Feature 6: Air Breakdown Prediction


The air breakdown is a physical phenomenon due to ionization which is caused by energetic electrons in a high electrical field. Ionization may make a conducting path, allowing a sharp current to increase.

Filter engineers need to take into account the following three mechanisms:

  1. multiplication breakdown
  2. ionization breakdown
  3. thermal-related high-power breakdown and detuning effects

This application will focus on the ionization breakdown mechanism and verify its accuracy in the simulation.

Calculation Step 1: Determine the band edge frequency

As the breakdown is only happening at the band edge where it has the maximum stored energy, the information at the band edge (14.84GHz) will be applied. One can still find the band edge frequency through the Group Delay plot.

Calculation Step 2: Obtain the maximum stored energy and normalized factor

The field calculator can obtain the maximum stored energy. The max stored energy can be verified by editing the input source.

Calculation Step 3: Obtain the Maximum E field

Calculation Step 4: Obtain the breakdown E field strength

Parameters reconsideration:

  • The reflection coefficient at the band edge
  • Uniform/Non-uniform unloaded Q in practical design

Assume the different power input level:

Ebreakdown = Enorm,max *Sqrt(P*0.68* WStoredEnergy)

Comparing with the Air breakdown threshold the maximum E field obtained in HFSS is the peak value, so the air breakdown E strength need to be transferred as RMS format.

A safety margin can be obtained comparing with the air breakdown threshold.


  • M. Yu, "Power-Handling Capability for RF Filters," IEEE Microwave Magazine, vol. 07, pp. 88-97, October 2007.
  • Qian Li, “Correlation between Simulation and Measurement of Microwave Resonator Power Handling ” Thesis, 2013