Power Combiner
Understanding Power Combiners
Power combining is the standard technique for achieving very high RF power levels when a single transistor or MMIC cannot provide enough power. By coherently adding the outputs of multiple amplifiers, combined power scales linearly with the number of devices.
Combiner Types
- Wilkinson: 2-way in-phase combiner. 100% efficiency when amplifiers are balanced. Resistive isolation absorbs mismatch.
- Corporate (binary tree): Cascaded 2-way dividers for 4, 8, 16, ... way combining. Equal path length to all ports.
- Radial: N-way symmetric structure. All ports equidistant from center. Compact for large N.
- Waveguide: Magic tee or hybrid-based. Lowest loss for high-power applications.
Combining Efficiency
- Perfect balance: 100% efficiency (all power adds).
- Phase imbalance of 10 degrees: 98.5% efficiency (0.07 dB loss).
- Phase imbalance of 30 degrees: 93.3% efficiency (0.3 dB loss).
Frequently Asked Questions
What is a power combiner?
A power combiner adds outputs from multiple amplifiers to achieve higher total power. Types: Wilkinson, corporate tree, radial, and waveguide. Efficiency depends on amplitude and phase balance between the combined amplifiers.
How many amplifiers can be combined?
Practical combiners: 2-32 amplifiers (corporate). Radial combiners: up to 64. Spatial combining (antenna array): thousands. Each doubling adds 3 dB but also adds combiner loss (typically 0.1-0.5 dB per stage).
What limits combining efficiency?
Amplitude and phase imbalance between amplifiers, combiner insertion loss, and mismatch between amplifier outputs and combiner ports. A 10-degree phase spread causes < 0.1 dB combining loss. Maintaining phase balance is the primary challenge.