Stub Transmission Line Notch Filter for Radar Anti-Jamming
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Solution Overview
Problem
Baseband radar systems are vulnerable to CW and narrow band jamming, which can cause false alarms and reduce the effectiveness of military applications, such as terminal altitude sensing for free-falling bombs, due to their inability to distinguish between legitimate signals and jamming signals within the same frequency range.
Innovation Solution
An anti-jam device is implemented using a main transmission line coupled with multiple short-circuited stub transmission lines, where each stub is a multiple of half wavelengths of the desired resonant frequency, providing a frequency stop band and attenuating CW signals while minimizing the impact on baseband pulses, allowing only the leading pulse of a pulse train to reach the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a narrow range gate is used to reduce false alarms from CW signals, then the probability of false alarms decreases, but the system complexity increases due to the need for a moving range gate
Solution Approach 1:
The invention extracts and removes the CW jamming signal component from the received signal by using a notch filter tuned to the jammer frequency, separating the harmful CW component from the useful baseband pulse signals, thereby eliminating false alarms without requiring complex moving range gate mechanisms
Solution Approach 2:
The invention introduces an intermediary notch filter between the receiver antenna and the baseband receiver that selectively attenuates CW jamming signals at specific frequencies while allowing baseband pulses to pass through, serving as a mediator that protects the receiver from jamming without adding mechanical complexity
2Measurement precision
If the receiver is made more sensitive to detect weak baseband pulses, then the detection capability improves, but the susceptibility to CW jamming increases
Solution Approach 1:
The invention applies local quality by making the receiver signal path selectively sensitive - highly sensitive to baseband pulse frequencies while being strongly attenuating at CW jammer frequencies through the notch filter, creating different sensitivity characteristics for different signal types at different locations in the frequency spectrum
Solution Approach 2:
The notch filter acts as an intermediary that allows weak baseband pulses to pass through to the sensitive receiver while blocking strong CW jamming signals, enabling the receiver to maintain high sensitivity without proportionally increased jamming susceptibility
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 configuration effectively cancels CW jamming signals over a narrow band of frequencies, ensuring the baseband receiver receives signals free of interference and maintaining the system's range resolution and accuracy, thus enhancing the radar's susceptibility to jamming resistance.
Implementation Method 1
Each of the stub transmission lines is of a length that is a multiple of a half wavelength of a desired resonant frequency and in combination provides a desired frequency stop band in the steady state operating condition
Implementation Method 2
a baseband pulse coupled to the main transmission line is a transient thereon and propagates to the input terminals of the receiver while experiencing attenuation caused only by the reflection coefficients at the coupling plane between the main transmission line and each of the stub transmission lines
Data Source
AI summary
A filter which highly attenuates CW signals within specified frequency bands while allowing baseband pulses to pass therethrough with relatively low attenuation is provided. The filter comprises a main transmission line and stub transmission lines that are coupled in parallel relationship with the main transmission line. Each of the stub transmission lines is terminated with a short circuit or other appropriate impedance and is of such a length that a pulse coupled thereto from the main transmission line and reflected from the terminating impedance will arrive at the coupling plane with the main transmission line after the pulse propagating on the main transmission line has completely passed the coupling plane, thus eliminating the possibility of cancellation of any portion of the propagating pulse. The length, spacing and terminating impedance of each of the stub transmission lines is selected to provide stop bands for CW signals so that a pulse is coupled to the output terminals of the filter that is substantially free of CW interfering signals that may exist at the input terminals thereof.