Asymmetric filters are filters whose response are asymmetric in shape. They are useful for many applications that may require a different requirements between the upper and lower stopband. For example difference in upper/lower cut-off frequency, selectivity and insertion loss. This week video, see an example of an asymmetric filter design that applies impedance scaling to make it a 50-ohm system and frequency transformation to scale its frequency to 1GHz cut-off.
When connecting different electrical networks to form a system design, impedance scaling is one of the factor to watch out for in designing. When the input impedance is different with the output impedance, the network is called unmatched. An unmatched network will result in performance loss to the signal passing through the network. In this demo video, observe how each components are transformed from a 1-Ohm impedance to 50-Ohm. Different components may require different ways of converting the impedance so that it becomes a matching network.
Every microwave filter starts with the lowpass prototype. From there, frequency transformation is applied to come out with the highpass, bandpass or bandstop filter types. Similarly, in the last part of the video, freqeuncy transformation is done to shift the lowpass filter up to the center frequency of 1GHz.