| 主权项 |
1. A traveling-wave loop antenna based on a metal ring cavity for generating a radio frequency orbital angular momentum (OAM), comprising said metal ring cavity with an annular slot circumferentially opened on a top surface, wherein:
said metal ring cavity is obtained through bending a rectangular waveguide which works at a TE10 mode; a height of a lateral surface of said metal ring cavity is a wide side a of said rectangular waveguide, and a width of said top surface of said metal ring cavity is a narrow side b of said rectangular waveguide; said annular slot is opened in the middle of said narrow side of said rectangular waveguide; a perimeter of said metal ring cavity is a longitudinal length of said rectangular waveguide; a circumferential propagation constant kφ of said metal ring cavity is equivalent to a longitudinal propagation constant k of said rectangular waveguide; two openings, which are ¼ of said perimeter apart with each other on said lateral surface of said metal ring cavity, are two excitation source ports, for connecting a metal waveguide; when said two excitation source ports are inputted with microwave sources having the same frequency and a phase difference of ±90°, an electromagnetic field in said metal ring cavity exhibits a traveling-wave distribution propagating circumferentially clockwise or counterclockwise; said traveling-wave loop antenna radiates an electromagnetic wave into free space from said annular slot; and a size of said metal ring cavity is adjusted, in such a manner that said circumferential propagation constant kφ of said metal ring cavity satisfies kφR=l, wherein R is a radius of said annular slot and l is an integer, so that said metal ring cavity realizes a conversion from a microwave guided-wave mode to an OAM mode and a generation of an OAM beam with an order of ±l in free space; whether the l is positive or negative is determined by whether said phase difference of said two excitation source ports is +90° or −90°. |
