The Efficiency of Conventional Microwave Tube is largely independent of Frequency upto a certain limit, when frequency increases beyond a certain limit efficiency drastically decreases.
There are few important points that need to be noted when Microwave frequency is increased
Interelectrode Capacitance
The Interelectrode capacitance in vacuum tubes at low or Medium frequency produce large Capacitive reactance with no serious efffect.
The Capacitive reactance become so smalll when the frequency drastically increased
Lead Inductance
Lead Inductance within the tube are effectively in parallel with the interelectrode capacitance, the net effect is to raise the frequency limit, However the inductance of the positive cathode lead is common to both the Grid plate Circuit.
This provide the path for Regenerative Feed back which reduces overall Circuit efficency.
Transient Time
Transient time is the time required for electrons to travel from the Cathode to the plate, this time time is insignficant at lower frequency .
However at the higher frequency the transient time become and appreciable portion of signal cycle and begins to hinder effeciency.
There are few important points that need to be noted when Microwave frequency is increased
- InterElectrode Capacitance
- Lead Inductance
- Electron Transit time
Interelectrode Capacitance
The Interelectrode capacitance in vacuum tubes at low or Medium frequency produce large Capacitive reactance with no serious efffect.
The Capacitive reactance become so smalll when the frequency drastically increased
Lead Inductance
Lead Inductance within the tube are effectively in parallel with the interelectrode capacitance, the net effect is to raise the frequency limit, However the inductance of the positive cathode lead is common to both the Grid plate Circuit.
This provide the path for Regenerative Feed back which reduces overall Circuit efficency.
Transient Time
Transient time is the time required for electrons to travel from the Cathode to the plate, this time time is insignficant at lower frequency .
However at the higher frequency the transient time become and appreciable portion of signal cycle and begins to hinder effeciency.
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