Fig. 4 The embedded balun with physical dimensions (unit:
mm)
Experiments and analysis: In order to demonstrate the performance
of the tangential E-probe with resonator and coupled balun proposed in
the paper, a conventional broadband tangential E-probe published in
[7] is used to compare. Fig. 5(a) is the physical picture of this
probe. The measurement setup is shown in Fig. 5(b), and the distance
between the tip of the probe and the microstrip line is 1 mm. In the
measurement, it should be noted that in order to obtain the maximum
electric field component, the probe was placed away from the center of
the standard microstrip line. After HFSS optimization simulation, it is
found that the peak value of the electric field of the microstrip line
is at 2 mm away from the center of the microstrip line. The comparison
between simulated results and measured ones is shown in Fig. 5(c). As
show in Fig. 5(c), measured results agree well with simulated ones
except for a little deviation in frequency between them.The simulated
result of the peak value captured by the probe is -24.39 dB at 1.320
GHz, while the measured one is -24.75 dB at 1.334 GHz. The possible
reasons is that there are machine tolerances in the manufacturing
process and at same time it is difficult to accurately control the gap
between the microstrip line and the tip of probe. Compared with the
traditional broadband probe, the value of |\(S_{12}\)|
is improved by improved by 18.81-dB at 1.334 GHz.
Conclusion: To improve the measurement sensitivity in narrow
band, a compact high-sensitivity tangential E-probe with resonator and
coupled balun is proposed and tested in this paper. The resonator
composed of open-circuited and short-circuited transmission line can
enhance the sensitivity. The coupled balun is to complete the transition
from differential-mode voltage into common-mode voltage. The
|\(S_{12}\)| measured by this probe is improved by
18.81 dB at 1.334 GHz. The compact high-sensitivity tangential E-probe
is more suitable for weak signal measurement.