Suitable substrate material for filter design

Hello everyone,
Which substrate material is suitable for Narrow-band Bandpass filter(coupled line type) at 10 GHz, A low dielectric material(like er=2.2) or high dielectric material(like er=10.2). I need to keep insertion loss as low as possible.Please help me out. Thanks and best regards

In terms of insertion loss, lower Er is better because your tracks will be wider and therefore lower conductor loss. That is, 2.2 is better.