- Millimetre-wave low-loss finline filters, with very sharp cutoff, consisting of a number of notches periodically spaced along the single-ridge finline are described. Measured passband insertion losses ranged 0.5 to 1 dB for Q-band (33 to 50 GHz) filters have been achieved. These results demonstrate the technological advance of millimetre-wave filters using finline integrated circuits. 1984, The Institution of Electrical Engineers. All rights reserved.