Definition of Power Splitters
A power splitter, also known as a power divider, is a device that splits the energy of one input signal into two or more output signals of equal or unequal energy. Conversely, it can also combine multiple signals into one output, in which case it can be called a combiner. A certain degree of isolation must be maintained between the output ports of a power splitter. It possesses advantages such as wide operating frequency range, low insertion loss, high gain and isolation, and stable performance.
The main technical parameters of a power splitter include power loss (including insertion loss, distribution loss, and reflection port loss), voltage standing wave ratio (VSWR) of each port, isolation between power distribution ports, amplitude balance, phase balance, power capacity, and bandwidth.
Principle of Power Splitters
A power splitter is a device widely used in wireless communication systems. Its main function is to split an input signal into multiple output signals while preserving the original signal characteristics. Passive power splitters work by using microstrip branch lines to construct a branch network and employing quarter-wavelength microstrip transmission lines for impedance matching, ensuring that the impedance seen from each port is equal to 50 ohms. This allows for efficient energy transfer while simultaneously splitting the circuit. Active power splitters are based on passive power splitters, adding amplifier circuitry to amplify the energy before distribution.
Power Splitters Technology Classification
power splitters can be classified from multiple technical dimensions, with different architectures determining their application scenarios.
Classification by Circuit Topology:
Resistive T-junction: Consists of a T-network formed by three resistors. Advantages include ultra-wide bandwidth and extremely low cost; disadvantages include high insertion loss (inherent loss > 6dB), no port isolation, and poor matching performance. Commonly used in low-performance, low-cost non-critical circuits.
Wilkinson power divider: Employs λ/4 transmission lines and isolation resistors. This is the most mainstream and classic architecture in engineering. Advantages include good port matching, high isolation between output ports, and low insertion loss (only theoretical distribution loss and minor conductor loss). Branch-line coupler: Consists of a ring structure with four λ/4 wires, achieving two 90° orthogonal outputs. Its advantages include symmetrical structure and ease of design and manufacture.
Ring bridge: Consists of a ring structure with three λ/4 wires and one 3λ/4 wire, achieving two 180° out-of-phase outputs.
Classification by output phase:
In-phase power splitter: Such as a Wilkinson power splitter.
90° quadrature power splitter: Such as a branch-line coupler.
180° out-of-phase power splitter: Such as a ring bridge.
Classification by output amplitude:
Equal power division ratio: The most common, such as two-way (-3.01dB), four-way (-6.02dB).
Unequal power division ratio: Achieves a specific power distribution ratio (e.g., -1dB/-5dB) according to system link budget requirements.
Core Components (Taking a Microstrip Wilkinson power divider as an Example)
Its physical implementation is fundamental to understanding its working principle, and it mainly consists of three parts:
Input Transmission Line: Its characteristic impedance is the system reference impedance Z₀ (typically 50Ω).
λ/4 Impedance Transformer Line: This is the core for achieving impedance matching. Two microstrip lines, each one-quarter (λ/4) the wavelength corresponding to the center frequency, have a characteristic impedance Z = Z₀√2 ≈ 70.7Ω (when Z₀ = 50Ω).
Isolation/Balancing Resistor: This is crucial for achieving port isolation. A resistor connected between the two output ports has a resistance R = 2Z₀ = 100Ω (when Z₀ = 50Ω).
For N-way power dividers, multiple two-way power splitters can be cascaded in a tree structure.
How Does a Power Divider Work?
The working principle of a power divider is based on transmission line theory and electromagnetic field coupling effects. Taking the most common Wilkinson power splitter as an example, its operation can be divided into three key stages:
1. Signal Input: The input signal enters the power splitter through the main transmission line. The transmission line is typically designed with a specific impedance (e.g., 50Ω or 75Ω) to match the impedance of the upstream and downstream devices and reduce signal reflection.
2. Energy Distribution: The input signal is distributed internally within the power splitter through branch transmission lines or coupling structures. Wilkinson power splitters use two microstrip lines of equal length to evenly distribute the input power to two output ports. Simultaneously, the two output ports are connected by isolation resistors to ensure reverse signal isolation and prevent cross-interference between ports.
3. Signal Output: The distributed signals are transmitted from each output port to the load device. Ideally, the power divider should ensure that the amplitude and phase of each output port are consistent, and that the impedance of the input and output ports are perfectly matched.
Applications of Power Splitters
Communication Base Stations: In 4G/5G base stations, power splitters distribute radio frequency (RF) signals to multiple antenna elements, enabling Multiple-Input Multiple-Output (MIMO) technology and improving network capacity and coverage. For example, an eight-channel power splitter can evenly distribute signals to eight antennas, supporting high-density user access.
Satellite and Broadcast Television Systems: Satellite receiving antennas use power splitters to distribute signals to multiple user terminals. In home scenarios, a single power splitter can connect multiple televisions in the living room, bedrooms, etc., avoiding redundant antenna installations.
Test and Measurement Equipment: In RF laboratories, power splitters distribute signal source outputs to multiple instruments such as spectrum analyzers and power meters, facilitating simultaneous testing. For example, when calibrating antennas, a power splitter ensures that the reference signal and the signal under test are acquired synchronously.
Radar and Navigation Systems: Phased-array radars use power splitters to distribute signals to hundreds of radiating elements, achieving beam scanning by adjusting the phase of the signals in each element. Aviation navigation equipment (such as the ILS instrument landing system) also relies on power splitters to ensure accurate signal coverage of the runway area.
