The linear phase filters can filter received signals without applying any phase distortion.
For this reason linear phase filters are utilized in many radarreceivers.
See the attached LPF.jpg
Another way of saying "linear phase" is to say "constant delay"...
so when you hear about filters with low group delay, it means that over some region of the passband they have a relatively equal delay (important for communications and radar).
there are a variety of filter types that are better than others for relative group delay (or phase linearity) -- I suggest researching group delay and you will gain a little more insight into the matter.
Here is a Nice document... **broken link removed**
You can use any RF/Microwave Software for design & simulation, for Filters Nuhertz Filter sysnthesis tool or AWR Microwave Office...
To optimize Group Delay & Phase deviation parameters of your filter design...