High-Power RF Power Splitter/Combiner Technology and Application Analysis

　　I. Core Definition and Scenario Boundaries of High-Power Devices

　　High-power RF power splitters/combiners are passive devices designed for high-power signal transmission and distribution. Their core characteristic is the ability to stably withstand high-power loads while maintaining low loss and high reliability. The definition of "high power" needs to be differentiated based on signal type: In continuous wave (CW) scenarios, the rated power is typically ≥20W, with some industrial and base station scenarios requiring 50-100W; in pulse scenarios (such as radar and RF heating), the peak power can reach 1kW-10kW, with pulse widths mostly between 1-100μs and duty cycles ≤10%.

　　The core application scenarios for these devices focus on the need for "multi-channel processing of high-power signals," including signal distribution in 5G macro base station remote radio units (RRUs), power combining in industrial RF heating systems, and multi-array signal distribution in radar transmission systems. In these scenarios, devices must simultaneously cope with the thermal stress and impedance matching pressure brought by high power, as well as the crosstalk suppression requirements between multiple channels, to avoid performance degradation or structural damage due to power overload.

　　II. Core Performance Indicator System for High-Power Devices

　　1. Power-Related Core Indicators

　　Rated Power Capacity: The power carrying capacity for both continuous wave and pulsed power must be clearly defined. For continuous wave devices, the long-term operating power at 25℃ must be specified (e.g., 50W CW@25℃). For every 10℃ increase in temperature, the power capacity must be dated by 10%-15%. For pulsed devices, the peak power, pulse width, and duty cycle must be specified (e.g., 1kW peak @ 10μs pulse width / 5% duty cycle) to avoid cumulative heat damage caused by exceeding the duty cycle limit.

　　Power Tolerance Redundancy: A power redundancy of 1.2-1.5 times must be reserved in the design. For example, a device rated at 50W must be able to withstand 75W power for a short period (duration ≤ 10 minutes) to prevent failure due to sudden power fluctuations.

　　1. **Reflected Power Tolerance:** The input port must be able to withstand reflected power ≥10% of the rated power (e.g., a 50W device can withstand 5W reflected power) to prevent reflected energy from damaging the internal structure of the device.

　　2. **Electrical Performance and Environmental Adaptability Indicators:**

　　Insertion Loss (IL): The IL of high-power continuous wave devices must be controlled within ≤0.5dB (for a 2-way splitter, including a theoretical 3dB shared loss, the total IL ≤3.5dB). For pulsed devices, due to concentrated power, the IL fluctuation must be ≤±0.1dB to avoid uneven loss leading to localized overheating.

　　Isolation: For multi-channel devices (e.g., a 4-way splitter), the isolation must be ≥20dB. In base station and radar scenarios, it needs to be increased to ≥25dB to prevent high-power crosstalk from damaging adjacent channel devices.

　　VSWR: The VSWR of the input/output ports should be ≤1.4 (typical value ≤1.3). Poor impedance matching in high-power scenarios will exacerbate reflections, leading to overheating of transmission lines and device connectors.

　　Temperature adaptability: Must operate stably within a wide temperature range of -40℃ to +85℃. During continuous operation at high temperatures (+85℃), IL variation should be ≤ ±0.2dB, and power capacity derating should comply with design specifications (e.g., from 50W to 40W).

　　Mechanical strength: Must withstand vibration testing at 10-2000Hz/8g. Device connectors (e.g., N-type, 7/16 DIN type) should have a mating life ≥ 500 cycles without poor contact or structural loosening.

　　III. Topology and Structure Design of High-Power Devices

　　1. High-Power Adaptation Optimization of Mainstream Topologies

　　(1) High-Power Modification of Wilkinson Topologies

　　Traditional Wilkinson topologies require enhancement for high-power scenarios: transmission lines should use large-section copper strips or copper tubes (cross-sectional area ≥ 2mm²) to replace conventional microstrip lines, improving current carrying capacity; isolation resistors should be power-type thin-film resistors (rated power ≥ 2W), and multiple resistors should be connected in parallel (e.g., two 100Ω/2W resistors in parallel, total power 4W) to distribute power loss; substrates should use high thermal conductivity materials (e.g., aluminum nitride ceramic, thermal conductivity ≥ 170W/m・K) to accelerate heat conduction and prevent resistor overheating and burnout.

　　This type of modification allows the Wilkinson structure to adapt to 50-100W continuous wave power, suitable for signal distribution in 5G macro base station RRUs. (2) High-Power Design of Cavity Topology

　　The cavity structure uses a metal cavity (mostly made of aluminum alloy or brass) as the signal transmission path, possessing inherent advantages in high power carrying capacity and heat dissipation: the inner wall of the cavity is silver-plated (thickness ≥3μm) to reduce conductor loss; a multi-cavity resonant structure is adopted to achieve signal distribution while suppressing harmonics (out-of-band rejection ≥40dB); heat sinks are integrated on the outside of the cavity, or air-cooling channels are designed to quickly dissipate the heat generated by high power.

　　Cavity topology is suitable for continuous wave or kilowatt-level pulse power scenarios above 100W, such as power combining in industrial RF heating systems.

　　(3) High-Power Adaptation of Branch Line Couplers

　　For wideband high-power requirements (e.g., 1-6GHz), branch line couplers need to use thickened branch transmission lines (copper core diameter ≥1mm) and add grounded heat sinks at the coupling nodes; a multi-section coupling structure is adopted to expand bandwidth while increasing power capacity, avoiding the risk of breakdown caused by power concentration in a single-section structure. This type of design allows the branch line coupler to withstand 30-50W continuous wave power, adapting to multi-band base station scenarios.

　　2. Thermal Management and Structural Reinforcement Design

　　Thermal Path Optimization: High thermal conductivity pads (such as copper foil pads, thermal conductivity ≥380W/m・K) are used between the transmission line and the housing to shorten the heat conduction path; key heat-generating components (such as isolation resistors) are directly attached to the metal housing, dissipating heat to the outside through the housing, reducing local temperature by 20-30℃.

　　Breakdown Protection Design: The internal air gap of the device is ≥0.5mm (≥1mm in high-power scenarios) to avoid high-voltage breakdown; the transmission line connectors are gold-plated to reduce contact resistance (≤5mΩ) and reduce contact heating.

　　Mechanical Reinforcement: The housing is made of thickened aluminum alloy (thickness ≥3mm) to prevent structural deformation caused by high-power vibration; the connectors and housing are double-fixed with threaded fasteners and spot welding to prevent loosening during long-term use.

　　IV. Material Selection and Process Specifications for High-Power Devices

　　1. Core Material Selection Principles

　　Transmission line materials should prioritize metals with high conductivity and thermal conductivity, such as oxygen-free copper (conductivity ≥ 5.8 × 10⁷ S/m, thermal conductivity ≥ 385 W/m・K). Silver or gold plating can be used to improve corrosion resistance and conductivity stability. For substrate materials, high-frequency substrates (e.g., high-frequency boards with a dielectric loss tangent tanδ < 0.004) can be used in low-to-medium power applications, while ceramic substrates (e.g., aluminum nitride, alumina ceramics) are required in high-power applications, balancing low loss and high thermal conductivity. The casing material is primarily aluminum alloy (e.g., 6061 aluminum alloy), which is lightweight and has good thermal conductivity. Copper alloys can be used in some high-power applications (with even higher thermal conductivity, but greater weight). Isolation resistors should be power-type thin-film resistors or metal oxide film resistors with a temperature coefficient ≤ 100 ppm/℃ to avoid resistance drift caused by temperature changes.

　　2. Key Process Requirements The transmission line processing must ensure dimensional accuracy (line width tolerance ≤ ±0.1mm) to avoid impedance deviation; the welding process should employ high-frequency induction welding or laser welding to ensure weld strength (tensile strength ≥ 5N) and conductivity, without any incomplete welds or weld beads; in the surface treatment process, the silver plating layer thickness must be ≥ 3μm and pass a 24-hour salt spray test without corrosion; during assembly, the internal air gap must be controlled (≥ 0.5mm), and inert gas protection (such as nitrogen) must be used to prevent internal oxidation.

　　V. Testing and Verification System for High-Power Devices

　　1. Power and Thermal Performance Testing

　　Long-term Rated Power Test: Operating continuously at rated power for 1000 hours at 25℃, monitoring IL changes (≤±0.2dB) and casing temperature (≤85℃), with no structural deformation or performance degradation;

　　Pulse Power Test: Continuously testing 10⁶ pulses according to rated pulse parameters (e.g., 1kW peak / 10μs pulse width / 5% duty cycle), with IL fluctuation ≤±0.1dB after the test, and no internal breakdown marks;

　　Thermal Distribution Test: Monitoring the device surface temperature during high-power operation using an infrared thermal imager, with hot spot temperatures ≤100℃ and no localized overheating (temperature difference ≤20℃).

　　2. Electrical Performance and Environmental Testing

　　Full-band Electrical Performance Testing: IL, isolation, and VSWR are tested using a vector network analyzer within the operating frequency band to ensure compliance with all specifications (e.g., one test point every 100MHz in the 1-6GHz band);

　　Temperature Cycling Test: 50 cycles at -40℃ to +85℃ (2 hours of temperature maintenance per cycle). After testing, the change in electrical performance indicators should be ≤±0.2dB;

　　Vibration and Shock Test: 8 hours of vibration testing at 10-2000Hz/8g, and 10 cycles of shock testing at 1000g/0.5ms. After testing, there should be no loosening of the connectors and no abnormalities in electrical performance.

　　VI. Typical Application Scenarios Analysis

　　1. High-Power Splitting of 5G Macro Base Station RRU

　　The output power of a 5G macro base station RRU is typically 50-100W (CW). It needs to distribute the signal to 2-4 antennas via a splitter. The splitter's rated power must be ≥50W, IL≤3.5dB (2 channels), isolation ≥25dB, and VSWR≤1.3. The technical solution adopts a modified Wilkinson topology, using copper strips (2mm² cross-sectional area) for the transmission line, aluminum nitride ceramic for the substrate, and an integrated heat sink in the casing. In practical applications, the splitter can stably withstand 50W continuous power, with power derating to 40W at 85℃, and IL fluctuation ≤0.15dB, adapting to the long-distance coverage requirements of macro base stations.

　　2. Industrial RF Heating Power Combining

　　Industrial RF heating systems (such as plastic welding and metal heat treatment) need to combine multiple 50-100W RF signals into a total power of 200-400W. The combiner's rated power must be ≥200W, IL≤0.4dB, and isolation ≥20dB. A cavity-type combiner topology is used, with a brass cavity (silver-plated inner wall) and an external air-cooling channel. In practical applications, it can stably combine 300W continuous power, with thermal imaging monitoring hotspot temperature ≤95℃ and out-of-band rejection ≥45dB, avoiding interference with surrounding equipment.

　　3. Pulse Radar Signal Splitting

　　Pulse radar transmitting systems need to distribute a 1kW peak signal (10μs pulse width / 5% duty cycle) to an 8-antenna array. The splitter's peak power must be ≥1kW, IL≤1.5dB (8 channels), and isolation ≥22dB. Employing a branch-line coupler topology, the transmission line uses copper tubing (1mm diameter) filled with inert gas to prevent oxidation. In actual testing, after 10⁶ consecutive pulses, the IL fluctuation is ≤0.1dB, with no internal breakdown, making it suitable for the high-power pulse transmission requirements of radar.

　　VII. Technological Development Trends

　　* **Wideband High-Power Integration:** Developing ultra-wideband high-power devices covering 1-18GHz, achieving 20-50W continuous power transmission through multi-section matching networks and cavity integration design, adapting to the signal processing needs of multi-band base stations and radar systems.

　　* **Intelligent Thermal Management:** Integrating miniature temperature sensors and controllable heat dissipation modules (such as miniature fans and thermoelectric coolers) to monitor device temperature in real time and dynamically adjust heat dissipation efficiency, keeping the temperature below 80℃ during high-power operation and improving the stability of power capacity.

　　Lightweight and miniaturized: By adopting new high thermal conductivity lightweight materials (such as silicon carbide reinforced aluminum alloy), the device volume is reduced by 30%-40% compared with traditional solutions while ensuring power carrying capacity, which is suitable for the miniaturization of base stations and the installation requirements of mobile radar.

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