High-Power PIN Diode Switch with Magnetically Coupled Microstrip Lines
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Solution Overview
Problem
High-power RF switching circuits for plasma processing systems face challenges in achieving sufficient signal isolation and stability while minimizing size and thermal issues, particularly in the VHF frequency range, due to limitations in existing PIN diode switches using quarter-wavelength resonant transmission lines.
Innovation Solution
A PIN diode switch design featuring microstrip-line-type, folded, quarter-wavelength resonant transmission lines with magnetically coupled and electrically connected parallel sections, arranged to reinforce local magnetic fields, increasing characteristic impedance and reducing RF losses, allowing for a smaller and more reliable switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quarter-wavelength resonant transmission lines are used in PIN diode switches, then isolation between output ports is improved, but the device size and thermal management complexity increase
Solution Approach 1:
The quarter-wavelength transmission line is segmented into multiple parallel sections that are magnetically coupled. This segmentation allows the same isolation performance to be achieved with a more compact structure, as the magnetic coupling between sections enables a reduced physical length while maintaining the required electrical length and isolation characteristics.
Solution Approach 2:
Multiple parallel transmission line sections are nested in close proximity with magnetic coupling, allowing them to share space efficiently. This nested arrangement achieves the required electrical length and isolation performance in a smaller physical footprint compared to traditional sequential arrangements.
2Reliability
If quarter-wavelength resonant transmission lines are used, then isolation is improved, but RF losses increase due to material resistance and dielectric losses
Solution Approach 1:
Dividing the transmission line into multiple parallel magnetically-coupled sections reduces the RF losses. Each section carries a portion of the signal, and the magnetic coupling between sections reduces the overall resistance and dielectric losses compared to a single long transmission line, while maintaining the same isolation performance.
3Ease of operation
If high RF voltage is applied to multi-turn coils, then DC conduction and RF isolation are achieved, but thermal problems and mechanical instability increase
Solution Approach 1:
The patent replaces traditional multi-turn coil structures with planar transmission line implementations. This substitution eliminates the mechanical complexity and thermal management issues associated with high-voltage coils, providing a more stable and reliable structure that is better suited for integrated RF circuits while maintaining DC conduction and RF isolation functions.
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
The design achieves high isolation and low RF losses, enabling reliable operation with reduced size and cost, suitable for high-power applications up to 5 kW, with measured isolation greater than 45 dB and insertion loss below 0.05 dB.
Implementation Method 1
arranged so that electrical current flows in substantially the same direction in adjacent substantially parallel sections to mutually reinforce the magnetic fields associated with the adjacent substantially parallel sections
Implementation Method 2
first and second transmission-line elements including a plurality of substantially parallel sections that are magnetically coupled
Implementation Method 3
the junction capacitance of PIN diode 105 allows a significant portion of the coupled microwave signal to pass through switch 100 when switch 100 is in the 'open' position
Implementation Method 4
PIN diode 105 is reverse biased, presenting very high impedance to the RF signal passing from input terminal 110 to output terminal 115
Implementation Method 5
PIN diode 105 is forward biased, presenting a very low impedance to the RF signal passing from input terminal 110 to the output terminal 115
Implementation Method 6
a distributed, constant-transmission-circuit, quarter-wavelength, resonant transmission line
Implementation Method 7
The impedance of the shorted-at-the-end, quarter-wavelength, resonant transmission line at resonant frequency theoretically should be infinite
Data Source
AI summary
A high-power PIN diode switch for use in applications such as plasma processing systems is described. One illustrative embodiment comprises an input terminal; an output terminal; and first and second transmission-line elements connected in parallel to the input and output terminals, each of the first and second transmission-line elements including a thermoconductive dielectric substrate and a microstrip line disposed on the thermoconductive dielectric substrate, the microstrip line including a plurality of substantially parallel sections that are magnetically coupled, electrically connected in series, and arranged so that electrical current flows in substantially the same direction in adjacent substantially parallel sections to mutually reinforce the magnetic fields associated with the adjacent substantially parallel sections.