Bandstop Filter

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rf997

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Hello, I am trying to make a bandstop filter that suppresses between 1710 MHz and 1880 MHz.
I tried many different topologies but did not get any results.

What kind of topology do you think I can use to provide these values?

My S11 features:
  • 1690MHz: -15dB
  • 1710MHz : -3dB
  • 1880MHz: -4dB
  • 1900MHz: -16dB
Click to expand...

My S21 features:
  • 1690MHz: -4dB
  • 1710MHz : -23dB
  • 1880MHz: -20dB
  • 1900MHz: -4dB
Click to expand...
 

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BigBoss said:
Specifications are too tight. It might be realized by microstrip structures but a Cavity Filter is better option.
It will be so sensitive to manufacturing tolerances.
Click to expand...
Unfortunately, I have to do it with a microstrip.
 

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volker@muehlhaus said:
Unfortunately it will not work. It's just impossible using real world PCB materials.

(It might be possible using superconductors.)
Click to expand...
I understand. So, is it possible to make a bandstop filter with a bandwidth of 170 MHz at the center frequency of 1795 MHz without taking into account the parameters given above?
 

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rf997 said:
I understand. So, is it possible to make a bandstop filter with a bandwidth of 170 MHz at the center frequency of 1795 MHz without taking into account the parameters given above?
Click to expand...
If you have 0.4 meter !! space, yes it's possible. But it will be very sensitive to manufacturing tolerances, believe me.
All you have to do is to design/find a filter with Adjustment Feature. Without adjustment, it will be very heavy headache.

 
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BigBoss said:
But it will be very sensitive to manufacturing tolerances, believe me.
Click to expand...
And the other question is: does this give acceptable insertion loss in the passband?
Maybe you can zoom in S21 to the range 0 to -10dB, to show what rf997 can expect.
 

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Thank you, you are right. When I do tolerance analysis, there are huge shifts even for 1% tolerance. So, is it possible to realize the following specs in practice when I loose the s21 values?
new s21 specs:
1690MHz: -4dB
1710MHz: -10dB
1880MHz: -10dB
1900MHz: -4dB
 

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Your filter's first response was too steep so you should loosen these specifications. For instance

S21
1690 MHz=-6..-8dB
1710 MHz=-15..-18dB
1880 MHz= -15..18dB
1910 MHz=-6..-8dB

Perhaps more relaxed. Tolerance for a Microstrip Line Filter is really tight if you work with a professional PCB manufacturers. Otherwise, they will be very troublesome.
Do not trust to ordinary Chinese PCB manufacturer because they use silk screen method for prototyping and obviously this brings very large mfg. tolerance errors.
Also they use "fake substrates".
 

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