Bidirectional same‐sense circularly polarized antenna using slot‐coupled back‐to‐back patches

In this letter, a dual‐patch antenna with bidirectional circular polarization of the same sense is proposed for coal mine and tunnel communications and positioning systems. The proposed antenna consists of two back‐to‐back patches with a common ground plane. We only feed one patch on the front side by microstrip feeding line, and the energy is coupled to the other patch on the back side through a slot, which is etched on the common ground. By properly truncating the corners of the dual patches, bidirectional radiation pattern is achieved with the right‐hand circular polarization on both front and back sides. Compared to previous designs for the same purpose, the proposed antenna is with a compact structure using only two layers of substrate and without using complex feeding networks, benefiting from the merits of small dimension, low cost, and easy fabrication. We have built the antenna prototype and taken the measurement. The measured impedance bandwidth for S 11<−10 dB is 90 MHz (2.44–2.53 GHz), and the measured 3‐dB axial‐ratio bandwidth is 20 MHz (2.455–2.475 GHz), agreeing well with the simulated results. The measured peak right hand circularly polarization gains are 3.70 dBic and 3.09 dBic for front and back directions.