SPMT Switching Calibration Module for VNA Accuracy
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Solution Overview
Problem
High-frequency Vector Network Analyzers (VNAs) face challenges in accurate calibration due to increasing losses and parasitics in switching structures, making it difficult to maintain sufficiently distinct calibration standards, which leads to accuracy degradation and repeatability issues.
Innovation Solution
A calibration module using single pole multi throw (SPMT) switches with solid state elements and a unique algorithm to generate hybrid reflect and transmission standards, allowing for more than three calibration impedances and a thru connection, with iterative calculations to converge error coefficients to a specified tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If electromechanical switching structures are used to reduce loss, then loss is reduced, but repeatability deteriorates and measurement speed decreases
Solution Approach 1:
The patent replaces electromechanical switching structures with solid-state switching elements (such as PIN diodes, FETs, or Schottky diodes) to eliminate mechanical wear and contact variability. This substitution maintains low loss while significantly improving repeatability and measurement speed, as solid-state switches have no moving parts and provide consistent electrical characteristics across multiple cycles.
2Productivity
If MMIC structures are used to generate calibration standards, then efficiency is improved, but startup cost increases and flexibility deteriorates
Solution Approach 1:
The patent divides the calibration system into separate functional modules: solid-state switching elements, calibration standards, and control circuitry. This segmentation allows each component to be optimized independently and enables modular assembly, reducing the complexity and cost of manufacturing compared to monolithic MMIC approaches while maintaining high efficiency.
Solution Approach 2:
The patent designs a universal calibration module that can accommodate multiple calibration standards and switching configurations through a single integrated architecture. The solid-state switching elements and control circuitry can be reconfigured to support different calibration procedures (e.g., TRL, SOLT) without requiring separate dedicated circuits for each function, thereby reducing startup cost while maintaining versatility.
3Measurement precision
If manual calibration procedures are used, then accuracy can be maintained at lower frequencies, but operator errors increase and maintenance requirements increase
Solution Approach 1:
The patent implements an automatic calibration system where the calibration module self-configures and self-calibrates without requiring manual intervention. The solid-state switching elements are precisely controlled by a controller to present calibration standards in a predetermined sequence, and the calibration algorithm automatically processes measurements to update error terms. This eliminates operator errors and reduces maintenance requirements while maintaining high accuracy.
4Adaptability or versatility
If switching structures are used at higher frequencies, then calibration can be performed, but parasitics increase and accuracy deteriorates
Solution Approach 1:
The patent replaces traditional electromechanical switches with solid-state switching elements that have minimal parasitic inductance and capacitance. The use of planar solid-state devices (PIN diodes, FETs) instead of three-dimensional electromechanical structures reduces parasitic effects, enabling accurate calibration at higher frequencies where conventional switches would introduce excessive parasitics.
Solution Approach 2:
The patent optimizes the electrical parameters of the switching elements and calibration standards to maintain sufficient separation between calibration states across a wide frequency range. By carefully selecting solid-state devices with appropriate impedance characteristics and adjusting the switching timing and control signals, the system maintains accurate calibration even at frequencies where parasitics would normally dominate.
Data Source
AI summary
A calibration module, for use in calibrating a VNA, includes ports connectable to the VNA, calibration standards, and single pole multi throw (SPMT) switches. Each SPMT includes a single pole terminal, multiple throw terminals and a shunt terminal corresponding to each multiple throw terminal. A switching path is between each throw terminal and the single pole terminal, and between each shunt terminal and the single pole terminal. Each switching path includes at least one solid state switching element. The calibration standards are selectively connectable to the ports of the calibration module by selectively controlling the switching elements. Each port of the calibration module is directly connected to a throw terminal of one of the SPMT switches. Also, unique algorithm are provided for calibrating a VNA when using a calibration impedance that is a hybrid of a reflect standard and a transmission standard, which can be achieved using the calibration module.