Microwave delay equalizer comprising a pair of distributed-constant_ elements as a directional coupler

A microwave delay equalizer for equalizing a delay distortion, inherent in an input signal of a microwave frequency band including a predetermined frequency, to produce an output signal of said frequency band, said output signal being substantially free of said delay distortion, said equalizer including an input and an output terminal for said input and output signals, respectively, a directional coupler having a first, a second, a third, and a fourth port, and a first and a second resonator coupled in said band to said directional coupler, said input and output terminals being substantially parallel to a predetermined direction having a first and a second sense and connected to said first and second ports, respectively, said coupler being capable of providing directional coupling in said band to make said input signal supplied thereto from said input terminal appear as said output signal supplied therefrom to said output terminal and appear as a pair of phase-shifted signals at said third and fourth ports, respectively, said phase-shifted pair having a phase difference relative to each other, said first and second resonators being resonant substantially to said frequency, wherein the improvement comprises:

• a grounded conductive base member having a principal surface having, in turn, a center area and a pair of side areas contiguous with said center area and disposed on either side thereof in a direction transverse to said predetermined direction;
• said first and second ports being disposed over said central area and offset with respect to one another along a direction transverse to said predetermined direction;
• said directional coupler comprising a first and a second distributed-constant element extended substantially along said predetermined direction from said first port in said first sense to said third port and from said second port in said second sense to said fourth port, respectively;
• and electromagnetically coupled to each other, each of said first and second distributed-constant elements having a length substantially equal to an odd integral multiple of a quarter wavelength of a signal in said each element of said frequency, said third and fourth ports being unconnected;
• said first and second resonators being disposed over respective ones of said side areas and connected to said conductive base member and electromagnetically coupled to said first and second distributed-constant elements, respectively.