How does a coaxial switch affect signal integrity
Coaxial Switch Signal Integrity Factors
Insertion Loss
- Resistive and Dielectric Losses from gold-plated contacts and PTFE dielectrics
- Typical values: 0.2 dB @ 10 GHz increasing to 0.5 dB @ 40 GHz
- Losses increase logarithmically with frequency
Design Consideration:
Select low-loss dielectrics and high-conductivity plating materials to minimize insertion loss at target frequencies
Return Loss and Impedance Mismatch
- Imperfect impedance matching causes signal reflections
- Quality switches maintain 20 dB return loss (99% power transmission)
- VSWR values above 1.2:1 indicate significant mismatch
Switching Transients
| Switch Type | Bounce/Transient | Settling Time |
|---|---|---|
| Electromechanical | Mechanical bounce | 10-20 ms |
| Solid-state (PIN diodes) | Capacitive transients | <100 μs |
Isolation
- Poor isolation leads to signal coupling between ports
- High-frequency switches require >60 dB isolation
- Critical for maintaining SNR in sensitive applications
Nonlinear Effects
- Harmonic Generation: 2 GHz input may produce 4 GHz/6 GHz harmonics
- PIM (Passive Intermodulation) from metal-to-metal junctions
- Particularly problematic in cellular and radar systems
Phase Shift
- Switches introduce frequency-dependent phase shifts
- Critical for phased-array antennas and coherent systems
- Phase linearity must be maintained across operating band
Measurement Note:
Phase stability should be tested under thermal cycling for applications with temperature variations