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

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.Comment: 18 pages, 9 figure

Experimental set-up.

<p>Subjects were asked to conduct wrist motion of the phantom limb in three conditions: (1) unilateral (phantom only), (2) bimanual, and (3) bimanual wrist movement with visual feedback of the phantom limb by way of a mirror reflection of the intact hand. Wrist joint angle of intact side and EMG activity of the FCR and EDL muscles in both side were recorded during ten different rhythmic wrist flexion-extension movement in each condition.</p

VAS results when Subject L carried out 5 sessions of 10 different bimanual wrist movements.

<p>As the imposed line chart clearly indicates, VAS tended to increase and R2 value gradually decreased with the repetition of the session.</p

Patients characteristics.

<p>Patients characteristics.</p

Psychophysical Evaluation of the Capability for Phantom Limb Movement in Forearm Amputees - Fig 4

<p>The profile of wrist ROM (A) and EMG amplitudes obtained from ECR and FCR muscles (C) in response to motion frequency. The relationship between VAS and ROM was shown in the right panel (B)</p

Summary of correlation analysis among VAS, wrist range of motion and EMG recorded from FCR and EDL muscles.

<p>In the left panel, blue and red circles indicate the absolute value of each parameter in Mirror– and Mirror+ conditions, respectively. In the center and right panels show the results of correlation analysis with the use of change rate induced by MVF. Regression line, the value of correlation coefficient and its statistical significance were indicated in each figure.</p

Experimental setup.

<p>Subject was asked to conduct bilateral wrist motion with (right) and without (left) visual feedback of the phantom limb by way of a mirror reflection of the intact hand. Middle panel shows waveforms of the wrist joint motion and EMG activity of the FCR and EDL muscles during rhythmic synchronous wrist flexion-extension movement.</p

Representation of the different two types of EMG changes due to MVF.

<p>Patient C (top panel) showed remarkable increase of VAS and EMG amplitude due to MVF while Patient G (bottom panel) did not show obvious changes in both VAS and EMG activities.</p

Effect of MVF on VAS (A), ROM (B), EMG activity of FCR (C) and ECR muscles (D).

<p>Each symbol indicates an individual subject data. The error bars indicate the standard deviation of the mean value. * Significant difference (p<0.05).</p

Patients characteristics.

<p>Patients characteristics.</p