A three element slot-based antenna which includes a dielectric circuit board, a metallic layer, a sensing antenna, a first narrow band antenna, a second narrow band antenna, a first tapered transmission line, a second tapered transmission line, a first microstrip transmission line and a second microstrip transmission line. The sensing antenna is a semi-hexagonal slot-line loop whereas each of the first narrow band antenna and the second narrow band antenna are formed as a semi-elliptical slot-line loop having an E-shaped base in the metallic layer. The first tapered transmission line and the second tapered transmission line is connected to first feed port and second feed port, respectively. The first microstrip transmission line and the second microstrip transmission line are connected to third feed port and fourth feed port, respectively. The antenna resonates with circular polarization in an ultra-high frequency sub-GHz responsive to input signal at each feed port.