Capacitive filters: they consist of a feed through capacitor inserted between the transmission line and ground.
If we consider the « cut off frequency » (fc) the frequency for which the attenuation is equal to -3 dB.
When measured, the insertion loss of this type of filter is equal to 20 dB/decade. This type is suitable for applications where source or input impedances are rather high (>1 ohm), and when sharp variations of the insertion loss curve are not required.