Tunable slot-ring antenna using varactors

A dual mode rectangular slot-ring antenna fed with a coplanar waveguide transmission line was tuned over a band of frequencies using varactors. The analysis demonstrated that when varactors are attached to the side slots of the 2.4-GHz rectangular slot-ring antenna, the second resonant frequency could be tuned over a 22% bandwidth around 3.7 GHz while the first resonance remains unchanged. The first resonant frequency could be tuned over a 4.4% bandwidth around 2.25 GHz when varactors were connected across the bottom slot. Consequently, varactors were placed across both side slots and across the bottom slot on the same antenna configuration. Results showed that both frequencies could be independently tuned when both sets of varactors are separately biased. A 7.3% frequency shift around 2.18 GHz and a 12.3% frequency shift around 4.05 GHz were registered. Agreements between simulations and prototypes results were achieved.