Design of a BAW Quadplexer Module Using AWR Software
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In the design presented in this application note, the BAW filters were configured into a quadplexer design, which was
simulated and realized to work with B3 and B7 LTE bands, covering between 1710MHz and 1880MHz and between 2500MHz
and 2690MHz, respectively. Two BAW duplexers were used in order to separate the TX and RX signals at the bands.
Specifications for the quadplexer were high in-band and cross-band isolation, good reflection loss (below 10dB), and fine
insertion low above -6dB. Figure 4 shows the basic circuit structure and ports defining the quadplexer.
Figure 4: Schematic of the quadplexer module
General Structure of the Quadplexer
The quadplexer is developed by combining two duplexers via a diplexer that consists of two filters. In order to design the
quadplexer, the S-parameters of the BAW duplexers provided in a Touchstone file were processed using AWR Microwave Office
software. Two options were evaluated for the creation of the common node for the two duplexers. One option was to design a
power divider/combiner based on a coupler that splits and combines input power to and from the duplexers. An ideal coupler
would introduce an additional 3dB of insertion loss for all frequencies, which was not desirable because of the two-fold
increase in the overall insertion loss. Option two was to design a frequency divider that switches lower frequencies to one
path and higher frequencies to another path, thereby avoiding much of the 3dB power loss incurred with a passive coupler
architecture. Once the system requirements of the quadplexer were defined, the diplexer and other network details were
designed. From the common node to the duplexers, the diplexer consisted of several sections, such as filters, matching
networks, and T-junctions. Figure 5 shows the general circuit model.
Figure 5: General structure of the quadplexer
