# High voltage tuning capacitor calculator. (V2400)

With this capacitor calculation tool, you can calculate and design the Air Isolated High Voltage tuning capacitor that is required for broadband tunable magnetic (H-field) transmit loop antennas. The magnetic loop antenna design calculator is part of the software as well and when you have defined your loop, the start-and stop frequencies which define Cmax and Cmin you can open this Capacitor Calculation tool from the Loop Antenna designer.

With the design parameters:

- square plate size in cm for the plates

- plate isolation distance in mm

- minimum and maximum capacitance in pF

- vertical plates offset

the final result from the calculator is the number of required **opposing plate areas** based on the sizes of the plates and the plate distance and the position offset. The number of capacitor plates on each side of the capacitor is half of this number plus one (dependent if the number is even or odd).

A very useful additional RF breakdown analysis is added to the tool. A general rule of thumb is that the breakdown voltage at DC is roughly 30kV when the distance between the plates equals 1 cm. But, when applying an AC voltage on the air isolated capacitor with increasing frequencies from 0Hz, the relative breakdown voltage starts dropping for frequencies above 22 kHz.

Reaching 1MHz a minimum in the relative breakdown is found, and for increasing frequencies >1MHz the relative breakdown increases again.

When you design your air isolated capacitor with this tool, you are warned when the peak RF voltage over the capacitor is in the danger zone with respect to the breakdown performance.

The additional RF breakdown analysis is based on work described in a thesis by Ivan Aponte, Texas Tech University, USA.

With permission from the author, his Thesis can be downloaded here.