GW Instek GRF-3300 Series Teacher Manual - Manual (Page 9)

16 Microstrip Line Filters
3 317
16-2-2. Solution
Referring to Table 7-5, since
Z/Zc=1.5 20dB attenuation is 20dB at 3GHz, the
order becomes 7. From Table 7-1, we find the normalized values of g1 to g8 as follows:
x g1=g7=0.4450
x g2=g6=1.2470
x g3=g5=1.8019
x g4=2.0000
x g8=1.0000
The equivalent circuit is illustrated in Figure 16-5.
4
L
5
C
7
C
6
L
3
C
2
L
1
C
Figure 16-5
We then convert the L, C value to electronic length by the following equations:
E
L
=LRo/Z
h
, for inductor (16-21)
E
L
=CZ
l
/Ro , for capacitor (16-22)
Ro is the filter impedance,
E is the wave number,
L
is the line length, L and C are
the normalized values, Z
h
and Z
l
are the highest and lowest line impedance, respectively.
According to Figure 16-3, g1, g3, g5 and g7 are capacitor sections in Z
l
, and g2,
g4 and g6 are inductor sections in Z
h
.
The PCB substrate is 1.2 mm thick, FR4 material,
H
r
= 4.4. In order to make the
PCB fabrication realistic, the line widths are adjusted to 0.5mm for Z
h
and 5mm for Z
l
before we start designing. The item left to be designed is the length of each section.