Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
A good explination may be found on Laverghetta - Microwave materials...
low loss laminates are divided into categories:
Hard (low rms surface roughness) - Soft PTFE based (higher roughness)
PTFE based are divided into:
Soft woven - Soft non-woven (microporous)
Soft low εr (i.e. 2-3) - mid εr (i.e. 6) - High εr (i.e. 10)
Soft tanδ at MHz -Soft tanδ at X band
Soft ED copper - Soft Rolled Copper
Soft low smoke - Soft not smoke specified
Soft dimensionally stable - Soft 100...200 ppm/°C
Generally all laminates are low loss. Loss is dominated by copper loss for freq.> few GHz.,
For filters, especially for narrow band, bandpass filter, both a good εr stability and a good diminsional stability over temperature is stongly required. Also the accurate knowlegde of εr and H dimension and associated uncertainties are important.
So, for my opinion, the preferred materials are:
Hard: 99.8% polished Alumina (Al2O3)
Soft: Rogers RT6002