Experimental evaluation of spectral efficiency from a circular array antenna producing a Laguerre-Gauss mode

Area of Science:

• Electromagnetics
• Antenna Theory
• Optical Communications

Background:

• Laguerre-Gauss (LG) modes offer potential for multiplexing data streams in radio systems, enhancing spectral efficiency.
• Characterizing the electromagnetic field is crucial for designing advanced communication and radar systems.

Purpose of the Study:

• To present four-dimensional volumetric electromagnetic field measurements of a circular antenna array designed for LG mode generation.
• To evaluate the far-field LG mode purity and spectral efficiency achievable with the antenna array.
• To determine the suitability of the generated LG modes for supporting various Quadrature Amplitude Modulation (QAM) schemes.

Main Methods:

• Utilized four-dimensional volumetric electromagnetic field measurements (x, y, z, frequency).
• Designed and analyzed an 8-element circular antenna array to produce a Laguerre-Gauss (LG) mode (l = +1) from 9-10 GHz.
• Evaluated far-field LG mode purity and spectral efficiency in terms of supported QAM modulation.

Main Results:

• The circular antenna array demonstrated sufficient LG mode purity to support Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK) over a 0.3 GHz bandwidth, yielding a spectral efficiency of 1.5 b/s/Hz per mode.
• Near the array's design frequency, 256-QAM modulation was supported over a 0.05 GHz band, achieving a spectral efficiency of 11 b/s/Hz per mode.
• The measurements provide practical insights into the performance of LG modes in radio frequency applications.

Conclusions:

• The characterized electromagnetic fields and demonstrated mode purity confirm the feasibility of using LG modes for spectrally efficient data transmission.
• The findings support the application of LG modes in advanced radio systems, including multiplexing and radar enhancement.
• This research contributes practical data for the successful design and implementation of future communication systems utilizing orbital angular momentum (OAM).