High-gain and low-RCS broadband circularly polarized metasurface antenna based on novel sequential-rotation feeding network

A high-gain and low-radar cross section (RCS) broadband circularly polarized metasurface antenna based on a novel sequential-rotation feeding network, comprising a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, a third metal layer, a fourth metal layer, a third dielectric substrate and a fifth metal layer, disposed sequentially from top to bottom, wherein

• structures of the first metal layer and the third metal layer are both composed of 2*2 large arrays, each of the large arrays being composed of 5*5 rectangular metal sheets inclining for 45 degrees and each provided with four metal strips, four sides of each of the metal sheets being grooved and having a metal branch introduced in to form a square metal unit, thereby constituting a large array of square metals, the large arrays having rotational symmetry with each other around a center;
• the second metal layer is a 10*10 square metal array, having a cycle equal to those of the first metal layer and the third metal layer, and each unit being a square metal ring;
• the fourth metal layer is a whole piece of metal with four slits dug out, the four slits having rotational symmetry with each other;
• a certain distance exists between the third metal layer and the fourth metal layer to define a resonant cavity so that electromagnetic waves are positively superposed in the distance to increase gain of radiation;
• and
• the fifth metal layer is a hybrid sequential-rotation feeding network consisting of microstrip lines, the microstrip line at an input end being divided into two ports by an equal power divider and a resistor, wherein one of the ports is connected to a C-type microstrip coupled line and then further divided into two paths by an equal power divider and a resistor, the two paths consisting of C-type coupled lines and having a fixed phase difference, and the other one of the ports is connected to a delay line and then to the same structure, the delay line having a fixed phase difference.