Discontinuity effect In Rf package design !!!

Hi all,

One of my observation while integrating the RF circuits in a package as stated below:

All the Rf circuits are fabricated in 10 mil alumina substrate hence the pattern width is ~ 0.25 mm and in few places we have used Isolators having pin width ~0.6mm ( 25 mil approx)( due to non availability of other isolators), all the RF circuits of the package are properly matched to 50 ohm but still i am unable to get a proper gain and output power!, even all the circuits are working properly when tested independently.My doubt goes to the discontinuity due to difference in the width of pattern of microstrip and isolator pin width.Is it ? since each circuit as well as isolators sees 50 ohm, difference in width really creates discontinuity ! Plz guide me.

Another reason may be all the inter stage connections are carried out by ribbons. Is it a cause of discontinuity !

What are the causes of discontinuity ?

Plz guide me to slove the problem

Avj

For your alumina substrate, line width is 0.25 mm as the permittivity is ~ 10. The isolator is mounted on its substrate with a lower permittivity, so its line width is 0.6 mm. Each substrate must be laid on ground to have the nominal 50 Ohm impedance.

It is possible that you laid the isolator on the alumina substrate. This is not correct. To keep the line impedance 50 Ohms, isolator must be laid on the ground to have 50 Ohms (respect to ground).
The best way is to mount the isolator on the ground and bring the alumina-based lines to its ports. Then you can use a short ribbon for connections and the discontinuity will be small, causing no problem.
How long your ribbons are? The shortest possible length is required. What is your frequency?

hi, we had mount the isolators on the chassis of the package and bring the pins of the isolators over the pattern of the microstrip and get it soldered ! but the width of the pin of the isolator is 0.625 mm and the pattern of the microstrip is 0.25mm and they are sitting over each other , but i do hope there will be considerable discontinuity in this process ? , kindly guide me, the frequency of operation is 14.5GHz, suppose the width of the isolator is same as that of the width of microstrip pattern, can i get a considerable increment in power ?

I think at 14.5 GHz some discontinuity can be a problem but a ribbon connection can work. If needed, use two-three ribbons, and make sure the ground connections are good, too,