In accordance with an embodiment, a circuit includes a mixer having a signal input port, a local oscillator input port and an output port, a lowpass filter circuit having an input coupled to the output port of the mixer and a terminal configured to be connected to a shunt capacitor, and a difference circuit having a first input coupled to the output port of the mixer, and a second input coupled to an output of the lowpass filter. The output of the difference circuit substantially rejects a DC signal component at the output port of the mixer.

A fine-tuning method of a true time delay system includes: a first reference unit for transmitting an applied RF signal without time delay; a first delay unit for transmitting the applied RF signal to be delayed as much as a first delay time; an input unit for transmitting the applied RF signal to the first reference unit or the first delay unit; a second reference unit for transmitting the RF signal transmitted from the first reference unit or the first delay unit without time delay; a second delay unit for transmitting the RF signal; a 12th switching unit for transmitting the RF signal transmitted from the first reference unit or the first delay unit to the second reference unit or the second delay unit; and an output unit for outputting the RF signal.