A varactor-tuned Gunn oscillator was constructed in an image-line circuit ingrated with a grating antenna. The combined circuit exhibited a 2 percent electronic tuning range corresponding to a frequency steerable range of 4 degrees. The circuit can be produced at low cost in the millimeter-wave frequency band.
Alex M. Kirk, Alex M. Kirk,
"Image-line voltage controllable active antennas", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15763Y (1 October 1991); doi: 10.1117/12.2297855; https://doi.org/10.1117/12.2297855