Simple high frequency (GHz) RF radiation detector
The ISS86 diode has a capacitance of 0.85 pF and, at 5 GHz this is an impedance magnitude of 37.45 Ω making it pretty unsuitable as a diode detector because, in the forward direction, it will rectify (what you want) but, in the reverse direction it will still have high AC conduction due to the 37.45 Ω capacitive reactance.
The MMBR941 has an \$f_T\$ of 8 GHz and this means that at 8 GHz the current gain has dropped to unity. At 4 GHz the current gain will double to 2 and, at 2 GHz \$h_{FE}\$ will be 4. In other words a fairly poor device for your targeted operating area.
The 2SC3356 has an \$f_T\$ at 7 GHz. Enough said.