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I just started working with microwave system.
I want to do experiment with the waveguide that I have made. The simple experiment like measuring the wavelength, the SWR, The power, The Atenuation, T-shunt, etc are what I want to perform.
What I need now is the Oscilator that can generate the X-band microwave signal (3cm), that I can use with the waveguides. I think approx 10 mWatt will be enough.
Gunndiode or Impatt diode is the common active device to use for waveguide oscillator. If you insists to use BJT or FET with a waveguide resonator:
1. Use BJT (or FET) load the E (S) by a capacitor and low impedance at the C (D) .
Play with the loading elements parameters in order to get "good" negative resistanse at the B (G) about -30 ohms. The equivalent circuit at the B (G) is a negative resistor in series with capacitor.
2. Add transmision line to the B )G) till the equivalent circuit is parallel resonator with negative resistance. (In smith chart S11 at B (G) goes from up to down vs frequency).
3. Now load this port by a parallel resonator (such as Dielectric resonator) and be sure the circuit works as oscillator. Use ADS Osc port tool for example.
4. Practice make an iris in the waveguide top in orderto couplr the B (G) transmision line to the waveguide. It works.
Why don't you use an old X band cavity for alarms ?.
It is tuned at 10595 MHz, but easily tunable around, power about 10 mW and requires only a 8 V dc.
Also is installed a Mixer diode useful for other applications.
The only drawback is that the RF is available only with a waveguide, you need a launcher for coaxial cable.
1. use two different ideal transformers in order to couple the parallel RLC resonator to the lines.
2. For feedback DRO as you are lloking for the gate is 50 ohm loaded. You can use this port as RF port. If you don't have conversion loss limitation use 3dB att. at the RF input port (Gate).
If you use two open stubs at the gate and the drain, you can use a diplexer at the source for output and for RF input.