5G Base Station RF Power Splitter/Combiner Technology and Application Analysis

　　I. Specific Requirements for 5G Base Station Scenarios

　　As core passive devices connecting the radio frequency unit (RU) and antenna array, the 5G base station RF power splitter/combiner needs to be designed to deeply adapt to the core characteristics of base stations: "multi-band, high power, high-density integration, and extreme environment tolerance." Specific requirements focus on three dimensions:

　　1. Frequency Band and Architecture Adaptation Requirements

　　It needs to cover the mainstream 5G operating frequency bands, including Sub-6GHz bands of 3.3~3.6GHz and 4.8~5.0GHz, and millimeter wave bands of 24GHz and 26GHz. Wideband devices need to support ultra-wideband coverage of 1.8~30GHz and adapt to multi-band co-location deployment. At the architectural level, macro base stations need to be compatible with 8-channel or higher Massive MIMO antenna arrays, while micro base stations need to meet the requirements of miniaturized integrated design, with splitters/combiners integrated with filters, antennas, etc., on the same PCB module.

　　2. Power and Signal Fidelity Requirements

　　Macro base station RU output power typically reaches 50~100W, and splitters need to support ≥20W continuous power (CW) carrying capacity and pulse power tolerance of over 100W. Micro base stations have lower power requirements (5~20W), but insertion loss needs to be controlled to ensure coverage. Meanwhile, 5G signals use 64QAM/256QAM high-order modulation, requiring device insertion loss fluctuation ≤0.2dB to avoid signal distortion leading to EVM (Error Vector Magnitude) degradation.

　　3. Environmental and Reliability Requirements

　　Outdoor macro base station equipment must withstand a wide temperature range of -40℃ to +65℃, 1000 hours of salt spray corrosion, and vibration of 10~2000Hz/10g. Indoor micro base stations, although operating in a milder environment, must meet IP54 protection standards and have a mean time between failures (MTBF) ≥ 100,000 hours, adapting to the 7×24-hour continuous operation requirements of base stations.

　　II. Base Station-Level Standards for Core Performance Indicators

　　1. Enhanced Basic Electrical Performance Indicators

　　Insertion Loss (IL): Sub-6GHz band 2-way splitter IL≤0.3dB (total IL≤3.3dB), 4-way splitter ≤6.5dB; millimeter-wave band 2-way splitter IL≤0.6dB (total IL≤3.6dB), requiring suppression of high-frequency losses through low-distribution materials and structural optimization.

　　Isolation: In Massive MIMO scenarios, the isolation of multi-channel splitters should be ≥25dB to avoid beamforming accuracy degradation caused by crosstalk between channels; in co-site deployments, the combiner isolation needs to be increased to ≥30dB to suppress adjacent frequency band interference.

　　VSWR: VSWR ≤1.35 across the entire frequency band, with input/output port impedance matching deviation ≤5%, reducing the impact of reflected power on the RU and preventing damage to the power amplifier.

　　Phase Consistency: For splitters with 8 or more channels, the phase difference between each port should be ≤±1.5°, and the phase fluctuation should be ≤±0.5° when the temperature changes by ±50℃, ensuring the beam pointing accuracy of Massive MIMO.

　　2. Environmental and Reliability Indicators

　　Temperature and Humidity Stability: After 50 cycles of testing at -40℃ to +65℃, IL change ≤ ±0.1dB, VSWR ≤ 1.4; 1000 hours of operation in a humid and hot environment of 95% RH/+65℃, no corrosion or performance degradation.

　　Power Load Stability: 1000 hours of continuous operation at rated power, IL decay ≤ 0.1dB, no thermal deformation or solder joint detachment; no functional failure under instantaneous overload (1.5 times rated power) for 10 minutes.

　　Electromagnetic Compatibility: Complies with 3GPP 38.141 standard, radiated interference ≤ 30dBμV/m (30MHz~6GHz), interference immunity ≥ 40dB, avoiding electromagnetic coupling with co-located equipment.

　　III. Base Station Dedicated Topology Design and Optimization

　　1. Base Station Adaptation Schemes for Mainstream Topologies

　　(1) Wilkinson Topology (Mid-to-High Frequency Mainstream)

　　This topology uses a combination of λ/4 transmission lines and isolation resistors, adapting to Sub-6GHz macro base stations and micro base stations. To address the high isolation requirements of base stations, a double-section λ/4 transmission line design increases the isolation from 20dB to 28dB. High-frequency thin-film isolation resistors are used, with power redundancy three times the actual power consumption, preventing overheating damage in high-power scenarios. In micro base stations, microstrip lines are used to implement this topology, with linewidth optimized according to the substrate dielectric constant (e.g., with a dielectric constant of 3.5, a 50Ω microstrip linewidth is approximately 2mm), achieving planar integration with the antenna array.

　　(2) Cavity Coupling Topology (High-Power Macro Base Station)

　　This topology consists of a metal cavity and a resonant structure, adapting to high-power scenarios above 50W. Out-of-band interference is suppressed by the frequency selectivity of the cavity resonator, achieving an out-of-band suppression of ≥45dB for the combiner. Simultaneously, the shielding characteristics of the cavity are utilized to control radiation loss to within 0.1dB. To adapt to multiple frequency bands, a multi-cavity cascaded design is adopted to achieve dual-band coverage of 3.3~3.6GHz and 4.8~5.0GHz, with insertion loss ≤0.2dB.

　　(3) Microstrip Integrated Topology (Micro Base Station/Small Station)

　　Based on multi-layer PCB technology, the branch line coupler structure is implemented, reducing the volume by 60% compared to traditional solutions. A defect grounding structure (DGS) is established on the bottom ground layer to suppress high-frequency harmonics and improve isolation by 1~2dB. A microstrip bandpass filter is connected in series at the input port to specifically suppress interference from adjacent frequency bands such as 2.4GHz WiFi, forming an integrated "branch-filter" module to meet the miniaturized integration requirements of micro base stations. 2. Key Performance Optimization Path

　　**Loss Control:** For the Sub-6GHz band, substrates with a dielectric constant of 3.0~3.5 and a dielectric loss tangent < 0.004 are selected. For the millimeter-wave band, low-loss substrates with a dielectric loss tangent < 0.001 are used. Thicker copper foil (≥35μm thickness) is employed to reduce skin effect loss.

　　**Power Carrying Capacity Enhancement:** Transmission lines use copper busbars or gold-plated copper strips, with a cross-sectional area designed to be 1.5 times the rated current. Connectors are N-type or 7/16-type, with gold-plated contacts to improve power carrying capacity and mating resistance.

　　**Miniaturization and Integration:** The micro base station uses LTCC (Low Temperature Co-fired Ceramic) technology to integrate splitters, filters, and power divider networks onto a multilayer ceramic substrate. The module size can be controlled within 20mm × 15mm × 3mm.

　　**Minimization and Integration:** The micro base station uses LTCC (Low Temperature Co-fired Ceramic) technology to integrate splitters, filters, and power divider networks onto a multilayer ceramic substrate. The module size can be controlled within 20mm × 15mm × 3mm. IV. Material Selection and Process Specifications

　　1. Core Material Selection

　　The dielectric substrate needs to be adapted to the frequency band and scenario: Sub-6GHz macro base stations use high thermal conductivity and low dielectric loss substrates with a dielectric constant of 3.0~4.0 and a thermal conductivity ≥1.5W/m・K to ensure heat dissipation; micro base stations use thin substrates with a thickness of 0.8~1.2mm to balance size and performance; millimeter-wave bands use ultra-low loss substrates with a dielectric constant of around 2.2 to suppress dielectric loss.

　　The conductor material is based on high conductivity copper with a gold-plated surface (thickness ≥1μm) to improve conductivity and corrosion resistance; high-power scenarios use copper-silver composite materials, which have a 10% higher conductivity than pure copper and reduce conductor loss.

　　Regarding shielding and shell materials, outdoor macro base stations use rust-resistant aluminum alloy with an anodized surface treatment and pass a 500-hour salt spray test; indoor micro base stations use ABS flame-retardant shells with integrated metal shielding layers, achieving a shielding effectiveness ≥40dB.

　　2. Key Process Specifications

　　The photolithography process must ensure microstrip line pattern accuracy ≤ ±0.05mm and edge burrs ≤ 0.02mm to avoid impedance abrupt changes leading to increased reflection loss. Reflow soldering is used, with temperature controlled at 230~250℃ and solder joint pull force ≥ 0.8N to ensure connection reliability in high-power scenarios.

　　For surface treatment, the copper foil surface uses immersion gold or gold plating, with plating adhesion meeting IPC-TM-650 standards and salt spray resistance ≥ 96 hours. The housing uses a sealed process, equipped with a waterproof sealing ring, achieving a protection rating of IP65 (outdoor) or IP54 (indoor).

　　IV. Testing, Verification, and System Integration

　　1. Base Station-Level Testing Standards and Methods

　　Electrical performance testing follows the 3GPP 38.141 standard, using a vector network analyzer for full-band parameter measurement. Before testing, SOLT calibration is required to eliminate cable and fixture losses, ensuring insertion loss test error ≤ 0.05dB. For Massive MIMO scenarios, additional phase consistency testing is required. Points are taken every 100MHz within the operating frequency band, and the phase difference between each port must be ≤±1.5°.

　　Environmental reliability testing includes: high and low temperature cycling test (-40℃~+65℃, 50 cycles), vibration test (10~2000Hz/10g, 8 hours), and salt spray test (5% NaCl solution, 500 hours). After testing, the IL change must be ≤±0.1dB, and VSWR ≤1.4.

　　System integration testing must be conducted in conjunction with the RU and antenna array to verify the impact of the splitter/combiner on the base station output power, EVM, and coverage range, ensuring EVM ≤-45dB (64QAM modulation) and coverage range deviation ≤5%.

　　2. Integrated Application Solutions

　　In macro base stations, the splitter is deployed at the RU output, distributing a single high-power signal to 8-16 antenna elements. It connects to the feeder via N-type connectors, with waterproof tape sealing the connection to prevent outdoor environmental interference. The combiner is used for multi-carrier signal combining, reducing the number of antennas and lowering deployment costs.

　　Micro base stations employ an integrated "splitter-antenna" design. The microstrip splitter and 4×4 MIMO antenna are integrated on the same PCB board, reducing feeder loss by 0.3-0.5dB. The module directly interfaces with the RU via board-to-board connectors, enabling rapid assembly.

　　In millimeter-wave base stations, the splitter is integrated with the antenna array using LTCC technology. The transmission line length is controlled within λ/2, and the radiation loss is ≤0.1dB. Simultaneously, a metal shielding cover isolates external electromagnetic interference, ensuring signal transmission fidelity.

　　V. Typical Application Scenarios Analysis

　　1. Macro Base Station Massive MIMO Splitting System

　　The application requirement is a 3.5GHz macro base station that needs to distribute the output signal of one 80W RU to eight antennas. Requirements include IL ≤ 6.5dB, isolation ≥ 25dB, VSWR ≤ 1.35, and tolerance to a temperature range of -40℃ to +65℃.

　　The technical solution adopts a dual-section Wilkinson topology. The substrate is a low-dissipation, high-frequency type. The transmission line is made of gold-plated copper strip. The isolation resistor has a power rating of 5W. The casing is made of rust-resistant aluminum alloy with IP65 protection.

　　Application results show that the full-band IL = 6.4dB, the phase difference between each port ≤ ±1.2°, the beamforming accuracy meets the coverage requirements, and the IL change after high-temperature testing is 0.08dB, making it suitable for long-term operation of outdoor macro base stations.

　　2. Integrated Micro Base Station Combiner Module

　　Application requirement: Indoor micro base stations need to combine two 20W signals for output, covering the 3.3~3.6GHz frequency band. Requirements: IL ≤ 0.3dB, isolation ≥ 22dB, module size ≤ 30mm × 20mm × 5mm.

　　Technical solution: Employs a microstrip integrated topology, using multi-layer PCB technology to achieve combining and filtering functions. The substrate thickness is 1mm, the conductor is 35μm thick copper foil, and the surface is gold-plated.

　　Application results show that the combined signal EVM ≤ -48dB, the module weighs only 5g, integrates seamlessly with the micro base station RU, offers flexible deployment, and is suitable for indoor coverage scenarios such as office buildings and shopping malls.

　　3. Millimeter-Wave Base Station Splitting System

　　The application requirement is a 26GHz millimeter-wave base station, needing to distribute one signal to four antennas, with an isolation level (IL) ≤ 3.8dB, isolation ≥ 25dB, and vibration resistance of 10~2000Hz/5g.

　　The technical solution employs LTCC process split-line couplers, with a low-dissipation ceramic substrate, silver-plated transmission lines, a lightweight metal casing, and internal silicone rubber reinforcement.

　　Application results show an IL of 3.7dB and a radiation loss of 0.08dB in the millimeter-wave band. Performance showed no degradation after vibration testing, making it suitable for 5G-A millimeter-wave sensing fusion scenarios.

　　VI. Technological Development Trends

　　**Multi-band Integration:** Develop broadband splitters/combiners covering Sub-6GHz and millimeter waves. Through multi-section matching networks and cavity-microstrip hybrid topologies, achieve ultra-wideband coverage from 1.8 to 30GHz with insertion loss ≤0.5dB, adapting to the multi-band collaborative requirements of 5G-A.

　　**Intelligent Monitoring:** Built-in miniature power and temperature sensors upload real-time data to the base station management system via the eCPRI interface. Alarms are triggered when insertion loss increases by ≥0.3dB or temperature exceeds 70℃, improving operational efficiency.

　　**Green and Energy-Saving Design:** Utilize low-dissipation, high-thermal-conductivity materials to optimize the heat dissipation structure, reducing device operating temperature by 15-20℃. Simultaneously, topology optimization reduces ineffective power loss, helping base stations achieve energy consumption reductions of over 10%.

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