Terminator3
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Hello! I design narrowband microstrip VCO based on s53mv's article (http://lea.hamradio.si/~s53mv/spectana/vco.html).
Instead of BJT i use FET transistor, then phasing lines (calculated for other S-parameters), and resonator microstrip arranged as classical 1-element microstrip filter, not "comb" as in original article. To my surprise very nice second harmonic appeared around oscillator. To check my calculations on feedback phasing lines based on S-parameters, i did not make any output microstrip! So oscillator is just microstrip loop with band-pass filter on one side and FET device on another.
Now i am in search of how to make microstrip output from this oscillator:
1st way) Put T-junction on gate phasing line, add 135deg line and 2*F0 band-pass filter. As couplig area of filter will be around 45deg at F0, then full microstrip length coming off T-junction would be 135+45=180 deg at F0. After fundamental frequency will be reflected by 2*F0 band-pass microstrip, it come back in-phase in parallel feedback loop (180+180=360)
2nd way) Put T-junction on gate phasing line, add 90 deg line at F0, 90 deg stub at F0, and make output line. It would work like biasing line at F0, blocking F0, and giving 2F0 at output. Disadvantage: waste of F0 at 90 deg stub.
3d way) Add directional microstrip coupler at 2F0. I doubt power would be small. But maybe this way oscillator loop would be very effective and output would be still higher than with T-JUNCTION?
Instead of BJT i use FET transistor, then phasing lines (calculated for other S-parameters), and resonator microstrip arranged as classical 1-element microstrip filter, not "comb" as in original article. To my surprise very nice second harmonic appeared around oscillator. To check my calculations on feedback phasing lines based on S-parameters, i did not make any output microstrip! So oscillator is just microstrip loop with band-pass filter on one side and FET device on another.
Now i am in search of how to make microstrip output from this oscillator:
1st way) Put T-junction on gate phasing line, add 135deg line and 2*F0 band-pass filter. As couplig area of filter will be around 45deg at F0, then full microstrip length coming off T-junction would be 135+45=180 deg at F0. After fundamental frequency will be reflected by 2*F0 band-pass microstrip, it come back in-phase in parallel feedback loop (180+180=360)
2nd way) Put T-junction on gate phasing line, add 90 deg line at F0, 90 deg stub at F0, and make output line. It would work like biasing line at F0, blocking F0, and giving 2F0 at output. Disadvantage: waste of F0 at 90 deg stub.
3d way) Add directional microstrip coupler at 2F0. I doubt power would be small. But maybe this way oscillator loop would be very effective and output would be still higher than with T-JUNCTION?
