How to design the linear phase wideband filter?

I am trying with a linear phase bandpass filter for wideband application(about 400MHz@1.25GHz). And the group-delay turns out no longer flat because of the nonlinearity while doing the lowpass to bandpass transform(i am using Lancast's lowpass prototype). Now i've found out Rhodes developed in his paper"Cascade Synthesis of Selective Linear Phase Filters(CT-19,1972)" a so-called"hyperbolic group delay prototype" to overcome the problem.

However there is no way i can get the right values for the lowpass prototype elements by his formulars and i am not sure where is wrong.

Is there anybody ever tried that kind of filters? Or there is some other to develop the broadband bandpass filter? Please help me out...

Regards

Please can somebody whoever has designed microwave linear-phase filters before, give me some advice on a properiate lowpass prototype? maybe without those J-inverters?

Thanks in advance!

You can use: G.Matthaei,L.Young "Microwave filters, impedance-matching networks, and coupling structures". The book is in the attachment module.

Dear ,
Try using 2 section , one low pass and the other high pass..and then cascade.
It will help

What do you mean by 'attachment module'? I have that book by hand, would you pls tell me which part specificly should i look into?

Thanks a lot!

Added after 3 minutes:

Yes, i remembered read about that kind of structure somewhere..and I will try to find out more about it...Thanks! and do you have any recommendations on the references i should read?

I mean - Edaboard.com Forum attachments module:
https://www.edaboard.com/attachments.php

Look in Secs. 1.05, 4.07, 4.08, 7.09 of the book, please.