Traveling-wave tube limiters

Good broad-band microwave limiters can be built by appropriately modifying conventional traveling-wave tubes. For example, with a single one-watt tube modified suitably the output power could be held constant to within ±½ db over a range of input power of approximately 20 db. By modifying two such tubes in the proper way and using them in cascade the range of input power for limiting could be increased to greater than 45 db, and this accomplished over a 700-mc frequency range centered at S band. This was done with commercially available traveling-wave tubes. All the necessary modifications were made from outside the tube envelope. Experimental results indicate that beam saturation for these tubes when operated conventionally occurs first under the attenuator section. By increasing the gain between the attenuator and the output coupler, the beam saturation can be made to occur first under the output coupler. This fact was of great use in the development of the limiters.