What is meant by cross coupling in the cavity filter ?

[mallelauma]

hi
waht is mean by cross coupling in the cavity filter ?
and also any one the idea about the coupling band width in the cavity combline filter plz ans any 1.

thank you

 

[Phytech]

cross coupling

Cross Coupling: coupling between non ajacent resonators.

Coupling bandwidth: Coupling coefficient times center frequency.

Hope this helps.

 

[citizen]

Re: cross coupling

thanks fo r your reply
and also can you give me the ans for what is mean by
external coupling(ke)?
thank you!!!!!!!!

 

[Phytech]

Re: cross coupling

thanks fo r your reply
and also can you give me the ans for what is mean by
external coupling(ke)?
thank you!!!!!!!!

External cpupling kin=(Ripple Band width)/(g0*g1), where g0, g1 are the g values for low pass prototype.

 

[citizen]

Re: cross coupling

hi phytech thank you,
this my example filter with 5th order
center fq:1000 mhz
band width :10 mhz
ripple:0.01

g1 value is 0.7563
now the value for the ke that is external coupling he has given as 12.56 mhz
but with 10 mhz band width it is not right know
then the band width here he has mentioned is not the ripple band width?
thyank you

 

[Phytech]

Re: cross coupling

hi phytech thank you,
this my example filter with 5th order
center fq:1000 mhz
band width :10 mhz
ripple:0.01

g1 value is 0.7563
now the value for the ke that is external coupling he has given as 12.56 mhz
but with 10 mhz band width it is not right know
then the band width here he has mentioned is not the ripple band width?
thyank you

Take your example, if ripple bandwidth is 10 MHz

g1=0.7559
ke=13.2 MHz
3-dB bandwidth of the filter is about 18.6 MHz assuming infinite resonator unloaded Q.

 

[citizen]

Re: cross coupling

hi thank you for your reply
i have another doubt ofcourse very basic one that
in chebyshew filter case bandwidth refers to the ripple bandwidth only know?
i wrote that:

g1 value is 0.7563
now the value for the ke that is external coupling he has given as 12.56 mhz

phytech wrote:

g1=0.7559
ke=13.2 MHz

here the great diference is there that in example he has that 12.56 mhz but from our calculation we are getting that 13.2 mhz
so that the spacing value also change a lot ,
what im asking is there any alternate equation for this?
thank you

 

[Phytech]

Re: cross coupling

hi thank you for your reply
i have another doubt ofcourse very basic one that
in chebyshew filter case bandwidth refers to the ripple bandwidth only know?
i wrote that:

g1 value is 0.7563
now the value for the ke that is external coupling he has given as 12.56 mhz

phytech wrote:

g1=0.7559
ke=13.2 MHz

here the great diference is there that in example he has that 12.56 mhz but from our calculation we are getting that 13.2 mhz
so that the spacing value also change a lot ,
what im asking is there any alternate equation for this?
thank you

Yes, you can find the formula in many filter books, such as "Microwave Filters,
Impedance-Matching Networks, and Coupling Structures" by Matthaei,
Young, and Jones. In your case,

g0=1
g1=2*sin(PI/10)/(sinh(ln(coth(Ripple/17.37)))).

 

[citizen]

Re: cross coupling

thank you phytech,

now i have cleared that equation for g values some times difference ?yes
ok i will follow matthaei book formule , thank you