Bandpass filter at 155Mhz

[guytoub]

Hi guys,

I want to design a narrow bandpass filter like this:
Fc=155 MHz
Bw= 2 MHz

With verry hard shapes.

I try to design with agilent genesys but i didn't have good result. -60 dB at fc
I use fixed inductances about 5nH
Does anyone have a method or a design for me please?

Thanks for your help

 

[G4BCH]

The Genesys filter designer does not have a topology that will give you a practical filter low loss that will meet this specification. You should be able to get better than 60dB insertion loss at centre frequency. Try the tubular filter with inductor Q of about 250. You do need to use good quality inductors and capacitors.
I would use a helical filter for this bandwidth and frequency. Google 'Helical filter design' and you will get an number of articles and some design software.
The filter will be physically large for low insertion loss.

Peter

 

[Ow@i$]

Try a free software FDA Filter Design Tool!!!
I have implemented a cohn crystal filter designed in this tool!!
it is good and easy to implement, and will suite your narrow bandwidth requirement

 

[guytoub]

Thanks smooth!

I found a lot of subject with your help now il going to study one of thème with your tool.


Best regards

 

[jiripolivka]

First your filter specification is wrong. Defining the pass band is not enough. You must define the rejection band and loss at selected frequencies. RF power and temperature and air humidity may b e important. Size and connectors (i/0 impedance) all is missing.

How can an engineer work with no data?

 

[guytoub]

First your filter specification is wrong. Defining the pass band is not enough. You must define the rejection band and loss at selected frequencies. RF power and temperature and air humidity may b e important. Size and connectors (i/0 impedance) all is missing.

How can an engineer work with no data?

Hi jiripolivka ,

Thanks for your reply,

You've right for my specifications about the filter but first, i wanted to Know what was the best technology to achieve it.
Now i can give you some of them .

Fc= 155 MHz
BW@ 3dB =2 MHz
VSWR 1,5:1
Impédance I/O 50 Ohms
Connectors = could be SMA or N
RF power <= 2Watts
Réjection : 30db at 140MHz and 160 MHz
Temperature =25 degree


I hope That you havé enough specifications because i'm not and engineer

Regards

 

[BigBoss]

Helical EM Coupled Resonator Filters are generally used to implement this type of filters.They are very bulky filters but it's worthy to try..

 

[guytoub]

Helical EM Coupled Resonator Filters are generally used to implement this type of filters.They are very bulky filters but it's worthy to try..

Is anyone have links or papiers about how to built these filters?

 

[G4BCH]

See the second paragraph of my reply above. There should find enough there to help you out.