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A phase shifter comprises a differential quadrature all-pass filter (QAF) including a balanced input port and two balanced output ports. A quadrature phase shift is manifested between the balanced output ports. The phase shifter also comprises a resistance-capacitance polyphase filter (PPF) section

A phase shifter comprises a differential quadrature all-pass filter (QAF) including a balanced input port and two balanced output ports. A quadrature phase shift is manifested between the balanced output ports. The phase shifter also comprises a resistance-capacitance polyphase filter (PPF) section defining two balanced input ports and two balanced output ports. The balanced input ports of the PPF are coupled to the balanced output ports of the QAF. The combination exhibits broad bandwidth and relatively low ohmic loss.

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1. A quadrature filter network comprising: a differential quadrature all-pass filter defining an input port and a pair of output ports comprising a first output port having an output I+ terminal, and an output I− terminal and a second output port having an output Q+ terminal, and an output Q− termin

1. A quadrature filter network comprising: a differential quadrature all-pass filter defining an input port and a pair of output ports comprising a first output port having an output I+ terminal, and an output I− terminal and a second output port having an output Q+ terminal, and an output Q− terminal, at which nominally mutually quadrature signals are generated;a resistance-reactance filter defining a pair of input ports, comprising a first input port having an input I+ terminal, and an input I− terminal; and a second input port having an input Q+ terminal, and an input Q− terminal and also defining at least an output port, said pair of input ports of said resistance-reactance filter being coupled to said pair of output ports of said differential quadrature all-pass filter, andwherein the input I+ terminal of the resistance reactance filter is connected to the output I+ terminal of the quadrature all-pass filter;the input I− terminal of the resistance reactance filter is connected to the output I− terminal of the quadrature all-pass filter;the input Q+ terminal of the resistance reactance filter is connected to the output Q− terminal of the quadrature all-pass filter; andthe input Q− terminal of the resistance reactance filter is connected to the output Q+ terminal of the quadrature all-pass filter. 2. The quadrature filter network of claim 1, wherein said output ports of said differential quadrature all-pass filter and said input ports of said resistance-reactance filter are balanced. 3. A phase-shifter comprising: a quadrature all-pass (QAP) filter circuit configured to receive a radio frequency input signal at an In+ terminal and at an In− terminal and configured to output I and Q outputs, wherein the I output is output at an I+ output terminal and at an I− output terminal, and the Q output is output at a Q+ output terminal and a Q− output terminal;a poly-phase filter (PPF) circuit coupled to said QAP filter circuit, the PPF circuit having:I and Q input ports, the I input port having an I+ input terminal and an I− input terminal; and the Q input port having a Q+ input terminal and a Q− input terminal; andI and Q output ports, the I output port having an I+ output terminal and an I− output terminal; and the Q output port having a Q+ output terminal and a Q− output terminal;wherein the PPF circuit is configured to receive the I and Q outputs of the QAP filter circuit at the I and Q input ports of the PPF circuit,wherein the I+ output terminal of the QAP filter circuit is coupled to the I+ input terminal of the PPF circuit, the I− output terminal of the QAP filter circuit is coupled to the I− input terminal of the PPF, the Q+ output terminal of the QAP filter is coupled to the Q− input terminal of the PPF circuit, and the Q− output terminal of the QAP filter circuit is coupled to the Q+ input terminal of the PPF circuit. 4. The phase-shifter of claim 3, wherein the QAP filter circuit comprises an inductive/capacitive filter. 5. The phase-shifter of claim 3, wherein the PPF filter circuit comprises a resistance-reactance circuit. 6. The phase-shifter of claim 3, wherein the input terminals of the QAP filter circuit are balanced. 7. A method of producing a quadrature phase shifted radio frequency signal comprising: receiving a radio frequency input signal at a differential quadrature all-pass (QAP) filter circuit;outputting from the QAP circuit, mutually quadrature signals at an I output at an I+ terminal and an I− terminal, and a Q output at a Q+ terminal and a Q− terminal;coupling the I+ terminal to an I+ input terminal of a poly-phase filter (PPF) circuit; and coupling the I− terminal to an I− input terminal of the PPF circuit;coupling the Q+ terminal to a Q− input terminal of the PPF circuit; and coupling the Q− terminal to a Q+ input terminal of the PPF circuit;outputting from the PPF circuit, mutually quadrature signals at an I output from an I+ output terminal and an I− output terminal, and a Q output from a Q+ output terminal and a Q− output terminal. 8. The method of claim 7, wherein said output ports of said differential quadrature all-pass filter and said input ports of said PPF circuit are balanced.