The low-loss high-conversion-efficiency and high-bandwidth dual-circular-polarization
terahertz antenna comprises an orthogonal converter and a
horn antenna, the other end of a first rectangular
waveguide and the other end of a second rectangular
waveguide are combined into a third port, and a step partition plate is arranged between the first rectangular
waveguide and the second rectangular waveguide on the front side of the third port. The
horn antenna is fixed on the orthogonal converter through a fixing part, a through hole is formed in the fixing part, the
pyramid horn antenna is communicated with the third port through the through hole in the fixing part, a plurality of
layers of square-like steps are arranged in the through hole, the plurality of
layers of square-like steps are composed of at least four
layers of steps, and the cross section of each layer of step is a quadrangle with arc-shaped end angles, namely a square-like shape. In the direction from the orthogonal converter to the horn antenna, the sectional area of each square-like step is gradually increased, and the arc
radius of each square-like step is gradually increased and is closer to a circle. The antenna has the characteristics of wide bandwidth, low
reflection loss and
high energy transmission efficiency.