[Paper Review] Generation of High-Purity Millimeter-Wave Orbital Angular Momentum Modes Using Horn Antenna: Theory and Implementation

Jian Ren, Kwok Wa Leung|arXiv (Cornell University)|Sep 7, 2017

Orbital Angular Momentum in Optics26 references3 citations

TL;DR

This paper proposes a novel horn antenna design that generates high-purity millimeter-wave orbital angular momentum (OAM) modes using higher-order modes of a circular horn. By leveraging mode combination techniques, the antenna achieves 87% mode purity for OAM states with indices l = +1 and l = -1, along with high gain (>12 dBi) and wide bandwidth (>15%), making it suitable for high-data-rate communications and radar applications in millimeter-wave and terahertz bands.

ABSTRACT

Twisted electromagnetic waves, of which the helical phase front is called orbital angular momentum (OAM), have been recently explored for quantum information, high speed communication and radar detections. In this context, generation of high purity waves carrying OAM is of great significance and challenge from low frequency band to optical area. Here, a novel strategy of mode combination method is proposed to generate twisted waves with arbitrary order of OAM index. The higher order mode of a circular horn antenna is used to generate the twisted waves with quite high purity. The proposed strategy is verified with theoretical analysis, numerical simulation and experiments. A circular horn antenna operating at millimeter wave band is designed, fabricated, and measured. Two twisted waves with OAM index of l=+1 and l=-1 with a mode purity as high as 87% are obtained. Compared with the other OAM antennas, the antenna proposed here owns a high antenna gain (over 12 dBi) and wide operating bandwidth (over 15%). The high mode purity, high antenna gain and wide operating band make the antenna suitable for the twisted-wave applications, not only in the microwave and millimeter wave band, but also in the terahertz band.

Motivation & Objective

• To develop a high-purity method for generating orbital angular momentum (OAM) modes at millimeter-wave frequencies.
• To address the challenge of achieving high mode purity, high gain, and wide bandwidth in OAM-generating antennas.
• To design, simulate, and experimentally validate a horn antenna capable of producing twisted electromagnetic waves with arbitrary OAM indices.
• To extend the applicability of OAM-based systems beyond microwave to millimeter-wave and terahertz bands.

Proposed method

• A circular horn antenna is designed to excite higher-order modes that inherently support helical phase fronts corresponding to OAM states.
• The mode combination method is employed to synthesize OAM modes of arbitrary order by coherently combining multiple higher-order modes.
• Theoretical analysis is conducted using electromagnetic field theory to model the helical phase structure and mode purity.
• Numerical simulations are performed using full-wave electromagnetic solvers to predict radiation patterns and mode purity.
• A physical prototype is fabricated and measured to validate the theoretical and simulated results.
• The antenna's performance is evaluated in terms of mode purity, gain, and bandwidth using near-field and far-field measurements.

Experimental results

Research questions

• RQ1 Can a horn antenna generate high-purity OAM modes at millimeter-wave frequencies using a mode combination approach?
• RQ2 What is the achievable mode purity, gain, and bandwidth of an OAM-generating horn antenna in the millimeter-wave band?
• RQ3 How does the proposed method compare to existing OAM antennas in terms of performance and scalability?
• RQ4 Can the antenna support arbitrary OAM indices while maintaining high performance across a wide bandwidth?

Key findings

• The fabricated horn antenna achieved a mode purity of 87% for OAM states with indices l = +1 and l = -1.
• The antenna demonstrated a high gain exceeding 12 dBi across the operating band.
• The operating bandwidth was greater than 15%, indicating wideband operation suitable for practical applications.
• Theoretical and simulated results were validated by experimental measurements, confirming consistency across all stages.
• The proposed design enables high-purity OAM mode generation in the millimeter-wave band, with potential extension to terahertz frequencies.
• The method supports the generation of OAM modes with arbitrary indices, offering flexibility for future communication and sensing systems.