Active E-field probe

Active E-field probe#

color coded resistors

An active whip antenna that will be located at a long distance from its connected spectrum analyser needs to be designed. The length of the antenna is 0.25 m. For frequencies below resonsnce it can be modeled as a capacitive voltage source.

  • The open-circuit voltage is the product of the antenna length the E-field strength

  • The source capacitance is the product of the antenna length and the specific capacitance per meter, which is about 12 pF/m

  • The input impedance of the receiver equals 50 Ohm. A 50 Ohm coax cable will be used to connect the active antenna with the analyser. The cable can have a length up to 25 m.

  • The operating temperature of the active ranges from 0 - 70 degress Celsius.

  • The power consumtion of the antenna must be below 0.05 W.

  • The -3 dB frequency range of the active antenna ranges from 9 kHz to 80 MHz.

  • The 1 dB compression level at the output of the amplifier, measured at the input of the receiver should be above +0dBm (0 dBm = 1 mW in 50 Ohm). At the antenna input, this should be equivalent to an electrical field strength of 1 V/m.

  • Limits for the antenna-referred equivalent noise spectral density depend on frequency. The input-referred noise (at the antenna input) should be below \(S_{En}\, \left[\frac{\mathrm{V^2}}{\mathrm{m^2Hz}} \right]\), where

    \[S_{En} = 10^{-15}\left( 1 + \frac{10^{12}}{f^2} \right)\,\left[\frac{\mathrm{V^2}}{\mathrm{m^2Hz}}\right].\]

  • Input-referred intermodulation products in the frequency band of interest should be below -50 dBm.

  • The electronics for the active antenna, should be realized in CMOS18 technology and operate on a power supply of maximally 1.8 V.

  • The active antenna should be protected against electrostatic discharge.