Multi-Stage GNSS LNA Filtering for L1 Band Interference Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing GPS-based devices with antenna LNA filters are inadequate in filtering out interference from stronger ground-based transmissions in the frequency spectrum near the L1 band, such as those from LightSquared's network, due to design assumptions based on weaker satellite signal strengths.
Innovation Solution
The implementation of a multi-stage LNA filter configuration, including a first LNA stage connected to an antenna, a second stage with a surface acoustic wave (SAW) filter and LNA, and a third stage with another SAW filter and LNA, to effectively attenuate out-of-band frequencies and maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If filters are designed based on assumptions about weak satellite signal strength in the 1525-1559 MHz band, then the filter design is simpler and cost-effective, but the filter cannot sufficiently attenuate stronger ground-based transmissions from networks like LightSquared
Solution Approach 1:
The filter is divided into multiple stages (first LNA stage, second LNA stage with SAW filter, third LNA stage with SAW filter) rather than using a single filter stage. This segmentation allows progressive attenuation of out-of-band frequencies while maintaining signal integrity, resolving the contradiction between design simplicity and interference rejection capability.
Solution Approach 2:
The patent changes the filtering parameters by using SAW filters with specific center frequencies (1575.42 MHz for L1 band) and bandwidths (20 MHz) that are optimized for GNSS signals. This parameter optimization enables the filter to effectively reject ground-based transmissions while preserving weak satellite signals, addressing the contradiction between ease of manufacture and interference protection.
2Object-affected harmful factors
If multi-stage LNA filter configuration with SAW filters is implemented, then out-of-band interference is significantly reduced, but device complexity increases
Solution Approach 1:
The patent merges the LNA (low-noise amplifier) and SAW filter functions into integrated stages, where each stage combines amplification and filtering capabilities. This merging reduces the overall device complexity compared to using separate LNA and filter components, while still achieving significant out-of-band interference attenuation.
Solution Approach 2:
Each LNA stage serves multiple functions: it amplifies the weak GNSS signals while simultaneously providing filtering through the integrated SAW filter. This multi-functionality reduces the need for additional separate components, thereby managing device complexity while maintaining effective interference rejection.
3Measurement precision
If filters assume weak signal strength from satellite transmissions, then positional accuracy can be maintained under normal conditions, but accuracy degrades when exposed to stronger ground-based transmissions
Solution Approach 1:
The multi-stage LNA filter with SAW filters is designed to preemptively counteract potential interference from ground-based transmissions before they can degrade the GNSS signal. By implementing progressive filtering stages tuned to the L1 band center frequency, the system prepares in advance to reject out-of-band signals, ensuring reliable positional accuracy whether the interference source is weak satellite signals or strong ground-based transmissions.
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 significantly reduces out-of-band interference while maintaining signal gain within the L1 band, improving positional accuracy of GNSS devices by effectively filtering stronger interference from ground-based transmissions.
Implementation Method 1
A second LNA stage, connected to the output of the first LNA stage, has a surface acoustic wave (SAW) filter and an LNA
Data Source
AI summary
A low-noise amplifier (LNA) filter for use with global navigation satellite system (GNSS) devices is disclosed. A first LNA stage, which is configured to connect to an antenna configured to receive GNSS signals, includes an LNA. A second LNA stage, which is connected to the output of the first LNA stage, has a surface acoustic wave (SAW) filter and an LNA. A third LNA stage, which is connected to the output of the second LNA stage, also has a SAW filter and an LNA.