This circuit uses a 2N4391 JFET to create a high frequency switch. The 2N4391 JFET provides a low on-resistance of 30 ohms and a high off-impedence (<0.2pF) when off. Other specs are: attenuation > 80dB @ 100MHz and insertion loss approximately 6dB. With proper layout and an "ideal" switch, the performance stated above can be readily achieved.