Tuning networks for single loop resonators
Embodiments of an SLR antenna having differential signal contacts and a tuning circuit configured to tune the at least one resonance frequency of the SLR antenna to a predetermined operational frequency are disclosed. Embodiments of a tuning circuit include a balun transformer connected between the differential signal contacts of the SLR antenna and a single-ended input/output contact, a first variable capacitance connected between the balun transformer and the single-ended input/output contact, and a variable reactive component connected between the differential signal contacts of the SLR antenna and between differential contacts of the balun transformer.
1. A shielded loop resonator (SLR) antenna circuit comprising:
an SLR antenna having differential signal contacts and at least one resonance frequency; and a tuning circuit configured to tune the at least one resonance frequency of the SLR antenna to a predetermined operational frequency, the tuning circuit including a balun transformer connected between the differential signal contacts of the SLR antenna and a single-ended input/output contact, a first variable capacitance connected between the balun transformer and the single-ended input/output contact, and a variable reactive component connected between the differential signal contacts of the SLR antenna and between differential contacts of the balun transformer.
2. The SLR antenna circuit of claim 1 wherein the operational frequency is lower than the at least one resonance frequency of the SLR antenna, and wherein the variable reactive component is a second variable capacitance.
3. The SLR antenna circuit of claim 2 wherein the second variable capacitance includes a bank of switchable capacitors.
4. The SLR antenna circuit of claim 3 wherein the first variable capacitance includes a variable capacitor.
5. The SLR antenna circuit of claim 2 wherein the tuning circuit further includes a third variable capacitance connected within the SLR antenna.
6. The SLR antenna circuit of claim 2 wherein the tuning circuit further includes a pair of fixed-value capacitors symmetrically connected to the differential signal contacts of the SLR antenna and to ground.
7. The SLR antenna circuit of claim 1 wherein the at least one resonance frequency of the SLR antenna includes a first resonance frequency and a second resonance frequency, and wherein the operational frequency is between the first and second resonance frequencies.
8. The SLR antenna circuit of claim 1 wherein the operational frequency is higher than the at least one resonance frequency of the SLR antenna, and wherein the variable reactive component is a variable inductor.
9. The SLR antenna circuit of claim 8 wherein the tuning circuit further includes a fixed-value capacitor connected between the differential signal contacts of the SLR antenna.
10. The SLR antenna circuit of claim 8 wherein the tuning circuit further includes a pair of fixed-value capacitors symmetrically connected to the differential signal contacts of the SLR antenna and to ground.
11. The SLR antenna circuit of claim 1 wherein the single-ended input/output contact is connected between ground and the first variable capacitance.
12. A shielded loop resonator (SLR) antenna circuit comprising:
an SLR antenna having differential signal contacts and at least one resonance frequency; and
a tuning circuit configured to tune the at least one resonance frequency of the SLR antenna to a predetermined operational frequency, the tuning circuit including a balun transformer connected between the differential signal contacts of the SLR antenna and a single-ended input/output contact, a first variable capacitance connected between the balun transformer and the single-ended input/output contact, and a variable reactive component connected between the differential signal contacts of the SLR antenna and between differential contacts of the balun transformer, the tuning circuit including a pair of fixed-value capacitors symmetrically connected to the differential signal contacts of the SLR antenna and to ground, and
wherein the operational frequency is lower than the at least one resonance frequency of the SLR antenna and the variable reactive component is a second variable capacitance, or
wherein the operational frequency is higher than the at least one resonance frequency of the SLR antenna and the variable reactive component is a variable inductor.