The plasma reflectarray/transmitarray antenna is a planar array, which reflects/transmits the incident fields radiating from a feed antenna. The plasma introduces a reconfigurable material for antenna applications. The proposed reflectarray/transmitarray unit cell consists of two plasma cylindrical ring tubes positioned along the top and bottom of a plasma square ground plane filled with argon gas. By controlling the ionized plasma gas density of the square ground plane, two modes of operations are obtained, reflectarray and transmitarray modes for the same unit cell. A 13 × 13 unit cell reflectarray/transmitarray antenna covering an area of 13.52×13.52 cm ² is proposed. The dimensions of the unit cells are identical with different argon gas densities according to the relative phases of the reflected/transmitted wave. The reflectarray is operating at 19.39 GHz, while the transmitarray is designed for 19.75-GHz applications. The radiation characteristics of the reflectarray/transmitarray single structure have been investigated. The gain and frequency bandwidth for the new configurations are presented. An electronic beam steering plasma transmitarray antenna from -380 to +380 is introduced. A full-wave analysis using the finite integration technique is used for design and analysis of the plasma reflectarray/transmitarray antenna.

A wideband circularly polarized (CP) multi-turns plasma helical antenna (HA) with reconfigurable bandwidth is investigated for wireless communications in the $x$ -band. The proposed plasma-based HA is suitable for integration with electronic circuit components used in system-on-chip applications. A parametric study on the effect of different design parameters on the antenna radiation characteristics is introduced. The antenna dimensions are optimized for wideband CP endfire radiation. The proposed antenna has an impedance matching bandwidth of 48%, a maximum gain of 8.5 dBi, and a wideband CP of 31%. The variation in the number of helix turns improves the antenna gain and bandwidth by changing the plasma frequency. An improvement in antenna gain and radiation efficiency is achieved by loading the antenna with shaped dielectric lenses with a different cross section. The endfire directional gain is improved to 11.5 dBi for hemispherical-shaped lens and 10.5 dBi for a quarter spherical lens with half-power beamwidth (HPBW) of 40°. The finite integration technique (FIT) is used to simulate and analyze the proposed structures.

Plasma antenna is an emerging technology that utilizes ionized gas as a conducting medium instead of metal. It is often convenient to represent the input impedance of the antenna by a lumped-element-equivalent circuit. Input impedance of the plasma dipole antenna is deduced using finite integration technique. A five-lumped-element equivalent circuit for the plasma dipole antenna variation with plasma frequency is investigated and optimized using the genetic algorithm (GA). The effect of plasma frequency and collision frequency of the ionized gas on input impedance variations of the plasma dipole antenna is studied with the help of the equivalent circuit model. Another equivalent circuit is synthesized using a rational function and GA. The Cauer realization method is used to deduce a new lumped-element equivalent circuit.