Function of PIN modulator in GUNN oscillator ?

The PIN Diode Modulator Circuit is actually a PIN Diode attenuator circuit in which the PIN diode is ?forward biased? by the signal wave while the RF Carrier Wave is also present in the PIN diode. The forward biased Resistance of the PIN diode is (relatively) slowly and continuously varied by the information signal waveform producing a Continuous Amplitude-Modulated RF wave. RF carrier frequency retains its sinusoidal wave-form while the amplitude envelope varies at the modulation frequency!