Gysel Power Divider

Overview

High-power divider topology with grounded isolation resistors for superior thermal management. Maintains Wilkinson-like performance (matched ports, high isolation) while enabling significantly higher power handling through direct heat-sinking of resistors to ground plane.

Topology

Output1 ──────┬──────[Z0, λ/4]──────┬─── R0
              │                     │
           [Z1, λ/4]                │
              │                     │
Input ────────|                 [Z4, λ/2]
              |                     │
           [Z1, λ/4]                │
              │                     │
Output2 ──────┴──────[Z0, λ/4]──────┴─── R0

Key features:

Two λ/4 input branches at Z₁
One λ/2 center line at Z₄
Two λ/4 output lines at Z₀
Two grounded isolation resistors R

Design Equations

Z₁ = √2 × Z₀ ≈ 1.414 × Z₀    (input quarter-wave arms)
Z₄ = Z₀ / √2 ≈ 0.707 × Z₀    (center half-wave line)
R = Z₀                         (grounded resistors)

For Z₀ = 50 Ω:

Parameter	Value
Z₁	70.7 Ω
Z₄	35.4 Ω
R	50 Ω

Advantages Over Wilkinson

Grounded resistors:
- Direct thermal path to ground plane
- Easy heat-sinking (metal slug, thermal vias)

Limitations

Larger size: λ/2 center section makes it bigger
- Gysel: ~1.5× area of Wilkinson
More complex: Five transmission lines vs. two
Unequal split difficult
Cost: Slightly more expensive (more PCB area, complexity)

Comparison with Wilkinson

Feature	Gysel	Wilkinson
Power handling	Very high	Moderate
Resistors	Grounded (2)	Floating (1)
Thermal management	Excellent	Poor
Size	Larger (λ/2 section)	Smaller
Complexity	More complex (5 TL)	Simple (2 TL)
Isolation	20-30 dB	20-30 dB
Bandwidth	20-30%	20-40%
Match	Excellent	Excellent
Cost	Higher	Lower
Unequal split	Difficult	Easy
Best for	High power	General use

References

[1] Gysel, U. H. (1975). “A New N-Way Power Divider/Combiner Suitable for High-Power Applications.” IEEE MTT-S Int. Microwave Symp. Digest, pp. 116-118.