Fig. 3. Simulated reflection coefficient at different states of the proposed 3-bit FRA.
Fig. 4 Measured reflection coefficient at different states and photograph of the proposed 3-bit FRA.
meander line is uniform, but the contribution of each bypassed section on frequency reconfiguration is not proportional to the length. As a result, the current distribution along the meander line is varying, and S3 becomes larger than S2. Aside from the phenomenon of increasing S3, Fig. 2 shows that the current path of each state is fundamentally the same as the equivalent structure of the corresponding state, and the bypassed sections are with no current.
Fig. 3 depicts the ultimate simulated S11 results at various states of the proposed antenna. The eight states are completely self-contained and have good impedance-matching performance over a frequency range of 1.14–1.6 GHz. Within the operating frequency band, the return loss, S11, is less than 10 dB. At the lowest working frequency (1.14 GHz), the size of the antenna is reduced to 0.19 λ0 × 0.08 λ0.
Table II. Simulated and measured resonance frequencies and operating bandwidths.