RF Switch Design
Understanding RF Switch Design
RF switches are found throughout every wireless system: antenna switching, band selection, T/R switching, and signal routing. The choice of switch technology determines insertion loss, isolation, linearity, and power handling.
Switch Technology Comparison
| Parameter | PIN Diode | FET | MEMS |
|---|---|---|---|
| Insertion loss | 0.3-1.0 dB | 0.3-1.5 dB | 0.1-0.3 dB |
| Isolation | 30-50 dB | 20-40 dB | 40-60 dB |
| Power handling | 1-100+ W | 0.1-2 W | 0.5-2 W |
| Switching speed | 1-100 ns | 1-10 ns | 1-100 us |
| DC power | 5-10 mA | ~0 | ~0 |
Frequently Asked Questions
How do I choose an RF switch?
PIN diode: high power (>2W), fast switching, high isolation. FET: low power, integrated, zero DC power. MEMS: lowest loss, highest isolation, slower switching. Application requirements determine the technology choice.
What is a series-shunt switch?
Combines a series switch element (open = isolate, closed = pass) with a shunt element to ground (closed = short residual signal). The shunt element improves isolation by 15-20 dB beyond the series element alone.
Can RF switches handle high power?
PIN diode switches: 100+ W CW at HF/VHF, 10-50 W at microwave. GaN FET switches: emerging for 5-20 W. For very high power (kW+): waveguide switches or ferrite switches. Power handling decreases with frequency.