A compact 3-D, circular line matched dipole (CLMD) antenna is presented in this paper. The realization of the antenna is based on Laser Direct Structuring (LDS) plastronic technology, enabling metallization on plastic parts. Cylindrical holder is chosen to carry the dipole, which implies high bending constraints on the antenna. Miniaturization of the radiating element is obtained by an effective use of 3-D space, resulting in a very low profile length dimensions of 0.14λ × 0.14λ × 0.05λ operating at 868 MHz. Specific attention is paid to the input impedance change due to conformation. An equivalent circuit model is proposed to take into account the conformation and design the matching line. Both simulated and measured results demonstrate good performances, with a 30 MHz bandwidth (i.e., a relative bandwidth of 3.5% with S11 < -10 dB) around the working frequency. The LDS prototype achieves a maximum gain of 1.2 dBi with a quasi-omnidirectional radiation pattern. This compact and conformed design presents a real interest for pervasive highly integrated ISM band IoT sensors.
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