Reconfigurable Plasma-Based Planar Array for Generating OAM Radio Waves in the Time Domain

The combination of orbital angular momentum (OAM) vortex and the time-modulated antenna arrays (TMAAs) is investigated in this paper. TMAA technique is introduced to enable beam scanning and managing sidelobe levels (SLLs). TMAAs use basic switches to modulate elements in a periodic sequence. This periodic modulation generates fundamental frequency and harmonic frequencies with sidebands appearing both above and below the fundamental frequency. Polarization mode is controlled by adjusting plasma conductivity (ionized or non-ionized). The proposed array is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8\times 8$</tex> unit cell elements to generate an OAM vortex beam. The effect of changing OAM integer numbered l=1, 2 and 3 and the effect of the first and third positive harmonics k=1 and 3 are investigated on the array design. Uniform, Chebyshev, Taylor, and binomial arrays are designed using the TMAA technique. It is noticed that increasing the OAM mode integer number <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l$</tex> decreases the gain and increases the beam width of the radiation pattern. The maximum gain achieved is 16.5 dBi at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l=1$</tex> using uniform array. Increasing the harmonic number <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k$</tex> decreases the maximum gain value and increases the null width. The maximum gain achieved is 15.2 dBi at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k=1$</tex> using Taylor array.