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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