Microwave semiconductor devices Microwave Tubes Microwave tubes 1 MW 1 KW 1W 1mW Higher power Limited life time High vacuum High potential Average power Microwave semiconductor devices Lower weight Smaller size Longer life time 0.3 1 3 10 30 100 300 Frequency (GHz)

Two possible methods of achieving high output power in microwave system High power tube oscillator Low power semiconductor oscillator High power tube amplifier

Important Parameters Peak power • Average power Efficiency • Gain Bandwidth • Frequency Harmonic and spurious power • Intermodulation products Manufacturability at low cost Relative complexity of operation Relative operating voltage Relative spurious level Gain (dB)  (%) Relative BW (%) Type 1 Low 2 6-15 20-50 1-10 Gridded tube High 40-60 30-70 1-5 Klystron 3 30-50 20-40 30-120 Helix tube 5-40 Coupled cavity tube

Average power Peak power Frequency (GHz) Frequency (GHz) 10 MW 1 MW 100 KW 10 KW 1 KW 100 W 0.3 1 3 10 30 100 300 Frequency (GHz) Average power Klystron Coupled cavity TWT Helix TWT Gridded tube 1000 MW 100 MW 10 MW 1 MW 100 KW 10 K W 0.3 1 3 10 30 100 300 Frequency (GHz) Peak power Coupled cavity TWT Klystron Gridded tube Helix TWT

Klystron Microwave input Microwave output Electron beam Beam collector Electron Gun Intermediate cavity

TWT

Major applications for TWTs include: Amplifiers: Space applications Radar Electron Counter Measure Missile Driver for other high power RF amplifiers

Missile TWTs for Active Seekers Features that influence the design include: Minimal size and weight; Narrow-to-moderate bandwidths;. Off-to-fully-operational turn-on times of one second or less; High efficiency; High reliability after long inactive storage periods. Normally, these TWTs are of the periodic-permanent-magnet (PPM) focused helix variety. They normally utilize unique cathode-heater designs to provide the very fast warm-up required. They typically have multiple stage depressed collectors with conduction cooling.