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

Responses evoked by double pulse stimulation.

<p>(A) Representative data from a single subject. Each sweep represents averaged waveform of 12 responses to double pulse stimulation (50-ms time interval) measured in the rTA, rSol, rMG, rVM, rBF, lTA, lSol, and lBF muscles. (B) Averaged group data (n = 10) of peak-to-peak amplitudes (mV) of the responses to the first and second stimulations. Each circle represents an individual data point. Paired t-test revealed significant differences in the group averages between the first and second responses in all of the recorded muscles. **, p<0.01; ***, p<0.001. Abbreviation: rTA, right tibialis anterior; rSOL, right soleus; rMG, right medial gastrocnemius; rVM, right vastus medialis; rBF, right biceps femoris; lTA, left tibialis anterior; lSOL, left soleus; lBF, left biceps femoris.</p

Averaged values (μV) of background EMG activities in each muscle obtained from the 10 subjects before (Pre), during (During), immediately after (Post 0), and 5 min after (Post 5) muscle stretching.

<p>Averaged values (μV) of background EMG activities in each muscle obtained from the 10 subjects before (Pre), during (During), immediately after (Post 0), and 5 min after (Post 5) muscle stretching.</p

Averaged values of passive-plantar flexion torque produced by the right ankle joint.

<p>The averaged values of passive-plantar flexion torque were calculated from the data of 10 subjects. The black lines (p<0.01) and gray lines (p<0.05) indicate the significant difference between intensity conditions.</p

Experimental setup.

<p>The machine was utilized to induce muscle stretching in the right calf muscles. The right ankle joint was passively moved into dorsiflexion by the rotation of the foot-plate. The black arrow in this figure indicates the direction of torque applied by the machine. Abbreviation: DF, dorsiflexion.</p