Flexible Uniplanar Electrically Small Directive Antenna Empowered by a Modified CPW-Feed

A flexible printed near-field resonant parasitic (NFRP) GPS L1 antenna that is a compact, efficient, directive radiator is demonstrated. The simple uniplanar design incorporates a capacitively loaded loop (CLL) resonator, which acts as the NFRP element, and a coplanar waveguide (CPW)-fed semi-loop antenna. A set of slots is introduced into the CPW feedline ground strips. The resulting meander-line-shaped CPW ground strips act as a driven dipole element that is capacitively coupled to the NFRP element in such a manner that when they are properly tuned, nearly complete matching to the 50-Ω source is achieved with no matching circuit, and the pair acts as a two-element endfire array. Parameter studies are reported to illustrate the nuances of the design and its operating mechanisms. The experimental results are in good agreement with their simulated values. The endfire realized gain is 3.57 dBi with a 13.44-dB front-to-back-ratio (FTBR) at its resonance frequency: 1.574 GHz (GPS L1), where the electrical size ka = 0.97. The flexibility of the proposed antenna is demonstrated both numerically and experimentally by mounting it on several cylindrical structures whose curvatures vary over a large range and by confirming that there is little impact on its operational frequency, impedance matching, bandwidth, and radiation characteristics.