A multiplexer circuit may include a first-frequency-quarter-wavelength transmission line extending between a junction between a common terminal and a second-frequency terminal, and a first-frequency low-impedance circuit electrically directly connecting the first transmission line to a circuit ground. In some examples, a second-frequency-quarter-wavelength transmission line may extend between the first transmission line and a third-frequency terminal. A second-frequency low-impedance circuit may electrically directly connect the second transmission line to the circuit ground. The first and second transmission lines and the first and second low-impedance circuits may provide a third-frequency transmission line. A further second-frequency low-impedance circuit may electrically couple the second terminal to the first transmission line. A third-frequency low-impedance circuit may electrically couple the second terminal to the circuit ground. The first-frequency, further second-frequency, and third-frequency low-impedance circuits and the first transmission line may provide in combination a second-frequency transmission line.