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.