When I series two SAW filter, why the attenuation less than sum both of them in stop band region. Each of them (in stop band) have 60dB attenuation but when series them, the attenuation is equal to 85dB. What happening? Why didn't reach to 120dB?
Then, I put a 20dB attenuation between them ( SG --> SAW1 --> 20dB attenuation --> SAW2--> SA ), and the attenuation is equal to 90dB, this meaning only 5dB attenuate with 20dB attenuation. What happening again?
However, the insertion loss is true when series. Each of the have 8dB insertion loss and when both of them is series the insertion loss equal to 16dB.
Thanks in advanced