RF Electronics Chapter 7: RF Filters Page 234
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Normalised De-normalised
q
1
= q
n
= 0.7654 Q
1
= Q
n
= 0.7654*1000/70 = 10.93
k
12
= k
34
= 0.8409 K
12
= K
34
= 0.8409*70/1000 = 0.05886
k
23
= 0.5412 K
23
= 0.5412*70/1000 = 0.03788
Substituting this into equations 7.13 and 7.14 and substituting the resulting a(0) and a(i)
into equations 7.11 and 7.12 gives the values for Z
oe
and Z
oo
shown below. Those values
are then entered into the TxLine program as shown in figure 7.40.
Table 7.3 Parallel coupled-line filter parameters.
Line a Z
oe
Z
oo
Width Space Length
0 0.3902 76.13 38.23 1.26 mm 0.12 mm 47.3 mm
1 0.09246 55.05 45.80 1.71 mm 1.08 mm 46.2 mm
2 0.05951 53.15 47.20 1.74 mm 1.57 mm 46.0 mm
3 0.09246 55.05 45.80 1.73 mm 1.2 mm 46.2 mm
4 0.3902 76.13 38.23 1.26 mm 0.12 mm 47.3 mm
Figure 7.40. Calculating line widths and coupling gaps.
Figure 7.41. Cadence AWR DE schematic for the 1 GHz filter
Those line geometries are then entered in a circuit schematic to give the circuit shown in
figure 7.41. End effects have been included by using the Microstrip filter element
"MCFIL". A 1 mm long taper has been added between each coupled section to ensure
that the coupled lines do not produce a short circuit at the transition in width. As a result,
all resonators are shortened by 0.5mm to keep the total resonator length the same. The
computer simulation software will produce a layout from the schematic as shown in figure
7.42. This layout can be plotted and produced as a PCB.
Figure 7.42. PCB layout for this filter produced by Cadence AWR DE.
RF Electronics: Design and Simulation
234 www.cadence.com/go/awr
