Omnidirectional-Radiating, Vertically Polarized, Wideband, Electrically Small Filtenna

An omnidirectional, vertically polarized (VP), wideband, electrically small near-field resonant parasitic (NFRP) filtenna is presented. First, a specially-engineered tridimensional inverted-F structure is developed as the driven element to replace the feed copper pin of the shorted top-hat loaded monopole, forming a new NFRP VP antenna with a smaller size, a wider fractional bandwidth (FBW), and a radiation null in the low frequency band edge. Next, a pair of C-shaped slots are etched on the NFRP element to further expand the FBW through introducing an additional resonance, and meanwhile bring a radiation null in upper frequency band edge. The collaboration of the upper and lower radiation nulls empowers the developed antenna an excellent band-pass filtering property. Particularly, the equivalent circuit and surface current distribution are demonstrated to provide a clear insight into the mechanism of the two radiation nulls. Then, the developed inverted-F driven structure is evolved into a coupling-fed version to further improve the FBW, size and filtering performance. Finally, the developed filtenna is fabricated, installed, and measured. The measured results, which are in good agreement with the simulated values, demonstrate that, with a low profile (
$0.069\mathbf {\mathrm {\lambda }} _{\mathrm{ L}}$
) and an electrically small size (ka = 0.74), the developed VP NFRP filtenna achieves a wide FBW of 32% and an enhanced peak realized gain of 6.1 dBi, exhibiting comprehensive advantages in the electric size, profile, FBW and realized gain.