Stepped Balun

Abstract

An exemplary balun includes a center conductor passing through a printed wiring board having multiple dielectric layers and a cage via disposed relative to the center conductor. The cage via includes 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 are part of a first arc and are connected to electrical ground via a first ground ring. The cage via includes a second set of cage vias that extend from the unbalanced connection partway through the printed wiring board. The second set of cage vias are part of a second arc and are connected to electrical ground via a second ground ring. The second arc is longer than the first arc.

Description

[Technical field]

[0001] This specification describes examples of stepped baluns and their exemplary applications. [Background technology]

[0002] A balun includes an electrical device configured to convert between balanced and unbalanced signal connections. Summary of the Invention

[0003] An exemplary balun includes a center conductor passing through a printed wiring board having multiple dielectric layers and a cage via disposed relative to the center conductor. The cage via includes 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 are part of a first arc and are connected to electrical ground via a first ground ring. The cage via includes a second set of cage vias that extend from the unbalanced connection partway through the printed wiring board. The second set of cage vias are part of a second arc and are connected to electrical ground via a second ground ring. The second arc is longer than the first arc. An exemplary balun may include one or more of the following features, either alone or in combination.

[0004] 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 and second distances may be different. The balun may also include a third set of cage vias extending a third distance through the printed wiring board from the unbalanced connection. 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 arc and may be connected to electrical ground via a third ground ring. The third arc may be longer than the first arc and shorter than the second arc. The balun may also include a fourth set of cage vias extending a fourth distance through the printed wiring board from the unbalanced connection. The fourth distance may be between the second and third distances. The fourth set of cage vias may be part of a fourth arc and may be connected to electrical ground via a fourth ground ring. The fourth arc may be longer than the third arc and shorter than the second 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 arc may be 360° around the center conductor.

[0005] The cage via may be a primary cage via. The balun may also include a secondary cage via connected to electrical ground. The secondary cage via may be arranged in an arc around the primary cage via. The secondary cage via may be arranged in a 360° arc around the primary cage via. The secondary cage via may extend from a layer of the printed wiring board where the unbalanced connection is located to a layer of the printed wiring board where the balanced connection is located.

[0006] The balun may include one or more tuning rings connected along the length of the center conductor. The one or more tuning rings may be configured to add capacitance to control how the impedance of the balun changes with the frequency of the signal passing through the balun. To achieve a target performance of the balun, the following parameters may be selected: diameter of the individual cage vias and center conductor, number of layers of a printed wiring board where each layer corresponds to a termination point of a set of cage vias, dielectric constants associated with the dielectrics of the multiple dielectric layers, and tuning rings associated with the center conductor to vary the capacitance associated with the balun.

[0007] 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 a phased array antenna having multiple antennas, each antenna including an analog transmitter / receiver module configured to generate a phase shift required to electronically steer an antenna beam. The balanced connection may be configured for connection to a 5G cellular tower antenna. The balanced connection may be configured for connection to a circuit board including a digital signal processor (DSP).

[0008] An exemplary balun includes a center conductor passing through a printed wiring board having multiple dielectric layers. The balun also includes a graduated transition between a balanced connection of the balun and an unbalanced connection of the balun. The graduated transition includes ground rings arranged in an arc and connected to an electrical ground. The ground rings increase in length from a first ground ring in the balanced connection to a second ground ring in the unbalanced connection. The graduated transition includes cage vias connected between the second ground ring and each of the other ground rings. An exemplary balun may include one or more of the following features, either alone or in combination.

[0009] The balun may include one or more tuning rings connected along the length of the center conductor. The one or more tuning rings may be configured to add capacitance to control how the impedance of the balun changes with the frequency of the 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 of a phased array including multiple antennas, each antenna including an analog transmitter / receiver module configured to generate a phase shift required to electronically steer an antenna beam. The balanced connection may be configured for connection to a 5G cellular tower antenna. The balanced connection may be configured for connection to a circuit board including a digital signal processor (DSP). The cage via may be a primary cage via. The balun may also include a secondary cage via connected to an electrical ground. The secondary cage via may be arranged in a 360° arc around the primary cage via.

[0010] An exemplary system includes a first balun and a second balun. Each of the first balun and the second balun includes a center conductor passing through a printed wiring board having a plurality of dielectric layers. The balun also includes a graduated transition between a balanced connection of the balun and an unbalanced connection of the balun. The graduated transition includes a ground ring arranged in an arc and connected to an electrical ground. The ground ring increases in length from the first ground ring at the balanced connection to the second ground ring at the unbalanced connection. The graduated transition includes a cage via connected between the second ground ring and each of the other ground rings. A transmission line is between the first balun and the second balun. The first balun is connected to the transmission line via its balanced connection and the second balun is connected to the transmission line via its balanced connection.

[0011] The devices, systems, and / or components thereof described herein may be configured through, for example, designing, building, arranging, installing, operating, and / or signaling.

[0012] Two or more of the features described herein, including in the Summary section of the present invention, may be combined to form an embodiment not specifically described herein.

[0013] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a perspective view of an exemplary stepped balun. [Diagram 2] 2 is a perspective view of a ground ring included in an exemplary stepped balun along with the stepped balun itself; FIG. [Diagram 3] 2 is a perspective view of a ground ring included in an exemplary stepped balun along with the stepped balun itself; FIG. [Figure 4] 2 is a perspective view of a ground ring included in an exemplary stepped balun along with the stepped balun itself; FIG. [Diagram 5] 2 is a perspective view of a ground ring included in an exemplary stepped balun along with the stepped balun itself; FIG. [Figure 6] FIG. 2 is a cutaway side view of a printed wiring board upon which an exemplary stepped balun may be constructed. [Figure 7] FIG. 2 is a transparent perspective view of an exemplary stepped balun. [Figure 8] FIG. 2 is a top view of an exemplary stepped balun. [Figure 9] FIG. 2 is a transparent perspective view of another exemplary stepped balun. [Figure 10] FIG. 10 is a top view of the example stepped balun of FIG. [Figure 11] FIG. 2 is a side view of an exemplary stepped balun. [Figure 12] 12 is a plot illustrating concentration variation of the electric field magnitude within the example stepped balun of FIG. 11. [Figure 13] 12A and 12B are perspective views of the example balun of FIG. 11 illustrating the concentration of surface current density. [Figure 14]1A and 1B are perspective views of an example stepped balun with secondary cage vias showing the concentration of surface current density. [Figure 15] FIG. 1 is a perspective view of a center conductor and cage via of an exemplary stepped balun using arrows to indicate current magnitude and direction. [Figure 16A] FIG. 1 is a perspective view of an exemplary stepped balun configured for millimeter wave applications. [Figure 16B] FIG. 16B is a top view of the example stepped balun of FIG. 16A. [Figure 17] FIG. 16B is a side view of the example stepped balun of FIG. 16A. [Figure 18] 16B is a plot illustrating concentration variation of the electric field magnitude within the example stepped balun of FIG. 16A. [Figure 19] FIG. 16B is a perspective view of the example balun of FIG. 16A illustrating the concentration of surface current density. [Figure 20] FIG. 2 is a transparent perspective view of an exemplary system for connecting two stepped baluns together on a transmission line. [Figure 21] FIG. 21 is a side view of the exemplary system of FIG. [Figure 22] 21 is a plot illustrating concentration variations of the electric field magnitude within the example stepped balun system of FIG. 20. [Figure 23] 21A and 21B are perspective views of the example system of FIG. 20 illustrating the concentration of surface current density. [Figure 24] FIG. 21 is a side view of conductors in a two-conductor transmission line used in the example system of FIG. 20 using arrows to indicate magnitude and direction on the conductors. [Diagram 25] 1 shows an electrically small S-band array radiator and a stepped balun configured to feed a phased array of such radiators. [Figure 26] FIG. 1 is a perspective view of an exemplary dual linearly polarized X-band array including a stepped balun. [Figure 27] 1A and 1B are diagrams showing two conductors in a balanced transmission line along with the electric and magnetic field lines of the two conductors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Like reference numbers in different drawings indicate like elements.

[0016] A balun includes an electrical device 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 that is connected to an electrical ground to reduce the amount of electrical interference that reaches the center conductor. The current in the center conductor is referenced to the outer conductor. Thus, the signal voltage on the center conductor varies depending on the electrical ground on the outer conductor. An example of a conductor in an unbalanced signal configuration is a coaxial cable. A balanced signal connection includes two conductors for a signal that have equal impedance to electrical ground and that may both be surrounded by a shield in some cases. The currents flowing through the two conductors are equal in magnitude, opposite in direction, and surrounded by magnetic field lines. The electric field between the conductors starts in one conductor and ends in the other conductor. The transmission of a signal through conductors in a balanced signal configuration may reduce the effects 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 a conductor in a balanced signal configuration is a dipole antenna connection.

[0017] Described herein is an exemplary balun referred to as a "stepped balun." Reference to a stepped balun may include any of its variations described herein. In one example, the stepped balun includes a center conductor passing through a printed wiring board having multiple dielectric layers. A graduated transition between the balanced connection of the balun and the unbalanced connection of the balun allows for conversion between the unbalanced connection and the balanced connection. In one example, the graduated transition includes ground rings configured in an arc connected to a common electrical ground. The ground rings decrease in length from a maximum ground ring at the unbalanced connection to a minimum ground ring at the balanced connection, thereby gradually changing between the unbalanced connection and the balanced connection. The graduated transition includes cage vias connected between the various ground rings. Cage vias are conductive structures, such as plated through holes, that are "cages" in the sense that they at least partially surround the center conductor.

[0018] FIG. 1 illustrates an example of a stepped balun 10. In this example, there are four stages defined by four ground rings 11, 12, 13, and 14 in the balun 10. As shown in more detail below, the ground rings 11, 12, 13, and 14 are electrically and physically connected to nine cage vias (cage vias are collectively named 18), seven cage vias, five cage vias, and three cage vias, respectively. Because there are four ground rings between the balanced connection 20 and the unbalanced connection 21, the stepped balun 10 is referred to as a four-stage balun. However, the stepped baluns described herein are not limited to the configuration shown in FIG. 1. For example, the number of stages and / or vias may vary in different implementations.

[0019] 2-5 show example layouts of ground rings and tuning rings (described below) in stages of balun 10. Arrows 14a, 13a, 12a, and 11a in balun 10 shown on the right of each figure indicate where the layer to the left is located. As shown in FIG. 3, ground ring 13 includes three holes for holding three cage vias that electrically and physically connect to and through ground ring 13. As shown in FIG. 4, ground ring 12 includes five holes for holding five cage vias that electrically and physically connect to and through ground ring 12. As shown in FIG. 5, ground ring 11 includes seven holes for holding seven cage vias that electrically and physically connect to and through ground ring 11. As shown in FIG. 1, ground ring 11 also electrically and physically connects to cage vias such as cage via 23 that terminates ground ring 11, i.e., does not pass through ground ring 11.

[0020] The stepped balun 10 includes a center conductor 24 that passes at a right angle through a printed wiring board (PWB), such as printed wiring board 25 of FIG. 6, which includes ground rings 11-14. The printed wiring board includes multiple dielectric layers 25a-25d and metal layers that form the ground rings. In this example, the printed wiring board includes at least four dielectric layers, although other numbers of dielectric layers may be used. The center conductor is a plated through hole through the printed wiring board.

[0021] An unbalanced electrical connection 21, an example of which is a coaxial connection, is included on one surface 25e of the printed wiring board 25. A balanced electrical connection 21 is included on the other, e.g., opposite, surface 25f of the printed wiring board 25. The balanced electrical connection includes both the center conductor and the ground ring 14. Both connections allow for interfacing to standard components such as a standard dipole antenna. FIG. 7 shows the stepped balun 10 as transparent. Here, the balanced and unbalanced connections may be more readily apparent than in FIG. 1.

[0022] In one example, the stepped balun 10 is configured to convert the fields and currents of an unbalanced transmission line into the fields and currents of a balanced two-conductor transmission line. The stepped balun is thus configured to convert a balanced electrical signal into an unbalanced electrical signal and an unbalanced electrical signal into a balanced electrical signal. In this context, the stepped balun can be considered a "field transformer." That is, the stepped balun 10 converts the electric (and magnetic) field distribution of the coaxial line into a two-conductor electric (and magnetic) field distribution over a relatively small electrical length. For example, as shown in Figures 1, 6, and 7, the ground ring (outer conductor) gradually changes arc length between the unbalanced connection 21 and the balanced connection 20 over the relatively short distance of the thickness of the printed wiring board. The stepped balun 10 also performs the reverse conversion.

[0023] As shown in FIG. 1 and FIG. 7, the stepped balun 10 includes cage vias 18 positioned relative to the center conductor 24. In this example, the cage vias are positioned in an arc around the center conductor 24 as shown. The arc of the cage vias corresponds to the shape of the ground rings, which are also in the arc. The size of the arcs progressively decreases from the unbalanced balun connection 21 to the balanced balun connection 20. For example, as shown in FIG. 5 and FIG. 7, close to the unbalanced connection 21, the arc (here a circle) of the ground ring 11 covers 360°. At the first step location towards the balanced connection, the arc of the ground ring 12 covers about 270° in this example. At the next step location towards the balanced connection, the arc of the ground ring 13 covers 180° in this example. At the next step location, i.e., the balanced connection 21, the arc of the ground ring covers 90° in this example. The cage vias are positioned along these arcs as shown in FIG. 1.

[0024] As noted above, the extent and length of the arcs - including the extent and length of the ground rings, and the span of the cage vias - may differ from those shown and may vary based on various factors, such as the depth of the printed wiring board. The cage vias and ground rings at each stage of the stepped balun are connected to the same electrical ground and are therefore configured to provide a gradual or stepped transition between balanced and unbalanced connections on opposing surfaces of the printed wiring board.

[0025] Referring to FIG. 8, the stepped balun 10 includes a first set of three cage vias 30a, 30b, 30c that extend all the way between the unbalanced connection 21 and the balanced connection 21. The first set of three cage vias is part of a first arc of cage vias connected to the ground ring 14. In this example, the ground ring 14 may extend along a length that covers about 90° or less of a circle around the center conductor 24. In this example, the unbalanced connection 21 includes a pseudo-coaxial connection configured for connection to a standard coaxial cable, although a pseudo-coaxial connection configured for connection to a customized coaxial cable may alternatively be used. The balanced connection 20 includes a two-conductor port for electrically connecting to a balanced transmission line. An exemplary two-conductor port includes a dipole antenna connection. Examples of antenna connections include, but are not limited to, two-terminal balanced-fed antennas, such as dipole antennas, bowtie antennas, sinusoidal antennas, spiral antennas, folded dipole antennas, biconical antennas, Yagyuuda antennas, and loop antennas.

[0026] The stepped balun 10 includes a second set of cage vias that are physically and electrically connected to the unbalanced connection 21 and to the ground ring 13. The cage vias in this set include cage vias 30a, 30b, and 30c, as well as cage vias 30d and 30e. Thus, there are five cage vias in the second set. The stepped balun 10 includes a third set of cage vias that are physically and electrically connected to the unbalanced connection 21 and to the ground ring 12. The cage vias in this set include cage vias 30a, 30b, 30c, 30d, and 30e, as well as cage vias 30f and 30g. Thus, there are seven cage vias in the third set. The stepped balun 10 includes a fourth set of cage vias that are physically and electrically connected to the unbalanced connection 21 and to the ground ring 11. The cage vias in this set include cage vias 30a, 30b, 30c, 30d, 30e, 30f, and 30g, along with cage vias 30h and 30i. Thus, there are nine cage vias in the third set. In this example, the ground ring 11 extends in a complete circle (360°) around the center conductor 24 to approximate the shield of a coaxial cable. Notably, the cage vias are discontinuous - i.e., there is a dielectric between the cage vias - so the cage vias may not behave exactly like a coaxial cable. Cage vias 30a-30i are also labeled in FIG. 1.

[0027] 1 and 7, and as described above, the ground rings, also referred to as the outer conductor rings, progressively decrease in arc length from unbalanced connection 21 to balanced connection 20, such that ground ring 11 is longer than ground ring 12, which is longer than ground ring 13, which is longer than ground ring 14. Stated another way, the ground rings progressively increase in arc length from balanced connection 20 to unbalanced connection 21, such that ground ring 14 is shorter than ground ring 13, which is shorter than ground ring 12, which is shorter than ground ring 11.

[0028] As discussed above, the exemplary stepped balun 10 has four dielectric layers. As also discussed above, a printed wiring board includes four dielectric layers. Thus, in this example, each ground ring is formed on the surface of one of the dielectric layers. In some implementations, there may be more or fewer dielectric layers, and in those implementations, there may be more or fewer ground ring layers or steps in the stepped balun. For example, the 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 the ground rings within them, so that the ground rings may not be located on the surface of each dielectric layer in the printed wiring board.

[0029] 1, 7, and 8, in some embodiments, there may be one or more (e.g., three) tuning rings (or tuning pads) 32 connected along the length of the center conductor 24 within the area surrounded by the cage via 18. That is, in some embodiments, the tuning rings may be between the center conductor and the cage via. The tuning ring or rings are configured to add capacitance to the stepped balun to control how the impedance of the stepped balun changes operation with changes in frequency of the signal passing through the stepped balun. The tuning rings may include capacitors - e.g., dielectrics between conductive plates - or other appropriately configured conductive and / or non-conductive materials. Any suitable number of tuning rings may be used. The number and location may depend on the target performance.

[0030] The cage vias in Figures 1-8 - the first set, the second set, the third set, and the fourth set - are referred to as primary cage vias. As shown in Figures 9 and 10, a stepped balun 40, which otherwise has the same structure as the stepped balun 10, may include a set of secondary cage vias 41. The primary cage vias 42 may be at a first radius 43 relative to the center conductor 46, and the secondary cage vias 41 may be at a larger radius 45 relative to the center conductor 46. The secondary cage vias 41 may fully or partially surround the primary cage vias 42 as shown in Figures 9 and 10, and may extend from the layer of the printed wiring board where the unbalanced connection is located (or adjacent to it) to the layer of the printed wiring board where the balanced connection is located. The secondary cage vias include conductive structures such as plated through holes that are "cage" in the sense that they at least partially surround the primary cage vias and, consequently, the center conductor. The secondary cage vias connect to the same electrical ground as the ground ring and the primary cage vias. The connections may be on the layer of the printed wiring board containing the balanced connections, on the layer of the printed wiring board containing the unbalanced connections, or on both layers. In some implementations, the secondary vias are arranged in a 360° arc around the primary cage vias. In this configuration, the secondary cage vias electromagnetically shield the stepped balun. In the stepped balun 40, there are eight secondary cage vias, although any suitable number may be used.

[0031] To vary the performance of the stepped balun - e.g., to achieve a target performance - the following parameters may be set or changed: diameter of the individual primary and / or secondary cage vias, diameter of the center conductor, number of layers of the printed wiring board, dielectric constants associated with the dielectrics of the multiple dielectric layers, and tuning rings associated with the center conductor to change the capacitance associated with the balun. Among other parameters, the distance between the center conductors, and the number and type of cage vias may also be varied.

[0032] In some embodiments, the stepped balun is relatively compact and is arranged vertically (orthogonally) through a printed wiring board. In some embodiments, the stepped balun reduces or minimizes the footprint of the device (unit cell) that contains the stepped balun. This is because the stepped balun has an area≦(λ / 2) 2 In this regard, the stepped balun may have application in phased array applications, as well as other applications where improved RF (radio frequency) performance and economical use of unit cell area, substrate thickness, and weight may be considerations.

[0033] In some embodiments, the four-stage balun is configured to operate anywhere over a five-octave bandwidth (e.g., 0.150 GHz (gigahertz) to 4.8 GHz) with relatively low loss performance. In an exemplary embodiment, for a stepped balun with a 50Ω GPO (standard coaxial) connector input impedance and a two-conductor output impedance that varies from 40Ω to 75Ω, the maximum signal loss is 0.290 dB (decibels) at 4.8 GHz for a two-conductor impedance of 75Ω. In an exemplary embodiment, the stepped balun has a 75Ω coaxial input and a 75Ω two-conductor output. In this embodiment, the return loss and insertion loss over the five-octave bandwidth is comparable to that of a 50Ω input and a 50Ω two-conductor impedance. The maximum insertion is 0.11 dB at 4.6 GHz in this example. In one example, a stepped balun with a 50Ω coaxial input and a 50Ω two-conductor output is frequency extendable to operate up to 30 GHz. The return loss and insertion loss are relatively low over the five octave bandwidth from 1.2 GHz to 38.4 GHz. The maximum insertion loss is 0.19 dB at 38.4 GHz in this example.

[0034] The stepped balun operates in a TEM (transverse electromagnetic) transmission mode. In this respect, the stepped balun can be considered to operate as a non-resonant transmission line or portion thereof operating in a TEM mode. Resonant mode losses due to higher order modes such as the TE11 mode are far beyond the four-stage balun configuration described herein. Using the TE11 mode cutoff frequency of a coaxial transmission line as a proxy for the TE mode cutoff frequency of the stepped balun, the following TE mode cutoff frequencies can be determined for the four-stage balun configuration and the four-stage mm-wave (millimeter wave) frequency configuration described below. 4-stage operating frequency band: 150MHz~4.8GHz ○TE11 mode cutoff frequency >13GHz 4 mm-wave frequency operating band: 1.2GHz~44.8GHz ○TE11 mode cutoff frequency >75GHz

[0035] In some embodiments, the rate of change of insertion phase versus frequency, referred to as group delay, is a consideration in commercial wireless communications, such as radar applications that transmit complex wideband waveforms, and 5G wireless applications that use complex modulation schemes. As mentioned above, the stepped balun operates in a TEM mode, which in some instances may result in a group delay that varies by 2 picoseconds (ps) or less over a five-octave bandwidth, making the stepped balun suitable for these types of applications.

[0036] The stepped balun may be implemented using standard printed wiring board materials and fabrication techniques. This may facilitate the use of the stepped balun with a phased array antenna where hundreds or thousands of unit cells are fabricated across several printed wiring boards, as described below. The stepped balun may be fabricated as follows: Imaging and copper etching operations may be performed on each dielectric layer of the printed wiring board. Lamination cycles may be performed on the resulting stack of dielectric layers in the printed wiring board. Drill and copper plate operations may be performed on the resulting stack. Finally, the stack may be back-drilled to produce cage vias.

[0037] In an exemplary configuration of a stepped balun, the primary cage vias are on a 0.140 inch (3.6 millimeter (mm)) diameter circle or arc (i.e., less than a full circle) around the center conductor. The secondary cage vias are on a 0.236 inch (6.0 mm) diameter circle around the center conductor. In this example, the stepped balun has an overall height of 0.143 inch (3.5 mm) and an aspect ratio of height to via diameter of 6. However, these are example dimensions. A stepped balun may have different dimensions.

[0038] FIG. 11 shows a side view of the stepped balun 48 components (including dielectric layer 50) with the dimensions described in the previous paragraph, along with a cut surface 49 at the two-conductor balanced port side of the stepped balun. The electric field magnitude is evaluated for a 2.4 GHz signal passing through the balun at this cut surface. FIG. 12 shows the variation of the electric field magnitude concentration 51 at the two-conductor ports 51a, 51b (center via pad and outer conductor ring, respectively) at the cut surface. In this example, the power in the outer region of the stepped balun is less than −50 dB compared to the peak power between the two conductors at the balanced connection of the balun. The secondary cage via is not included in this example. As shown in FIG. 12, the larger electric field magnitude is concentrated between the center via pad and the outer conductor ring.

[0039] 13A and 13B show the surface current density magnitude 52 for stepped balun 48 between its center conductor 55, three of its cage vias 56, and the top outer conductor ring 57. Secondary cage vias are not included in the example of FIGS. 13A and 13B. FIGS. 14A and 14B show the surface current density magnitude for stepped balun 60 having the configuration of FIG. 1 and also having secondary cage vias 61 as in balun 40 of FIG. 9. As evidenced by its heavy shading, secondary cage via 41 grounded to the primary cage via has negligible surface current density. Electromagnetic energy 62 is concentrated between the center conductor 55a, the center via pad 53a, and the top outer conductor pad connected to the three primary cage vias (vias 56 in FIG. 13A).

[0040] FIG. 15 illustrates the surface current direction of a primary cage via in an exemplary stepped balun, such as balun 10. The maximum current vector 64 on the center conductor 65 points downward toward the two outer conductor vias 68, 69. The maximum current vector 66 on the two outer conductor cage vias points 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, approximately 150 A / m (amperes per meter). The two opposing cage vias 68, 68 each have a surface current of approximately 75 A / m. The secondary cage vias are not included in FIG. 15.

[0041] 16A and 16B show diagrams of an exemplary four-stage balun 70 configured for operation at mm-wave (millimeter-wave) frequencies. The stepped balun 70 has a 50 Ω coaxial input. The stepped balun 70 includes four stages with physical and electrical connections to nine cage vias, seven cage vias, five cage vias, and three cage vias, respectively, like the stepped balun 10 of FIG. 1. However, the stepped balun 70 includes sixteen secondary cage vias 71 surrounding a primary cage via 72. In this example, the primary cage vias 72 lie on a 0.024 inch (6 mm) diameter circle 74 relative to a center conductor 75. The secondary cage vias 71, which are electrically connected to the same electrical ground as the primary cage vias, lie on a 0.038 inch (9.6 mm) diameter circle 76 relative to the center conductor 75. All vias are 0.0048 inch (0.12 mm) in diameter. The vias may be fabricated using standard microvia processes. In this example, the microvia aspect ratio is 0.75:1 for each via.

[0042] Figure 17 shows a stepped balun 70 having the dimensions described in the previous paragraph along with a cutaway 78 at the two conductor balanced port side of the stepped balun where the electric field magnitude is evaluated for a 19.2 GHz signal. Figure 18 shows the concentration 79 of the electric field magnitude at the two conductor port 80 of the stepped balun 70. The power outside the balun area is less than -55 dB compared to the peak power between the two conductors.

[0043] Figure 19 shows the magnitude of the surface current between the central via 81 and the primary cage via 72 for the stepped balun 70. The current and electric field (shown in Figure 18) are concentrated between the central via 81 and the interior of the primary cage via 72a. There is a small current density on the secondary cage via 71.

[0044] FIG. 20 illustrates an exemplary system 85 having a first stepped balun 86, a second stepped balun 87, and a transmission line 88 between the first and second stepped baluns. The transmission line 88 is a two-conductor balanced transmission line. The first and second stepped baluns are connected to the transmission line via their respective balanced connections. A coaxial cable may be connected to the unbalanced connections of the stepped baluns 86 and 87. In the embodiment of FIG. 20, the stepped baluns 86 and 87 do not include secondary cage vias. However, secondary cage vias may be used with either or both of the stepped baluns. FIG. 21 illustrates the system 85 with a cut 89 along the transmission line 88 where the electric field magnitude is evaluated for a 19.2 GHz signal.

[0045] Figure 22 shows the concentration 90 of the electric field magnitude at a cut surface. Figures 23A and 23B show the magnitude of the surface current density of the system 85. The maximum current density 92 on the two conductor transmission line 88 is on the transmission line-i.e., conductor-surfaces that face each other. Figure 24 shows the vector surface current density magnitude between conductors 88a and 88b in the two conductor transmission line 88. The maximum current density on the two conductor transmission line is on the surfaces of conductors 88a and 88b that face each other. The currents are equal and 180 degrees out of phase.

[0046] The stepped balun may be configured for use with standard radiators (e.g., antennas), such as dipole radiators. The stepped balun may also be configured for use with phased array antenna configurations, as described herein. The stepped balun may be configured for use with narrowband (≦20% tunable bandwidth) to wideband (>20% tunable bandwidth) to multi-octave tunable bandwidths, two-port balanced-fed antennas, such as dipole antennas, bowtie antennas, sinusoidal antennas, and spiral antennas.

[0047] Antennas such as those identified above may be used in a variety of systems, including, but not limited to, phased array radars, 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. Exemplary applications of this type may include sensors mounted on aircraft, helicopters, drones, and the like. In these applications, the stepped balun, which is lightweight, low-profile, and capable of performing multiple tasks, may be configured for use with 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, such as dual-band radars utilizing low-frequency search (e.g., UHF bands (300 MHz to 3 GHz)) and high-frequency resolution track (e.g., C-band (4 GHz to 8 GHz)).

[0048] An electrically or physically small antenna may require an electrically or physically small balun. FIG. 25 shows a stepped balun 95 configured to feed an electrically small S-band array radiator 96 with an ohmic input impedance of 60 Ω. The coaxial port 97 of the stepped balun 95 includes a 50 Ω GPO connector. In this example, the combined total signal loss from 2.2 GHz to 2.6 GHz using a 0.5 inch (12.7 mm) by 0.5 inch (12.7 mm) unit cell (λ / 10 by λ / 10 unit cell) is less than 0.2 dB. The S-band array radiator 96 and stepped balun are part of a phased array 98 that includes multiple S-band array radiators and stepped baluns of the same type. In the phased array, each antenna includes an analog transmitter / receiver module configured to generate the phase shift required to electronically steer the antenna beam.

[0049] The stepped balun may be configured for use with bowtie radiators. In this regard, FIG. 26 shows an exemplary dual linearly polarized X-band array 99. Each cell of the array 100 has a vertical and horizontal bowtie radiator. Both linearly polarized radiators may be fed by the stepped balun.

[0050] The stepped balun may be configured for use with a dual linearly polarized radiator. An exemplary polarized radiator with a common phase center may require that orthogonal electric fields be provided to each pair of antenna terminals. The stepped balun may be configured to rotate its electric field by rotating its outer conductor at any angle relative to the center conductor. For example, in a stepped balun, the cage vias of the stepped balun may be rotated relative to the center conductor. As a result, the electric field may rotate from electric field 102 in FIG. 27A to electric field 103 in FIG. 27B.

[0051] As mentioned above, the stepped balun may be configured for use with 5G cellular applications. In this regard, an exemplary 5G handset includes up to 10 antennas. More antennas means less antenna area, so 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 5G mobile phone handsets. In this regard, the five octave band performance of some embodiments of the stepped balun covers the following 5G frequency bands: i. "Low Band 5G". 600-850MHz, 50-250Mbps. The 4-stage design covers this frequency band. ii. "Mid-band 5G". 2.5~3.7GHz, 100~900Mbps. A four-stage mmWave frequency design covers this frequency band. iii. "High Band 5G". 25~39GHz, ≦1.8Gbps. The four-stage mmWave frequency design covers this frequency band. Additionally, antenna arrays deployed on cell towers may require low-loss front ends to reduce the mains power and air-cooling requirements of power amplifiers, which are important cost drivers for 5G performance. Stepped baluns, which are relatively low-loss and capable of operating over a wide band, may be configured for use in MIMO (large-input / large-output) 5G systems. Stepped baluns may reduce the mains power and potentially reduce the weight of the antenna / feed assembly.

[0052] 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 may be configured for use in DSP backplane assemblies where component area is extremely limited to provide a low loss, low dispersion wideband balun signal conversion from an unbalanced transmission line (e.g., a coaxial connector) to the two-terminal input of the differential amplifier. Additionally, 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.

[0053] The stepped balun may be configured for use with medical applications, as described above. In this regard, there is a need for compact, lightweight RF antennas for medical applications such as tumor imaging, cancer treatment, etc., where lower microwave frequencies (e.g., L-band or S-band) are required to penetrate deeper into the human body to image tumors. In one example, the 3 inch (76.2 mm) by 3 inch S-band array of FIG. 25 may be part of a medical diagnostic and / or treatment system.

[0054] Any "electrical connection" as used herein may include a direct physical connection, or a wired or wireless connection that may or may not include intervening components, but that nevertheless allows electrical signals to flow between the connected components. Any "connection" that includes electrical circuitry that allows signals to flow is an electrical connection, unless otherwise specified, and not necessarily a direct physical connection, regardless of whether the word "electrical" is used to modify the "connection."

[0055] Elements of the different embodiments described may be combined to form other embodiments not specifically described above. Elements may be omitted from the systems described above without adversely affecting their operation or the operation of the system in general. Additionally, various separate elements may be combined into one or more individual elements to perform the functions described herein.

[0056] Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. A balun, a center conductor extending through a printed wiring board comprising a plurality of dielectric layers; a cage via disposed relative to the center conductor, a first set of cage vias extending between an unbalanced connection terminal of the balun and a balanced connection terminal of the balun, the first set of cage vias being part of a first arc and connected to electrical ground via a first ground ring; a second set of cage vias extending partially through the printed wiring board from the unbalanced connection terminal, the second set of cage vias being part of a second arc and connected to the electrical ground via a second ground ring, the second arc being longer than the first arc; The cage via comprising: Equipped with a balun.

2. a distance from the balanced connection terminal to the unbalanced connection terminal is a first distance, a second set of the cage vias extending a second distance through the printed wiring board; The balun is a third set of cage vias extending a third distance through the printed wiring board from the unbalanced connection terminal, the third distance being greater than the second distance and less than the first distance, the third set of cage vias being part of a third arc and connected to the electrical ground via a third ground ring, the third arc being longer than the first arc and shorter than the second arc; The balun of claim 1 further comprising:

3. a fourth set of cage vias extending a fourth distance through the printed wiring board from the unbalanced connection terminal, the fourth distance being between the second distance and the third distance, the fourth set of cage vias being part of a fourth arc and connected to the electrical ground via a fourth ground ring, the fourth arc being longer than the third arc and shorter than the second arc; The balun of claim 2 further comprising:

4. 4. The balun of claim 3, wherein there are 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.

5. The balun of claim 1, wherein the second set of cage vias are arranged around a 360° circumference around the center conductor.

6. the cage via is a primary cage via; the balun further comprises a secondary cage via connected to the electrical ground, the secondary cage via being disposed in an arc around the primary cage via. The balun of claim 1 .

7. The balun of claim 6 , wherein the secondary cage vias are arranged 360° circumferentially around the primary cage via.

8. The balun of claim 7 , wherein the secondary cage via extends from the dielectric layer of the printed wiring board on which the unbalanced connection terminal is located to the dielectric layer of the printed wiring board on which the balanced connection terminal is located.

9. 10. The balun of claim 1, further comprising one or more tuning rings connected along a length of the center conductor, the one or more tuning rings configured to add capacitance to control how the impedance of the balun changes with frequency of signals passing through the balun.

10. 2. The balun of claim 1, wherein the following parameters are selected to achieve a target performance of the balun: diameters of individual cage vias and the center conductor, the number of layers of the printed wiring board where each layer corresponds to a termination point of a set of cage vias, dielectric constants associated with the dielectrics of the plurality of dielectric layers, and a tuning ring associated with the center conductor to vary a capacitance associated with the balun.

11. the unbalanced connection terminal is configured for connection to a coaxial cable; the balanced connection terminal is configured for connection to an antenna; The balun of claim 1 .

12. the unbalanced connection terminal is configured for connection to a coaxial cable; the balanced connection terminal is configured for connection to a phased array of antennas, each antenna comprising an analog transmitter / receiver module configured to generate a phase shift required to electronically steer an antenna beam; The balun of claim 1 .

13. the unbalanced connection terminal is configured for connection to a coaxial cable; The balanced connection terminal is configured for connection to a 5G mobile communication tower antenna. The balun of claim 1 .

14. the unbalanced connection terminal is configured for connection to a coaxial cable; the balanced connection terminal is configured for connection to a circuit board including a digital signal processor (DSP); The balun of claim 1 .

15. A balun, a center conductor extending through a printed wiring board comprising a plurality of dielectric layers; a graduated transition between the balanced connection terminal of the balun and the unbalanced connection terminal of the balun, the graduated transition comprising ground rings arranged in an arc and connected to an electrical ground, the ground rings increasing in length from a first ground ring on the dielectric layer of the printed wiring board on which the balanced connection terminal is located to a second ground ring on the dielectric layer of the printed wiring board on which the unbalanced connection terminal is located, the graduated transition further comprising a cage via connected between the second ground ring and each of the other ground rings; Equipped with a balun.

16. one or more tuning rings connected along the length of the central conductor, the one or more tuning rings configured to add capacitance to control how the impedance of the balun changes with frequency of signals passing through the balun; The balun of claim 15 further comprising:

17. the unbalanced connection terminal is configured for connection to a coaxial cable; the balanced connection terminal is configured for connection to a phased array of antennas, each antenna comprising an analog transmitter / receiver module configured to generate a phase shift required to electronically steer an antenna beam; The balun of claim 15.

18. the unbalanced connection terminal is configured for connection to a coaxial cable; The balanced connection terminal is configured for connection to a 5G mobile communication tower antenna. The balun of claim 15.

19. the unbalanced connection terminal is configured for connection to a coaxial cable; the balanced connection terminal is configured for connection to a circuit board including a digital signal processor (DSP); The balun of claim 15.

20. the cage via is a primary cage via; the balun further comprises a secondary cage via connected to the electrical ground, the secondary cage vias being disposed 360° circumferentially around the primary cage via. The balun of claim 15.

21. 1. A system comprising: A first balun according to claim 15; A second balun according to claim 15; a transmission line between the first balun and the second balun, the first balun being connected to the transmission line via the balanced connection terminal, and the second balun being connected to the transmission line via the balanced connection terminal; A system comprising:

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