Voltage Multiplier - Cockcroft-Walton Capacitance Value
Start at a minimum of 10uW/cm² or -20dBm/cm²  or 5 mV/mm E-field.

Needs impedance matched antenna complete circuit

Use a tuned rectangular patch antenna or rectenna with impedance matching network then  smallest Cockcroft–Walton doublers into an open loop *with π/4 to  π/2 radius..errhm I meant  λ/4 to  λ/2 radius... with suitable transmission line impedance matching striplines and at least 10 stages.

Need variable f generator

to measure s21 or DC out with f input

Another method is use Bennet doubler using  e-VEH with a motion of 5mm_DA at low frequency ( e.g. 10~30 Hz) to demodulate the steady amplitude RF field.

Sch. Diodes must be low C and ESL

Low parasitic impedance: C&lt; 0.05 pF, Ls &lt; 0.2 nH

Dielectric substrate must be low loss tangent

like ceramic, teflon or  special polyamide or https://plastics.ulprospector.com/datasheet/e120881/arlon-25n

must be small SMT for diode low pF for loop antenna

like 0201 SMD suitable for >>10GHz to prevent C divider loading and great efficiency.

Choose largest RF cap possible in smallest package  e.g 0201 if possible.


use reputable suppliers with s parameters like Murata, TDK etc.
must be very low loss tangent NPO type material or better ceramic
Consider 50~100pF  with much higher SRF.


Expect 1V at maybe >> -15dBm and 3.3V at -5dBm with > 10 stages 

other


There is always an optimum limit to n- stage doublers based on impedance ratios and loads, leakage.
plan on $200 budget for proto unless you get free samples for all materials. (ha!)