Simulation of Plasma Antenna Parameters

Transcription

1 May 216, Volume 4, Issue 5, ISSN Simulation of Plasma Antenna Parameters Prince Kumar and Rajneesh Kumar Department of Physics, Dr. H S. Gour Central University, Sagar (M. P), India Abstract In this paper a simulation study of a short plasma antenna is presented which is based on electromagnetic software. Using the model, different antenna parameters such as S-Parameter, radiation pattern, directivity, gain and return loss of the plasma antenna are calculated. Results suggests that plasma antenna have four resonance frequencies ranging from 1 MHz to 2 GHz. At different resonance frequencies, different radiation pattern are obtained. 1. Introduction An antenna according to Webster s dictionary define as a conducting metallic device for transmitting and receiving radio signals here by replacing the conducting metallic material with the plasma to work as an antenna is called plasma antenna. As plasma has charged particles ions and electrons so it has conductivity[1]. Previous studies proved that it is possible to use plasma element as a antenna to transmit and receive radio signals is known as plasma antenna[2]. Plasma antenna is a device that has various advantages in the field of communication, the main advantage of plasma antenna is that it can be switched off and on electrically which change the antenna appearance just by switch on and off the electrical power[3]. It has been investigated that by changing operating parameters e.g. working pressure, driven frequency, input power, radius of glass tube, length of plasma column and argon gas, single plasma antenna can be transformed to array plasma antenna, helical antenna and spiral antenna which shows Reconfigurability of plasma antenna[4, 5]. Plasma density and plasma conductivity change the plasma frequency so it is possible to retune the same plasma antenna for different frequency. A smart plasma antenna can steer the radiation pattern in different directions electronically[6]. So on the basis of above advantages plasma antenna now become an intrusting topic for research. Most of the work on plasma antennas deals with experimental approach and lack of discussion about the resonance frequency and radiation pattern dependency. Therefore present study is devoted to understand the relation between resonance frequencies with the radiation pattern which gives us almost all the antenna parameters of the plasma antenna using High Frequency Structure Simulator (HFSS). 2. Theory and Plasma parameters For the weakly ionized plasma in which the collision frequency is higher than the wave frequency(v m ω) the conductivity can be calculated by the formula is written blow[7]. σ = e2 n e m e v m (1) Here e is the electronic charge, n e is the electron density, m e is the mass of electron and v m is the collision frequency. Plasma in terms of electromagnetic properties is a non-homogeneous, non-linear and dispersive environment. Permeability ( μ ), conductivity (σ ) and permittivity ( ε ) in plasma can be varied in terms of frequency and other parameters and make plasma a special environment. As a result, for any frequency of the incident wave and in any density of ionization, one particular response occurs. Radiated electromagnetic waves on plasma will absorb, scatter or pass through. We can choose to absorb, scatter or pass through with changing the basic parameters like electron density and collision frequency. The relative permittivity of plasma is defined by [8]: ε r = ε r jε r = 1 ω(ω jv) 256 Prince Kumar and Rajneesh Kumar ω p 2 (2)

2 May 216, Volume 4, Issue 5, ISSN where ω p is plasma frequency, ω is operating frequency and ν is collision frequency. One must distinguish the difference between the plasma frequency and the operating frequency of the plasma antenna. The plasma frequency is a measure of the amount of ionization in the plasma and the operating frequency of the plasma antenna is the same as the operating frequency of a metal antenna. Plasma frequency is equal to [8]: ω p = 4πn e e 2 m e (3) 3. Simulations To design a plasma antenna on HFSS firstly we have to define plasma material that needs to define plasma conductivity, permittivity and plasma density which are calculated theoretically. For this model of plasma antenna the the electron density is chosen to be n e ~ 1 16 m -3 and the collision frequency v m ~ Hz. Hence from (1) the plasma conductivity is σ = 22.5 simens/m 3 and from (3) the plasma frequency is ω p = 1 6 Hz[3] Design of Antenna Based on HFSS, A model of plasma antenna can be founded easily with assign values. The experimental parameters are taken from[3]. Fig.1 indicate experimental setup.a plasma antenna of similar parameters and configuration as experimental is designed on HFSS software shown in Fig.1, it consists a glass tube of cm long and 3 cm in diameter, a plasma column is developed inside the tube and filled all volume of glass tube so plasma is taken inside the glass tube and mentioned that at higher operating frequencies density of plasma is uniform, an aluminum ground plate of mm in diameter and a thickness of 2 mm is taken at the one end of the glass tube and a port as a source assigned in between the plasma column and ground plate. An air volume object is designed as a radiation boundary infinitely far from the antenna. At the gap between the plasma column and aluminum disk monopole antenna port is assigned. Fig. 1 Experimental Plasma Antenna Simulated design of Plasma Antenna 4. Results 4.1. Return Loss The return loss of an antenna is measure of how much power is reflected by the antenna towards the source when its works like a transmitter and towards atmosphere when it is a receiver. It is due to impedance mismatch between antenna and transmission line. The higher values of return loss are needed to be a good 257 Prince Kumar and Rajneesh Kumar

3 db(s(1,1)) International Journal of Engineering Technology, Management and Applied Sciences May 216, Volume 4, Issue 5, ISSN antenna because higher the return loss represents lower the mismatch. S-parameters describe the input-output relationship between ports (or terminals) in an electrical system. The s11 parameter represents how much power is reflected from antenna in certain frequency. Any frequency at which s11 has minimum value is called resonance frequency of the antenna and at that frequency antenna will transmit maximum power[9] For Plasma Antenna of 3 cm in diameter and cm in length The Fig.2 indicates the S-parameters shown in for plasma antenna of 3 cm in diameter and cm in length are shown in Fig.1. This graph shows that the plasma antenna has four resonance frequencies in the frequency sweep between 1 MHz to 1 GHz. The resonance frequencies for the copper antenna are 3 MHz, 75 MHz, MHz and 17 MHz. Table. 1 indicates the resonance frequencies and its corresponding return losses. XY Plot db(s(1,1)) Setup1 : Sw eep Freq [GHz] Fig. 2 S-Parameter for Plasma Antenna of diameter of 3 cm and length cm 258 Prince Kumar and Rajneesh Kumar No. Resonance Frequency (MHz) Return Loss (db) Table. 1 Resonance frequencies with corresponding return loss 4.2. Radiation Pattern The radiation pattern is an important property of the antenna. The power received at a point by a receiving antenna is a function of the position of the receiving antenna with respect to the transmitting antenna. At a constant radius from transmitting antenna graph of the received power is called the power pattern which is a spatial pattern. The special pattern of the electro-magnetic field is called field pattern. A cross section of this field pattern in any particular plane is called radiation pattern in that plane. In this paper radiation pattern for gain of antenna is observed. Gain is an impotent parameter for antenna which is useful measure describing the performance of an antenna although the gain of the antenna is closely related to directivity. The only difference between gain and directivity is that directivity is based entirely on the shape of

4 May 216, Volume 4, Issue 5, ISSN the radiated power pattern but gain taken into account antenna efficiency as well as its directional capabilities. Higher gain in one direction means lower gain in other directions. High gain antennas allow longer range in one direction, but need to be pointed accurately. Low gain antennas have lower range, but can receive signals from wider span of directions[1] Radiation Pattern at Resonance Frequency 3 MHz Fig. 3 and Fig. 3 are radiation pattern at resonance frequency MHz for the plasma antenna. Fig. 3 indicates elevation pattern and Fig. 3 indicates azimuthal pattern. Radiation Pattern 19 Radiation Pattern Freq='.33GHz' Phi='deg' Freq='.33GHz' Phi='5deg' 6 Freq='.33GHz' Phi='1deg' Freq='.33GHz' Phi='15deg' 9 Freq='.33GHz' Phi='2deg' Freq='.33GHz' Theta='deg' Freq='.33GHz' Theta='-178deg' Freq='.33GHz' Theta='-176deg' 6 Freq='.33GHz' Theta='-174deg' 9 Freq='.33GHz' Theta='-172deg' - Freq='.33GHz' Phi='25deg' - Freq='.33GHz' Theta='-17deg' - - Fig. 3 Radiation pattern for Theta at resonance frequency 3 MHz Radiation pattern for Phi at resonance frequency 3 MHz Radiation Pattern at Resonance Frequency 75 MHz Fig. 4 and Fig. 4 are radiation pattern at resonance frequency 75 MHz for the plasma antenna. Fig. 4 indicates elevation pattern and Fig. 4 indicates azimuthal pattern. Radiation Pattern 15 Radiation Pattern Freq='.75GHz' Phi='deg' Freq='.75GHz' Phi='5deg' 6 Freq='.75GHz' Phi='1deg' Freq='.75GHz' Phi='15deg' 9 Freq='.75GHz' Phi='2deg' Freq='.75GHz' Theta='deg' Freq='.75GHz' Theta='-178deg' 6 Freq='.75GHz' Theta='-176deg' 9 Freq='.75GHz' Theta='-174deg' Freq='.75GHz' Theta='-172deg' - Freq='.75GHz' Phi='25deg' - Freq='.75GHz' Theta='-17deg' - - Fig. 4 Radiation pattern for Theta at resonance frequency 75 MHz Radiation pattern for Phi at resonance frequency 75 MHz Radiation Pattern at Resonance Frequency MHz Fig. 5 and Fig. 5 are radiation pattern at resonance frequency MHz for the plasma antenna. Fig. 5 indicates elevation pattern and Fig. 5 indicates azimuthal pattern. 259 Prince Kumar and Rajneesh Kumar

5 May 216, Volume 4, Issue 5, ISSN Radiation Pattern 8 Radiation Pattern Freq='1.2GHz' Phi='deg' Freq='1.2GHz' Phi='5deg' 6 Freq='1.2GHz' Phi='1deg' Freq='1.2GHz' Phi='15deg' 9 Freq='1.2GHz' Phi='2deg' Freq='1.2GHz' Theta='deg' Freq='1.2GHz' Theta='-178deg' Freq='1.2GHz' Theta='-176deg' Freq='1.2GHz' Theta='-174deg' Freq='1.2GHz' Theta='-172deg' - Freq='1.2GHz' Phi='25deg' - Freq='1.2GHz' Theta='-17deg' - - Fig. 5 Radiation pattern for Theta at resonance frequency MHz Radiation pattern for Phi at resonance frequency MHz Radiation Pattern at Resonance Frequency 17 MHz Fig. 6 and Fig. 6 are radiation pattern at resonance frequency 17 MHz for the plasma antenna. Fig. 6 indicates elevation pattern and Fig. 6 indicates azimuthal pattern. Radiation Pattern 11 Radiation Pattern Freq='1.7GHz' Phi='deg' Freq='1.7GHz' Phi='5deg' 6 Freq='1.7GHz' Phi='1deg' Freq='1.7GHz' Phi='15deg' 9 Freq='1.7GHz' Phi='2deg' Freq='1.7GHz' Theta='deg' Freq='1.7GHz' Theta='-178deg' Freq='1.7GHz' Theta='-176deg' 6 Freq='1.7GHz' Theta='-174deg' 9 Freq='1.7GHz' Theta='-172deg' - - Freq='1.7GHz' Phi='25deg' - - Freq='1.7GHz' Theta='-17deg' Fig. 6 Radiation pattern for Theta at resonance frequency 17 MHz Radiation pattern for Phi at resonance frequency 17 MHz 5. Discussion In the experiment work reported in earlier papers[7, 8] the operating frequency varied from 5 MHz to 1 MHz where as in this simulation study S-Parameter calculated for the same plasma antenna and the study suggested that to better operation for this antenna the operating frequencies are 3 MHz, 75 MHz, MHz and 17 MHz. So the directivities, gain and return loss are calculated in this simulation study for this plasma antenna at these operating frequencies shown in Table. 2. The study suggest that this plasma antenna has radiation patterns near to omnidirectional pattern at operating frequency 3 MHz, at this frequency return loss of antenna is db, directivity of this antenna is and gain is As the operating frequency changed to second resonance frequency 75 MHz, return loss of antenna is calculated db and the antenna becomes directive and the directivity and gain changed to and respectively. Now operating frequency changed to third resonance frequency MHz return loss of antenna is calculated db and radiation patterns are more directive than earlier, the directivity and gain at this operating frequencies are and respectively. At the fourth resonance frequency results are very 26 Prince Kumar and Rajneesh Kumar

6 May 216, Volume 4, Issue 5, ISSN interesting, at this frequency return loss of antenna is db radiation pattern are more directive and directivity and gain raised to and respectively. No. Operating frequency Directivity Gain Return Loss (db) Table. 2 Resonance frequencies with corresponding Directivity, Gain and Return Loss 6. Conclusion The simulation study is conducted for a short plasma antenna using HFSS. With the help of S-parameter, resonance frequencies are determined as 3 MHz, 75 MHz, 1.2 GHz and 1.7 GHz. Further resonance frequencies are used as operating frequencies. Plasma antenna parameters such as radiation pattern, directivity, gain and return loss etc are obtained. Results indicate that operating frequency increases up to 1.7 GHz directivity and gain increases. This study may help to optimize the antenna design for industrial applications of plasma antenna. References 1. J. A. Bittencourt, Fundamentals of Plasma Physics. 3 rd Ed., Springer International Addition. 2. Rajneesh Kumar, Plasma Antenna LAMBERT Academic Publishing GmbH & Co. KG ; (211). 3. Rajneesh Kumar, Dhiraj Bora, Experimental Study of Parameter of a Plasma Antenna, Plasma Science and Technology, Vol. 12, No. 5 (21). 4. Rajneesh Kumar, Dhiraj Bora, A Reconfigurable Plasma Antenna, Journal of Applied Physics 17, 533 (21). 5. Rajneesh Kumar, Dhiraj Bora, Wireless Communication Capability of A Reconfigurable Plasma Antenna, Journal of Applied Physics 19, 633 (211). 6. T. Anderson, Plasma Antennas Artech House; ISBN: ; (211). 7. Y. Raizer, Gas Discharge Physics (Springer, Berlin, 1991). 8. Francis. F. Chen, 1974, Introduction to Plasma Physics and Controlled Fusion, 2 nd Ed., Springer International Addition. 9. Kraus John D, Marhefka Ronald J. 23, Antennas for all applications. 3 rd Ed., Tata McGraw-Hill Edition, New Delhi, India. 1. Balanis. 1938, Antenna Theory: Analysis and Design/Constantine A. Bilanis. 2 nd Ed. Wille Edition. 261 Prince Kumar and Rajneesh Kumar