Electrically Small, Near-Field Resonant Parasitic Monopole Antenna With Large Gain-Bandwidth Product and Harmonic Modes Migration

An electrically small, near-field resonant parasitic (NFRP) monopole antenna with harmonic modes migration is proposed. The evolution of the inner-driven and outer NFRP elements, respectively, contribute to performance improvement. On the one hand, decreasing the inner driven element's size can help expand the rejection band and meanwhile enhance the filtering performance. On the other hand, vertically grounding the lumped capacitors on the NFRP element can maintain a relatively high broadside directivity and impedance matching bandwidth, which leads to a large gain-bandwidth-product (GBWP) value when the electrical size is reduced. The comparative study is presented to validate the proposed antenna's advantages, and the working mechanism is illustrated from the current distribution and equivalent circuit perspectives. A prototype is fabricated and measured, and the experimental results are consistent with the simulated ones, considering the potential errors. The measured ratio between the frequency at the higher edge of the RG rejection band (–10 dBi suppression) and the working frequency can be up to 3.95.