RF Boresighting Continuous Calibration Signal Injection
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Solution Overview
Problem
Conventional Direction Finding (DF) systems face accuracy issues due to phase and amplitude distortions caused by temperature, vibration, and time-variant effects in RF and IF components, which existing calibration methods, such as switched calibration, are insufficient to correct, resulting in bearing angle inaccuracies of around 1 degree.
Innovation Solution
The method involves continuously injecting a calibration signal into the receiver, allowing for simultaneous routing of both the external signal and the calibration signal on the same RF transmission line, with the calibration signal being frequency offset or code division multiplexed, enabling real-time correction without interrupting signal collection, and expanding to include multiple architectures for narrowband, pulse, and wideband boresighting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switched calibration method is used to correct phase and amplitude errors, then bearing angle accuracy is improved, but calibration frequency must be increased from once per day to continuous operation to address millisecond-scale time variant perturbations
Solution Approach 1:
The patent implements continuous calibration by simultaneously injecting calibration signals along with external signals through RF couplers into the receiver channels. This allows calibration to occur without interrupting signal collection, addressing the time-variant perturbations that occur on millisecond scales by continuously updating correction factors rather than performing periodic switched calibration.
Solution Approach 2:
The patent merges the calibration signal path with the external signal path using RF couplers, allowing both signals to coexist on the same transmission line. This combining approach enables simultaneous calibration and signal collection, eliminating the need to switch between calibration and operational modes.
2Ease of operation
If switched calibration is performed once per day or per flight, then system operation is simple, but bearing angle accuracy degrades to roughly 1 degree due to non-linear time variant errors
Solution Approach 1:
The system performs calibration continuously by injecting calibration signals throughout signal collection, ensuring correction factors are constantly updated to track time-variant perturbations. This continuous operation maintains bearing angle accuracy below 1 degree by addressing errors as they occur rather than allowing them to accumulate between periodic calibrations.
Solution Approach 2:
The system extracts calibration data from the received calibration signals and uses this feedback to continuously update correction factors for phase and amplitude errors. This real-time feedback mechanism allows the system to adapt to changing conditions and maintain high accuracy without manual intervention.
3Productivity
If calibration signal is injected simultaneously with external signal on the same RF transmission line, then signal collection continues without interruption, but signal processing complexity increases due to frequency offset and code division multiplexing requirements
Solution Approach 1:
The patent uses frequency offset to distinguish calibration signals from external signals in the frequency domain. By transmitting calibration signals at different frequencies and using code division multiplexing with unique codes for each channel, the system enables selective extraction of calibration data through spectral separation and correlation processing, managing the complexity through structured signal design.
4Ease of manufacture
If narrowband boresight source is used for calibration, then RF tuning is not necessary, but calibration effectiveness is reduced for wideband signals
Solution Approach 1:
The patent employs code division multiplexing where each receiver channel is assigned a unique calibration code. This allows a single narrowband boresight source to simultaneously calibrate multiple channels across wide bandwidths by encoding channel-specific information in the time domain through unique codes, making the calibration system universally applicable to both narrowband and wideband signals without requiring RF tuning adjustments.
Data Source
AI summary
The present invention, Methods for RF or Acoustic Boresighting, is a collection of various methods of accounting for and correcting for the errors that occur in a receiver during signal collection, and are an extension of patent Ser. No. 10/185,022, by using Radio Frequency coupling as opposed to switches. These updated methods enable a means to ensure a collected signal can be calibrated at any point during the signal collection period without having to cease signal collection in order to switch in a reference signal. These methods also account for signal bandwidth and signal type, including wideband, pulse, and continuous signals.