An antenna structure (100, FIG. 1-FIG. 5c) comprising: a ground plane (G1, FIG. 1); a continuous and closed conductive loop comprising: a feed terminal connected to a feed signal (Sf1, FIG. 2); an intermediate grounding terminal for: conducting to the ground plane (G1, FIG. 1) via an intermediate impedance (z1, FIG. 2) during a second operation mode, and ceasing conducting via the intermediate impedance during a first operation mode; and a tail grounding terminal connected to the ground plane via an inductive tail impedance; a head section extending from the feed terminal to the intermediate grounding terminal along the loop; and an intermediate section extending from the intermediate grounding terminal to the tail grounding terminal along the loop, and conductively connecting the head section; wherein the head section is configured to support a half-wave resonance of a third wavelength during the second operation mode, the intermediate section is configured to support a half-wave resonance of a second wavelength during the second operation mode, and the head section and the intermediate section are configured to jointly support a half-wave resonance of a first wavelength during the first operation mode. a ground plane (G1, FIG. 1); a continuous and closed conductive loop comprising: a feed terminal connected to a feed signal (Sf1, FIG. 2); an intermediate grounding terminal for: conducting to the ground plane (G1, FIG. 1) via an intermediate impedance (z1, FIG. 2) during a second operation mode, and ceasing conducting via the intermediate impedance during a first operation mode; and a tail grounding terminal connected to the ground plane via an inductive tail impedance; a head section extending from the feed terminal to the intermediate grounding terminal along the loop; and an intermediate section extending from the intermediate grounding terminal to the tail grounding terminal along the loop, and conductively connecting the head section; wherein a feed terminal connected to a feed signal (Sf1, FIG. 2); an intermediate grounding terminal for: conducting to the ground plane (G1, FIG. 1) via an intermediate impedance (z1, FIG. 2) during a second operation mode, and ceasing conducting via the intermediate impedance during a first operation mode; and conducting to the ground plane (G1, FIG. 1) via an intermediate impedance (z1, FIG. 2) during a second operation mode, and ceasing conducting via the intermediate impedance during a first operation mode; and a tail grounding terminal connected to the ground plane via an inductive tail impedance; a head section extending from the feed terminal to the intermediate grounding terminal along the loop; and an intermediate section extending from the intermediate grounding terminal to the tail grounding terminal along the loop, and conductively connecting the head section; wherein the head section is configured to support a half-wave resonance of a third wavelength during the second operation mode, the intermediate section is configured to support a half-wave resonance of a second wavelength during the second operation mode, and the head section and the intermediate section are configured to jointly support a half-wave resonance of a first wavelength during the first operation mode.