Generalized Resistive Power Divider Design

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  • Author: Greg Adams
The resistive twoway power splitter, which divides an RF input signal equally between its two output ports, is well documented. This basic divider uses the topology of all three resistors having a value of Z0/3. The unequal divider of Figure 2 splits the input power unequally between its two output ports. Design equations have been published for this splitter, where ports 1, 2 and 3 are all matched to the same impedance Z0. A power splitter with the same topology as Figure 2 can be designed so that port 3 is matched to some impedance other than Z0. There are two reasons to design the resistor network for a different impedance at port 3. First, it may be convenient in applications where, for instance, both 50 ohm and 75 ohm outputs are desired. Second, when the resistor network is designed for a port 3 impedance higher than Z0, there will be less attenuation at port 3, resulting in unequal power at the output ports as well as different impedances. For instance, if the splitter is designed for 3 dB loss at port 2, with all ports matched to 50 ohms, the attenuation at port 3 will be 15 dB. If we raise the port 3 impedance to 85 ohms, the attenuation at port 3 will only be 8.5 dB. If extreme bandwidth isn’t needed, a reactive network can be used to transform the port 3 impedance back to 50 ohms if desired.