[SOLVED] Phase noise degradation in TWT

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shashy.br

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i am designing an X band transmitter module and have selected TWT as the amplification source for attaining a power level of 300W at the output,
The phase noise at the Input of the TWT is -70dBc/Hz @ 100Hz offset from the carrier at 8.1 GHz ,

1) Does the TWT(Travelling Wave Tube) induce any phase noise degradation ?

2)Is there any calculation for the calculation of degradation?
 

To my experience, the phase noise is generated by oscillators. Only recently it was found that amplifiers also contribute but their contribution to phase noise is some 30-60 dB lower than that from the oscillators.

TWTs are used still in satellite transponders; I have not seen any significant phase noise in the complete channel attributed to the TWT. TWTs are wideband and high-gain devices while the phase noise affecting the demodulator is mostly concentrated around the carrier generated by oscillators. MOst of the phase noise spectrum is from ~ zero to ~100 kHz from the carrier; compare to ~1 GHz TWT bandwidth.
 
Yes, TWT will add some phase noise. You should be able to get this information from the manufacturer for your specific TWT.

For reference, the attachment has some phase noise plots for MPM (TWT).
 

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  • L3 - MPM for RADAR.pdf
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Thank you jiripolivka and pstuckey for sharing your knowledge , i will come back with the data from the vendor
 

Dear all,

I have got the data from the vendor mentioning that the phase noise of my TWT is -100dBc/Hz @ 100Hz offset and at vibration it becomes -75dBc/Hz@100Hz offset.

Also i needed clarification whether the TWT cathode voltage ripple might cause phase noise degradation ? should i start a new thread for this topic?
 


The value of -100 dBc/Hz is so very deep compared to all other sources that it can be neglected.
In oscillators it is known that all vibrations do affect strongly the phase noise close to the carrier.
One can assume that also the cathode voltage as well as other TWT voltages will contribute.

You can certainly start a deeper investigation. As the TWTs are gradually being replaced by solid-state Amplifiers, it will vanish with them sooner or later.
 
Thanks for the reply ,

I will try and implement SSPA based transmitters for future applications.
 

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