Performance of uniform circular PBGS Assisted BPF
Theoretical results are produced for
different geometries of uniform circular PBGS assisted BPF. To see the effect
of uniform circular PBGS in harmonic suppression the performance of reference
BPF is shown. Finally the insertion loss performances of a standard BPF and
uniform circular PBGS assisted BPF are shown to compare the results.
· Performance of reference BPF
The performance of standard asymmetric coupled
line BPF is reproduced. The performance as obtained from the simulation result
is shown in Fig. 5.4. The presence of spurious transmission around 15 GHz is
obvious in case of a reference BPF. At this frequency maximum value of return
loss is found to be 9 dB and insertion loss is found to be 2.5 dB. At 7.5 GHz,
which is the frequency of interest, the maximum value of return loss is 22.5 dB
and insertion loss is 0.5 dB. For
harmonic suppression 2-D array of uniform circular PBGS are used in the ground
plane of a reference BPF.
Fig. 5.4: IE3D simulated S-parameters
performances of a standard coupled line BPF. Substrate is RT/Duroid having
dielectric constant of 10.2 and height of 0.635 mm.
· Performance of BPF on 2-D array of uniform circular PBGSs
The
harmonic is suppressed due to application of 2-D array of uniform circular
PBGSs as shown in Fig. 5.5.
Fig. 5.5: Theoretical S-parameters performances of a BPF with
2-D uniform circular PBGSs. Substrate is RT/Duroid having dielectric constant
of 10.2 and height of 0.635 mm.
The
return loss performance at second harmonic should ideally be zero for proper
harmonic suppression. But the maximum value of return loss is here 2 dB and the
value of insertion loss 9.5 dB. It is clear that the uniform circular PBGSs are
not exact under the lines. So they are not strong enough to suppress the
transmission at second harmonic frequency.
· Performance of BPF on dense 2-D array of uniform circular PBGSs
Fig.
5.4 shows the simulation result of a BPF
with 2-D PBGSs that are denser than conventional 2-D square lattice structure.
In this case they are rectangular lattice structure. It is seen that at 7.5 GHz
the maximum return loss is 25 dB and the maximum return loss at 15 GHz is about
to zero dB. The insertion loss is more than 30 dB. Significant suppression is
achieved here.
· Performance of BPF with three line uniform circular PBGSs
The BPF is simulated where the PBGSs are under
two 50-ohm line and the central coupled lines. The performance is shown in Fig.
6.24. In this structure, the uniform circular PBGSs are situated under two
50-ohm lines and the central coupled line. From the simulation results it can
seen that at 15 GHz the maximum value of return loss is about 1 dB only and the
insertion loss is found to be 11 dB.
Fig. 5.6: Simulated S-parameters performance of BPF
when it is loaded by dense 2-D uniform circular PBGSs. Substrate is RT/Duroid having dielectric constant of 10.2
and height of 0.635 mm.
Harmonic
suppression is not satisfactory. In addition to this, the return loss
performance at fundamental frequency is poor.
Fig. 6.24: Simulated
S-parameters performances of a BPF with three line uniform circular PBGSs. Substrate is RT/Duroid having dielectric constant of 10.2
and height of 0.635 mm.
· Performance of BPF with uniform circular PBGSs under two extreme 50 ohm lines
Thinking
over the philosophy that the EM propagation takes place through the 50-ohm line
first, uniform circular PBGSs are used under two 50-ohm lines only to see their
effect in harmonic suppression. The simulation result is shown in Fig. 5.7.
Fig. 5.7: Simulated
S-parameters performances of a BPF where two 50-ohm lines are only perturbed
with uniform circular PBGSs. Substrate is RT/Duroid having dielectric constant of 10.2
and height of 0.635 mm.
It
can be seen that the result is not promising at all. Rather the performance at
fundamental and second harmonic frequencies the performances are worse.
· Performance of BPF with uniform circular PBGSs under all the lines
Finally
PBGS is used just under all the lines. The design provides S-parameters
performances as shown in Fig. 5.8. It can be seen that at 7.5 GHz the maximum
return loss is more than 30 dB. At 15 GHz the maximum return loss is zero dB
and the insertion loss 30 dB. In this case significant improvements in
fundamental and second harmonic frequencies are achieved. Only small ripple in
transmission band is noticed that can be controlled with resizing the uniform circular
PBG elements.
Fig. 5.8: Theoretical
S-parameters performances of a BPF when uniform circular PBGSs are situated
under all the lines. Substrate is RT/Duroid having dielectric constant of 10.2
and height of 0.635 mm.
· Comparison of S21 Performances
Finally optimized reference and uniform
circular PBGS assisted BPF are fabricated. The measured insertion loss
performances are shown in Fig. 5.9.
Fig. 5.9: Measured
insertion loss performances of an optimized BPF. Substrate is Taconic having dielectric constant of 10 and
height of 0.635 mm.
From the measured result it can be seen
that the fundamental frequency is little bit shifted and the second harmonic
also. For the reference BPF the average 3 dB insertion loss and 10 dB return
loss bandwidths are 7.18% and 5.96% respectively. On the other hand uniform
circular PBGS assisted BPF provides maximum 26 dB return loss at fundamental
frequency. Average insertion loss at second harmonic is found to be 26 dB. 3 dB
insertion loss and 10 dB return loss bandwidths are found to be 16.02% and
15.2% respectively. So uniform circular PBGS assisted BPF improves the
performances in terms of return loss, insertion loss and BW.
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