Filter Parameters

Rejection

The attenuation provided by a filter at frequencies outside its passband, quantifying the ability to suppress unwanted signals, measured in dB relative to the passband insertion loss

Category: Filter Parameters

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Understanding Rejection

Rejection specifications define the minimum attenuation at specific frequencies or frequency ranges in the stopband. Higher rejection requires more filter sections (poles) or steeper roll-off topologies, but increases insertion loss and group delay variation.

Key rejection specifications include adjacent channel rejection, image rejection, and spurious response rejection. The shape factor (ratio of stopband to passband bandwidth at specified attenuation levels) characterizes the transition steepness.

Common Questions

Frequently Asked Questions

How is rejection different from isolation?

Rejection refers to frequency-selective attenuation by a filter, while isolation refers to port-to-port leakage in components like circulators, switches, or couplers.

What determines achievable rejection?

Filter order (number of poles), topology (Chebyshev vs Butterworth vs elliptic), and the quality factor (Q) of the resonators determine the achievable rejection.

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