Sinusoidal is ideal for this application.
The problem is that didn't give a full specification, so the vacancies have to be filled up first.What about phase shift oscillators?
And what about delay networks?
Unfortunately, I only implemented amplifiers or filters, as well as nonlinear functions, but no oscillator or integrator circuits with high speed (> GHz GBW) OPs. So I can't help you with the detail design. I'm just convinced, that they are feasible. The acceptable phase error should be specfied, however. If the I/Q signals are fed to mixers, I wonder if the suggested frequency divider and respective square wave signals won't be the more convenient solution?
You could try generating the quardature at a fixed frequency and mixing down with two matched downconverters. This eases the requirement on wide bandwidth for the quad hybrid and allows for it to be adjusted.
You could use a 3dB hybrid coupler.
Yes mixing with a higher frequency oscillator could produce the losc signal and filtering of the mixer products would be easierThe last one can be solved with a frequency conversion, i.e., insead of a 1-30 MHz VCO, use for example a 51-80 MHz VCO and beat it with 50 MHz.
No, only one of the inputs needs to be in quadrature to simplify things this wants to be the fixed frequency, but it does not have to be the local oscillator. The variable frequency input is split by an in phase hybrid. As to which one is the local oscillator, if you can keep the level of variable frequency input constant then the fixed frequency would be best being the LO as it is easier to keep a fixed frequency from leaking out and becoming a problem in other parts of your system than it is a variable frequency.One of the two downconverters will then need a 90 deg local oscillator, wouldn't it?
Not really. The phase characteristic of the post-mixer filter does not matter. The output of that filter will be in quadrature with the PLL input regardless of the phase at the input of the filter. The accuracy of the quadrature depends only of the phase detector.In the example given by zorro you would have to supress the 50MHz adequately ( lots of setctions ) while still maintaining good phase match, better than 1 degree, between the filters at 30MHz.