dual gate mosfet as rf switch????

[PanosR123]

Hi all,

I am currently trying to perform backscattering modulation for an RF link operating at the UHF band. The data rate that I intend to use is low (audio signals). Could I use a dual gate mosfet as a shunt switch at the terminals of the backscatterer antenna? Do I have to control both gates every time a bit is sent?
Any ideas for my design?

Thanks in advance,
Pan

 

[vfone]

You can use a dual-gate MOSFET for this application, even for higher frequencies than audio.
You don't have to control both gates, just one, (usually the gate nr 2) when the other gate has a constant voltage bias.

 

[jiripolivka]

You can try the dual-gate mosfet but a better device is a PIN diode. At UHF band, you can use PIN diodes from an UHF TV tuner, such diodes need a forward current of ~ 5-10 mA to represent a UHF "short-circuit", and a reverse bias of 2-3V as "open circuit". I have tried such device ~25 years ago and it works.
For suitable PIN diodes, you can also check Philips, I used their PIN diodes, too.
If your RF power is < 10 mW, you can even try a detector diode pulsed through ~1 kOhm from a TTL signal; try one polarity giving the best modulation. To modulate your antenna with a PIN diode, from a TTL signal I would reduce the resistor to ~100 Ohms.

 

[PanosR123]

Your comments are really helpfull. I am aware of PIN switching, but I can't use it because it requires a relatively high current (~mA) while the power consumption of the backscattering system must be as low as possible (< 1 mA). This is the reason why I've been thinking of the dual gate mosfet as the most suitable solution. I might try using the detector diode in order to find out if this method results to a sufficient modulation depth.