S-Band Solid State amplifier development activities

To drive the high power klystrons used in electron accelerators in RRCAT we have undertaken an endeavour to develop state of art solid state S-Band microwave amplifiers indigenously. High power amplifier in S-Band are not easily available and are also quite costly. Indigenous development of amplifiers will not only reduce cost of microwave systems but also increase reliability and efficiency. S-Band pulsed amplifier systems of up to 1kW in S-Band have been developed using a modular design approach in which several gain stages matched to 50 ohms are combined in series to provide high gain and power.

Class C, NPN, S-Band pulsed power transistors have been utilized in these amplifier systems due to their higher efficiency and ruggedness. These amplifiers are being used in microwave systems of the 10 MeV electron LINAC, 20 MeV injector Microtron and for 45MW S Band accelerator component test facility being developed at RRCAT.


indigenously developed S-Band amplifier used as driver for 45MW S-Band klystron used in accelerator component test facility
configuration of the amplifier
Fig. 1 1kW indigenously developed S-Band amplifier used as driver for 45MW S-Band klystron used in accelerator component test facility. Right hand image shows the configuration of the amplifier.

The 1kW microwave amplifier has been constructed with four 300 W S Band Class C NPN transistors independently matched to 50 ohms at the input and the output stage. The matching network was been fabricated on a low loss substrate. Wilkinson divider and combiners have been used to combine the four amplifiers. The amplifier has been built in three separate stages consisting of divider, transistor amplifier pallet and combiner which have been independently tested before assembling. Isolators have been used at the output of each transistor in order to protect it from reverse power.
Input Power in dBm
Fig.2 Gain response of the 1kW amplifier module
 
Pulse shape obtained using a peak power analyzer after 60dB attenuation. (O/P Power 1kW pulsed)
Fig. 3 Pulse shape obtained using a peak power analyzer after 60dB attenuation. (O/P Power 1kW pulsed)
 
300W amplifier developed using two 160W transistors combined via planar Wilkinson combiner
image is of 1 : 4 wilkinson combiner used in 1kW amplifier module
Fig4. 300W amplifier developed using two 160W transistors combined via planar Wilkinson combiner. Right side image is of 1 : 4 wilkinson combiner used in 1kW amplifier module.
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