Patch antenna characterization in a high-voltage corona plasma

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Morys, Marcin M.
Durgin, Gregory D.
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In order to improve efficiency and reliability of the world's power grids, sensors are being deployed for constant status monitoring. Placing inexpensive wireless sensors on high-voltage power lines presents a new challenge to the RF engineer. Large electric field intensities can exist around a wireless sensor antenna on a high-voltage power line, leading to the formation of a corona plasma. A corona plasma is a partially ionized volume of air formed through energetic electron-molecule collisions mediated by a strong electric field. This corona can contain large densities of free electrons which act as a conducting medium, absorbing RF energy and detuning the sensor's antenna. Through the use of low-profile antennas and rounded geometries, the possibility for corona formation on the antenna surface is greatly reduced, as compared with wire antennas. This study looks at the effects of a corona plasma on a patch antenna, which could be used in a power line sensor. The corona's behavior in the presence of an electromagnetic plane wave is analyzed mathematically to understand the dependence of attenuation on frequency and electron density. A Drude model is used to convert plasma parameters such as electron density and collision frequency to a complex permittivity that can be incorporated in antenna simulations. Using CST Microwave Studio, a 5.8 GHz patch antenna is simulated with a plasma material on its surface, of varying densities and thicknesses. Power absorption by the plasma dominates the power loss, as opposed to detuning. A wideband patch is simulated to show that the detuning effects by the plasma can be further reduced. Power absorption by the plasma is significant for electron densities greater than 10¹⁸ m⁻³. However, small point corona are found to have little effect on antenna radiation.
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