The filter unit has a center frequency and comprises a first dielectric substrate, a first conducting plane, and at least one transmission arrangement. The at least one transmission arrangement comprises a shunt node which has a shunt connection to the conducting plane. The electrical length of the shunt connection defines the center frequency of the filter unit. The transmission arrangement further comprises a plurality of transmission lines connected in series between an input port and an output port, wherein each port is connectable to auxiliary systems with a system impedance. Moreover, each transmission line has a characteristic impedance and wherein the characteristic impedance of each transmission line is less than the system impedance.