How do I spec a phase matched cable assembly pair for a balanced or differential system?
Phase-Matched Cable Specification
Phase-matched cable pairs are used in balanced (differential) systems, dual-channel receivers, phased array feed networks, and interferometers where the signal path lengths must be identical. The phase match tolerance depends on the application: phased arrays may require ±1° at 18 GHz, while a test setup may accept ±5° at the same frequency.
| Parameter | Semi-Rigid | Conformable | Flexible |
|---|---|---|---|
| Loss (dB/m at 10 GHz) | 0.8-2.5 | 1.0-3.0 | 1.5-5.0 |
| Phase Stability | Excellent | Good | Fair |
| Bend Radius | Fixed after forming | Hand-formable | Continuous flex OK |
| Shielding (dB) | >120 | >90 | >60-90 |
| Cost (relative) | 2-5x | 1.5-3x | 1x |
Frequently Asked Questions
How tight can phase matching be?
Standard: ±5° at the highest frequency. Precision: ±2°. Ultra-precision: ±0.5° (requires individual trimming and testing, costs 3-5× standard pricing). Phase match of ±0.1° is achievable for short cables at lower frequencies but requires specialized manufacturing.
Does the number of cables in the set matter?
Phase matching gets harder with more cables. A pair (2 cables) is straightforward. A set of 4 requires matching all cables to the same reference. For large sets (16, 64, or more for phased arrays), statistical matching from the same production lot may be acceptable rather than individual matching.
Can I verify phase match in the field?
Yes. Use a VNA to measure S21 phase of each cable with the same test setup. The phase difference between cables at each frequency point is the phase match. Compare to the specification. Account for VNA measurement uncertainty (typically ±0.5° for a well-calibrated setup).