Ece 662 microwave electronics l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 33

ECE 662 – Microwave Electronics PowerPoint PPT Presentation


  • 108 Views
  • Uploaded on
  • Presentation posted in: General

ECE 662 – Microwave Electronics. Klystrons March 31, April 7, 2005. General Characteristics. Efficiency about 40% Power output Cw:  1MW Pulsed:  100MW @ 10 GHz Power Gain 15 to 70 dB Frequency  100 GHz Characteristics High pulse and CW power Medium bandwidth (2-15 %).

Download Presentation

ECE 662 – Microwave Electronics

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Ece 662 microwave electronics l.jpg

ECE 662 – Microwave Electronics

Klystrons

March 31, April 7, 2005


General characteristics l.jpg

General Characteristics

  • Efficiency about 40%

  • Power output

    • Cw:  1MW

    • Pulsed:  100MW @ 10 GHz

    • Power Gain 15 to 70 dB

    • Frequency  100 GHz

  • Characteristics

    • High pulse and CW power

    • Medium bandwidth (2-15 %)


General characteristics5 l.jpg

General Characteristics


Input cavity l.jpg

Input Cavity

+


Input cavity8 l.jpg

Input Cavity


Bunching of electrons l.jpg

Bunching of Electrons


Time distance applegate diagram l.jpg

Time/Distance Applegate Diagram


Beam coupling coefficient l.jpg

Beam coupling coefficient


Beam coupling coefficient14 l.jpg

Beam coupling coefficient


Electron bunching process l.jpg

Electron Bunching Process

The net result of beam transit through the cavity is a sinusoidal

Beam velocity modulation at cavity frequency 

Faster electrons “catch” up with slower electrons. At a certain

Distance L the electrons have “bunched” together. Here (at L)

A second cavity is placed in order to induce microwave fields

In the “output” of “catcher” cavity.


Electron bunching process16 l.jpg

Electron Bunching Process

The distance from the buncher grid to the location of the of dense electron bunching for the electrons at tb is L = v0 (td -tb).

Distances for electrons at ta and tc are

L = vmin (td -ta) = vmin (td -tb+/(2)) (1)

L = vmax (td -tc) = vmax (td -tb-/(2)) (2), where

vmin= v0 {1-(V1)/(2V0)}; V0 =½(m/e)(v02), V1 =Ed, and

vmax= v0 {1+(V1)/(2V0)}; equations (1) and (2) become

L = v0(td -tb)+{v0 /(2)-v0[(V1)/(2V0)](td-tb)-v0[(V1)/(2V0)]/(2)}

L = v0(td -tb)+{-v0 /(2)+v0[(V1)/(2V0)](td-tb)+v0[(V1)/(2V0)]/(2)}


Electron bunching process17 l.jpg

Electron Bunching Process

For electrons at ta, tb, and tc to meet at the same distance L means that terms in both brackets {} must = 0. therefore

td -tb = [(2V0)/(v0 V1)][v0/(2)][1-(V1)/(2V0)] ~ V0/V1,

L ~ v0V0/V1 (space charge neglected & not max degree of bunching)

Transit time in the field free region between grids is

T = t2 - t1 = L/ v(t1) = T0 {1 - [(V1)/(2V0)] sin [t1 - (d)/(2v0)]}

where T0=L/v0 and used (1 + x)-1 ~ 1- x; In radians

T = t2 - t1 = L/ v0 - X sin [t1 - (d)/(2v0)], where

X = (L/ v0) [(V1)/(2V0)] = Bunching parameter of a Klystron


Electron bunching process18 l.jpg

Electron Bunching Process

At the buncher gap a charge dQ0 passing through at a time interval dt0 is given by dQ0 = I0 dt0 = i2 dt2, by conservation of charge, where i2 = current at the catcher gap.

t2 = t0 +  + T0 {1 - [(V1)/(2V0)] sin [t0 + (d)/(2v0)]}

dt2 / dt0 = 1 - X cos [t0 + (d)/(2v0)]

i2 (t0) = I0 / {1 - X cos [t0 + (d)/(2v0)]} = current arriving at catcher.

Using t2 = t0 +  + T0 ,

i2 (t2) = I0 / {1 - X cos [t2 - (L/v0) - [(d)/(2v0)]}

Plot i2 for various X (corresponding to different L providing  and (V1)/(2V0 ) are fixed.)


Electron bunching process20 l.jpg

Electron Bunching Process

 Electron bunching corresponds to current peaks that take place and for X  1; i2 is rich in harmonics of the input frequency which is the resonant frequency of both cavities. (Klystron can be run as a harmonic generator).

Beam current at the catcher is a periodic waveform of period 2/ about a dc current.  expand i2 in a Fourier Series:


Electron bunching process21 l.jpg

Electron Bunching Process


Cavity spacing l.jpg

Cavity Spacing


Catcher cavity l.jpg

Catcher Cavity

Phase of catcher gap voltage must be maintained in such a way that the bunched electrons as they pass through the grids encounter a retarding phase. Thus kinetic energy is transferred to the field of the catcher grid.The fundamental component of the induced current is given by:


Catcher cavity output power l.jpg

Catcher Cavity- Output Power

Rsho = wall resistance of catcher cavity

RB = beam loading resistance

RL = external load resistance

RSH = effective Shunt resistance

I2 = If = fundamental component of the beam current at the catcher cavity

V2 = fundamental component of the catcher gap voltage

Output power delivered to the catcher and the load is given by


Efficiency and mutual conductance of klystron l.jpg

Efficiency and Mutual Conductance of Klystron


Output of klystron l.jpg

Output of Klystron


Reflex klystron oscillator l.jpg

Reflex Klystron Oscillator

Can make an amplifier

oscillate by providing

regenerative feedback

to input terminals.

Simpler is reflex - single

cavity oscillator, but

lower power, 10-500mW,

1-25 GHz, 20-30 % eff.

Widely used in radars.

Key here is to have electrons be repelled such that they return to the

gap in the form of a bunch. Time electron of velocity vi spends in the

gap-repeller space dr is given by


Reflex klystron oscillator30 l.jpg

Reflex Klystron Oscillator

The t1 electrons see

accelerating phase and penetrate farthest into gap-repeller space.

The t3 electrons see

decelerating phase

and spend least time

in gap-repeller space.

Note they all return

when Rf is maximum

in accelerating phase

to give energy back to gap fields.


Reflex klystron oscillator31 l.jpg

Reflex Klystron Oscillator

Theoretical Output Characteristics

of a typical X-band reflex Klystron

for a fixed accelerator voltage, V0.

Average transit time should correspond to (N+3/4) cycles of Rf time where N=0, 1, 2, 3. Optimum positive feedback at cavity resonance, f, occurs when

Frequency, f, changes slightly with repeller voltage - more tuning by

mechanically adjusting the cavity. In general: High Q, Low BW.


Reflex klystron oscillator32 l.jpg

Reflex Klystron Oscillator

Following the same analysis of the 2-cavity klystron amplifier, the

bunching parameter for the reflex is


Reflex klystron oscillator33 l.jpg

Reflex Klystron Oscillator

Note the peak is at

X=2.408, X J1(X)=1.25


  • Login