Multicavity kylstron amplifier

1. APPLICATION OF
MULTI-CAVITY
KLYSTRON AMPLIFIER

2. • The design of the multicavity klystron, together with all the remaining
tubes described here, relies on the fact that transit time will sooner or
later terminate the usefulness of any orthodox tube.
• They therefore use the transit time, instead of fighting it.
• It provided much higher powers than had previously been obtainable at
these frequencies.
MULTICAVITY KLYSTRON :-

3.  It is seen that a high-velocity electron beam is formed, focused and
sent down a long glass tube to a collector electrode which is at a high
positive potential with respect to the cathode.
 The beam passes gap A in the buncher cavity, to which the RF signal to
be amplified is applied, and it is then allowed to drift freely, without
any influence from RF fields, until it reaches gap B in the output or
catcher cavity.
 oscillations will be excited in the second cavity which are of a power
much higher than those in the buncher cavity, so that a large output can
be achieved.
1. TWO CAVITY KLYSTRON AMPLIFIER

4.  Consider the situation when there is no voltage across the gap. Electrons
passing it are unaffected and continue on the collector with the same
constant velocities they had before approaching the gap.
 After an input has been fed to the buncher cavity, an electron will pass gap
A at the time when the voltage across this gap is zero and going positive.
Let this be the reference electron y. It is of course unaffected by the gap,
and thus it is shown with the same slope on the Applegate diagram as
electrons passing the gap before any signal was applied.

5.  Four cavities are shown in the klystron amplifier schematic diagram
and up to seven cavities have been used in practice. Partially bunched
current pulses will now also excite oscillations in the intermediate
cavities, and these cavities in turn set up gap voltages which help to
produce more complete bunching.
 Having the extra cavities helps to improve the efficiency and power
gain considerably. The cavities may all be tuned to the same frequency,
such synchronous tuning being employed for narrowband operation
 It should be noted that cavity Q is so high that stagger tithing is a
“must” for bandwidths much over 1 percent.
MULTICAVITY KLYSTRON AMPLIFIER

6.  Multicavity klystron amplifiers suffer from the noise caused
because bunching is never complete, and so electrons arrive at
random at the catcher cavity. This makes them too noisy for use in
receivers, but their typically 35-dB noise figures are more than
adequate for transmitters.
2. THREE CAVITY KLYSTRON AMPLIFIER:-
Fig. 3 cavity klystron Amplifier

7. Fig.Four cavity klystron amplifier

8.  The multicavity klystron is used as a medium-, high- and very high-
power amplifier in the UHF and microwave ranges.
 The frequency range is from about 250 MHz to over 95 GHz.
 The gain of klystrons ranges from 30-35 dB at UHF to 60-65 dB in the
microwave range.
 The two-cavity klystron oscillator has fallen out of favor, having been
displaced by CW magnetrons, semiconductor devices and the high gain
of klystron and TWT amplifiers.
PERFORMANCE AND APPLICATIONS:

9. DIFFERENT APPLICATIONS OF KLYSTRON AMPLIFIER:-

10. 1.UHF-TV TRANSMITTER:-
Frequency range:-0.5GHZ-0.9GHZ
Power required:- 55kW
Television broadcasting uses UHF channels between 503 and 694 MHz

11. • UHF television broadcasting is the use of ultra high frequency (UHF) radio
for over-the-air transmission of television signals. UHF frequencies are used
for both analog and digital television broadcasts.
• UHF channels are typically given higher channel numbers, like the US
arrangement with VHF channels 2 to 13, and UHF channels numbered 14 to
83.
• Major telecommunications providers have deployed voice and data cellular
networks in UHF/VHF range. This allows mobile phones and mobile
computing devices to be connected to the public switched telephone
network and public Internet.
• UHF television broadcasting fulfilled the demand for additional over-the-air
television channels in urban areas. Today, much of the bandwidth has been
reallocated to land mobile, trunked radio and mobile telephone use. UHF
channels are still used for digital television.

12. Complete block schematic of T.V transmitter.

13. 2.Satellite Communication at ground station
Frequency range:- 6-14GHz
Power required:- 8kW

14. In satellite communication, the Intermediate Frequency (IF) can be chosen as 70
MHz by using a transponder having bandwidth of 36 MHz. Similarly, the IF can
also be chosen as 140 MHz by using a transponder having bandwidth of either
54 MHz or 72 MHz.
Up converter performs the frequency conversion of modulated signal to higher
frequency. This signal will be amplified by using High power amplifier. The
earth station antenna transmits this signal.
During reception, the earth station antenna receives downlink signal. This is a
low-level modulated RF signal. In general, the received signal will be having
less signal strength. So, in order to amplify this signal, Low Noise
Amplifier (LNA) is used. Due to this, there is an improvement in Signal to Noise
Ratio (SNR) value.
RF signal can be down converted to the Intermediate Frequency (IF) value,
which is either 70 or 140 MHz. Because, it is easy to demodulate at these
intermediate frequencies.

15. 3.RADAR TRANSMISSION

16.  The radar transmitter produces the short duration high-power rf pulses of energy
that are radiated into space by the antenna. The radar transmitter is required to
have the following technical and operating characteristics:
 The transmitter must have the ability to generate the required mean RF power and
the required peak power
 The transmitter must have a suitable RF bandwidth.
 The transmitter must have a high RF stability to meet signal processing
requirements
 The transmitter must be easily modulated to meet waveform design requirements.
 The transmitter must be efficient, reliable and easy to maintain and the life
expectancy and cost of the output device must be acceptable.
 The radar transmitter is designed around the selected output device and most of
the transmitter chapter is devoted to describing output devices therefore:

17.  One main type of transmitters is the keyed-oscillator type. In this transmitter one stage or tube,
usually a magnetron produces the rf pulse. The oscillator tube is keyed by a high-power dc pulse of
energy generated by a separate unit called the modulator. This transmitting system is called POT
(Power Oscillator Transmitter). Radar units fitted with a POT are either non-coherent or pseudo-
coherent.
 Power-Amplifier-Transmitters (PAT) is used in many recently developed radar sets. In this system the
transmitting pulse is caused with a small performance in a waveform generator. It is taken to the
necessary power with an amplifier following (Amplitron, Klystron or Solid-State-Amplifier). Radar
units fitted with an PAT are fully coherent in the majority of cases.
 The picture shows the typical transmitter system that uses a magnetron oscillator and a waveguide
transmission line. The magnetron at the middle of the figure is connected to the waveguide by a
coaxial connector. High-power magnetrons, however, are usually coupled directly to the waveguide.
Beside the magnetron with its magnetes you can see the modulator with its thyratron. The impulse-
transformer and the pulse-forming network with the charging diode and the high-voltage transformer
are in the lower bay of this rack.
 Solid-state transmit/receive modules appear attractive for constructing phased array radar systems.
However, microwave tube technology continues to offer substantial advantages in power output over
solid-state technology. Transmitter technologies are summarized in the following table.

19. 4.POWER OSCILLATOR
 It is possible to produce oscillations in a klystron device which has only one cavity,
through which electrons pass twice.
 This is the Reflex Klystron Oscillator, which will now be described. The Reflex Klystron
Oscillator is a low-power, low-efficiency microwave oscillator. It has an electron gun
similar to that of the multicavity klystron but smaller. Because the device is short, the
beam does not require focusing.
 Having been formed, the beam is accelerated toward the cavity, which has a high positive
voltage applied to it and, as shown, acts as the anode. The electrons overshoot the gap in
this cavity and continue on to the next electrode, which they never reach.
 This repeller electrode has a fairly high negative voltage applied to it, and precautions are
taken to ensure that it is not bombarded by the electrons.
 Accordingly, electrons in the beam reach some point in the repeller space and are then
turned back, eventually to be dissipated in the anode cavity.
 If the voltages are properly adjusted, the returning electrons given more energy to the gap
than they took from it on the outward journey, and continuing oscillations take place .

21. Thank you!!!