Coupling network with two series all=pass circuits - connecting each output of zero-degree coupler to inputs of ninety-degree coupler

摘要

The coupling network has a 3dB 90 deg. coupler connected to all pass circuits. A 3dB 0 deg. coupler (1) has two outputs (7, 8) each connected via a first all-pass filter (3, 4) and a second all-pass filter (3, 4) and a second all-pass filter (5, 6) to one of the two inputs (9, 10) to the 3dB 90 deg. couple (2). The coupling network's input signal (E) is applied to the input of the 3dB 0 deg. coupler whilst its two outputs (A1, A2) are taken from the 3dB 90 deg. coupler. The all-pass filters are designed so that a phase difference of roughly 90 deg. exists between the inputs of the 90 deg. coupler at the upper cut-off frequency whilst at the lower cut-off frequency the phase difference is roughly 0 deg.