Active Noise Source Coupler Layout for Wideband Radiometer Calibration
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Solution Overview
Problem
Existing active noise sources for microwave and millimeter-wave radiometers have noise bandwidth limitations due to SPDT switch design and challenges in achieving a well-defined cold noise source, leading to suboptimal calibration performance.
Innovation Solution
A new active noise source design featuring two switched-biased noise amplifier branches with a directional coupler, allowing for broader noise bandwidth and improved matching, using synchronized biasing and noise-generating devices like resistors or semiconductor devices, and a Lange coupler for noise signal combination and output matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an SPDT switch is used to switch between hot and cold noise sources, then the noise source can be toggled between ON and OFF states, but the noise bandwidth is limited and matching between the noise amplifier and switch becomes challenging
Solution Approach 1:
The patent divides the single switched-biased noise amplifier into two separate switched-biased noise amplifier branches. Each branch independently switches between hot and cold states, avoiding the bandwidth limitations and matching issues of a single SPDT switch configuration. This segmentation allows broader noise bandwidth while maintaining switching capability.
2Device complexity
If a single switched-biased noise amplifier is used, then the structure is simple, but it is very challenging to get a well-defined cold noise source
Solution Approach 1:
The patent combines two switched-biased noise amplifier branches with a directional coupler to merge their noise outputs. This merging approach creates a well-defined cold noise source by combining the characteristics of both branches, achieving superior cold noise definition while managing system complexity through the directional coupler architecture.
3Reliability
If noise bandwidth is expanded, then broader frequency coverage is achieved, but matching and definition of cold noise source becomes more challenging
Solution Approach 1:
The patent introduces a directional coupler as an intermediary device between the two noise amplifier branches and the output. This intermediary component facilitates broadband operation by properly combining the noise signals while maintaining impedance matching and defining the cold noise source characteristic across the expanded frequency bandwidth.
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 improved output matching and wideband operation with a flat Excess Noise Ratio (ENR) characteristic, enhancing calibration accuracy and reliability for radiometers by providing a well-defined broadband noise signal.
Implementation Method 1
two switched-biased noise amplifier branches with a directional coupler, allowing for broader noise bandwidth and improved matching, using synchronized biasing and noise-generating devices like resistors or semiconductor devices
Implementation Method 2
a directional coupler having a pair of input ports connected to combine noise outputs from the first and second switched-biased noise amplifiers
Data Source
AI summary
An active noise source apparatus includes a pair of a first and second switched-biased noise amplifier branches (22, 23). A directional coupler (24) having a pair of input ports (3, 4) connected to combine the noise outputs from the first and second switched-biased noise amplifiers. One output port (4) of the directional coupler (24) is connected to a matched termination (Rtermination) and another output port (2) of the directional coupler (24) is connected to an output (25) of the active noise source.