Strapping Theory
For those
interested in the nature of magnetron strapping,
the following
information can be of significance
(pdf)
Keywords:
Cavities, pi-mode,
B -mode, For the eight-cavity magnetron the
n = 4 mode is the pi-mode and has the electric-field pattern in the interaction
space is the pi-mode and has the electric-field pattern in the interaction space
(space between cathode and the anode where the electrons and fields interact),
The pattern of the next-simpler mode (n = 3) of eight-cavity magnetron is
shown..., The n = 0 mode is not employed in a resonant-cavity magnetron because
the fields of this mode do not enter the individual anode cavities, and thus the
cavities do not control the frequency of the mode, ...two component modes are
present simultaneously and the resultant pattern may take a variety of forms
depending upon the relative amplitudes of the components, For example, for the n
= 1 mode.. the pattern is rotated 90 deg if different pairs of anode segments
operate in parallel..., An undesired mode causes interference with pi-mode
operation if its frequency is very nearly equal to the frequency of the pi-mode,
The field in the interaction space is consequently distorted from the
pi-mode..., The impedance presented to the interaction space depends upon the
ratio of the width of segments between adjacent cavities to the width of the
cavity slots and this ratio must be kept reasonably low, Thus a large number of
small cavities is required with the result that undesired modes occur at
frequencies very near that of the pi-mode, Four methods of strapping.....,
Embedding the straps in the block-partially isolates the straps from the
interaction space and thus minimizes the distortion in the interaction-field
pattern caused by the presence of the straps..., The way in which straps
influence magnetron operation may be explained in terms of additinal reactive
elements they introduce into the resonator system.. because each strap can carry
conduction current between the segments joined.. the strap has the effect of
connecting the two segments through an inductance, Since a displacement current
can also flow between a strap and a segment it passes over.. each strap is
coupled to a segment through a shunt capacitance, In the pi-mode each strap
joins segments that are at the same voltage so that only the shunt capacitance
is important....., The combined effect of strap inductance and capacitance is to
reduce the resonator inductance to increase its capacitance slightly.. with the
net result of an increase in the lower order mode frequencies, As a result of
strapping therefore the resonant frequencies of all modes are shifted in a
manner that increases the separation between pi/mode frequency and the
frequencies of all other modes, The extent to which strapping increases the
frequency separation of the modes depends upon the strapping system used,
Unwanted modes may be further suppressed by introducing an asymmetry into the
strapping system.., In the absence of strap breaks degenerate modes may assume
any angular position about the resonator axis.. because these modes normally
take up a position that yields least coupling to the output circuit... strong
oscillations in the modes are possible..
In the meantime,
Rod Burman sent me some photos of a test rig, of which the thinks that it was
used for:
cold-strapping-tuning
Consider also,
or go back to: J. Sayers strapping patent US2546870
Reagard also,
or go back to: H-J Fischer's paper on multi cavity
strapping
Back to:
LMS10 versus CV64
Consider also,
or go back to: Boot and Randall's famous cavity
magnetron patents of 1941
Back to:
Handbooks papers and product information