What's the catch with these JFETs?
There are no catches (lol) Only Specs

The s-parameters start at 2GHz 

CEL
! CE3520K3
! N-channel HJ-FET
! Vds = 2 V Id = 6 mA
# Hz S  MA   R 50
!      f            S11               S21               S12               S22
!    Hz        MAG       ANG       MAG       ANG        MAG        ANG       MAG       ANG
2000000000 0.98035944 -29.159311 4.3293347 149.29152 0.02862794 67.64743 0.65920687 -24.487707


What is the purpose?

In the meantime, WHAT's ALL THIS STUFF ABOUT ...?    

GaAs pHEMT JFETs



It's just balancing act



A delicate balancing act.



Just start with good Design Specs,  including DFM, DFT , then perform DVT and if passes all tests. Congrats, Its Perfect.


or startover until it passes your design specs.



Or do it right the 1st time with better specs.

REF



20 Years ago HP R&amp;D came up with this

To address the growing handset power amplifier needs for the emerging
Personal Communications Services (PCS) markets, a 3-volt, single-supply,
enhancement-mode pseudomorphic high-electron-mobility transistor (E-PHEMT)
has been developed. 

The device exhibits +33dBm output power and 65% drain efficiency at 1.88 GHz.

Consider a state of the art FET buffered Differential Probe specs




Using MGF4919G


REF