Patent ID: 7408424

Claim:
An RF circuit having at least one selected operating frequency and comprising: a first I/O port for connection to a source termination by at least one first signal carrying terminal; a second differential I/O port for connection to a load termination by a pair of second signal carrying terminals; a phase shifting device having an electrical length substantially less than 180° at a selected differential mode operating frequency, said phase shifting device comprising a first section and a second section, each section comprising a first end and a second end, each of said at least one first signal carrying terminal being coupled to a respective first end of a section of said phase shifting device, each of said pair of second signal carrying terminals being connected to a respective section of said phase shifting device, and said second ends of said sections being connected together at a circuit node; a first loading shunt device connected to said first end of said first section; a second loading shunt device connected to said first end of said second section, said first and said second loading shunt devices having a capacitance, C A of: C A = 1 ω 1 ⁢ Z 0 ⁢ cot ⁡ ( 2 ⁢ π λ ⁢ L ) ; where Z 0 is the characteristic impedance of the phase shifting device L is the physical length of the phase shifting device, ω 1 is the angular frequency of a signal at said selected differential mode operating frequency in which a differential mode component of a signal at said differential mode operating frequency is to be passed by the circuit, and λ is the wavelength corresponding to ω 1 ; and a capacitive element connected at said circuit node and having a capacitance C B of: C B = 2 ω 2 ⁢ Z 0 ⁢ cot ⁡ [ 2 ⁢ π λ ⁢ ( L - e ) ] where ω 2 is the angular frequency of a signal at a selected common mode operating frequency in which a common mode component of a signal at said common mode operating frequency is to be attenuated by the circuit, and e is the length between said first end and a point along the section of said phase shifting device to which respective second signal carrying terminals are connected.