Techniques are provided for a broadband microwave/millimeter-wave balanced-to-unbalanced transformer (balun). A balun implementing the techniques according to an embodiment includes a first impedance matching network configured to reduce insertion and return losses of a single-ended signal at a first port of the balun. The balun also includes a first planar bifilar coupled transmission line coupled to the first impedance matching network and configured to transform the single-ended signal into a differential signal. The balun further includes a second planar bifilar coupled transmission line coupled to the first bifilar coupled transmission line and configured to compensate for amplitude and phase imbalance induced on the differential signal by the first bifilar coupled transmission line. The balun further includes a second impedance matching network coupled to both planar bifilar coupled transmission lines and configured to reduce insertion and return losses of the differential signal at second and third ports of the balun.

A balun includes an unbalanced terminal; balanced terminals; first and second main lines; and first and second sub-lines. The first main line has an end connected to the unbalanced terminal. The second main line has an end connected to the first main line and an end that is open. Each of the first and the second sub-lines is connected between the balanced terminal and a reference potential, respectively. The second sub-line includes a first partial line connected to the balanced terminal, and a second partial line connected between the first partial line and the reference potential. The second main line includes a third partial line connected to the first main line, and a fourth partial line connected to the third partial line. The distance between the first partial line and the third partial line is shorter than the distance between the second partial line and the fourth partial line.

A filter circuit includes a branch line coupler and a balun circuit having an input terminal connected to the branch line coupler to receive a signal, a first line connected to the input terminal and having a length comparable to a quarter of an electrical length of one wavelength at a frequency of the signal, a second line connected to the input terminal and having a length comparable to the quarter, a third line connected to the second line and having a length comparable to the quarter, and a fourth line connected to the third line and electromagnetically coupled to the first line, the fourth line having a length comparable to the quarter, wherein an end of the first line and an end of the fourth line are both connected to a ground or open-circuited, or are connected to two respective terminating resistors whose resistance values are equal.

A balun includes first to fourth lines and a stack. A plurality of first conductor layers forming the first and third lines are located in a first region in the stack. A plurality of second conductor layers forming the second and fourth lines are located in a second region in the stack. A ground conductor layer is located closer to the second region than to the first region. The plurality of second conductor layers include a conductor layer pair where a distance between two conductor layers is smallest.

Baluns with integrated matching networks are provided herein. In certain embodiments, a balun structure includes a first pair of coupled lines, a second pair of coupled lines and a transmission line. Additionally, a first port of the balun is connected to a reference voltage by way of a first line of the first pair of coupled lines, the transmission line, and a first line of the second pair of coupled lines. Furthermore, a second port of the balun is connected to the reference voltage by way of a second line of the first pair of coupled lines, while a third port of the balun is connected to the reference voltage by way of a second line of the second pair of coupled lines. The first port serves as an unbalanced signal terminal, while the second port and the third port serve as positive and negative signal terminals.

A balun includes an unbalanced terminal, balanced terminals, and lines, and converts a signal between an unbalanced line and an balanced line. A first line is connected between the unbalanced terminal and a reference potential. A second line is connected between the balanced terminal and the reference potential, and is coupled to the first line. A third line is connected between the balanced terminal and the reference potential, and is coupled to the first line. A fourth line is connected in parallel to the second line, and is coupled to the third line. The fourth line is configured such that a signal with an opposite phase to that of a signal passing through the third line passes through the fourth line.

Embodiments relate to a transformer-based impedance matching network that may dynamically change its characteristic impedance by engaging different inductor branches on a primary side and optionally, on the secondary side. A primary side transformer circuit includes a primary inductor (311) and secondary inductor (321) configured to provide impedance matching over a first frequency band. One or more additional inductor branches (314A, 314B, are switchably coupled to either or both of the primary and secondary inductors to modify the impedance matching characteristics over additional operating frequencies. One or more LC filter branches (321, 322, 326, 327, 336, 330) can be included at the output of the secondary side to filter harmonic frequencies in each of the operating frequency bands.

A balun is enhanced with design features that extend the operational bandwidth of the balun allowing the balun to operate at lower frequencies. The design enhancements also suppress resonances that otherwise cause sudden power drops at a resonance frequency while a load is connected between the balun's differential outputs.

A filter circuit includes a branch line coupler and a balun circuit having an input terminal connected to the branch line coupler to receive a signal, a first line connected to the input terminal and having a length comparable to a quarter of an electrical length of one wavelength at a frequency of the signal, a second line connected to the input terminal and having a length comparable to the quarter, a third line connected to the second line and having a length comparable to the quarter, and a fourth line connected to the third line and electromagnetically coupled to the first line, the fourth line having a length comparable to the quarter, wherein an end of the first line and an end of the fourth line are both connected to a ground or open-circuited, or are connected to two respective terminating resistors whose resistance values are equal.

A balun includes first to fourth lines and a stack. A plurality of first conductor layers forming the first and third lines are located in a first region in the stack. A plurality of second conductor layers forming the second and fourth lines are located in a second region in the stack. A ground conductor layer is located closer to the second region than to the first region. The plurality of second conductor layers include a conductor layer pair where a distance between two conductor layers is smallest.