RF Combiner Device Reducing Passive Intermodulation Distortion
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Solution Overview
Problem
Passive inter-modulation distortion (PIM) in radio frequency communication systems, particularly in Distributed Antenna Systems (DAS), causes spurious frequencies to interfere with reception, leading to desensitization due to non-linear devices and imperfect connections, with third-order inter-modulation distortion (IMD3) being the most significant issue.
Innovation Solution
A combiner device with bandpass and low-pass/high-pass filters is used to assign downlink and uplink frequency bands to different antenna connectors, exploiting antenna isolation to minimize IMD3 products, thereby reducing interference and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple radio frequency signals are combined in a non-linear device, then signal distribution capability is improved, but passive inter-modulation distortion occurs generating spurious frequencies that interfere with reception
Solution Approach 1:
The combiner device is divided into multiple independent combination units (M1, M2, etc.), each handling specific frequency bands. This segmentation prevents all signals from interacting in a single non-linear environment, thereby reducing passive inter-modulation distortion while maintaining the ability to distribute multiple radio frequency signals across different antennas.
Solution Approach 2:
Bandpass filters and low-pass/high-pass filters are introduced as intermediary components between signal sources and combination units. These filters selectively pass desired frequency bands while blocking others, preventing unwanted frequency interactions that would generate inter-modulation products in non-linear devices.
2Device complexity
If downlink and uplink signals share the same antenna connector, then device complexity is reduced, but third-order inter-modulation distortion products fall within the reception band causing desensitization
Solution Approach 1:
The system separates downlink and uplink signal paths by assigning them to different antenna connectors (ANT1 for downlink, ANT2 for uplink). This physical segmentation prevents third-order inter-modulation distortion products generated in downlink signals from interfering with uplink reception, thereby maintaining reception sensitivity while managing connector assignments systematically.
Solution Approach 2:
Different antenna connectors are assigned different functional qualities: ANT1 is optimized for downlink transmission while ANT2 is optimized for uplink reception. This local differentiation ensures that each connector handles signals appropriate to its function, preventing inter-modulation interference from affecting reception quality.
3Reliability
If bandpass filters are added to each combination unit to reduce inter-modulation products, then signal quality is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
Instead of using a single complex filter system, the patent divides the filtering function across multiple combination units, each with its own bandpass filter configured for specific frequency bands. This segmented approach improves signal quality by preventing inter-modulation products while distributing the complexity across modular units that are easier to manufacture and maintain.
Solution Approach 2:
Bandpass filters are configured with specific frequency parameters tailored to each combination unit's assigned bands. By optimizing filter parameters (center frequency, bandwidth, rejection characteristics) for each unit's specific function, the system achieves high signal quality without requiring overly complex universal filtering solutions.
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 solution significantly reduces the amplitude of inter-modulation products, enhancing signal quality by distributing downlink signals across both antenna connectors, achieving a better Carrier-to-PIM ratio and minimizing IMD3 interference within the uplink frequency band.
Implementation Method 1
the first and the second combination units M1 and M2 can comprise respective bandpass filters F1-F8 (typically in cavity or ceramics) suitably connected to respective signal connectors CON1-CON8
Implementation Method 2
low-pass filters can be present suitably connected between the signal connectors CON 1-CON8 and the respective bandpass filters F and able to attenuate any harmonic frequencies
Implementation Method 3
exploiting antenna isolation to minimize IMD3 products, thereby reducing interference and improving signal quality
Data Source
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AI summary
The system for the distribution of radio frequency signals, includes a combiner device of radio frequency signals having a plurality of signal connectors, a first antenna connector operatively connected to a first group of signal connectors and a second antenna connector operatively connected to a second group of signal connectors, and two antennas or a dual polarization antenna (A) connected to the antenna connectors, and a distribution device of radio frequency signals connected to the signal connectors. And, depending on the frequency band of the inter-modulation products of third order or higher generated by two downlink signals, one or more signal connectors from the first group or the second group is assigned to the downlink signals.