Design of a BAW Quadplexer Module Using AWR Software
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T-Junction
The matching network and combining filters ensured that both filters are matched to the common node and had acceptable
isolation between them. The two circuits were combined using a T-junction with a feasible tuning impedance via length and
width of transmission lines. The T-shaped connector had two transmission line sections at both ends. It was decided to
provide a high, preferably infinite, impedance for Filter A at the load of Filter B for that particular frequency, and vice versa.
Figure 12 shows the circuit model of the T-junction.
Figure 12: The T-junction model circuit with impedance notations
The input impedance of the T-junction was required to meet the following criteria in order to achieve satisfactory impedance
matching:
Z
A
and Z
B
are the input impedance of the input of diplexer at the junction looking into the lower and the upper part.
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Z
A1
and Z
B1
are the 50Ω microstrip transmission lines that transform the low impedance at the input to the open circuit for counter
frequency for both sides. Z
A2
and Z
B2
are the high impedance microstrip transmission lines which are combined with the 50Ω
lines in order to increase the effective impedance of the input.
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Figure 13 shows the circuit element dimensions that satisfy
the equation criteria.
Figure 13: Circuit elements and dimensions of the T-junction
