Compact broadband DC-block filter

A compact DC-block broadband filter has been designed and fabricated with a simple and efficient evolutionary design process in this paper. The DC-block filter is based on parallel-coupled three-line structure which can realize a stronger coupling coefficient to reduce the stringent requirements of the line width and spacing comparing to the traditional double-line structure. The simulated fractional bandwidth of the three-line DC-block filter is increased by 16 % than the parallel double-line filter. And the measured responses of the fabricated filter characteristics are in good agreement with the simulated values. The DC-block broadband filter could be widely used in millimeter-wave wide-band mixers, amplifiers, switches and multipliers, etc.