Patent Description:
Baluns include electrical devices configured to convert between a balanced signal connection and an unbalanced signal connection.

<CIT> discloses a circuit board whose metallization comprises at least one coplanar stripline for supplying signals to a radiator, in particular a mobile communication radiator. In this arrangement, the circuit board comprises a field converter, which is electrically connected to the coplanar stripline and which conducts a coaxial field through at least one layer of the circuit board and converts it into the coplanar stripline field of the coplanar stripline.

<NPL>, discloses a probe-fed dipole antenna with parasitic patches as the element for wideband and wide-scanning planar-phased arrays. The printed dipole antenna with parasitic patches is directly matched with an SMA connector through the modified probe structure.

<CIT> discloses a broad band Balun produced by taking the approach of gradually perturbing the field structure from one form to the other over a given distance. In an example the transition from one field structure to another is carried out by cutting a wedge shape out of a cable. Any shape however can be removed from the cable commensurate with forming a match condition, as long as the transition is gradual.

<CIT> discloses a circuit board whose metallization comprises at least one coplanar stripline for supplying signals to a radiator, in particular a mobile communication radiator. In this circuit board arrangement, the circuit board comprises a field converter, which is electrically connected to the coplanar stripline and which conducts a coaxial field through at least one layer of the circuit board and converts it into the coplanar stripline field of the coplanar stripline.

In a first aspect, the present disclosure provides a balun comprising: a center conductor configured to pass through a printed wiring board comprised of multiple dielectric layers; and cage vias arranged relative to the center conductor, the cage vias comprising: a first set of cage vias that extend between an unbalanced connection to the balun and a balanced connection to the balun, the first set of cage vias being part of a first circular arc and being connectable to electrical ground through a first ground ring; and a second set of cage vias that extend from the unbalanced connection part-way through the printed wiring board, the second set of cage vias being part of a second circular arc and being connectable to the electrical ground through a second ground ring, the second circular arc being longer than the first circular arc.

The distance from the balanced connection to the unbalanced connection may be a first distance. The second set of cage vias may extend a second distance through the printed wiring board. The first distance and the second distance may be different. The balun may also include a third set of cage vias that extend from the unbalanced connection a third distance through the printed wiring board. The third distance may be greater than the second distance and less than the first distance. The third set of cage vias may be part of a third circular arc and may be connected to the electrical ground through a third ground ring. The third circular arc may be longer than the first circular arc and shorter than the second circular arc. The balun may also include a fourth set of cage vias that extend from the unbalanced connection a fourth distance through the printed wiring board. The fourth distance may be between the second distance and the third distance. The fourth set of cage vias may be part of a fourth circular arc and may be connected to the electrical ground through a fourth ground ring. The fourth circular arc may be longer than the third circular arc and shorter than the second circular arc. There may be three vias in the first set of cage vias, five vias in the third set of cage vias, seven vias in the fourth set of cage vias, and nine vias in the second set of cage vias. The second circular arc may be <NUM>° around the center conductor.

The cage vias may be primary cage vias. The balun may also include secondary cage vias connected to the electrical ground. The secondary cage vias may be arranged in a circular arc around the primary cage vias. The secondary cage vias may be arranged in a <NUM>° circular arc around the primary cage vias. The secondary cage vias may extend from a layer of the printed wiring board at which the unbalanced connection is located to a layer of the printed wiring board at which the balanced connection is located.

The balun may include one or more tuning rings connected along a length of the center conductor. The one or more tuning rings may be configured to add capacitance to control how impedance of the balun changes with frequency of a signal passing through the balun. The following parameters may be selected to achieve target performance for the balun: diameters of individual cage vias and the center conductor, a number of layers of the printed wiring board with each layer corresponding to a termination point of a set of cage vias, a dielectric constant associated with dielectric in the multiple dielectric layers, and tuning rings associated with the center conductor to change a capacitance associated with the balun.

The unbalanced connection may be configured for connection to a coaxial cable. The balanced connection may be configured for connection to an antenna. The antenna may be an antenna in a phased array having multiple antennas, in which each antenna includes an analog transmitter/receiver module configured to create phase shifting required to electronically steer an antenna beam. The balanced connection may be configured for connection <NUM> cellular telephone tower antenna. The balanced connection may be configured for connection to a circuit board containing a digital signal processor (DSP).

In a second aspect, the present disclosure provides a balun comprising: a center conductor configured to pass through a printed circuit wiring board comprised of multiple dielectric layers; and stepped transitions between a balanced connection of the balun and an unbalanced connection of the balun, the stepped transitions comprising ground rings arranged in circular arcs and connectable to electrical ground, the ground rings increasing in length from a first ground ring at the balanced connection to a second ground ring at the unbalanced connection, the stepped transitions further comprising cage vias connected between the second ground ring and each other ground ring.

The balun may include one or more tuning rings connected along a length of the center conductor. The one or more tuning rings may be configured to add capacitance to control how impedance of the balun changes with frequency of a signal passing through the balun. The unbalanced connection may be configured for connection to a coaxial cable. The balanced connection may be configured for connection to an antenna in a phased array that includes multiple antennas, in which each antenna includes an analog transmitter/receiver module configured to create phase shifting required to electronically steer an antenna beam. The balanced connection may be configured for connection <NUM> cellular telephone tower antenna. The balanced connection may be configured for connection to a circuit board containing a digital signal processor (DSP). The cage vias may be primary cage vias. The balun may also include secondary cage vias connected to the electrical ground. The secondary cage vias may be arranged in a <NUM>° circular arc around the primary cage vias.

In a third aspect the present disclosure provides a system comprising: a first balun according to the second aspect; a second balun according to the second aspect; and a transmission line between the first balun and the second balun, the first balun being connected to the transmission line through the balanced connection and the second balun being connected to the transmission line through the balanced connection.

Each of the first balun and the second balun includes a center conductor that passes through a printed circuit wiring board having multiple dielectric layers. The balun also includes stepped transitions between a balanced connection of the balun and an unbalanced connection of the balun. The stepped transitions include ground rings arranged in circular arcs and connected to electrical ground. The ground rings increase in length from a first ground ring at the balanced connection to a second ground ring at the unbalanced connection. The stepped transitions include cage vias connected between the second ground ring and each other ground ring.

The apparatus, systems, and/or components thereof described herein may be configured, for example, through design, construction, arrangement, placement, operation, and/or signaling.

Two or more of the features described in this specification, including in this summary section, may be combined to form implementations not specifically described in this specification.

Like reference numerals in different figures indicate like elements.

Baluns include electrical devices configured to convert between a balanced signal connection and an unbalanced signal connection. An unbalanced signal connection includes an electromagnetic shield surrounding a center conductor. The shield is an outer conductor connected to electrical ground to reduce the amount of electrical interference reaching the center conductor. The current in the center conductor is referenced to the outer conductor. Accordingly, a signal voltage in the center conductor varies in relation to the electrical ground at the outer conductor. An example of conductors in an un-balanced signal configuration is a coaxial cable. A balanced signal connection includes two conductors for a signal, which have an equal impedance relative to electrical ground and which may both be surrounded by shielding in some examples. The currents through the two conductors are equal in magnitude, opposite in direction, and enclosed by magnetic field lines. The electric field between the conductors starts on one conductor and ends on the other conductor. Transmission of a signal over conductors in a balanced signal configuration may reduce the influence of noise or interference from external electric fields. Conductors in a balanced signal configuration may also be less susceptible to ground loops than conductors in an unbalanced configuration. An example of conductors in a balanced signal configuration is a dipole antenna connection.

Described herein is an example balun, called a "stepped balun". References to a stepped balun may include any of its variants described herein. In an example, the stepped balun includes a center conductor that passes through a printed wiring board having multiple dielectric layers. Stepped transitions between the balanced connection of the balun and the unbalanced connection of the balun enable conversion between the unbalanced connection and the balanced connection. In an example, the stepped transitions include ground rings configured in circular arcs that are connected to a common electrical ground. The ground rings decrease in length from a largest ground ring at the unbalanced connection to a smallest ground ring at the balanced connection, thereby gradually changing between an unbalanced connection and a balanced connection. The stepped transitions include cage vias connected among the various ground rings. The cage vias are electrically conductive structures, such as plated through-holes, that are "cage" in the sense that they surround, at least partly, the center conductor.

<FIG> shows an example of a stepped balun <NUM>. In this example, there are four steps defined by four ground rings <NUM>, <NUM>, <NUM>, and <NUM> in balun <NUM>. As described in more detail below, ground rings <NUM>, <NUM>, <NUM>, and <NUM> are connected electrically and physically, respectively, to nine cage vias (the cage vias are labeled <NUM> collectively), seven cage vias, five cage vias, and three cage vias. Stepped balun <NUM> is referred to as a four-step balun because there are four ground rings between the balanced connection <NUM> and the unbalanced connection <NUM>. However, the stepped baluns described herein are not limited to the configuration shown in <FIG>. For example, the numbers of steps and/or vias may be different in different implementations.

<FIG> show example layouts of the ground rings and tunings rings (described below) at steps of balun <NUM>. Arrows 14a, 13a, 12a, and 11a at balun <NUM> shown in the right of each figure show where the layer at the left is located. As shown in <FIG>, ground ring <NUM> includes three holes to hold three cage vias that connect electrically to and physically to and through ground ring <NUM>. As shown in <FIG>, ground ring <NUM> includes five holes to hold five cage vias that connect electrically to and physically to and through ground ring <NUM>. As shown in <FIG>, ground ring <NUM> includes seven holes to hold seven cage vias that connect electrically to and physically to and through ground ring <NUM>. As shown in <FIG>, ground ring <NUM> also connects electrically and physically to cage vias, such as cage via <NUM>, that terminate at ground ring <NUM> - that is, that do not pass through ground ring <NUM>.

Stepped balun <NUM> includes a center conductor <NUM> that passes orthogonally through a printed wiring board (PWB), such as printed wiring board <NUM> of <FIG>, containing ground rings <NUM> to <NUM>. The printed wiring board includes multiple dielectric layers 25a to 25d and metal layers that form the ground rings. In this example, the printed wiring board includes at least four dielectric layers; however, other numbers of dielectric layers may be used. The center conductor is a plated through-hole via through the printed wiring board.

Unbalanced electrical connection <NUM>, an example of which is a coaxial connection, is included on one surface 25e of printed wiring board <NUM>. Balanced electrical connection <NUM> is included on the other - for example, the opposite - surface 25f of printed wiring board <NUM>. The balanced electrical connection includes both the center conductor and the ground ring <NUM>. Both connections enable interfacing to standard components, such as a standard dipole antenna. <FIG> shows stepped balun <NUM> as transparent. Here, the balanced and unbalanced connections may be more readily apparent than in <FIG>.

In an example, stepped balun <NUM> is configured to transform the fields and currents of an unbalanced transmission line into those for a balanced, two-conductor transmission line. The stepped balun thus is configured convert balanced electrical signals to unbalanced electrical signals and unbalanced electrical signals to balanced electrical signals. In this context, the stepped balun can be viewed as a "field transformer". That is, stepped balun <NUM> transforms the coaxial line electric (and magnetic) field distribution into a two-conductor electric (and magnetic) field distribution over a relatively small electrical length. For example, as shown in <FIG>, <FIG>, and <FIG>, the ground rings (outer conductors) change in arc length gradually (stepwise) between unbalanced connection <NUM> and balanced connection <NUM> over the thickness of a printed wiring board, which is a relatively short distance. Stepped balun <NUM> performs the opposite transformation as well.

As shown in <FIG> and <FIG>, stepped balun <NUM> includes cage vias <NUM> arranged relative to the center conductor <NUM>. In this example, the cage vias are arranged in circular arcs around center conductor <NUM>, as shown. The circular arcs of the cage vias correspond to the shape of the ground rings, which are also in circular arcs. The sizes of the circular arcs progressively decrease from unbalanced balun connection <NUM> to balanced balun connection <NUM>. For example, as show in <FIG> and <FIG>, proximate to unbalanced connection <NUM>, the circular arc (a circle here) for ground ring <NUM> covers <NUM>°. At the location of the first step towards the balanced connection, the circular arc for ground ring <NUM> covers about <NUM>° in this example. At the location of the next step towards the balanced connection, the circular arc of ground ring <NUM> covers about <NUM>° in this example. At the location of the next step, that is, at the balanced connection <NUM>, the circular arc covers about <NUM>° in this example. The cage vias are arranged along these circular arcs as shown in <FIG>.

As noted above, the extent and the lengths of the circular arcs - including the extent and lengths of the ground rings and spans of the cage vias - may be different than those shown and may vary based on a variety of factors, such as depth of the printed wiring board. The cage vias and ground rings at each step of the stepped balun are connected to the same electrical ground and are, therefore, configured to provide gradual or stepped transition between the balanced and unbalanced connections at opposite surfaces of the printed wiring board.

Referring to <FIG>, stepped balun <NUM> includes a first set 30a, 30b, 30c of three cage vias that extend all the way between unbalanced connection <NUM> and balanced connection <NUM>. The first set of three cage vias is part of first circular arc of cage vias connected to ground ring <NUM>. In this example, ground ring <NUM> may extend along a length that covers about <NUM>°, or less, of a circle around center conductor <NUM>. Unbalanced connection <NUM>, in this example, includes a pseudo-coaxial connection that is configured for connection to a standard coaxial cable; however, a pseudo-coaxial connection configured for connection to customized coaxial cable may instead be used. Balanced connection <NUM> includes a two-conductor port to connect electrically to a balanced transmission line. An example two-conductor port includes a dipole antenna connection. Examples of antenna connections include, but are not limited to, two-terminal balanced feed antennas, such as, dipole antennas, bow-tie antennas, sinuous antennas, spiral antennas, folded dipole antennas, bi-conical antennas, yagi-uda antennas, and loop antennas.

Stepped balun <NUM> includes a second set of cage vias that are physically and electrically connected to unbalanced connection <NUM> and to ground ring <NUM>. The cage vias in this set include cage vias 30a, 30b, and 30c, along with cage vias 30d and 30e. Accordingly, there are five cage vias in the second set. Stepped balun <NUM> includes a third set of cage vias that are physically and electrically connected to unbalanced connection <NUM> and to ground ring <NUM>. The cage vias in this set include cage vias 30a, 30b, 30c, 30d, and 30e, along with cage vias 30f and <NUM>. Accordingly, there are seven cage vias in the third set. Stepped balun <NUM> includes a fourth set of cage vias that are physically and electrically connected to unbalanced connection <NUM> and to ground ring <NUM>. The cage vias in this set include cage vias 30a, 30b, 30c, 30d, 30e, 30f, and <NUM>, along with cage vias <NUM> and 30i. Accordingly, there are nine cage vias in the third set. In this example, ground ring <NUM> extends in a complete circle (<NUM>°) around center conductor <NUM> to approximate a shield of a coaxial cable. Notably, the cage vias are discontinuous - that is, there is dielectric between them - so they may not operate precisely like a coaxial cable. Cage vias 30a through 30i have also been labeled on <FIG>.

As shown in <FIG> and <FIG> and as previously noted, the ground rings, also referred to as outer conductor rings, progressively decrease in arc length from unbalanced connection <NUM> to balanced connection <NUM> such that ground ring <NUM> is longer than ground ring <NUM>, ground ring <NUM> is longer than ground ring <NUM>, and ground ring <NUM> is longer than ground ring <NUM>. Stated alternatively, the ground rings progressively increase in arc length from balanced connection <NUM> to unbalanced connection <NUM> such that ground ring <NUM> is shorter than ground ring <NUM>, ground ring <NUM> is shorter than ground ring <NUM>, and ground ring <NUM> is shorter than ground ring <NUM>.

As noted, there are four ground rings in example stepped balun <NUM>. As also noted previously, there are four dielectric layers included on printed wiring board. Accordingly, in this example, each ground ring is formed on a surface of one of the dielectric layers. In some implementations, there may be more or fewer dielectric layers and, in those examples, more or fewer ground ring layers or steps in the stepped balun. For example, a stepped balun may include four, five, six, seven, eight, or more steps configured as described herein. In some implementations, the dielectric layers may be manufactured with ground rings inside of them and, as such, the ground rings may not be located on the surfaces of individual dielectric layers in the printed wiring board.

Referring to <FIG>, <FIG>, and <FIG>, in some implementations, there may be one or more (e.g., three) tuning rings (or tuning pads) <NUM> connected along a length of center conductor <NUM> within the area enclosed by cage vias <NUM>. That is, in some implementations, the tuning rings may be between the center conductor and the cage vias. The one or more tuning rings are configured to add capacitance to the stepped balun in order to control how impedance of the stepped balun changes operation with changes in frequency of a signal passing through the stepped balun. The tuning rings may include capacitors - for example, dielectric between conductive plates - or other appropriately configured conductive and/or nonconductive materials. Any appropriate number of tuning rings may be used. Their numbers and positions may be dictated by a target performance.

The cage vias of <FIG> - the first, second, third, and fourth sets - are referred to as primary cage vias. As shown in <FIG>, a stepped balun <NUM>, which otherwise has the same structure as stepped balun <NUM>, may include a set of secondary cage vias <NUM>. Primary cage vias <NUM> may be at a first radius <NUM> relative to center conductor <NUM>, and secondary cage vias <NUM> may be at a larger radius <NUM> relative to center conductor <NUM>. The secondary cage vias <NUM> may surround the primary cage vias <NUM> in whole as shown in <FIG>, or in part, and may extend from a layer of the printed wiring board at which the unbalanced connection is located (or proximate thereto) to a layer of the printed wiring board at which the balanced connection is located. The secondary cage vias include electrically conductive structures, such as plated through-holes, that are "cage" in the sense that they surround, at least partly, the primary cage vias and, consequently, also the center conductor. The secondary cage vias connect to the same electrical ground as the ground rings and the primary cage vias. Connection may be at the layer of the printed wiring board containing the balanced connection, at the layer of the printed wiring board containing the unbalanced connection, or at both layers. In some implementations, the secondary vias are arranged in a <NUM>° circular arc around the primary cage vias. In this configuration, the secondary cage vias electromagnetically shield the stepped balun. In stepped balun <NUM>, there are eight secondary cage vias, however, any appropriate number may be used.

To vary the performance of the stepped balun - for example, to achieve a target performance - the following parameters may be configured or changed: diameters of individual primary and/or secondary cage vias, a diameter of the center conductor, a number of layers of the printed wiring board, a dielectric constant associated with dielectric in the multiple dielectric layers, and tuning rings associated with the center conductor to change a capacitance associated with the balun. Distances between the center conductors and the numbers and types of cage vias may also be varied, among other parameters.

In some implementations, the stepped balun is relatively compact and vertically (orthogonally) arranged through the printed wiring board. In some implementations, the stepped balun reduces or minimizes the footprint of a device (a unit cell) containing the stepped balun. This may be relevant for wideband, wide-scan angle phased array applications having a unit cell an area ≤ (λ/<NUM>)<NUM>. In this regard, the stepped balun may have applicability for phased array applications and other applications where improved RF (radio frequency) performance and economical use of unit cell area, substrate thickness, and weight may be a consideration.

In some implementations, the four-step balun is configured to operate anywhere over a five-octave bandwidth (e.g., <NUM> (gigahertz) to <NUM>) at relatively low-loss performance. In an example implementation, in a stepped balun having a 50Ω GPO (standard coaxial) connector input impedance and a two-conductor output impedance varying from 40Ω to 75Ω, the maximum signal loss is <NUM>. 290dB (decibels) at <NUM> for a two-conductor impedance of 75Ω. In an example implementation, a stepped balun has a 75Ω coaxial input and 75Ω two-conductor output. In this implementation, the return loss and insertion loss over a five-octave bandwidth is comparable to the 50Ω input and 50Ω two-conductor impedance return loss and insertion loss. The maximum insertion is <NUM>. 11dB at <NUM> in this example. In an example, a stepped balun having a 50Ω coaxial input and 50Ω two-conductor output is scalable in frequency to operate at up to <NUM>. The return loss and insertion loss are relatively low over a five-octave bandwidth of <NUM> to <NUM>. The maximum insertion loss is <NUM>. 19dB at <NUM> in this example.

The stepped balun operates in a TEM (transverse electromagnetic) transmission mode. In this regard, the stepped balun can be considered to operate as a non-resonant transmission line, or portion thereof, operating in the TEM mode. Resonant-mode losses, due to higher order modes like the TE11 mode, are far above the four-step balun configuration described herein. Using the TE11 mode cut-off frequency of a coaxial transmission line as a proxy for the TE11 mode cut-off frequency of the stepped balun, the following TE11 mode cut-off frequencies may be determined for the four-step balun configuration and the four-step mm-wave (millimeter wave) frequency configuration described below:.

In some implementations, the rate of change of insertion phase versus frequency, which is called the group delay, is a consideration in radar applications that transmit complex, wideband waveforms and also in commercial wireless communications such as <NUM> (fifth-generation of mobile telecommunications technology) wireless applications that use complex modulation schemes. As previously explained, the stepped balun operates in the TEM mode which, in some examples, may result in a group delay that changes in less than or equal to two picoseconds (ps) over a five-octave bandwidth, making the stepped balun appropriate for these types applications.

The stepped balun may be implemented using standard printed wiring board materials and fabrication techniques. This may facilitate use of the stepped balun with phased array antennas, as described below, in which hundreds or thousands of unit cells are fabricated across a number of printed wiring boards. The stepped balun may be fabricated as follows. An image and copper etch operation may be performed for each dielectric layer of a printed wiring board. A lamination cycle may be performed for a resulting stack of the dielectric layers in the printed wiring board. A drill and copper plate operation may be performed or the resulting stack. Finally, the stack may be back-drilled to produce the cage vias.

In an example configuration of the stepped balun, the primary cage vias are on a <NUM> inches (<NUM> millimeter (mm)) diameter circle or arc (that is, less than a full circle) around the center conductor. The secondary cage vias are on a <NUM> inches (<NUM>) diameter circle around the center conductor. In this example, the total height of the stepped balun is <NUM> inches (<NUM>) and the height-to via diameter aspect ratio is six. These, however, are examples of dimensions. Stepped baluns may have different dimensions than these.

<FIG> shows a side view of a components of a stepped balun <NUM> (including dielectric layers <NUM>) having the dimensions described in the preceding paragraph, along with a cut plane <NUM> at the two-conductor balanced port side of the stepped balun. Electric field magnitude is evaluated for a <NUM> signal through the balun at this cut plane. <FIG> shows variations in electric field magnitude concentrations <NUM> at the two-conductor ports 51a, 51b (center-via pad and outer conductor ring, respectively) at the cut plane. In this example, the power outside the stepped balun region is less than -50dB relative the peak power between the two conductors at the balun's balanced connection. Secondary cage vias are not included in this example. As shown in <FIG>, greater electric field magnitudes are concentrated between the center-via pad and outer conductor ring.

<FIG> show, for stepped balun <NUM>, a surface current density magnitude <NUM> between its center conductor <NUM>, three of its cage vias <NUM>, and top outer conductor ring <NUM>. Secondary cage vias are not included in the example of <FIG>. <FIG> show a surface current density magnitude for a stepped balun <NUM> having the configuration of <FIG> and also having secondary cage vias <NUM> as in balun <NUM> of <FIG>. As is evident by their dark shading, secondary cage vias <NUM>, grounded to the primary cage vias, have negligible surface current density. Electromagnetic energy <NUM> is concentrated between the center conductor 55a and center-via pad 53a, and top outer conductor pad connected to the three primary cage vias (vias <NUM> in <FIG>).

<FIG> show the surface current density directions for primary cage vias in an example stepped balun such as balun <NUM>. The largest current vector <NUM> on the center conductor <NUM> faces the two outer conductor vias <NUM>, <NUM>, and points downward. The largest current vectors <NUM> on two outer conductor cage vias point upward. The current densities are equal, and opposite in direction in this example. The maximum magnitude of the current density is on the center conductor and is about <NUM> A/m (amperes-per-meter). The two facing cage vias <NUM>, <NUM> each have a surface current of about <NUM> A/m. Secondary cage vias are not included <FIG>.

<FIG> show views of an example four-step balun <NUM> configured for operation at mm-wave (millimeter-wave) frequencies. Stepped balun <NUM> has a 50Ω coaxial input. Stepped balun <NUM>, like stepped balun <NUM> of <FIG>, includes four steps having physical and electrical connections to nine cage vias, seven cage vias, five cage vias, and three cage vias, respectively. However, stepped balun <NUM> includes sixteen secondary cage vias <NUM> surrounding the primary cage vias <NUM>. In this example, primary cage vias <NUM> are on a <NUM> inch (<NUM>) diameter circle <NUM> relative to center conductor <NUM>. Secondary cage vias <NUM>, which are electrically connected to the same electrical ground as the primary cage vias, are on a <NUM> inch (<NUM>) diameter circle <NUM> relative to center conductor <NUM>. All vias are <NUM> inches (<NUM>) in diameter. The vias may be fabricated using a standard microvia processes. The microvia aspect ratio is <NUM>:<NUM> for each via in this example.

<FIG> shows stepped balun <NUM> having the dimensions described in the preceding paragraph along with a cut plane <NUM> at the two-conductor balanced port side of the stepped balun, where the electric field magnitude is evaluated for a <NUM> signal. <FIG> shows the electric field magnitude concentrations <NUM>, at the two-conductor port <NUM> of stepped balun <NUM>. The power outside the balun region is less than -55dB relative the peak power between the two conductors.

<FIG> shows, for stepped balun <NUM>, a surface current density magnitude between center via <NUM> and primary cage vias <NUM>. The currents, and the electric field (shown in <FIG>), are focused between center via <NUM> and inside of primary cage vias 72a. There is a small current density on secondary cage vias <NUM>.

<FIG> shows an example system <NUM> having a first stepped balun <NUM>, a second stepped balun <NUM>, and a transmission line <NUM> between the first stepped balun and the second stepped balun. Transmission line <NUM> is a two-conductor balanced transmission line. The first and second stepped baluns are connected to the transmission line through their respective balanced connections. Coaxial cables may be connected to the unbalanced connections of stepped baluns <NUM> and <NUM>. In the implementation of <FIG>, stepped baluns <NUM> and <NUM> do not include secondary cage vias. However, secondary cage vias may be used with either or both stepped baluns. <FIG> shows system <NUM> with a cut plane <NUM> along transmission line <NUM>, where electric field magnitude is evaluated for a <NUM> signal.

<FIG> shows the electric field magnitude concentrations <NUM> at the cut plane. <FIG> show the surface current density magnitude of system <NUM>. The maximum current densities <NUM> on the two-conductor transmission line <NUM> are on the transmission line - that is, the conductor - surfaces facing each other. <FIG> shows the vector surface current density magnitude between conductors 88a and 88b in two-conductor transmission line <NUM>. The maximum current densities on the two-conductor transmission line are on the surfaces of conductors 88a and 88b that face each other. The currents are equal and <NUM>° out of phase.

The stepped balun may be configured for use with standard radiators (e.g., antennas) such as the dipole radiator. The stepped balun also may be configured for use with phased array antenna configurations, as described herein. The stepped balun may be configured for use with narrow-band (≤ <NUM>% tunable bandwidth), to wide-band (> <NUM>% tunable bandwidth), to multi-octave tunable bandwidth two-terminal balanced feed antennas, such as a dipole antenna, a bow-tie antenna, a sinuous antenna, a spiral antenna, and the like.

Antennas such as those identified above may be used in a variety of systems including, but not limited to, a phased array radar, communication antennas and arrays, remote sensing arrays, and medical imaging antennas and arrays (e.g., microwave based tumor imaging). The stepped balun may be used for low-profile, low-loss, wide scan-angle, multi-band performance applications. Example applications of this type may include sensors on aircraft, helicopters, drones, and the like. In these applications, the stepped balun, which may be lightweight, low profile, and perform multiple tasks, may be configured for use over multiple frequency bands. Such frequency bands may include, but are not limited to, frequency bands for weather radar, collision avoidance, ground terrain mapping, and/or electronic warfare. The stepped balun may be configured for use with ground and ship based radar systems, for example, for dual-band radars that take advantage of low frequency search (e.g., UHF (ultra-high frequency) band (<NUM> to <NUM>)) and higher frequency resolution track (e.g., C-Band (<NUM> to <NUM>)).

An electrically or physically small antenna may require an electrically or physically small balun. <FIG> shows a stepped balun <NUM> configured to feed an electrically small, S-Band array radiator <NUM> having a 60Ω ohm input impedance. The coaxial port <NUM> of stepped balun <NUM> includes a 50Ω GPO connector. In this example, the total combined signal loss is less than or equal to <NUM>. 2dB from <NUM> to <NUM> using a <NUM> inch (<NUM>) x <NUM> inch (<NUM>) unit cell (a λ/<NUM> x λ/<NUM> unit cell). S-Band array radiator <NUM> and the stepped balun are part of phased array <NUM> containing multiple S-Band array radiators and stepped baluns of the same type. In a phased array each antenna includes an analog transmitter/receiver module configured to create phase shifting required to electronically steer an antenna beam.

The stepped balun may be configured for use with bow-tie radiators. In this regard, <FIG> shows an example dual-linear polarized X-Band array <NUM>. In each cell of array <NUM>, there is a vertical and horizontal bow-tie radiator. Both linear polarized radiators may be fed by a stepped balun.

The stepped balun may be configured for use with a dual-linear polarized radiator. An example polarized radiator having a common phase-center may require each pair of antenna terminals to be fed with orthogonal electric fields. The stepped balun may be configured to rotate its electric field by rotating its outer conductor through any angle relative to the center conductor. For example, in a stepped balun, the cage vias of the stepped balun may rotated relative to center conductor. As a result, the electric fields may rotate from fields <NUM> in <FIG> to fields <NUM> in <FIG>.

As noted previously, the stepped balun may be configured for use with <NUM> cellular applications. In this regard, example <NUM> handsets include up to <NUM> antennas. More antennas means less antenna area; therefore, it may be advantageous to reduce antenna size while maintaining antenna efficiency. The stepped balun may be configured to provide an efficient, electrically and physically small antenna and balun for <NUM> cellular telephone handsets. In this regard, the five-octave band performance of some implementations of the stepped balun covers the following <NUM> frequency bands.

Furthermore, antenna arrays deployed on cellular phone towers may require low-loss front-ends to reduce power amplifier prime power and air-cooling requirements, which are key cost drivers for <NUM> performance. The stepped balun, which is relatively low loss and operable over a wide band, may be configured for use in a MIMO (Massive Input/ Massive Output) <NUM> system. The stepped balun may reduce prime power and possibly reduce the weight of the antenna/ feed assembly.

The stepped balun may be configured to connect to a circuit board containing a digital signal processor (DSP). In this regard, components, such as differential amplifiers, used in DSP applications require differential signal inputs. The stepped balun maybe configured for use on a DSP backplane assembly, where component area is extremely limited, to provide a low-loss, low dispersion, wideband balun signal transformation from an unbalanced transmission line (e.g., a coaxial connector) to the two-terminal input of the differential amplifier. In addition, higher data rates require faster pulse rise/fall times. The multi-gigahertz, low dispersion performance of the stepped balun may be configured to handle pulse rise times that are on the order of nanoseconds.

The stepped balun may be configured for use with medical applications, as noted. In this regard, there is a need for compact, lightweight RF antennas for medical applications such as tumor imaging, cancer therapy, and the like, where lower microwave frequencies (e.g., L- or S- Band) are required for penetration deep into the human body to image tumors. In an example, the <NUM> inch (<NUM>) x <NUM> inch S-Band Array of <FIG> may be part of medical diagnostics and/ or therapy system.

Any "electrical connection" as used herein may include a direct physical connection or a wired or wireless connection that includes or does not include intervening components but that nevertheless allows electrical signals to flow between connected components. Any "connection" involving electrical circuitry that allows signals to flow, unless stated otherwise, is an electrical connection and not necessarily a direct physical connection regardless of whether the word "electrical" is used to modify "connection".

Elements of different implementations described may be combined to form other implementations not specifically set forth previously. Elements may be left out of the systems described previously without adversely affecting their operation or the operation of the system in general. Furthermore, various separate elements may be combined into one or more individual elements to perform the functions described in this specification.

Claim 1:
A balun (<NUM>) comprising:
a center conductor (<NUM>) configured to pass through a printed wiring board (<NUM>) comprised of multiple dielectric layers (25a-25d); and
cage vias (<NUM>) arranged relative to the center conductor, the cage vias comprising:
a first set (30a-30c) of cage vias that extend between an unbalanced connection (<NUM>) to the balun and a balanced connection (<NUM>) to the balun, the first set of cage vias being part of a first circular arc and being connectable to electrical ground through a first ground ring (<NUM>); and
a second set (30a-30i) of cage vias that extend from the unbalanced connection part-way through the printed wiring board, the second set of cage vias being part of a second circular arc and being connectable to the electrical ground through a second ground ring (<NUM>), the second circular arc being longer than the first circular arc.