The Amplitron is a crossed-field amplifier characterized by high peak and average power output, broad bandwidth, exceptionally high efficiency, but low gain.
Description of Amplitron:
· A drawing of the workings of an Amplitron is shown in Fig. 8.30.
· The electrons originate from a continuously coated cathode coaxial to the RF circuit.
· No external heater power is usually required for starting the Amplitron or during operation.
· The anode consists of a series of vanes. It acts as both a slow-wave RF circuit with which the electrons interact and as an electrode for the collection of electrons.
Figure 8.30 Basic structure of the Amplitron.
The Amplitron is a crossed-field device in that the electron beam is perpendicular to both the electric and magnetic fields, just as in the magnetron.
· The space-charge waves in the Amplitron are formed by the interaction between the electron beam and the crossed electric and magnetic fields.
· Figure 8.30 show that the electron beam reenters the interaction space.
· The RF output and the RF input are decoupled.
· In this sense, the RF circuit of the Amplitron is related more to that of the traveling-wave tube than to the magnetron.
· The nonreentrant circuit of the Amplitron permits a broader bandwidth than the reentrant circuit of the conventional magnetron oscillator.
· The Amplitron behaves as a saturated amplifier rather than as a linear amplifier.
· The characteristic of a saturated amplifier is that the magnitude of the RF output is independent of the RF input, but dependent on the d-c input.
· A saturated amplifier is compatible with frequency modulation, and it may be used with radars designed with pulse compression.
· The conversion efficiency of an Amplitron is defined as follows
Efficiency= (RF power output — RF power input)/modulator power input to Amplitron