Partially Strapdown Radar Antenna Inertia Reduction
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Solution Overview
Problem
The addition of stabilizing gyros to a gimbal-mounted antenna in radar-guided missiles increases antenna inertia, worsening response times, especially when engaging highly maneuverable targets.
Innovation Solution
A partially strapdown angle tracking radar system using a steerable beam antenna with a recursive estimator and inertial reference unit, converting body rate and receiver signals into electronic frame coordinates to estimate target direction and angular velocity, and guiding the missile with a Kalman filter-based system that accounts for gyro and receiver errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If stabilizing gyros are added to a gimbal-mounted antenna, then antenna stability is improved, but antenna inertia increases and response time worsens
Solution Approach 1:
The system separates the stabilization function from the antenna assembly by using a strapdown inertial reference unit fixed to the missile body, while the antenna remains lightweight and gimbal-mounted without additional gyros. This segmentation allows each component to perform its function optimally without the penalty of added inertia.
Solution Approach 2:
The patent introduces an electronic frame of reference as an intermediary between the physical antenna and the target tracking system. This electronic frame, maintained by the strapdown inertial reference unit, allows the antenna to remain stationary while the beam is electronically steered to track the target, eliminating the need for heavy mechanical stabilization.
2Measurement precision
If a gimbal-mounted antenna with stabilizing gyros is used, then target tracking accuracy is improved, but system complexity and inertia increase
Solution Approach 1:
The patent replaces the mechanical stabilization system (gimbals with mounted gyros) with a strapdown inertial reference system that uses accelerometers and rate gyros fixed to the missile body. This substitution eliminates complex mechanical linkages while maintaining tracking accuracy through computational methods and an electronic frame of reference.
Solution Approach 2:
The system creates an electronic copy of the inertial reference frame that is processed computationally to determine target position and velocity. This electronic frame serves as a virtual model that replaces the need for direct mechanical measurement, simplifying the physical system while maintaining measurement precision.
3Measurement precision
If body rate signals and receiver output signals are converted to electronic frame coordinates, then estimation accuracy of target direction and angular velocity is improved, but processing complexity increases
Solution Approach 1:
The patent employs a recursive estimator that continuously processes body rate signals and receiver output signals in the electronic frame of reference, using feedback loops to refine estimates of target direction and angular velocity. This feedback mechanism improves accuracy by constantly updating estimates based on new measurements while accounting for system dynamics.
Solution Approach 2:
The system transforms physical measurements into a different coordinate system (electronic frame) that simplifies the mathematical processing of target motion parameters. By changing the reference frame parameters, the system can more accurately estimate target direction and angular velocity while managing processing complexity through appropriate coordinate transformations.
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
This solution improves the estimation of target direction and angular velocity, enhancing the missile's guidance capabilities and reducing the impact of gyro and receiver errors, thereby improving response times against maneuverable targets.
Implementation Method 1
an inertial reference unit fixed relative to the body of the missile... consisting of rate gyros i.e., without accelerometers... pitch and yaw rate gyros
Implementation Method 2
The inertial reference unit preferably includes accelerometer means to measure the missile body acceleration
Implementation Method 3
the recursive estimator, comprising a seven state extended Kalman filter... the estimator may comprise a five state extended Kalman filter... the estimator may then comprise a Kalman filter
Implementation Method 4
a steerable beam antenna... for steering the antenna beam onto the target... to provide alignment of one of the coordinates and the estimated sightline
Data Source
AI summary
An angle tracking radar system particularly for a missile with a steerable antenna and gyros strapped down to the missile body—a ‘partially strapdown’ system. The body rate signals, body acceleration signals where provided, and target position signals are converted into an electronic reference frame which is controlled to align with the target sightline, the above body and target signals being employed to produce estimates of target direction, sightline rate and sightline acceleration for use in controlling the missile.