阅读说明：本技术 射频电路中的增材制造技术（amt）法拉第边界 (Additive Manufacturing Technology (AMT) Faraday boundaries in radio frequency circuits ) 是由 S·M·阿札德佐伊 J·E·贝内迪克特 J·P·黑文 T·V·席基纳 A·R·索思沃思 于 2018-11-08 设计创作，主要内容包括：一种射频电路,包括至少一个介电基板、形成在介电基板中的沟槽以及沟槽中的电连续导电材料。射频电路还可包括第一介电基板、第二介电基板,并且在第一介电基板和第二介电基板中形成沟槽。一种制造电磁电路的方法,包括：提供至少一个介电基板；在所述至少一个介电基板中机加工沟槽；以及采用导电材料填充沟槽以形成电连续导体。(A radio frequency circuit includes at least one dielectric substrate, a trench formed in the dielectric substrate, and an electrically continuous conductive material in the trench. The radio frequency circuit may further include a first dielectric substrate, a second dielectric substrate, and a trench formed in the first dielectric substrate and the second dielectric substrate. A method of manufacturing an electromagnetic circuit, comprising: providing at least one dielectric substrate; machining a trench in the at least one dielectric substrate; and filling the trench with a conductive material to form an electrically continuous conductor.)

1. A radio frequency circuit, comprising:

at least one dielectric substrate;

a trench formed in the dielectric substrate; and

electrically continuous conductive material in the trench.

2. The radio frequency circuit of claim 1, wherein the electrically continuous conductive material is configured to at least partially contain an electromagnetic field within a confined area of the radio frequency circuit.

3. The radio frequency circuit of claim 1, wherein the electrically continuous conductive material is configured to at least partially isolate a first circuit portion disposed within the layer of the at least one dielectric substrate from a second circuit portion disposed within the layer of the at least one dielectric substrate.

4. The radio frequency circuit of claim 3, wherein at least one of the first circuit portion and the second circuit portion is configured to operate in at least one of a microwave frequency range or a millimeter wave frequency range.

5. The radio frequency circuit of claim 3, wherein the first circuit portion is configured to operate in a first frequency range and the second circuit portion is configured to operate in a second frequency range that overlaps the first frequency range.

6. The radio frequency circuit of claim 3, wherein the first circuit portion is configured to operate in a first frequency range and the second circuit portion is configured to operate in a second frequency range, at least one frequency in the second frequency range being within an octave of at least one frequency of the first frequency range.

7. The radio frequency circuit of claim 1, further comprising first and second dielectric substrates, the trench being formed in the first and second dielectric substrates.

8. The radio frequency circuit of claim 7, further comprising: a first ground plane disposed on a bottom surface of the second substrate; and a second ground plane disposed on a top surface of the second substrate, a portion of the second ground plane forming a signal trace including a terminal pad.

9. The radio frequency circuit of claim 8, further comprising a vertical conductor secured to the terminal pad of the signal trace.

10. The radio frequency circuit of claim 9, wherein the electrically continuous conductive material at least partially surrounds the vertical conductor.

11. A method of manufacturing an electromagnetic circuit, the method comprising:

providing at least one dielectric substrate;

machining a trench in the at least one dielectric substrate; and

the trench is filled with a conductive material to form an electrically continuous conductor.

12. The method of claim 11, wherein providing the at least one dielectric substrate comprises providing a first dielectric substrate and a second dielectric substrate, the trench being formed in the first and second dielectric substrates.

13. The method of claim 12, further comprising forming a first ground plane on a bottom surface of the second substrate and a second ground plane on a top surface of the second substrate, a portion of the second ground plane forming a signal trace including a terminal pad.

14. The method of claim 13, further comprising securing a vertical conductor to the terminal pad of the signal trace.

15. The method of claim 14, wherein the electrically continuous conductive material at least partially surrounds the vertical conductor.

16. A method of manufacturing an electromagnetic circuit, the method comprising:

milling a conductive material disposed on a first substrate to form a signal trace, the signal trace including a terminal pad;

bonding a second substrate to the first substrate to substantially encapsulate the signal traces and terminal pads between the first and second substrates;

drilling holes in the second substrate to provide access holes to the terminal pads;

milling through the first and second substrates to form a trench, the trench being at least partially located around the terminal pad;

depositing a conductor into the access hole, the conductor forming an electrical connection with the terminal pad; and

depositing a conductive ink into the trenches to form electrically continuous conductors within the first and second substrates.

17. The method of claim 16, wherein the electrically continuous conductor is configured to at least partially isolate a first circuit portion disposed within the first substrate from a second circuit portion disposed within the second substrate.

18. The method of claim 17, wherein at least one of the first circuit portion and the second circuit portion is configured to operate in at least one of a microwave frequency range or a millimeter wave frequency range.

19. The method of claim 17, wherein the first circuit portion is configured to operate within a first frequency range and the second circuit portion is configured to operate within a second frequency range that overlaps the first frequency range.

20. The method of claim 17, wherein the first circuit portion is configured to operate in a first frequency range and the second circuit portion is configured to operate in a second frequency range, at least one frequency in the second frequency range being within an octave of at least one frequency in the first frequency range.

Background

Radio Frequency (RF) and electromagnetic circuits may be fabricated using conventional Printed Circuit Board (PCB) processes. Conventional PCB manufacturing processes may include lamination, plating, masking, etching, and other complex process steps, and may require multiple steps, expensive and/or hazardous materials, multiple iterations, a large amount of labor, etc., all of which result in higher costs and slower turnaround times. In addition, conventional PCB fabrication processes allow for limited capability of small feature sizes such as the size of signal traces (e.g., striplines) and the size of dielectric materials between conductors (e.g., thickness of dielectric, inter-via spacing, etc.), thus limiting the range of highest frequency signals that can be supported by such circuits.

Disclosure of Invention

Aspects and embodiments described herein provide simplified circuit structures and methods of making the same for conveying electrical signals, particularly radio frequency signals, within a circuit, and more particularly, provide enhanced isolation of signals into the microwave and millimeter wave ranges between components and along signal lines by providing a continuous electromagnetic boundary (e.g., electrical conductor) within the circuit. The circuits, structures, and fabrication methods described herein use subtractive and additive fabrication techniques to provide vertical (e.g., extending between layers) trenches filled with conductive material as electromagnetic boundaries to provide electromagnetic isolation within the circuit, thereby achieving a substantially continuous boundary to provide enhanced isolation for higher frequency operation than conventional techniques, such as ground vias (via).

Various signal conductors, faraday boundaries, and other circuit structures can be fabricated much simpler and with smaller feature sizes than conventional techniques. Such circuit configurations are suitable for operation in the microwave and millimeter wave ranges.

Other aspects, examples, and advantages are discussed in detail below. The embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to "an embodiment," "some embodiments," "alternative embodiments," "various embodiments," "one embodiment," or the like are not necessarily mutually exclusive and are intended to mean that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. The various aspects and embodiments described herein may comprise means for performing any of the described methods or functions.

One aspect of the present application is directed to a radio frequency circuit that includes at least one dielectric substrate, a trench formed in the dielectric substrate, and an electrically continuous conductive material in the trench.

Embodiments of the radio frequency circuit may also include a first dielectric substrate and a second dielectric substrate, wherein trenches are formed in the first and second dielectric substrates. The radio frequency circuit may further include: a first ground plane disposed on a bottom surface of the second substrate; and a second ground plane disposed on the top surface of the second substrate, wherein a portion of the second ground plane forms a signal trace including a terminal pad. The radio frequency circuit may also include a vertical conductor secured to the terminal pad of the signal trace. An electrically continuous conductive material may at least partially surround the vertical conductors. The electrically continuous conductive material may be configured to at least partially contain an electromagnetic field within a confined area of the radio frequency circuitry. The electrically continuous conductive material may be configured to at least partially isolate a first circuit portion disposed within the layer of the at least one dielectric substrate from a second circuit portion disposed within the layer of the at least one dielectric substrate. At least one of the first circuit portion and the second circuit portion may be configured to operate in at least one of a microwave frequency range or a millimeter wave frequency range. The first circuit portion may be configured to operate in a first frequency range and the second circuit portion may be configured to operate in a second frequency range that overlaps the first frequency range. The first circuit portion may be configured to operate in a first frequency range and the second circuit portion may be configured to operate in a second frequency range, wherein at least one frequency in the second frequency range is within an octave (octave) range of at least one frequency in the first frequency range.

Another aspect of the present application is directed to a method of manufacturing an electromagnetic circuit. In one embodiment, the method comprises: providing at least one dielectric substrate; machining a trench in at least one dielectric substrate; and filling the trench with a conductive material to form an electrically continuous conductor.

Embodiments of the method may further comprise: a first ground plane is formed on a bottom surface of the second substrate and a second ground plane is formed on a top surface of the second substrate, a portion of the second ground plane forming a signal trace including a terminal pad. The method may also include securing the vertical conductor to a terminal pad of the signal trace. An electrically continuous conductive material may at least partially surround the vertical conductors. Providing at least one dielectric substrate may include providing a first dielectric substrate and a second dielectric substrate, forming trenches in the first and second dielectric substrates.

Another aspect of the present application is directed to a method of manufacturing an electromagnetic circuit. In one embodiment, the method comprises: milling a conductive material disposed on a first substrate to form a signal trace, the signal trace including a terminal pad; bonding a second substrate to the first substrate to substantially encapsulate the signal traces and the terminal pads between the first and second substrates; drilling through the second substrate to provide access holes for the terminal pads; milling through the first and second substrates to form a trench at least partially surrounding the terminal pad; depositing a conductor into the access hole, the conductor forming an electrical connection with the terminal pad; and depositing a conductive ink into the trench to form an electrically continuous conductor within the first substrate and the second substrate.

Embodiments of the method may also include the electrically continuous conductor being configured to at least partially isolate a first circuit portion disposed within the first substrate from a second circuit portion disposed within the second substrate. At least one of the first circuit portion and the second circuit portion may be configured to operate in at least one of a microwave frequency range or a millimeter wave frequency range. The first circuit portion may be configured to operate in a first frequency range and the second circuit portion may be configured to operate in a second frequency range that overlaps the first frequency range. The first circuit portion may be configured to operate in a first frequency range and the second circuit portion may be configured to operate in a second frequency range, wherein at least one frequency in the second frequency range is within an octave of at least one frequency in the first frequency range.

Drawings

Various aspects of at least one embodiment are discussed below with reference to the accompanying drawings, which are not intended to be drawn to scale. The accompanying drawings are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the disclosure. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

In the figure:

FIG. 1 is a schematic diagram of one example of an electromagnetic circuit portion including a Faraday wall;

FIG. 2 is a schematic illustration of a stage in the manufacture of the electromagnetic circuit portion of FIG. 1;

FIG. 3 is a schematic illustration of another stage in the manufacture of the electromagnetic circuit portion of FIG. 1;

FIG. 4 is a schematic illustration of another stage in the manufacture of the electromagnetic circuit portion of FIG. 1;

FIG. 5 is a schematic illustration of another stage in the manufacture of the electromagnetic circuit portion of FIG. 1;

FIG. 6 is a schematic illustration of another stage in the manufacture of the electromagnetic circuit portion of FIG. 1;

FIG. 7 is a schematic diagram of another example of an electromagnetic circuit including a Faraday wall; and

figure 8 is a flow chart of a method of fabricating a faraday wall.

Detailed Description

Aspects and examples described herein provide, in various circuits, signal conductors (e.g., signal traces, striplines, inter-layer "vertical" feed lines) and reference surfaces and conductors (e.g., ground planes, faraday boundaries, or "walls") suitable for fabrication of various circuit boards including radio frequency circuit embodiments. Aspects and examples described herein advantageously apply additive and subtractive manufacturing techniques to provide structures for transmitting and containing various signals, particularly radio frequency signals in the microwave and millimeter wave ranges (e.g., up to 300GHz or higher).

In some embodiments, signal traces (e.g., conductors) can be formed on a dielectric substrate by machining (e.g., milling) a portion of the cladding (e.g., electroplated copper) from the surface of the substrate.

In some embodiments, wires may "vertically" carry signals between layers within a circuit board (e.g., to/from signal traces) and may be used to feed signals to or from various other layers or circuit components such as waveguides, radiators (e.g., antennas), connectors, or other circuit structures. Such "vertical" interlayer signal feeds can be formed by machining holes in one or more dielectric substrates, applying solder to one or more conductor surfaces, inserting a length of wire (e.g., copper wire) into the hole, and reflowing (reflow) the solder to ensure connection mechanically and electrically.

In some embodiments, a continuous conductive structure may be formed in one or more dielectric substrates by machining a trench and filling the trench with a conductor, such as a conductive ink applied using 3D printing techniques, to form an electromagnetic boundary. Such electromagnetic boundaries may enforce boundary conditions for electromagnetic signals, for example, to control or limit the pattern of signals and/or characteristic impedances, or may provide isolation to limit signals to regions of an electromagnetic circuit, such as faraday boundaries, to prevent signals of one region of the circuit from affecting another region of the circuit, such as shielding.

The fabrication processes described herein may be particularly suitable for producing, for example, circuit structures having small circuit features capable of supporting electromagnetic signals, for example, in the range of 8 to 75 GHz or higher, up to 300GHz or higher, using suitable subtractive (e.g., machining, milling, drilling, cutting, stamping) and additive (e.g., filling, flowing, 3D printing) fabrication equipment. Electromagnetic circuit structures in accordance with the systems and methods described herein may be particularly suitable for applications in 28 to 70GHz systems including millimeter wave communication, sensing, ranging, and the like. The described aspects and embodiments may also be suitable for lower frequency ranges, such as in the S band (2-4GHz), X band (8-12GHz), or other bands.

It is to be understood that the embodiments of the methods and apparatus discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The method and apparatus are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. The examples of specific embodiments provided herein are for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive such that any term described using "or" may indicate singular, more than one, and all of the described terms. Any reference to front and back, left and right sides, top and bottom, upper and lower, ends, sides, vertical and horizontal, etc., is intended to facilitate description and is not intended to limit the present systems and methods or their components to any one positional or spatial orientation.

The term "radio frequency" as used herein is not intended to be limited to a particular frequency, range of frequencies, band of frequencies, spectrum, etc., unless the context clearly indicates and/or specifically dictates otherwise. Similarly, the terms "radio frequency signal" and "electromagnetic signal" are used interchangeably and may refer to signals of various suitable frequencies for propagating information-bearing signals for any particular implementation. Such radio frequency signals are typically constrained at the low end by frequencies in the kilohertz (kHz) range, and at the high end by frequencies up to hundreds of gigahertz (GHz), and specifically include signals in the microwave or millimeter wave range. In general, systems and methods consistent with those described herein may be adapted to process non-ionizing radiation at frequencies lower than conventional in the optical arts, such as lower than, for example, infrared signals.

Various embodiments of radio frequency circuits may be designed with dimensions selected and/or nominally manufactured dimensions to operate at various frequencies. Suitable dimensions can be selected from general electromagnetic principles and are not described in detail here.

The methods and apparatus described herein may support smaller arrangements and sizes than conventional processes can support. Such conventional circuit boards may be limited to frequencies below about 30 GHz. The methods and apparatus described herein may allow or accommodate the manufacture of smaller sized electronic circuits, suitable for radio frequency circuits intended to operate at higher frequencies, using safer and less complex manufacturing processes and at lower costs.

Electromagnetic circuits and methods of manufacture thereof according to the description herein include various additive and subtractive manufacturing techniques to produce electromagnetic circuits and components capable of handling higher frequencies with lower profiles, reduced cost, production cycle time, and design risks as compared to conventional circuits and methods. Examples of techniques include machining (e.g., milling) conductive material from the surface of a substrate to form signal traces (e.g., signal conductors, striplines) or apertures, which may be much smaller in size than allowed by conventional PCB processes, machining one or more substrates to form trenches, depositing printed conductive ink into the trenches using 3D printing techniques to form a continuous electrical barrier (e.g., faraday wall) (as opposed to a series of ground vias with minimal spacing between them), a "vertical launch" signal path is formed (and/or printed) by machining (e.g., milling, drilling, or punching) a hole through a portion of the substrate and placing a wire therein to make electrical contact with a signal trace disposed on the surface of the substrate (or counter substrate), and depositing the printed resistive ink using 3D printing techniques to form the resistive component.

Any of the above example techniques and/or other example techniques (e.g., soldering and/or solder reflow) may be combined to fabricate various electromagnetic components and/or circuits. Aspects and examples of such techniques are described and illustrated herein with respect to a radio frequency interconnect to pass vertically in one dimension along a layer of an electromagnetic circuit and in another dimension through to other layers of the circuit to contain and transmit electromagnetic signals. The techniques described herein may be used to form various electromagnetic components, connectors, circuits, assemblies, and systems.

Fig. 1 shows an example of an electromagnetic circuit structure 100, which may be part of a larger electromagnetic circuit. The circuit structure 100 includes a pair of dielectric substrates 110 bonded together and having signal traces 120 encapsulated therebetween. The signal traces 120 are electrical conductors configured to carry electromagnetic signals within an electrical circuit, such as within the circuit structure 100, and may be formed by machining away a cladding layer, such as electroplated copper, from the surface of either substrate 110. The signal traces 120 also have electrical connections formed on the terminal pads, such as by solder, to "vertical" conductors 130, which "vertical" conductors 130 may be, for example, wires disposed within machined holes in the substrate 110 b. Thus, the conductors 130 and signal traces 120 form an electrically continuous signal transmission, and each may transmit and provide signals outside the range of the portion shown in fig. 1.

In some embodiments, a ground plane 140 may be provided and may be formed by a conductive cladding layer disposed on the "bottom" surface of the substrate 110 a. An additional ground plane 150 may be provided on the "top" surface of the substrate 110 b. For example, the ground plane 150 may be formed of a conductive clad layer disposed on the substrate 110 b. A portion of the conductive cladding may be removed by machining (e.g., milling) to provide a ground plane of an appropriate physical size, shape, or extent, such as to be suitable for use as the ground plane 150 of the signal traces 120.

The circuit structure 100 also includes faraday walls 160, sometimes referred to as "electrically continuous conductive material," which are conductors that provide an electromagnetic boundary that "runs vertically" through the substrate 110. The faraday walls 160 can be formed by machining trenches through the substrate 110 down to the ground plane 140 and filling the trenches with a conductive material, such as a conductive ink applied using additive manufacturing techniques such as 3D printing. When cured (set), the conductive ink may form a substantially electrically continuous conductor. As shown, the trench in which the faraday wall 160 is formed does not pierce or extend through the ground plane 140. Thus, the faraday wall 160 can be in electrical contact with the ground plane 140. Additionally, the "top" 160 of the faraday wall may be in electrical contact with the ground plane 150, which may be achieved by a small amount of overfill of the machined trenches to ensure contact between the conductive ink and the ground plane 150 and/or by applying solder, for example.

As shown in fig. 1, the ground plane 140, the ground plane 150, and the faraday wall 160 together form a substantially electrically continuous conductor that provides a boundary for signals carried by the signal traces 120. In some embodiments, the ground planes 140, 150 and faraday wall 160 are arranged in dimensions that are selected to control or limit the propagation mode of signals carried by the signal traces 120 and/or to establish a characteristic impedance for signals carried by the signal traces 120. In certain embodiments, the ground planes 140, 150 and the faraday wall 160 may be positioned such that only Transverse Electromagnetic (TEM) signal modes may propagate along the signal trace 120. In other embodiments, the faraday wall 160 can be positioned to isolate one portion of the circuit from another portion of the circuit without forcing a particular propagation mode and/or without affecting the impedance of any particular signal.

As noted above, structure 100 is merely an example and a portion of a structure in which an electromagnetic circuit may be provided. Further scope of the substrate shown may accommodate various circuit components, and additional substrates with additional layers to accommodate additional circuit components may be provided in various embodiments. In general, a portion of a circuit may be disposed on a particular layer and may include a ground plane above and/or below, and other portions of the entire circuit (or system) may be present in different areas of the same layer or on other layers.

Fig. 2 illustrates a partial structure 100a of the circuit structure 100 in one stage of fabrication, in accordance with aspects and embodiments of the systems and methods described herein. The partial structure 100a includes a substrate 110a, which substrate 110a may be provided with a conductive (e.g., copper) cladding layer on each surface. In this example, the substrate 110a has a conductive clad 112 on one surface, and the conductive clad 112 serves as a conductive material forming the signal trace 120. Also in this example, the substrate 110a has a conductive cladding layer on the opposite surface to serve as the ground plane 140. The signal traces 120 may be formed by machining away at least a portion 122 of the cladding layer 112, leaving a portion of the conductive material different from the rest of the cladding layer 112 to serve as the signal traces 120. Various examples may provide other types of circuit components disposed adjacent to the surface of the substrate 110a, and may provide conductors for the surface to carry signals, and may provide faraday boundaries for the surface to isolate signals to or from the circuit components. As shown, the signal traces include terminal pads 124.

Fig. 3 shows another partial structure 100b of the circuit structure 100 at another stage of manufacture. For this partial structure 100b, the substrate 110b is aligned with the substrate 110a to be bonded together. In some examples, a temporary bond or fixation may be applied, and a permanent bonding step may be applied at a later time, such as a permanent bond that may require heating or baking to cure or ensure bonding. A hole 132 may be machined through the substrate 110b, the hole 132 positioned to align with a portion of the signal trace 120. For example, the holes 132 may be aligned with terminal ends of the signal traces 120. Various examples may have holes aligned with other portions of the signal traces and/or with portions of other types of circuit components. In various embodiments, the "top" surface of the substrate 110b may include: a conductive cladding layer, which can be used to provide a ground plane if desired; and may be machined away to form various other structures, components, or portions of the ground plane having a desired shape or extent.

Referring to fig. 2, the conductive cladding 112 forming the signal trace 120 (e.g., by machining away the portion 122) may be equivalently associated with the substrate 110b, e.g., on the "bottom" side in the case of fig. 3, rather than with the substrate 110 a. In other words, the conductive material from which the signal traces 120 are provided may be a conductive cladding associated with either substrate 110. Furthermore, the signal traces 120 or other circuit components (e.g., present between the substrates 110) may be provided in various embodiments, from different materials, and/or by other means.

Fig. 4 shows another partial structure 100c of the circuit structure 100 at another stage of manufacture. For the partial structure 100c, the conductors 130 are shown in the holes 132. Solder may be provided on the conductor 130 and/or a terminal end (e.g., terminal pad 124) of the signal trace 120 (e.g., an adjacent one of the conductors 130), and the solder may be reflowed to ensure a physical and electrical connection between the signal trace 120 and the conductor 130. For example, the application of heat to the exposed end of the conductor 130 may conduct through the conductor 130 and at least partially melt the solder to ensure the connection. Solder reflow may be performed at various points in the manufacturing process. For example, a subsequent solder application to secure another component to the exposed end of the conductor may provide heat to complete reflow of the solder at the joint between the signal trace 120 and the conductor 130.

Fig. 5 shows another partial structure 100d of the circuit structure 100 in another stage of manufacture. For the partial structure 100d, the trench 162 is milled through the substrate 110. In this example, the trench 162 is milled through the substrate 110 to the conductive cladding forming the ground plane 140 without piercing the ground plane 140. In some embodiments, the complete ground plane 140 may provide some structural support for portions of the structure 100d when the trenches are empty.

Fig. 6 shows another partial structure 100e of the circuit structure 100 at another stage of fabrication. In the partial structure 100e, the trench 162 is filled with a conductive filler 164 to form the faraday wall 160. The conductive filler 164 may be in electrical contact with the ground plane 140 to form a substantially electrically continuous ground boundary. As described above with respect to fig. 1, additional ground planes 150 can be included and the conductive filler 164 can be electrically connected to the ground plane 150 by physical contact at locations along the faraday wall 160 and/or by further application of solder to electrically couple with the ground plane 150. In some embodiments, the completed ground plane 140 and solidified (e.g., cooled, solidified) conductive filler 164 may provide structural support to the structure 100e, for example, in place of material machined away to form the trench 162.

As described above, the position of the faraday wall 160 can be selected based on its effect on the signal carried by the signal trace 120. In various embodiments, the faraday wall can be positioned to provide isolation without regard to the effect on the signal in any particular manner other than to provide isolation. For example, and referring to figure 7, a circuit structure 700 is shown that includes various faraday walls 760 positioned to reduce or eliminate signal leakage (e.g., radio frequency energy) between various portions of the circuit structure 700. In other words, faraday wall 760, sometimes referred to as being an electrically continuous conductive material, is configured to at least partially contain an electromagnetic field within a confined area of circuit structure 700. In this example, the circuit configuration 700 implements a 4: 1 signal combiner/divider, each of which provides electrical access to various signal traces 720 interconnecting three wilkinson dividers 724. For example, the signal trace 720 and the wilkinson divider 724 may be disposed on an intermediate layer of the circuit board. Faraday wall 760 may extend into the plane of the figure, to the ground plane "below", and up to the "top" surface of circuit structure 700 (e.g., through the intervening layers where signal trace 720 and wilkinson divider 724 are present). Each access conductor 730 may be a conductor, such as a length of wire, that passes through a hole extending from the "top" surface down to the intermediate layer to make electrical contact with the signal trace 720. As described above, faraday wall 760 is formed by machining portions of circuit structure 700 to form trenches, and filling the trenches with a conductive material, such as a conductive ink, which may be applied using additive manufacturing techniques.

Still referring to figure 7, as shown, the faraday wall 760a is configured to at least partially isolate a first circuit portion 770a disposed within a layer of the circuit structure 700 from a second circuit portion 770b disposed within the layer of the circuit structure. In one embodiment, the first circuit portion 770a and the second circuit portion 770b are configured to operate in at least one of a microwave frequency range or a millimeter wave frequency range. In a certain embodiment, the first circuit portion 770a is configured to operate in a first frequency range and the second circuit portion 770b is configured to operate in a second frequency range that overlaps the first frequency range. In another particular embodiment, the first circuit portion 770a is configured to operate in a first frequency range and the second circuit portion 770b is configured to operate in a second frequency range, at least one frequency in the second frequency range being within an octave of at least one frequency in the first frequency range.

In one embodiment, forming the faraday wall 760 (e.g., forming an electrically continuous conductor) does not include any of partial or complete immersion in a fluid, plating, masking, etching, or dissolving steps.

Figure 8 shows a method 800 of fabricating a faraday wall. The method 800 includes machining away portions of one or more substrates of the circuit structure to form trenches (block 810), and filling the trenches with a conductive material, such as a conductive ink (block 820). Forming the trench is a subtractive step on the material and filling the trench is an additive step on the material. In various embodiments, the conductive ink may be applied into the channels using 3D printing techniques.

Other advantages of the systems and methods described herein may be realized. For example, conventional PCB fabrication may limit circuit feature sizes such as the width of signal traces, thereby limiting the maximum frequencies at which conventionally fabricated electromagnetic circuits may be used. Furthermore, the substrate thickness may affect the characteristic impedance (e.g., due to distance to a ground plane disposed on the opposite surface) related to the width of the traces. Thus, the wider traces required by conventional PCB processes result in the selection of a thicker substrate (to maintain a particular characteristic impedance), thereby limiting how thin a circuit can be manufactured. For example, a common recommendation under conventional PCB manufacturing includes a total thickness of about 60 mils (0.060 inches). In contrast, electromagnetic circuits according to the described aspects and embodiments may have circuit boards with small sides (low profiles) down to a thickness of about 10 mils or less, while signal line traces have widths of about 4.4 mils, or 2.7 mils, or less, and interconnect geometries substantially flush with the surface of the circuit board using additive manufacturing techniques.

Ground vias generally provide electrical connectivity between ground planes (e.g., on opposing surfaces of a substrate) and provide isolation of traces from signals of other traces that may be nearby. Conventional ground vias are drilled holes of about 8 mils or greater in diameter and are required to be spaced apart a minimum distance to maintain the structural integrity of the board. Thus, the ground vias are leaky structures, exhibiting losses of electromagnetic signals, especially at higher frequencies. Since various applications require the support of higher frequency signals, the minimum spacing between ground vias acts like a larger opening through which relatively small wavelengths of electromagnetic energy can escape.

In contrast, electromagnetic circuits and methods according to aspects and embodiments described herein use additive manufacturing techniques, allowing for an electrically continuous faraday boundary that may be further electrically coupled to a ground plane. Thus, an electrically continuous structure is provided that is disposed vertically through one or more substrates (e.g., between opposing surfaces of the substrates) to form a "faraday wall" that confines an electromagnetic field. In various embodiments, such a faraday wall can electrically couple two or more ground planes. Further in various embodiments, such faraday walls may confine and isolate the electromagnetic field from adjacent circuit components. In some embodiments, such faraday walls may implement boundary conditions to confine electromagnetic signals to local Transverse Electromagnetic (TEM) fields, e.g., to confine signal propagation to TEM modes.

In various embodiments, various subtractive (machining, milling, drilling), additive (printing, filling), and adhesive (bonding) steps may be performed in various sequences using soldering and reflow operations as desired to form an electromagnetic circuit having one layer or any number of substrate layers, which may include one or more faraday boundaries as described herein.

A common method for making any of a variety of electromagnetic circuits includes milling a conductive material disposed on a substrate to form circuit features. The method may include printing (or deposition, e.g. by 3D printing, additive manufacturing techniques) additional circuit features, e.g. resistors formed from resistive ink. The method may include depositing solder on any feature as desired. The method may further include milling (or drilling) through the substrate material (and/or conductive material) to form an opening such as a void or trench, and for example, includes depositing or printing (e.g., by 3D printing, additive manufacturing techniques) a conductive material (e.g., conductive ink or wire) into the void/trench to form a faraday wall or vertical signal emitter (e.g., copper). Any of these steps may be performed in a different order, repeated, or omitted for a given circuit design. In some embodiments, multiple substrates may be involved in the manufacture of the electromagnetic circuit, and the method includes combining other substrates, other milling and filling operations, and other soldering and/or reflow operations as desired.

Having described several aspects and methods for fabricating at least one embodiment of an electromagnetic circuit, the above description may be used to produce various electromagnetic circuits having a total thickness of 10 mils (0.001 inch, 254 micrometers) or less, and may include signal traces, for example, traces as narrow as 4.4 mils (111.8 micrometers), 2.7 mils (68.6 micrometers), or even as narrow as 1.97 mils (50 micrometers), depending on the tolerances and precision of the various milling and additive manufacturing equipment used. Thus, the electromagnetic circuits described herein may be suitable for microwave and millimeter wave applications including S-band, X-band, K-band, and higher frequencies, and various embodiments are capable of accommodating frequencies above 28GHz and up to 70GHz or higher. Some embodiments may be applicable in the frequency range up to 300GHz or higher.

Additionally, an electromagnetic circuit according to the description herein may have sides that are sufficiently thin (e.g., 10 mils or less thick) and have a correspondingly light weight to be suitable for outer space applications; including a folded structure that can be deployed by unfolding when positioned outside space.

Furthermore, electromagnetic circuits manufactured according to the methods described herein can accommodate cheaper and faster prototyping without the use of corrosive chemicals, masks, etching, plating, and the like. A simple substrate with pre-plated conductive material disposed on one or both surfaces (sides) may form the core starting material and all elements of the electromagnetic circuit may be formed by milling (subtractive, drilling), filling (printing of additive, conductive and/or resistive inks) and bonding one or more substrates. Simple solder reflow operations and insertion of simple conductors (e.g., copper wires) are achieved by the methods and systems described herein.

Furthermore, electromagnetic circuits manufactured according to the methods described herein may accommodate deployment on non-planar surfaces or designs requiring non-planar surfaces. Thin, small-sided electromagnetic circuits such as those described herein and others can be fabricated using milling, filling, and bonding techniques as described herein to produce electromagnetic circuits having any desired profile, to be adhered to a surface (e.g., a vehicle) or to support, for example, complex array structures.

An appendix, including various additional details and aspects, is filed concurrently herewith and is hereby incorporated into and made a part of this specification.

Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only.