gap analysis ltcc
Why did you build the filters in stripline configuration (two groundplanes) instead of microstrip configuration (single goundplane)? Was it really required to avoid cavity mode propagation, stop band attenuation, etc?
Are you sure you have manufactured the stripline filters using the right Duroid substrate material, i.e. are you sure of the epsilon-r is the same in the simulations as in the material? In addition, what does the stripline look like? The stripline filter layer stack shall consist of:
groundplane
dielectric material (Rogers Duroid)
stripline conductor (etched copper track)
dielectric material (Rogers Duroid)
groundplane
A microstrip filter consists of:
microstrip conductor (etched copper track)
dielectric material (Rogers Duroid)
groundplane
Duroid thickness is important as well. Most stripline filters consist of a dual copper side Duroid substrate and a cover laminate (single copper side). The dual copper side substrate has etched tracks on one side and unbroken copper on the other side. The cover laminate is put ontop the etched filter, having the ground copper plane facing away from the etched filter tracks. Now. it's important the cover laminate is pressed against the filter tracks for maintaining correct dielectric thickness. No vertical air gap is allowed. Pressure is usually applied via two chassis halfes where in between the filter is mounted. When the two chassis halfes is assembled, the stripline filter stack is squeezed together.
filterman said:
I designed some filters ( interdigital ) using Serenede 8.7 or Eagleware.
But tested filters have bad return loss , also rejection is not like simulation. Anyone design and test ? Any comments that might help put design right.
frequency was 2-3ghz n=11 rogers4003 60mil 1-0.5oz copper with film to join them toghether.