Quadrature compensation for orthogonal signal channels

In a system for generation of a carrier for operation with inphase and quadrature data channels, the system comprising:

• an inphase data channel and a quadrature data channel, each of said channels including a first multiplying means, a second multiplying means, and a limiter of signal amplitude interconnecting an output port of said first multiplying means with a first input port of said second multiplying means, said first multiplying means in each channel having an input port for receiving a composite input data signal having orthogonal components;
• an oscillator outputting a reference carrier, and a variable phase offset means for coupling the carrier from said oscillator to each of said data channels, said first multiplying means in each of said channels having a second input port for receiving the carrier from said variable phase offset means, said variable phase offset means outputting inphase and quadrature components of said carrier differing in phase from each other by a nominal value of ninety degrees, the carrier inphase component being applied to said first multiplying means of said inphase channel and the carrier quadrature component being applied to said first multiplying means of said quadrature channel;
• wherein, in said inphase channel, said second multiplying means multiplies together output signals of said limiter of said inphase channel and said first multiplying means of said quadrature channel to provide an inphase channel output signal and, in said quadrature channel, said second multiplying means multiplies together output signals of said limiter of said quadrature channel and said first multiplying means of said inphase channel to provide a quadrature channel output signal;
• said system further comprises a first summing means for extracting a difference between the channel output signals to provide a control signal for said oscillator to establish a frequency of the carrier outputted by said oscillator;
• a second summing means for summing together the channel output signals to provide a command signal for said variable phase offset means to adjust the phase difference between the carrier components, thereby to compensate for a deviation in orthogonality of the components of the input data signal;
• and
• said variable phase offset means comprises a quadrature hybrid unit which includes a first port serving as a primary input port, a second port serving as an output port which provides one-half of power present at said first port with a phase lag of ninety degrees, a third port serving as an auxiliary input port, and a fourth port serving as a further output port providing one-half of power present at said first port with a phase lag of one hundred eighty degrees;
• a power divider connecting a carrier input port of said variable phase offset means to said first and said third ports of said quadrature hybrid unit, said power divider applying a relatively large fraction of carrier power from said oscillator to said first port of said quadrature hybrid unit and a relatively small fraction of the carrier power to said third port of said quadrature hybrid unit;
• and
• a variable attenuator interconnecting said power divider with said third port of said quadrature hybrid unit, said attenuator having circuitry for varying attenuation of a signal applied to said third port of said quadrature hybrid unit in accordance with the command signal of said second summing means, said second port of said quadrature hybrid unit outputting the inphase carrier component to said inphase channel, and said fourth port of said quadrature hybrid unit outputting the quadrature carrier component to said quadrature channel.