Magnetron Axial Vane Extensions Decouple Cathode
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Solution Overview
Problem
Magnetrons face issues with high r.f. fields due to capacitive coupling between the cathode and anode, leading to power loss, undesirable radiation, and arcing, which limits their operation at higher frequencies and power levels, especially when the end hat of the cathode terminates below the anode vanes.
Innovation Solution
The magnetron employs axial extensions on alternate vanes that are not connected to the output coupler, providing capacitive coupling similar to that between the cathode and the output coupler, effectively decoupling the cathode from the output and allowing operation at higher frequencies and power levels, including when the end hat terminates below the anode vanes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If neutralising pegs are used to decouple the cathode from the output, then power loss and arcing are reduced, but the magnetron cannot operate at higher frequencies and power levels due to voltage breakdown
Solution Approach 1:
The invention transitions from radial extensions (neutralising pegs) to axial extensions on the vanes. This dimensional change allows the extensions to reach the cathode end hat even when it terminates below the anode vanes, enabling decoupling at higher frequencies and power levels where radial pegs would cause voltage breakdown
Solution Approach 2:
The axial extensions on the vanes act as intermediaries that provide capacitive coupling between the vanes and the cathode end hat. This intermediate coupling structure allows for effective decoupling without the voltage breakdown issues that limit radial pegs at high power levels
2Length of moving object
If the end hat of the cathode terminates below the ends of the anode vanes, then the magnetron structure is compact, but decoupling cannot be achieved with radial extensions due to voltage breakdown
Solution Approach 1:
By extending the vanes axially rather than radially, the invention can reach the cathode end hat in configurations where it terminates below the anode vanes. The axial direction provides the necessary reach without creating the large radial gaps that cause voltage breakdown in compact configurations
3Loss of energy
If a decoupling plate is used to decouple the cathode from the output, then power loss is reduced, but the plate must be sized to be resonant at the operating frequency, limiting design flexibility
Solution Approach 1:
Instead of using a single decoupling plate that must be resonant at the operating frequency, the invention segments the decoupling function into multiple axial extensions on individual vanes. These extensions provide distributed capacitive coupling that achieves decoupling without requiring resonant plate sizing
Solution Approach 2:
The axial extensions on the vanes serve as intermediaries that provide distributed capacitive coupling between the vanes and the cathode end hat. This distributed approach achieves decoupling without the resonant frequency constraints that apply to decoupling plates
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively decouples the cathode from the output, reducing power loss and arcing, enabling stable operation at higher frequencies and power levels, and maintaining the desired π mode without voltage breakdown issues.
Implementation Method 1
The extensions are provided on alternate vanes and are arranged to provide capacitive coupling to the cathode end hat
Implementation Method 2
The magnetron has a cathode arranged coaxially within an anode which has a plurality of resonant cavities defined by vanes
Data Source
Figure 1~2
Figure 3~4
AI summary
A magnetron has a first set of vanes 30 etc which connect by legs 52 to a coaxial output coupler 51 and a second set of vanes 19 etc which (in one embodiment) alternate with the vanes of the first set and are not connected to the output coupler. The vanes of each set are held, for example, by strap rings which may be distributed along the length of the anode, at the same potential as each other, and the polarity of the vanes of one set is opposite to that of the other set. A problem with such a magnetron is that there is capacitive coupling between the cathode and the output coupler 51, which can lead to the coaxial TEM mode propagating along the cathode. According to the invention, additional capacitive coupling is introduced by means of axial extensions 19a etc on the ends of the set of vanes 19 etc which are not connected to the output coupler, and by choice of dimensions, the cathode is substantially decoupled from the output coupler because of the opposite polarity of the two sets of vanes.