubt related to interconnections are as:

a. In case of RF chain, where three LNAs are cascaded( all three Circuits have been fabricated on alumina substrate and mounted on individual kovar) and these amplifiers have been interconnected with ribbons, What will be the effect of inductance of the ribbons used in interconnections and how the behavior of the cascaded circuits changes!!!!. Is the overall gain may change??/ Noise figure may be effected and how??/ Shift in frequency due to impedance change ??And how to solve this problem practically!!!

b. In the LO section active doubler have been cascaded with a driver amplifier and they have been interconnected using ribbon, since the doubler is the nonlinear circuit and it has been interconnected with the driver amplifier( in between them a fiter is there to filter out un-wanted harmonics of the multiplier) what will be the effect of the inductance of the ribbon in their overall performance??

c.In the down converter section a schottky diode mixer followed by an IF filter also connected by ribbons, here how the inductance of the ribbon play its role!!!

LO section and the down converter have been mounted in the package, some differences have been observed from simulation, is this due to inductance of the ribbon???, Yet to mount the Rf section since it is a high gain chain!! what will be effect of inductance in that section!!

 

[jiripolivka]

Hi guys,

I just want to share one of the point related to the design of the microwave/Rf packages ,operating at ku-band, during the design of the rf package which consist of Rf section (three LNAs cascaded together), LO section ( Active doubler circuit, and a driver amplifier) and a down converter section( a schottky diode based mixer and an IF filter), all these sections are mounted in a common package, now my doubt related to interconnections are as:

a. In case of RF chain, where three LNAs are cascaded( all three Circuits have been fabricated on alumina substrate and mounted on individual kovar) and these amplifiers have been interconnected with ribbons, What will be the effect of inductance of the ribbons used in interconnections and how the behavior of the cascaded circuits changes!!!!. Is the overall gain may change??/ Noise figure may be effected and how??/ Shift in frequency due to impedance change ??And how to solve this problem practically!!!

b. In the LO section active doubler have been cascaded with a driver amplifier and they have been interconnected using ribbon, since the doubler is the nonlinear circuit and it has been interconnected with the driver amplifier( in between them a fiter is there to filter out un-wanted harmonics of the multiplier) what will be the effect of the inductance of the ribbon in their overall performance??

c.In the down converter section a schottky diode mixer followed by an IF filter also connected by ribbons, here how the inductance of the ribbon play its role!!!

LO section and the down converter have been mounted in the package, some differences have been observed from simulation, is this due to inductance of the ribbon???, Yet to mount the Rf section since it is a high gain chain!! what will be effect of inductance in that section!!

Ribbon interconnects are used for the lowest inductance in cases like you described. In fact, the best way is no interconnects if possible. In Ku-band LNBs and similar devices produced on sngle substrates, there are no interconnects, no ribbons. All connecting lines are 50-Ohm microstrip on an uninterrupted substrate.
In active and passive MMICs, interconnects are often made by multiple gold wires in parallel to replace ribbons which are more difficult to weld by existing process.

 

[abhijitrc]

In our case now it is not possible to produce all the LNBs on a single substrate, in this situation we have to integrate all the three LNBs using ribbon, Plz let me know how to minimize the effect of inductances of ribbon!!

 

[jiripolivka]

In our case now it is not possible to produce all the LNBs on a single substrate, in this situation we have to integrate all the three LNBs using ribbon, Plz let me know how to minimize the effect of inductances of ribbon!!

Ribbon is always a compromise but the best one. I would suggest to use the same width as the microstrip line has, set the substrates as close as possible to each other, and make sure the grounds of the substrates are not interrupted. In MMICs, often a short 50-Ohm microstrip line made of a soft (rogers) substrate is used as needed, and interconnected on both sides with multiple parallel wires or ribbons.
Test the design n a VNA over the band of interest to be sure it works well. Lay the ribbon like you would the active microstrip conductor.