A filter unit with a center frequency, comprising: a first dielectric substrate having a first surface portion and a second surface portion; a first conducting plane located on the first surface portion; and at least one transmission arrangement located on the second surface portion, wherein the at least one transmission arrangement comprises: - a shunt node having a shunt connection to the conducting plane, wherein an electrical length of the shunt connection defines the center frequency of the filter unit and - a plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m) connected in series between an input port and an output port, each port connectable to auxiliary systems (31, 32) with a system impedance; wherein each transmission line (23-1,..., 23-n, 24-1,..., 24-m) has a characteristic impedance (Za-1,..., Za-n, Zb1,..., Zb-m); and wherein the characteristic impedance (Za-1,..., Za-n, Zb1,..., Zb-m) of each transmission line (23-1,..., 23-n, 24-1,..., 24-m) is less than the system impedance, and wherein the plurality of transmission lines are symmetrical about the shunt node with regard to at least the characteristic impedances (Za-1,..., Za-n, Zb1,..., Zb-m) of the plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m), and wherein the shunt node is a single shunt node; wherein the plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m) is divided into a first segment and a second segment, wherein the first segment is connected between the input port and the shunt node, and wherein the second segment is connected between the output port and the shunt node; characterized in that the first segment and the second segment each comprise at least four transmission lines (23-1,..., 23-n, 24-1,..., 24-m) connected in series. a first dielectric substrate having a first surface portion and a second surface portion; a first conducting plane located on the first surface portion; and at least one transmission arrangement located on the second surface portion, wherein the at least one transmission arrangement comprises: - a shunt node having a shunt connection to the conducting plane, wherein an electrical length of the shunt connection defines the center frequency of the filter unit and - a plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m) connected in series between an input port and an output port, each port connectable to auxiliary systems (31, 32) with a system impedance; wherein each transmission line (23-1,..., 23-n, 24-1,..., 24-m) has a characteristic impedance (Za-1,..., Za-n, Zb1,..., Zb-m); and wherein the characteristic impedance (Za-1,..., Za-n, Zb1,..., Zb-m) of each transmission line (23-1,..., 23-n, 24-1,..., 24-m) is less than the system impedance, and - a shunt node having a shunt connection to the conducting plane, wherein an electrical length of the shunt connection defines the center frequency of the filter unit and - a plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m) connected in series between an input port and an output port, each port connectable to auxiliary systems (31, 32) with a system impedance; wherein each transmission line (23-1,..., 23-n, 24-1,..., 24-m) has a characteristic impedance (Za-1,..., Za-n, Zb1,..., Zb-m); wherein the plurality of transmission lines are symmetrical about the shunt node with regard to at least the characteristic impedances (Za-1,..., Za-n, Zb1,..., Zb-m) of the plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m), and wherein the shunt node is a single shunt node; wherein the plurality of transmission lines (23-1,..., 23-n, 24-1,..., 24-m) is divided into a first segment and a second segment, wherein the first segment is connected between the input port and the shunt node, and wherein the second segment is connected between the output port and the shunt node; characterized in that the first segment and the second segment each comprise at least four transmission lines (23-1,..., 23-n, 24-1,..., 24-m) connected in series.