Single RF Feed GNSS-Iridium Isolation via Diplexer Segmentation
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Solution Overview
Problem
Conventional systems face challenges in isolating Iridium signals from Global Navigation Satellite System (GNSS) signals using a single radio frequency (RF) feed, leading to signal saturation and reduced modem sensitivity due to the proximity of frequencies and limitations in filtering Iridium signals, especially when supporting multiple GNSS constellations.
Innovation Solution
A tracking system employing a radio frequency (RF) signal circulator, an Iridium modem, a low noise amplifier (LNA), a diplexer, a GNSS receiver, and Iridium filter, along with a switch to manage signal transmission and reception modes, ensuring at least 25 dB isolation and maintaining modem sensitivity by filtering out Iridium signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a diplexer is used to isolate GNSS and Iridium signals, then signal isolation is improved, but GNSS receiver sensitivity deteriorates due to insertion loss
Solution Approach 1:
The system divides the signal processing path into separate branches: a GNSS signal path and an Iridium signal path. The diplexer separates the combined RF signals into these distinct paths, allowing independent processing. This segmentation enables effective isolation of harmful Iridium signals from the GNSS receiver while maintaining signal quality through dedicated processing paths.
Solution Approach 2:
The diplexer acts as an intermediary device between the antenna and the signal processors. It mediates the interaction between GNSS and Iridium signals by directing GNSS signals to the GNSS receiver and Iridium signals to the Iridium modem, preventing direct interference while maintaining signal integrity through controlled signal routing.
2Object-affected harmful factors
If filtering Iridium signals in the GNSS path is performed, then signal isolation is improved, but system complexity increases and jamming may occur
Solution Approach 1:
Instead of filtering Iridium signals within the GNSS processing path, the system segments the signal paths at the diplexer stage. This creates a separate Iridium signal path that is processed independently by the Iridium modem, eliminating the need for complex filtering operations in the GNSS path and preventing potential jamming while maintaining clean signal separation.
Solution Approach 2:
The Iridium signal is extracted from the combined RF signal at the diplexer and routed to a dedicated Iridium modem for processing. This extraction removes the Iridium signal from the GNSS processing path entirely, eliminating the need for complex filtering operations and preventing interference with GNSS receiver functionality.
3Device complexity
If a single RF feed is used, then device complexity is reduced, but signal isolation between Iridium and GNSS deteriorates
Solution Approach 1:
The system merges the reception of GNSS and Iridium signals through a single antenna and initial RF feed path, then uses a diplexer to separate them into dedicated processing paths. This merging approach maintains simple hardware architecture while achieving effective signal isolation through the diplexer's frequency-selective routing capabilities.
Solution Approach 2:
The single RF feed path serves multiple functions: it receives both GNSS and Iridium signals, and through the diplexer's frequency-selective properties, it can be configured to route different frequency bands to appropriate processors. This multi-functionality allows a single feed structure to handle multiple signal types while maintaining isolation through intelligent signal routing.
4Object-affected harmful factors
If conventional filtering is used to isolate Iridium signals, then signal rejection is limited to three degrees, but supporting multiple GNSS constellations with frequency differences becomes problematic
Solution Approach 1:
The system segments the signal processing architecture into a GNSS signal path and an Iridium signal path, with each path having dedicated filtering and processing capabilities. This segmentation allows the GNSS path to be optimized for multiple constellations with different frequencies while the Iridium path handles Iridium signal isolation, resolving the conflict between signal rejection and multi-constellation adaptability.
Solution Approach 2:
The system uses dynamic signal routing through the diplexer that adapts to different frequency bands. The diplexer's frequency-selective properties dynamically route GNSS signals (L1, L2, L5 bands) to the GNSS receiver and Iridium signals to the Iridium modem, enabling flexible support for multiple constellations while maintaining effective Iridium signal isolation.
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
The system effectively isolates Iridium signals from GNSS signals using a single RF feed, maintaining sensitivity for both Iridium and GNSS modems, and supports multiple GNSS constellations with improved signal rejection, enhancing the overall performance of the tracking system.
Implementation Method 1
a radio frequency (RF) signal circulator; an iridium modem coupled to a first port of the circulator via a switch; an antenna coupled to second port of the circulator, wherein the circulator passes a signal transmitted by the iridium modem to the antenna when the switch is switched to a first mode
Implementation Method 2
a low noise amplifier (LNA) coupled to a third port of the circulator, wherein the circulator passes received RF signals received from the antenna to the low noise amplifier
Implementation Method 3
a diplexer coupled to an output of the low noise amplifier; a global navigation satellite system (GNSS) receiver coupled to a first output of the diplexer through a GNSS filter
Implementation Method 4
a global navigation satellite system (GNSS) receiver coupled to a first output of the diplexer through a GNSS filter, wherein the GNSS filter filters out iridium signals
Implementation Method 5
an iridium filter coupled to a second output of the diplexer, wherein the iridium filter filters out GNNS signals
Data Source
AI summary
A tracking system comprising: a radio frequency (RF) signal circulator; an iridium modem coupled to first port of the circulator; an antenna coupled to second port of the circulator, wherein the circulator passes a signal transmitted by the modem to the antenna when the switch is switched to a first mode; a low noise amplifier (LNA) coupled to third port of the circulator, wherein the circulator passes RF signals received from the antenna to the LNA; a diplexer coupled to an output of the LNA; a GNSS receiver coupled to a first output of the diplexer through a GNSS filter; an iridium filter coupled to a second output of the diplexer; wherein the switch couples the iridium filter to the modem when the iridium modem is in a receiving mode, and wherein the switch couples the modem to the first port when the modem is in a transmitting mode.