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An inverted-F antenna is provided that has a resonating element arm and a ground element. A shorting branch of the resonating element arm shorts the resonating element arm to the ground element. An antenna feed that receives a transmission line is coupled to the resonating element arm and the ground

An inverted-F antenna is provided that has a resonating element arm and a ground element. A shorting branch of the resonating element arm shorts the resonating element arm to the ground element. An antenna feed that receives a transmission line is coupled to the resonating element arm and the ground element. One or more impedance discontinuity structures are formed along the resonating element arm at locations that are between the shorting branch and the antenna feed. The impedance discontinuity structures may include shorting structures and capacitance discontinuity structures. The impedance discontinuity structures may be formed by off-axis vertical conductors such as vias that pass through a dielectric layer separating the antenna resonating element arm from the ground element. Capacitance discontinuity structures may be formed from hollowed portions of the dielectric or other dielectric portions with a dielectric constant that differs from that of the dielectric layer.

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1. An inverted-F antenna comprising: an antenna ground element;a resonating element arm that is shorted to the antenna ground element at a shorting branch of the resonating element arm;an antenna feed coupled to the resonating element arm and the antenna ground element;a shorting structure that shor

1. An inverted-F antenna comprising: an antenna ground element;a resonating element arm that is shorted to the antenna ground element at a shorting branch of the resonating element arm;an antenna feed coupled to the resonating element arm and the antenna ground element;a shorting structure that shorts the resonating element arm to the antenna ground element at a location between the shorting branch and the antenna feed;a dielectric layer between the resonating element arm and the antenna ground element; anda capacitance discontinuity structure in the dielectric layer. 2. The inverted-F antenna defined in claim 1 wherein the resonating element arm comprises a planar resonating element arm conductor and wherein the antenna ground element comprises a planar antenna ground element. 3. The inverted-F antenna defined in claim 2 wherein the dielectric layer comprises printed circuit board dielectric and wherein the resonating element arm conductor comprises a T-shaped trace on the dielectric. 4. The inverted-F antenna defined in claim 1 wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, wherein the dielectric layer comprises a planar dielectric layer between the planar resonating element arm conductor and the planar antenna ground element, and wherein the capacitance discontinuity structure is in the planar dielectric layer adjacent to the resonating element arm conductor. 5. The inverted-F antenna defined in claim 4 wherein the capacitance discontinuity structure comprises a hollow region adjacent to the planar resonating element arm conductor. 6. The inverted-F antenna defined in claim 4 wherein the planar dielectric layer has a first dielectric constant and wherein a portion of the planar dielectric layer serves as the capacitance discontinuity structure and has a second dielectric constant that is different than the first dielectric constant. 7. The inverted-F antenna defined in claim 4 wherein the planar dielectric layer has a first dielectric constant and wherein a portion of the planar dielectric layer serves as the capacitance discontinuity structure and has a second dielectric constant that is less than the first dielectric constant. 8. An inverted-F antenna comprising: an antenna ground element;a resonating element arm that is shorted to the antenna ground element at a shorting branch of the resonating element arm;an antenna feed coupled to the resonating element arm and the antenna ground element;a capacitance discontinuity structure that introduces an altered capacitance to the resonating element arm at a location along the resonating element arm that is between the shorting branch and the antenna feed; anda dielectric layer between the resonating element arm and the antenna ground element, wherein the dielectric layer comprises at least one portion that serves as the capacitance discontinuity structure. 9. The inverted-F antenna defined in claim 8 wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, and wherein the dielectric layer comprises a planar epoxy dielectric layer between the planar resonating element arm conductor and the planar antenna ground element. 10. The inverted-F antenna defined in claim 8 wherein the resonating element arm comprises a planar resonating element arm conductor, wherein the antenna ground element comprises a planar antenna ground element, and wherein the a dielectric layer is between the planar resonating element arm conductor and the planar antenna ground element. 11. The inverted-F antenna defined in claim 10 wherein the at least one portion of the dielectric layer that serves as the capacitance discontinuity structure comprises portions that define at least one gas-filled hollow region adjacent to the planar resonating element arm conductor that serves as the capacitance discontinuity structure. 12. The inverted-F antenna defined in claim 10 wherein the at least one portion of the dielectric layer that serves as the capacitance discontinuity structure is adjacent to the planar resonating element arm conductor. 13. The inverted-F antenna defined in claim 12 wherein the dielectric layer has a first dielectric constant and wherein the portion of the dielectric layer that serves as the capacitance discontinuity structure has a second dielectric constant that is different than the first dielectric constant. 14. The inverted-F antenna defined in claim 13 further comprising: a shorting structure that shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is between the shorting branch and the antenna feed. 15. The inverted-F antenna defined in claim 14 wherein the shorting structure comprises at least one via that passes through the dielectric layer and electrically connects the resonating element arm to the antenna ground element. 16. The inverted-F antenna defined in claim 15 wherein the resonating element arm comprises an elongated conductive member having a central longitudinal axis and wherein the via of the shorting structure is connected to the elongated conductive member at a location that is laterally offset from the central longitudinal axis in a lateral direction perpendicular to the central longitudinal axis. 17. The inverted-F antenna defined in claim 16 wherein the elongated conductive member comprises a lateral protrusion and wherein the via of the shorting structure is connected to the elongated conductive member at the protrusion. 18. The inverted-F antenna defined in claim 8 further comprising: a shorting structure that shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is between the shorting branch and the antenna feed. 19. An electronic device, comprising: a radio-frequency transceiver;a transmission line coupled to the radio-frequency transceiver to receive and transmit radio-frequency signals; andan antenna having: a dielectric layer;an antenna ground element;a resonating element arm that is separated from the antenna ground element by the dielectric layer and that is shorted to the antenna ground element by a shorting branch of the resonating element arm at an end of the resonating element arm;an antenna feed that is coupled to the resonating element arm and the antenna ground element and that receives the transmission line; andat least one via that passes from the resonating element arm to the antenna ground element through the dielectric layer and shorts the resonating element arm to the antenna ground element at a location along the resonating element arm that is located between the shorting branch and the antenna feed, wherein there is no flat plane that passes through substantially all of the shorting branch, the antenna feed, and the via. 20. The electronic device defined in claim 19 wherein the dielectric layer comprises a portion of a printed circuit board and wherein the shorting branch comprises at least one shorting branch via through the dielectric layer. 21. The electronic device defined in claim 19 wherein the at least one via comprises at least four vias. 22. The electronic device defined in claim 19 wherein there is no straight line that passes through the shorting branch, the antenna feed, and the via.