Coupled Line BPF Problem

Hi all,

I am designing a coupled line microstrip BPF with center frequency of 1.67 GHz. The ideal simulation (with even and odd impedances) is great but when I shift to use microstrip lines, the response is worse.

The point is that the filter response is such that it passes the frequencies in the range of double of its passband. In other words, it has a flat response centered at 3.34 GHz which is not desired (I want to filter those frequencies as well as my BPF is placed after a mixer).

Could anyone please help me on how to enhance the response of my filter to filter those frequencies and also how to improve its S11 as it is not as desired (<-15 dB)!

Thanks

i hope that paper will help you
http://www.ijeei.org/docs-3904550494c2ac15da882f.pdf

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you could calculate your lines
http://www.qsl.net/yo4hfu/Microstrip.html

You need to realize that a 1/2 λ at 1.6GHz is ≡ 1λ at 3.2GHz, so this effect will always be true. You can
add a LPF that Rolls off at ~ 2.3GHz.

Cheers

Thanks for the paper..

The equality at 1.67 and 3.34 is due to what?!

I cannot enhance the response without adding a LPF?

Since if I add a LPF, then the filter is going to be lengyhy!

Regards