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The distribution of the electron density along a plasma antenna can influence the antenna’s performance. But little has been done in this regard in former studies. In this paper, a model of a practical plasma antenna with an inhomogeneous distribution of electron density is founded according to the transmission-line equivalent theory of a metal monopole, from which the current distribution and the radiation pattern of a plasma antenna with appropriate parameters are calculated. The results show that the electrical current distribution, the maximum radiation direction, and the beamwidth of a plasma antenna vary with electron density distributions. To validate the model, the plasma antenna with the same parameters is also simulated based on electromagnetic software HFSS. It is found that the results from the two ways are almost consistent.

Compared with the conventional metal antenna, plasma antennas use ionized gas as the conducting medium instead of metal, which have excellent potentials for applications and have attracted intensive interest of researchers [

The electrical current distribution of the plasma antenna can be expressed mathematically and analogously to that of a monopole. According to the transmission-line equivalent theory of a metal monopole, the current distribution along the antenna can be written as

For a metal monopole, the far-field radiation is well known as

Using (

For a practical plasma antenna, the plasma column of a radius

If we assume

The electron density along the plasma antenna decreases almost linearly and can be expressed approximately as [

Using (

Normalized radiation pattern of the plasma antenna.

Real part and imaginary part of the wave vector

From Figure

Current distribution along the plasma antenna.

Moreover, we found another model of the plasma antenna based on HFSS, which is a useful tool in the field of antenna design. When setting up the model, we should pay attention to the dielectric constant and the conductivity of the plasma, because they are both involved with the electron density, the collision frequency, and the communication signal frequency. For the plasma antenna with the liner distribution of electron density, its dielectric constant and conductivity vary axially even with the same communication signal frequency. Here, to be convenient for simulation, the plasma antenna is divided into sufficient segments, in which the electron density is assumed uniform. As a result, the dielectric constants and conductivities of adjacent segments will have a little discrepancy. These settings will benefit the veracity of the simulation. Figure

HFSS model of the plasma antenna with 13 segments.

To compare with the first model and its calculating results, the same parameters are set in the HFSS model. The plasma antenna is divided into 13 segments. The length of the first 12 segments from the bottom is 8 cm each while that of the last is 4 cm. We find that results acquired from the model with 13 segments are almost the same as those from the model with 20 segments, so 13 segments are enough for our simulation. Figure

Radiation pattern of the plasma antenna from HFSS model.

Electrical current distribution along the plasma antenna from HFSS model.

Taking the electron density distribution of plasma into account, a model of the practical plasma antenna is founded, from which we can calculate electrical current distributions and radiation patterns of plasma antennas. The results calculated with appropriate parameters show that the electrical current distribution, the maximum radiation direction, and the beamwidth of the plasma antenna vary due to different density distributions. As for the plasma antenna, the electron density distribution is vitally important to its performance. Different from the case of the uniform electron density, signal attenuation augments due to the linear decline of the plasma density from the bottom to the top, so the plasma antenna can be viewed as a type of antenna with a continuously varying resistive loading. Because the model only needs the condition that a communication signal must propagate as a surface wave along the plasma antenna, the results from the model can be extended to other communication signal frequencies if the electron plasma angular frequency is higher than the communication signal angular frequency. The results from the model we set up in this paper are in close agreement with those from the HFSS model. This model seems useful in studying the plasma antenna.

The authors declare that there is no conflict of interests regarding the publication of this paper.

This work is supported by the Fund of National Defense Pre-Research (Grant no. 07048).