Radiometer Replacement Signal Mechanism for Pulsed Mode Saturation
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Solution Overview
Problem
Radiometers used for calibrating radars face issues with signal saturation and non-linearities during temperature measurement, leading to biased and reduced precision estimates due to the radiometer's self-noise temperature, especially when operating in pulsed mode with close frequency bands.
Innovation Solution
A radiometer with a replacement signal mechanism that replaces the detected or filtered signals during prevention intervals to maintain the corrected signal within a targeted range, using a sample-and-hold device or switch circuit to form a replacement signal of constant or zero value, thereby preventing saturation and non-linearities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the radiometer operates in pulsed mode with detection periods and rest periods, then the radar can be calibrated without interference from radar transmissions, but the signal may saturate and exit the targeted range causing non-linearities and reduced measurement precision
Solution Approach 1:
The patent applies preliminary action by forming a replacement signal in advance during rest periods before the detection period begins. The replacement signal is prepared using the last valid filtered signal value, so that when saturation occurs during detection, the correction means can immediately use this pre-prepared replacement signal to maintain the corrected signal within the targeted range, preventing non-linearities before they occur.
Solution Approach 2:
The patent introduces a replacement signal as an intermediary element between the filtered signal and the correction process. When the filtered signal exits the targeted range, the replacement signal acts as a mediator to substitute for the invalid filtered signal, allowing the correction means to continue operating within linear conditions while the filtered signal recovers.
2Measurement precision
If the low-pass filtering time constant is increased to improve signal-to-noise ratio, then measurement precision improves, but the speed of establishing temperature estimates is reduced due to memory effects
Solution Approach 1:
The patent applies dynamics by making the effective filtering time constant adaptive rather than fixed. When saturation is detected, the replacement signal mechanism dynamically resets the filtering process, effectively reducing the memory effects of the low-pass filter. This allows the system to maintain high precision during normal operation while quickly recovering from saturation events, thus improving overall measurement speed without sacrificing precision.
3Measurement precision
If the radiometer uses a long sliding time window for low-pass filtering, then noise is reduced and signal quality improves, but the delay in establishing the video signal increases
Solution Approach 1:
The replacement signal is formed in advance during rest periods, storing the last valid filtered signal value. When saturation occurs, this pre-computed replacement signal is immediately applied, avoiding the need to wait for the long sliding time window to naturally recover. This preliminary preparation significantly reduces the time loss associated with signal establishment while maintaining the noise reduction benefits of long filtering windows during normal operation.
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The radiometer (2) has a formation unit (212) for forming a replacement signal to replace a signal (Sd) representative of a temperature detection period, a signal (Sf) or a bias signal (Sb) representative of noise temperature. A control unit (221) controls the formation during a prevention interval. The interval starts at the end of the detection period with a delay of positive/null duration and terminates at the start of the next detection period with a delay of positive duration. The delay durations are less than a duration of rest period and a duration of detection period, respectively. An independent claim is also included for a method for measuring temperature of a radiometric scene using a radiometer.