Which one of the following is transferred locking electron device C antenna?

A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.

This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.

A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.

Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.