Parallel Feed Board Base Station Antennas With Low-PIM Stripline
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Solution Overview
Problem
Current base station antenna feed networks suffer from high insertion loss due to microstrip transmission lines and numerous solder joints, which can cause passive intermodulation (PIM) distortion, degrading RF communications performance.
Innovation Solution
The design incorporates a stripline printed circuit board positioned between parallel electrically conductive reflectors, with radiating elements having feed stalks that extend through multiple PCBs and reflectors, reducing the need for solder joints and utilizing a novel connection scheme to minimize PIM distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microstrip transmission lines are used in the feed network, then the antenna can be constructed with conventional PCB technology, but insertion loss increases and electrical performance degrades
Solution Approach 1:
The patent transitions from microstrip transmission lines to stripline transmission lines, changing the electromagnetic field configuration from surface-level to fully embedded between ground planes. This parameter change in transmission line topology reduces radiation losses and improves confinement of RF energy, thereby reducing insertion loss while maintaining PCB manufacturability
Solution Approach 2:
The patent introduces a stripline structure as an intermediary transmission line type between the RF port and radiating elements. The stripline acts as a mediator that provides better electromagnetic confinement and lower loss compared to microstrip, while still being implementable with standard PCB fabrication processes
2Reliability
If numerous solder joints are used to connect phase cables to PCBs, then electrical connections can be established, but PIM distortion increases and RF performance degrades
Solution Approach 1:
The patent extracts and eliminates the phase cables and their associated solder joints from the feed network. By integrating the feed network directly into the PCB traces (using stripline technology), the design removes the external cable connections that were sources of PIM distortion, while maintaining reliable electrical connections through controlled impedance PCB trace design
Solution Approach 2:
The patent merges the phase shifter, power divider, and feed network functions directly into the PCB structure. By combining these previously separate components into a single integrated PCB assembly with stripline traces, the design eliminates multiple interconnection points and solder joints that were generating PIM distortion
3Loss of energy
If stripline feed network is used, then insertion loss is reduced, but electrical connections to individual radiating elements become more difficult
Solution Approach 1:
The patent utilizes the third dimension (Z-axis) by embedding transmission lines between ground planes within the PCB thickness. This dimensional approach allows stripline connections to reach radiating elements mounted on the PCB surface without requiring complex lateral routing, maintaining ease of connection while achieving low loss through the embedded stripline structure
Data Source
AI summary
A base station antenna assembly includes: first and second reflectors, the first and second reflectors having first and second sides, being electrically conductive and being disposed generally parallel to each other to form a gap therebetween; a stripline printed circuit board (PCB) positioned in the gap between the first and second reflectors; a first PCB mounted on the first side of the first reflector; a second PCB mounted on the first side of the second reflector so that the second PCB is positioned in the gap; and at least one first radiating element mounted to a first side of the first reflector, the at least one first radiating element having first and second stalks extending through the first PCB, through the first reflector, through the stripline PCB, through the second PCB, and to the second reflector.