ISM Band Direction-Finding Antenna with Improved Front-to-Back Ratio

In this study, a direction-finding array antenna with an improved front-to-back ratio was developed by inserting meander slots into the ground plane of an electrically small antenna. The proposed ground slot structure improves direction-finding capabilities while maintaining the electrically compact structure of the antenna. The overall size of the antenna is 58 mm×58 mm×40 mm, with each array element measuring 40 mm×22 mm×1.6 mm. The antenna consists of eight elements attached to a vertical column, forming an octagonal structure that affords omnidirectional detection. The measured S11 bandwidth (≤−10 dB) is between 2.37 and 2.48 GHz. At 2.44 GHz, the maximum gain is −2.71 dBi, the 3-dB beamwidth occurs at an elevation angle of 74.2° and azimuth angle of 84.4°, and the front-to-back ratio is 8.89 dB.