Fig. 5. Photograph of the proposed 3-bit FRA.
Results and discussion:The
measured results of the reflection coefficient and the photograph of the
antenna prototype are given in Fig. 4 and Fig. 5. The S11 results are
measured with an Agilent N5230A vector network analyzer. Eight
independent states are observed with the operating frequency switched
from 1.04 GHz to 1.51 GHz. Good impedance matching and low return loss
are obtained for each state, and the simulated and measured working
frequency and bandwidth at each state are compared in Table II. Except
for a small frequency shift of approximately 74 MHz on average for each
state, agreement between the simulation and the measurement results is
good. The measured bandwidths are larger than the simulated ones, and
this is possibly caused by the resistive loading of the biasing
components and switches in practical designs. Furthermore, Fig. 4(a)
shows a few unexpected perturbations on the S11 curves
caused by the parasitic effect of biasing lumped elements. Fig. 5 gives
a photograph of the fabricated prototype antenna.