return loss is not good

hi to all,
i have designd a combline round rod filter (3.7-3.8ghz)but the return loss is not good in the pass band......
is tuning of the tap points may change return loss?
or any other solution for this ??
here i got the band width exactly double to my designd one .....
means when i designed for 100 mhz i got 200mhz bandwidth
and when i designd for 90 mhz i got 180 mhz band width

so any suggession to improve return loss and reduce my band width
( im thinking that by scaling means designing for 50 mhz will get 100mhz band width is it works for this filter)

i tried the some tips which are suggested here in this forum as
increse spacing and order but im not getting my required filter............
any one clarify these doubts plzzzzzzzzzzzzzzzzzz..............

thank you one and all

http://www.macom.com/TechApps/pdf/Na...esign10_07.pdf

See the website I have downloaded in following file
You will get the help you need.
Best of luck
Abhishekabs

thank you for u r posting i have that paper but i dont have equipment now so im asking is thgere any tuninng or changes made to filter so that the return loss may be improved..............
anyway thank you for u r help if u have idea about this post here
\ thank you