LNA Input Matching Circuit for Jamming Rejection
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Solution Overview
Problem
Existing antenna devices face challenges in reducing cost while enhancing anti-jamming performance, as they require additional circuit elements to block jamming waves, leading to increased size and expense.
Innovation Solution
Incorporating a frequency selection circuit within the initial-stage low-noise amplifier that acts as a filter, setting a high-pass or band-pass cutoff frequency to reject jamming frequencies, thereby eliminating the need for external filters and simplifying the device structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trap circuit or band-elimination filter is provided on the input side of the initial-stage LNA to block jamming waves, then anti-jamming performance is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the frequency selection function and impedance matching function into a single circuit structure. The input matching circuit is designed to simultaneously serve as a high-pass filter with a cutoff frequency of 900 MHz and an impedance matching network, eliminating the need for a separate trap circuit or band-elimination filter. This merging of functions reduces device complexity while maintaining anti-jamming performance.
Solution Approach 2:
The input matching circuit is designed to perform multiple functions: impedance matching between the antenna and LNA, and frequency selection to block jamming waves. By making the matching circuit universal and multi-functional, the patent eliminates the need for additional dedicated filter components, thereby reducing overall device complexity.
2Reliability
If a trap circuit or band-elimination filter is provided on the input side of the initial-stage LNA to block jamming waves, then anti-jamming performance is improved, but device size increases
Solution Approach 1:
The patent merges the frequency selection function and impedance matching function into a single circuit structure. The input matching circuit is designed to simultaneously serve as a high-pass filter with a cutoff frequency of 900 MHz and an impedance matching network, eliminating the need for a separate trap circuit or band-elimination filter. This merging of functions reduces device complexity while maintaining anti-jamming performance.
3Adaptability or versatility
If the pass band of the initial-stage LNA is set to cover all frequency bands for general use, then adaptability is improved, but the device becomes vulnerable to jamming waves from cellular phones and other services
Solution Approach 1:
The patent introduces a dynamic frequency selection mechanism through the high-pass filter with a cutoff frequency of 900 MHz. This dynamic filtering approach allows the LNA to adaptively reject frequencies below the cutoff (including cellular phone bands) while maintaining passivity for higher frequency bands intended for satellite communication, thus resolving the contradiction between broad adaptability and jamming vulnerability.
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 approach effectively blocks jamming waves near the intended signal frequency band, reducing the device's size and cost while maintaining effective signal amplification and frequency selection.
Implementation Method 1
a frequency selection circuit supplied with said input signal for selecting a pass band intended for use from said input signal to produce a selected signal having the pass band, said frequency selection circuit serving as a filter having a low-side cutoff frequency near to said pass band on its low-frequency side, thereby cutting off frequencies lower than the low-side cutoff frequency
Implementation Method 2
a low-noise amplification portion supplied with the selected signal for amplifying the selected signal to produce the amplified signal
Implementation Method 3
said input matching circuit comprising a capacitor and at least one inductor, said capacitor and said at least one inductor having predetermined capacitance and inductance values so as to form a filter having a low-side cutoff frequency near the pass band on its low-frequency side
Implementation Method 4
said input matching circuit comprising a capacitor and at least one inductor, said capacitor and said at least one inductor having predetermined capacitance and inductance values so as to form a filter having a low-side cutoff frequency near the pass band on its low-frequency side
Data Source
AI summary
To provide an antenna device adapted to interrupt jamming waves and enable cost reduction, a high-pass filter (HPF) adapted to interrupt general-use frequencies at least near a low-frequency side of a pass band intended for use is provided as a frequency selection circuit 11A on the antenna 1 side in an initial-stage LNA 2A. By setting a low-side cutoff frequency to 900 MHz, it is possible to prevent reception of frequencies in a general-use frequency band with a high frequency of use as jamming waves. That is, for example, it is possible to prevent reception of frequencies in 800 to 900 MHz band for mobile cellular telephones and higher harmonics thereof as jamming waves. Further, since an additional filter is not required in the antenna device, the circuit structure can be simplified.