Section III: Measurement and Results
A BSF prototype using the proposed concept is developed on Rogers 4350B
substrate. The BSF is connected by two ports, both connected to the
defected ground and also to the 50 ꭥ microstrip line as shown in Figs. 8
and 9. The external SMD capacitors are soldered on the excitation slots
of the semi-H shaped DGS. The S-parameters are then measured using
Keysight E5063A VNA over a frequency range of 0.4 to 0.95 GHz. The
measured results are plotted in Fig. 10 and apparently there are three
clear resonant frequencies. The measured result is in agreement with the
circuit simulation and EM simulation results given in Fig. 7 and
therefore validate the tri-band filter design technique.
Fig.8 -> Fabricated Ground Plane of the DGS showing Semi-H
Defect
Fig.9-> Fabricated Top Plane of the DGS showing microstrip
feed line and ports.
Fig.10-> Measured Results of the Multi-band DGS filter
It can be seen that slight shift in frequencies has taken place and this
can be attributed to the presence of the external SMD capacitors. These
SMD capacitors help in size reduction and are relatively easy to solder
but suffer from poor tolerances. It has been observed that tolerances of
even ∓ 0.25 pF can cause significant shift in the resonant frequency. In
brief, the shifting of resonant frequencies can be overcome by using
lower tolerance capacitors. Furthermore, the rejection in the measured
values at the three frequencies is different when compared to the EM and
circuit simulation values due to the port,solder and connector losses.