DAS Duplexed Port Isolation Circuit for Small Frequency Gaps
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Solution Overview
Problem
Distributed antenna systems (DASs) face challenges in providing adequate isolation between downlink and uplink communications paths when the frequency gap between them is small, leading to potential signal distortion and oscillations due to leakage.
Innovation Solution
The implementation of a frequency-independent isolation circuit using a directional coupler and circulator to isolate uplink communications signals from downlink paths, independent of the frequency gap, ensuring effective separation and minimizing signal interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a duplexer is used to isolate downlink and uplink communications paths, then isolation between paths is achieved, but the isolation effectiveness deteriorates when the frequency gap between downlink and uplink signals is small
Solution Approach 1:
The patent introduces a circulator as an intermediary device between the downlink and uplink communications paths. The circulator directs signals in a specific rotational direction, allowing downlink signals to pass through to remote antenna units while preventing uplink signals from leaking back to the downlink path. This mediator device effectively isolates the two paths regardless of frequency separation.
Solution Approach 2:
The patent replaces the traditional frequency-dependent duplexer (which relies on electromagnetic filtering based on frequency gaps) with a circulator-based system that uses signal direction control. This substitution eliminates the dependency on frequency separation and provides consistent isolation effectiveness across different frequency gaps.
2Reliability
If a frequency-independent isolation circuit is implemented using directional coupler and circulator, then isolation effectiveness is maintained across all frequency gaps, but device complexity increases
Solution Approach 1:
The circulator performs multiple functions within a single device: it directs downlink signals to remote antenna units, prevents uplink signal leakage to the downlink path, and provides isolation without requiring frequency-based filtering. This multi-functionality reduces the need for additional frequency-dependent components.
Solution Approach 2:
The patent changes the isolation mechanism from frequency-based (duplexer) to direction-based (circulator). By changing the fundamental parameter used for signal separation from frequency to propagation direction, the system achieves frequency-independent isolation while using a compact, integrated circuit approach.
3Reliability
If costly duplexer components are used to achieve isolation, then signal separation is achieved, but system cost increases
Solution Approach 1:
The patent replaces expensive, frequency-dependent duplexer components with a circulator-based isolation circuit that provides equivalent or superior isolation performance. The circulator approach uses simpler, more cost-effective components that do not require precise frequency tuning or multiple filtering elements.
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 provides reliable isolation between uplink and downlink signals, even with small frequency gaps, preventing signal distortion and maintaining communication quality in DASs, while supporting a wide range of radio bands without the need for costly duplexer components.
Implementation Method 1
a directional coupler to isolate an uplink communications signal from the downlink communications path
Implementation Method 2
to isolate the uplink communications signal from the second portion of the downlink communications signal directed to the third coupler port
Data Source
AI summary
Frequency independent isolation of duplexed ports in distributed antenna systems (DASs) is disclosed. Instead of providing a duplexer in a DAS that provides frequency dependent separation between downlink and uplink communications signals, an isolation circuit is provided. The isolation circuit is coupled to a duplexed port that provides downlink communications signals to the DAS and receives uplink communications signals from the DAS. To isolate uplink communications signals from the downlink communications path, the isolation circuit includes a directional coupler. The directional coupler provides frequency independent isolation between uplink communications signals and a downlink communications path in the DAS. Further, to isolate downlink communications signals from the uplink communications path, the isolation circuit includes at least one circulator isolator. The circulator(s) acts as a one-direction device, allowing uplink communications signals to flow to the directional coupler with minimal attenuation while significantly attenuating downlink communications signals flowing from the directional coupler.