TCAS Antenna Phase Calibration for Omnidirectional Pattern
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Solution Overview
Problem
The integration of TCAS and Mode S functions in the Integrated Surveillance System (ISS) requires the TCAS antenna to form an omnidirectional pattern, but uncontrolled phase differences in the antenna cables and ISS components due to length variations and environmental changes degrade this pattern, affecting the functioning of the ISS, especially the Mode S functions.
Innovation Solution
A self-calibrating transmitter system with a phase offset device and processor that determines and compensates for phase shifts in the antenna cables and ISS components, allowing the TCAS antenna to maintain an omnidirectional pattern, even when the aircraft is in motion, by adjusting phase offsets to ensure all antenna ports are in phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the TCAS antenna is used for both TCAS and Mode S functions in the Integrated Surveillance System, then the system integration and versatility are improved, but the antenna cable length differences cause uncontrolled phase shifts that degrade the omnidirectional pattern
Solution Approach 1:
The patent applies parameter changes by adjusting the phase shift introduced by each cable through electronic phase compensation. The system measures the actual phase shift of each cable and introduces an equal and opposite phase shift to compensate, thereby maintaining the required phase relationships for omnidirectional operation despite cable length variations.
Solution Approach 2:
The patent implements feedback by measuring the actual phase shift of each antenna cable using a signal generator and phase detector, then using this measurement to calculate and apply the appropriate compensation phase shift. This closed-loop approach ensures that the omnidirectional pattern is maintained despite variations in cable characteristics.
2Reliability
If cable replacement is performed to restore functionality, then the system reliability is improved, but the new cable may have different length and phase characteristics that require recalibration
Solution Approach 1:
The patent applies self-service by enabling the system to automatically measure and compensate for cable phase shifts without requiring manual intervention or external calibration equipment. The built-in signal generator and phase detector allow the system to self-calibrate, reducing maintenance time and complexity.
Solution Approach 2:
The patent applies preliminary action by performing the phase calibration measurement and compensation setup as a routine maintenance procedure. By establishing the calibration process in advance and making it part of the system's normal operation, the patent ensures that cable replacements can be quickly integrated without extensive recalibration.
3Stability of the object's composition
If environmental conditions and cable bundling are controlled to maintain phase stability, then the phase shift consistency is improved, but the system flexibility and ease of installation are reduced
Solution Approach 1:
The patent replaces mechanical control methods (physical cable routing constraints, fixed installations) with an electronic measurement and compensation system. Instead of controlling phase stability through mechanical means, the system uses electronic phase detection and adjustment to achieve the same result, thereby eliminating the need for restrictive installation requirements.
4Manufacturing precision
If the cable length differences are minimized during installation, then the initial phase alignment is improved, but the phase drift over time and temperature changes still occurs
Solution Approach 1:
The patent implements feedback by continuously monitoring or periodically measuring the phase shift of each cable and adjusting the compensation accordingly. This ongoing feedback mechanism corrects for phase drift caused by temperature changes, aging, and other environmental factors, maintaining stable operation over the system's lifetime.
Data Source
AI summary
Measurements of frequency and/or phase are taken at the signal ports (S1-S4) of an ISS device (10). These measurements are used to determine phase errors within the ISS device, and phase errors due to the antenna cables (C1-C4). On port, (e.g., S1) is selected as the reference port and then, based on these determined phase errors, offsetting phase errors are determined to correct the phase for the other ports (e.g., S2, S3, S4) with respect to the reference port. The signals at the antenna ports (A1-A4) are then in phase when an omnidirectional antenna pattern is desired from the TCAS antenna array (16). One in embodiment the frequency of the calibration signal is fixed; in another embodiment two different, fixed frequencies are used; and in still another embodiment the frequency is swept to achieve a predetermined measured phase difference.