LCnetgen Example 2, E-Field Antenna

An E-field dipole probe consisting of two 10cm diameter spheres positioned vertically with centers 1 metre apart. The dipole center is 2.5 metres off the ground.

Input File

The input file dipole.in contains

   height = 2.5          ; Height of the dipole center
   sphere_diam = 0.1     ; 10cm diameter spheres
   spacing = 1.0         ; Sphere centers one metre apart
   preamp_diam = 0.05    ; Space for preamp at center of dipole
   
   electrode {
   
      name upper_sphere
   
      sphere {
         center 0, 0, height + spacing/2
         radius sphere_diam/2
      }
   
      wire {
         end1 0, 0, height + spacing/2 - sphere_diam/2
         end2 0, 0, height + preamp_diam/2
         wirad 24 awg
      }
   }
   
   electrode {
   
      name lower_sphere
   
      sphere {
         center 0, 0, height - spacing/2
         radius sphere_diam/2
      }
   
      wire {
         end1 0, 0, height - spacing/2 + sphere_diam/2
         end2 0, 0, height - preamp_diam/2
         wirad 24 awg
      }
   }
   
   ground {
      center 0, 0, 0
      axis 0, 0
   }
   
   field {
      electric 0, 0   ; Vertical E-field
   }
   
Generate a spice circuit with the command
   lcng -o spice dipole

Test Circuit One

Create a test circuit with a resistor to ground from each sphere, representing the bias resistors of a differential front-end amplifier. The 5th pin of the sub-circuit is an input which sets the field strength. This is connected to a 1V AC source to represent a 1 V/m field in the model.

The file dipole-test.spice contains

   Dipole
   .OPTIONS NOMOD NOPAGE
   .AC DEC 10 1 10K
   .PRINT AC V(2) V(1)
   
   .INCLUDE dipole.spice
   
   * 1 volt AC applied to pin 5
   Vin 3 0 DC 0 AC 1.0 180
   
   X1 0 1 2 3 dipole
   RB1 0 1 1G
   RB2 0 2 1G
   
   .END
Run this with
   ngspice -b dipole-test.spice > dipole-test.out
Plotting the voltage on the two spheres gives

Above the corner frequency the upper sphere carries about 2.9 volts and the lower sphere about 2.1 volts. If the system is modelled without the connecting wires so that the spheres are isolated, the voltages induced are 3.0 and 2.0. The unavoidable presence of the connecting wires has reduced the effective length of the dipole from 1.0 to 0.8 metres.