Planar QPSK demodulator

DETAILED DESCRIPTION It is an object of this invention to provide a QPSK demodulator in which there is no need for a RF-IF crossover.
It is a further object of this invention to provide such a demodulator which can be constructed in MIC form without the need for holes, connectors, cables or vias.
It is a still further object of this invention to provide a QPSK demodulator in which the RF ports are adjacent one another and in which the IF ports are adjacent one another and in which there is no need for any of the RF and IF signals to leave the plane of the assembly.
These and other objects are achieved according to the present invention by providing RF input ports which are adjacent one another and processing the RF signals through a novel arrangement of 90.
degree.
, 3dB couplers so that the IF output ports can be adjacent one another.
All of the necessary signal crossing is done on the RF side of the system and, therefore, there is no need for any of the signals to leave the plane of the MIC assembly.
In the preferred embodiment, the RF.
sub.
1 signal is supplied to an in-phase power splitter, one output of which is provided as an input to a first 90.
degree.
, 3dB coupler, the other input to which is the RF.
sub.
2 signal.
The outputs of the first coupler are used as inputs to a second identical coupler, one output of which is provided as a RF input to a first mixer.
The other output of the power splitter is fed as one input to a 90.
degree.
, 3dB coupler, the other to which is connected to a resistive termination so that it acts as a power splitter.
The outputs of this third 90.
degree.
3dB coupler are then used as inputs to a fourth 90.
degree.
3dB coupler, one output of the fourth coupler being used as a RF.
sub.
1 input to a second mixer.
The other outputs of the second and fourth mixers are supplied as inputs to a fifth 90.
degree.
3dB coupler, the outputs of which are the phase-orthogonal RF.
sub.
2 inputs to each of the first and second mixers.
The first through fourth couplers are preferably identical and the fifth coupler is preferably a branch line coupler so that a line of symmetry may be maintained between the mixers