A branch-line coupler, adapted to radio frequency circuits, includes an input port, a first output port, a second output port, an isolated port, a first transmission line, a second transmission line, a first bent branch line, and a second bent branch line. The first transmission line is electrically connected between the input port and the first output port, and carries two open branches. The second transmission line is electrically connected between the isolated port and the second output port, and carries two open branches. The first bent branch line is electrically connected between the input port and the isolated port. The second bent branch line is electrically connected between the first output port and the second output port. The open branches of the first transmission line and the second transmission line resemble the bone structure of a fish skeleton.

A Doherty power amplifier and a device are disclosed. In a combiner of the Doherty power amplifier, a first input port and a termination port are open coupled by at least two coupled microstrip lines and/or a second input port and an output port are open coupled by at least two coupled microstrip lines. Therefore, a balanced amplitude bandwidth may be obtained and may be much broader than that of the existing solutions, in addition, a controllable size or a potentially small size may be realized. Furthermore, the Doherty power amplifier in this disclosure may provide large 2.sup.nd harmonic suppression to meet product spectrum mask requirements.

A hybrid coupler includes a 90° hybrid coupler and a first quarter wavelength conductive stub. The 90° hybrid coupler includes a coupling section, a first input transmission line that is coupled to the coupling section, a second input transmission line that is coupled to the coupling section, a first output transmission line that is coupled to the coupling section and a second output transmission line that is coupled to the coupling section. The first quarter wavelength conductive stub is coupled to the second output transmission line.

The present application discloses embodiments that relate to an electromagnetic apparatus. In one aspect, the present apparatus includes a circuit board configured to propagate an electromagnetic signal. The apparatus also includes a waveguide configured to propagate an electromagnetic signal. The apparatus further includes a coupling port configured to couple a signal between the circuit board and the waveguide, where the coupling port has dimensions based on a desired impedance of the port.

A branch-line coupler of reduced size but comparable performance includes a first transmission line, a second transmission line, a first bent transmission line, and a second bent transmission line. The first transmission line includes a first strip transmission line, a first branch transmission line, and a second branch transmission line. The first strip transmission line extends along a predetermined direction, the first and second branch transmission lines being slotted. The first and second branch transmission lines are symmetrical around a first axis and around a second orthogonally-disposed axis. The first bent transmission line is electrically connected to the terminals of the first and second transmission lines on one side, and the second bent transmission line is electrically connected to the terminals of the first and second transmission lines on the other side.

Embodiments of a method and an apparatus for a quadrature hybrid are disclosed. In an embodiment, a quadrature hybrid includes a first port, a second port, a third port, a fourth port, first, second, and third inductors, first, second, third, and fourth capacitors, and a first variable capacitor tuning network connected between the first port and the fourth port, and a second variable capacitor tuning network connected between the second port and the third port.

Techniques and apparatuses are described that implement a smart device-based radar system capable of detecting human vital signs using a compact circularly-polarized antenna. A radar system includes at least one compact circularly-polarized antenna with a patch antenna and a quadrature hybrid coupler. The quadrature hybrid coupler is on a separate plane that is above or below the patch antenna. By vertically stacking the patch antenna with the quadrature hybrid coupler, lateral dimensions of the radar system can be reduced relative to other antenna configurations or designs. The quadrature hybrid coupler can also have a ring-shape design to improve isolation and polarization purity of the compact circularly-polarized antenna relative to a rectangular design. The compact circularly-polarized antenna enables a radar system operating at frequencies between approximately 1 gigahertz (GHz) and 24 GHz to be implemented within a variety of small smart devices.

The present application discloses embodiments that relate to an electromagnetic apparatus. In one aspect, the present apparatus includes a circuit board configured to propagate an electromagnetic signal. The apparatus also includes a waveguide configured to propagate an electromagnetic signal. The apparatus further includes a coupling port configured to couple a signal between the circuit board and the waveguide, where the coupling port has dimensions based on a desired impedance of the port.

A radio-frequency switching apparatus that can be used to turn a signal path on or off or to attenuate a radio-frequency signal. The switching apparatus comprises at least one radio-frequency input, at least one radio-frequency output, at least one transmission line providing a signal path between the at least one radio-frequency input and the at least one radio-frequency output, and at least one transition metal oxide portion. The radio-frequency switching apparatus also comprises direct current blocking means electrically coupled between the at least one transition metal portion and the at least one radio-frequency input. The radio-frequency switching apparatus also comprises biasing means for providing a bias across the at least one transition metal oxide portion such that power transferred between the radio-frequency input and the radio-frequency output is controlled by controlling the bias level across the at least one transition metal oxide portion.

A signal level control element comprises a substrate having conductive formations defining a substrate integrated wave-guide arrangement disposed at least partly within the substrate; the substrate integrated waveguide arrangement providing a quadrature hybrid coupler having first and second pairs of signal ports, such that a signal introduced to a port of one pair of the first and second pairs is provided with equal amplitude but a 90 degree phase difference to both ports of the other pair of the first and second pairs; in which a port of the first pair is configured to receive an input signal and the other port of the first pair is configured to provide an output signal; and termination circuitry connected to the ports of the second pair, the termination circuitry providing, for each port of the second pair, a respective termination having a variable impedance dependent upon a respective control signal.