PDF《resonator antenna》

Simulation of plasma filled hemispherical cavity as dielectric resonator antenna G Trenchev, Zh Kissóvski Faculty of Physics, Sofia University "St.

Kliment Ohridski",

5 James Boucher Blvd, Sofia, Bulgaria E-mail: [email protected], [email protected] Abstract. Plasma antennas are becoming an increasingly interesting research topic because of their uncommon characteristics. They are highly configurable, can be turned on and off rapidly, and exhibit lower thermal noise compared to metal antennas. In recent years, research has been conducted on cylindrical plasma columns sustained by DC, RF or microwave field, and their application as leaky wave antennas or as regular monopole antennas. Dielectric resonator antennas (DRA) with high dielectric permittivity are known for their small size and excellent operating characteristics for modern mobile communications (WiMAX, LTE). Hemispherical dielectric resonator antennas are characterized by simple shape, high radiation efficiency and wide bandwidth. Hemispherical DRA with a low density weakly ionized plasma as dielectric material will combine the positive features of plasma and dielectric antennas, and is particularly interesting, as antennas of this type have not been studied yet. The hemispherical plasma antenna is simulated with Ansoft HFSS in the microwave S-band. Obtained radiation pattern and bandwidth show the advantages of hemispherical plasma antennas for future communication technology. 1. Introduction Using a dielectric material as a resonator antenna has been studied extensively and has become more common in recent years [1]. Dielectric resonator antennas are characterized with high efficiency (typically 95-99%), small dimensions and low manufacture cost. They can be produced in almost any form and size, and can be excited by microstrip lines, slots and coaxial probes. Materials with dielectric permittivity of 2-100, as well as layered dielectrics have been studied theoretically and experimentally as resonator antennas with high success. Low-temperature plasma has been studied and considered an adequate replacement for metal in antennas because of its low thermal noise, instant turn-on, and configurable radiation pattern. The applicability and efficiency in the RF range as leaky-wave antennas has been demonstrated in many experiments [3]. Operation of the cylindrical plasma antennas with plasma column sustained by surface waves as resonant antennas in the microwave S-band is still under research [4]. A hemispherical plasma resonator antenna with a low density weakly ionized plasma as dielectric material will combine the positive features of plasma and dielectric antennas. The main goal of our research is to study plasma as a substitute to dielectrics in a hemispherical DRA and to achieve a realistic model through computer-aided simulations. 2. Methods of simulation The operation of the plasma resonator antenna depends on the relative permittivity of plasma. Plasma permittivity is evaluated as: ( ) ν ω ω ω ε j p p ? ? =

2 1 , (1) where ωp stands for plasma frequency, ω is the angular frequency of the microwave signal, and ν is the frequency of elastic collisions between electrons and neutrals. Formula for plasma frequency is:

2 /

1 0

2 ? ? ? ? ? ? ? ? = e p m ne ε ω , (2) where n is the plasma density, e C electron charge, me - electron mass, ε0 - vacuum dielectric constant. Considering the relation between (1) and (2), it is clear that dielectric permittivity of plasma depends on electron density and the collision frequency. In this research we assume that the hemisphere is filled with argon gas at low pressure of p =