Radio frequency antenna circuit
Presented is radio frequency antenna circuit for portable and/or compact electronic devices. Embodiments comprise an antenna connected to an unbalanced current feeding arrangement. The unbalanced feeding arrangement may generate common mode currents which increase the overall radiation resistance and efficiency of the antenna circuit.
1. A radio frequency antenna circuit for a portable electronic device comprising:
first and second antenna elements;
an inductive element connected between the first and second antenna elements; and
a feed line comprising first and second electrical conductors connected to the inductive element, wherein a connection arrangement of the first and second electrical conductors to the inductive element is asymmetrical.
2. The radio frequency antenna circuit of claim 1 , wherein the first and second electrical conductors are connected toward one end of the inductive element and at different distances from a central point of the inductive element.
3. The radio frequency antenna circuit of claim 1 , wherein the first and second antenna elements are arranged parallel to each other and spaced apart with a dielectric substrate material provided therebetween.
4. The radio frequency antenna circuit of claim 1 , wherein the first and second antenna elements are configured to resonate at a first frequency, and wherein the inductive element and the first and second antenna elements have a combined resonant frequency at a second frequency that is different from the first frequency.
5. The radio frequency antenna circuit of claim 4 , wherein a maximum dimension of the first and second antenna elements is not more than half of a wavelength of the second frequency.
6. The radio frequency antenna circuit of claim 1 , wherein the first and second antenna elements are configured to generate a first common mode current component in the feed line, and the asymmetrical connection of the first and second electrical conductors are configured to generate a second common mode current component in the feed line.
7. The radio frequency antenna circuit of claim 1 , further comprising:
a receiver or transmitter unit; and
a matching unit connected between the receiver or transmitter unit and the feed line, the matching unit being configured to substantially match an impedance of the radio frequency antenna circuit to an impedance of the receiver or transmitter unit.
8. The radio frequency antenna circuit of claim 4 , wherein the first frequency is substantially equal to the second frequency.
9. A portable electronic device comprising the radio frequency antenna circuit according to claim 1 .
10. The portable electronic device of claim 9 , wherein the portable electronic device is a hearing aid.