Several embodiments of an envelope tracking active circulator is disclosed with a method to cascade them. In an active transistor based circulator (active circulator), gate (base) and drain (collector) bias voltage can be adjusted by RF or microwave input envelop signal. This is called envelop tracking active circulator. In this concept, input RF signal is detected by detection circuit, such as detection diode or coupler and converted into low frequency envelop signal by the proper filtering circuitry. The generated envelop signal controls the supply voltage of the drain and gate with the proper function of the envelop signal to improve active circulator insertion loss, isolation and power handling capability. This concept can be applied to any type of solid-state FET (Field effect transistor) transistor based active circulator, as long as they have bias dependent trans-conductance and capacitances inside. For a BJT (bipolar junction transistor) based active circulator, base bias current supply modulator will be used instead of voltage supply modulator.

Disclosed is an apparatus and a method for facilitating a first frequency filtering and a second frequency filtering together with nonreciprocal frequency conversion for electromagnetic isolation.

A multi-port active circulator where each of a plurality of FET transistors has (i) a gate connected to an associated port of the multi-port active circulator via a capacitor of an associated one of a plurality of first RF chokes, each of the first RF chokes being connected to a gate of an associated FET transistor of said plurality of transistors, the associated port of said associated FET transistor and to a power supply bias connection; (ii) a source connected to a common point; and (iii) a drain connected to the gate of the same FET transistor by a feedback circuit and connected to the gate of a neighboring FET transistor via a capacitor of one of a plurality of second RF chokes, each of which coupling gates and drains of neighboring FET transistors via capacitors thereof and being connected to another power supply bias connection.

A multi-port active circulator where each of a plurality of FET transistors has (i) a gate connected to an associated port of the multi-port active circulator via a capacitor of an associated one of a plurality of first RF chokes, each of the first RF chokes being connected to a gate of an associated FET transistor of said plurality of transistors, the associated port of said associated FET transistor and to a power supply bias connection; (ii) a source connected to a common point; and (iii) a drain connected to the gate of the same FET transistor by a feedback circuit and connected to the gate of a neighboring FET transistor via a capacitor of one of a plurality of second RF chokes, each of which coupling gates and drains of neighboring FET transistors via capacitors thereof and being connected to another power supply bias connection.

A multi-port active circulator includes a plurality of cascode circuits coupled to one another in a ring. Each respective cascode circuit of the plurality of cascode circuits is coupled to a respective port of a plurality of ports. Each respective cascode circuit includes a common source transistor, a common gate transistor coupled to the common source transistor, and a feedback circuit coupled from the common gate transistor to the common source transistor. Each common source transistor of each respective cascode circuit is coupled to a common junction point.

A multi-port active circulator includes a plurality of cascode circuits coupled to one another in a ring. Each respective cascode circuit of the plurality of cascode circuits is coupled to a respective port of a plurality of ports. Each respective cascode circuit includes a common source transistor, a common gate transistor coupled to the common source transistor, and a feedback circuit coupled from the common gate transistor to the common source transistor. Each common source transistor of each respective cascode circuit is coupled to a common junction point.

Disclosed is an apparatus and a method for facilitating a first frequency filtering and a second frequency filtering together with non-reciprocal frequency conversion for electromagnetic isolation.