An eleven element log-periodic dipole-array (LPDA) antenna, occupying a surface area of only 90 x 52 mm2, printed on an ultra-thin flexible Kapton substrate of thickness 0.035 mm , is proposed. The antenna operates with a stricter 10 dB reflection coefficient bound in the frequency bands 2.75-3.53 GHz and 4-6.2 GHz. For a less stringent bound of 6 dB (which is acceptable for wearable applications), it operates in the wider range of 2.7-6.8 GHz. The antenna has an end-fire radiation pattern with a maximum measured gain of 6 dBi. The flexibility of the antenna is illustrated by reflection and radiation pattern measurements for three different radii, i.e., 50, 30, and 10 mm in both the convex and concave configurations. It is experimentally demonstrated that LPDA exhibits stable input-impedance characteristics and consistent radiation properties over the whole operating band under all bending conditions. The low cost, light weight, and flexible design, as well as the broadband performance in both concave and convex bent configurations, prove the suitability of the antenna for the contemporary flexible electronic devices.
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