Laterally tapered frequency selective limiter

Abstract

A method and apparatus are disclosed for a frequency selective limiter (FSL) with a magnetic material substrate having a tapered thickness and supporting a transmission line having segments and bends, the segments having different widths and being generally parallel to each other such that each segment traverses the substrate over a constant thickness of the substrate.

Description

[Background technology]

[0001] As known in the art, a frequency selective limiter (FSL) is a nonlinear passive device that strongly attenuates radio frequency (RF) or microwave signals (both referred to below as RF signals) above a certain threshold power level, while simultaneously allowing signals below the threshold power level to pass with negligible loss, referred to as insertion loss. One feature of an FSL is its frequency selectivity, which limits high power, while low power signals close in frequency to the limiting signal are substantially unaffected (i.e., the FSL attenuates such signals by only insertion loss).

[0002] A typical implementation of an FSL includes a stripline transmission line structure using two layers of ferrite material, typically yttrium iron garnet (YIG), arranged around a stripline, which has a fixed length and fixed width along the length of the FSL, and a constant magnetic field is applied to the ferrite. Such a structure is relatively simple to fabricate, and when using single crystal ferrite, it provides the ferrite with an appropriate RF magnetic field to achieve a threshold power level of about 0 decibels per milliwatt dBm. One known method to lower the threshold power level is to use a low impedance stripline, at the expense of increased insertion loss. An external matching structure can be used to improve the impedance match to the external circuit, but this technique reduces the bandwidth and increases the insertion loss of the FSL. A permanent bias magnet can be attached to or near the FSL structure to generate a bias magnetic field. The direction of the DC magnetic field relative to the strongest RF magnetic field is usually parallel or perpendicular. The strength of the magnetic field within the structure is one factor in determining the operating bandwidth of the limiter.

[0003] Conventional FSL devices may include in-plane tapering of the signal conductor width using various coplanar microstrip transmission lines with both parallel and perpendicular bias. The purpose of tapering is to reduce insertion loss in the region below the absorption threshold. However, in the prior art, the conductor width is only tapered along the signal propagation direction. Summary of the Invention

[0004] An embodiment of the present disclosure provides a method and apparatus for a laterally tapered microstrip frequency selective limiter (FSL). In an embodiment, the FSL includes a tapered substrate thickness perpendicular to the transmission line. A plurality of transmission line segments are defined across the wafer, with each line segment having a constant width determined by the thickness of the YIG such that a characteristic impedance of, for example, 50 Ω is maintained over the length of the line segment. Connections between adjacent transmission lines can be formed on alternating substrate materials, which maintains a parallel magnetic bias in the YIG substrate. This allows for a longer frequency selective limiter in a compact YIG region with a simple single tapered substrate. Compared to known biplanar waveguide approaches such as those shown in U.S. Pat. No. 10,707,547, which is incorporated herein by reference, the microstrip approach can provide higher limiting per unit length.

[0005] In an embodiment, each line segment has a different width because each line segment has a different substrate thickness. The input to the FSL is connected to the adjacent narrower microstrip line using the widest line on the thickest YIG. This provides a tapered FSL while maintaining the geometry of the microstrip line. In an embodiment, an FSL with a tapered substrate can also be provided with striplines.

[0006] In some embodiments, the magnetic material of any of the transmission line structures may include ferrite materials, which may include one or more of the following: yttrium iron garnet (YIG), single crystal (SC) YIG, polycrystalline (PC) YIG, hexagonal ferrite, or various doped YIG materials, as well as calcium vanadium garnet (CVG), lithium ferrite, or nickel zinc ferrite.

[0007] In one aspect, a frequency selective limiter (FSL) comprises: a substrate including a magnetic material and having opposing first and second surfaces, the substrate tapering from a first thickness to a second thickness less than the first thickness; and a transmission line disposed in association with the first surface of the substrate, the transmission line having segments and bends, the segments being generally parallel to one another, each segment traversing the substrate over a thickness of the substrate.

[0008] The FSL may further include one or more of the following features: a first one of the segments is wider than a second one of the segments; each of the segments has a constant width across the substrate; the first one of the segments has the widest width and traverses the substrate at a location where the thickness of the substrate is greater than any of the other segments; as the thickness of the substrate decreases, the thickness of each adjacent segment decreases; the substrate includes an yttrium iron garnet (YIG) material; the non-magnetic substrate supports a bend in the transmission line; the transmission line has a microstrip configuration; the transmission line has a stripline configuration; different ones of the segments provide different ranges of power attenuation; the magnetic field source provides a constant bias magnetic field that is substantially parallel to the RF magnetic field in the magnetic material; and / or the magnetic field source provides a constant bias magnetic field that is substantially perpendicular to the RF magnetic field in the magnetic material.

[0009] In another aspect, a method for providing a frequency selective limiter (FSL) includes using a substrate including a magnetic material and having opposing first and second surfaces, the substrate tapering from a first thickness to a second thickness less than the first thickness, and disposing a transmission line relative to the first surface of the substrate, the transmission line having segments and bends, the segments being generally parallel to one another, each segment traversing the substrate over a constant thickness of the substrate.

[0010] The method may further include one or more of the following features: a first one of the segments is wider than a second one of the segments; each of the segments has a constant width across the substrate; the first one of the segments having the widest width traverses the substrate at a location where the substrate thickness is greater than any of the other segments; as the substrate thickness decreases, the thickness of each adjacent segment decreases; the substrate includes an yttrium iron garnet (YIG) material; using a non-magnetic substrate to support the transmission line bend; and / or different ones of the segments provide different ranges of power attenuation.

[0011] The foregoing and other objects, features and advantages will become apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. [Brief description of the drawings]

[0012] [Figure 1A] FIG. 2 illustrates a top view of a laterally tapered microstrip frequency selective limiter (FSL) according to an exemplary embodiment of the present disclosure. [Figure 1B]1B illustrates a side view of the laterally tapered microstrip FSL of FIG. 1A according to an exemplary embodiment of the present disclosure. [Figure 1C] 1B illustrates an isometric view of the laterally tapered microstrip FSL of FIG. 1A according to an exemplary embodiment of the present disclosure. [Figure 1D] FIG. 1 is an isometric view of a laterally tapered, stripline-configured FSL according to an exemplary embodiment of the present disclosure. [Diagram 2] FIG. 1 is a waveform diagram illustrating the response characteristics of an exemplary laterally tapered FSL, in accordance with an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An exemplary embodiment of a laterally tapered microstrip frequency selective limiter (FSL) includes tapering the thickness of a substrate, such as a YIG material, in a direction perpendicular to the microstrip lines. A plurality of microstrip lines, such as five, may be defined across the wafer. Each microstrip line has a constant width determined by the thickness of the YIG such that a characteristic impedance, such as 50 ohms, is maintained over the length of the microstrip line. Connections, such as bends, between adjacent microstrip line segments are formed on alternating non-magnetic substrate material, thereby maintaining a parallel magnetic bias on the YIG material. This allows for a longer microstrip frequency selective limiter in a compact YIG region with a simple single tapered substrate.

[0014] FIG. 1 illustrates an exemplary laterally tapered frequency selective limiter (FSL) 100 according to an exemplary embodiment of the present disclosure. In an exemplary embodiment, a transmission line 102, such as a microstrip line, meanders back and forth in a parallel bias orientation over a substrate 104, such as YIG. In an embodiment, magnetic field sources 106a, 106b, such as magnets and / or coils, are placed on either side of the substrate to provide a desired bias field. The transmission line 102 may include several bends 108, such as 180 degree bends (see FIG. 1C), such that the transmission line reverses direction and returns through the substrate 104. The bends 108 may be connected to the segments with respective conductive bonds 109, such as wire bonds or ribbon bonds. In an embodiment, each segment 110a, 110b, 110c, 110d, 110e of the transmission line has a uniform width across the substrate 104 and has a different width from adjacent segments. In an embodiment, the bend 108 in the transmission line overlaps a non-magnetic material 112, such as a ceramic material. The ground plane 105 may support the magnetic substrate 104. The ground plane 103 may support the non-magnetic substrate 112. The ground plane 103 and the ground plane 105 may be coupled to form a common ground plane.

[0015] In the embodiment shown in FIG. 1B, looking to the left of the top view of FIG. 1A, the substrate 104 has a linear taper from a first thickness T1 to a second thickness T2. In the embodiment, the FSL has an input 114 near the first thickness T1 of the substrate 104 and an output 116 near the second thickness T2. Each segment 110 of the transmission line has a uniform width across the substrate 104, so that the segment has a fixed thickness as it traverses the substrate 104. In the embodiment, the width of the segment 110 may become narrower as the thickness of the substrate 104 decreases. A ground plane 105 may support the magnetic substrate 104.

[0016] In another embodiment, the taper is non-linear, for example, stepped, arcuate, ridged, etc. It will be appreciated that any practical geometry may be used to define the taper shape of the substrate thickness that meets the needs of a particular application.

[0017] It will be appreciated that in any practical configuration, the segment width may vary relative to the thickness of the magnetic substrate to provide damping characteristics that meet the needs of a particular application. For example, adjacent segments may be of similar width. FSL embodiments may include magnetic substrates having non-linearly tapered thicknesses and segments having corresponding widths to provide desired damping characteristics.

[0018] In another embodiment, a laterally tapered frequency selective limiter (FSL) 100' is provided in a YIG superstrate and ground plane coupled stripline configuration. In the exemplary embodiment of FIG. 1D, a magnetic superstrate 118 is placed on top of the transmission line segment 110 on the top surface of the magnetic substrate 104. In the same manner as the magnetic substrate 104, the magnetic superstrate 118 is similarly tapered in thickness across its width. A ground plane 119 may be added on top of the magnetic superstrate 118, forming a stripline transmission line with the signal line 110 referenced to the ground planes 105 and 119. The ground planes 105 and 119 may be coupled to form a common ground potential. The length of the magnetic superstrate 118 is shorter than the magnetic substrate 104, which may allow the transmission line segment 110 to be accessed and joined to the transmission line bend 108 on the non-magnetic substrate 112.

[0019] According to some embodiments of the present disclosure, magnetic field sources 106a, 106b may be positioned along the length of transmission line 102 parallel to segments 110a-110e. In the example of FIG. 1A, FSL 100 includes a first magnetic field source 106a positioned on one side of transmission-line structure 102 along the thickest side of substrate 104, and a second magnetic field source 106b positioned on the opposite side of transmission-line structure 102 along the thinnest side of the substrate. Magnetic field sources 106a, 106b may be positioned to generate a DC magnetic field (i.e., a "bias field") perpendicular to segments 110 during operation.

[0020] In some embodiments, the magnetic field sources 106a, 106b provide a constant bias magnetic field that is approximately parallel to the RF magnetic field in the magnetic material 104. In other embodiments, the magnetic field sources 106a, 106b provide a constant bias magnetic field that is approximately perpendicular to the RF magnetic field in the magnetic material 104. In embodiments, the constant bias magnetic field may be at an angle between perpendicular and parallel to the RF magnetic field in the magnetic material 104.

[0021] 2 illustrates the limiting characteristics (gain vs. input power 202 and output power vs. input power 200) of an exemplary laterally tapered FSL in accordance with an exemplary embodiment of the present disclosure. As can be seen, tapered segments such as segments 110a-110e of FIGS. 1A-1C occupy different power ranges 204a, 204b, 204c, 204d, 204e. Once limiting is implemented in a first stage, the next stage reduces the amount of YIG that can be overdriven, targeting the power level of the next lower power range.

[0022] In the illustrated embodiment, the FSL has a YIG thickness of 250 μm on the input side (T1) and 150 μm on the output side (T2). The total length of the five segments 110 is 135 mm.

[0023] The first plot 200 shows the input power P in Output power P out indicates P outThe range is from 0dBm to approximately 30dBm on a scale of + / -40dBm, and P in The range of P is 0dBm to 60dBm. in The power is attenuated during the effective power range until P reaches saturation at about 50 dBm, which is the saturation of the device. in The figure shows the gain for P in As the gain 202 increases from about 15 dBm to about 50 dBm, the gain 202 typically decreases linearly in dB.

[0024] In an embodiment, each of the transmission line segments receives an input power P in 1A, which is the narrowest segment, corresponds to a first absorption in the input power range 204a from about 17 dBm to about 23 dBm. A second input power range 204b adjacent to the first input power range 204a corresponds to an input power of about 23 dBm to about 31 dBm until saturation is reached. The power range of the segments is inversely proportional to the width of the segments, and all widths are selected to provide a characteristic impedance of 50 Ω for the thickness of the magnetic substrate directly below the segments.

[0025] It will be appreciated that any practical number of segments and input power ranges may be provided to meet the needs of a particular application.

[0026] Exemplary embodiments of the FSL may provide advantages over known restrictors. For example, the transmission line may be patterned with a constant width microstrip line transversely on a YIG with a tapered thickness. This may be easier to design and manufacture than other conventional FSL configurations. The transverse orientation of the transmission line allows for a serpentine FSL with a desired number of segments that restrict the total to meet the needs of a particular application. The transverse structure also allows for a compact structure with a simple linear taper compared to a vertical structure of the same waveguide length.

[0027] An embodiment of a laterally tapered frequency selective limiter (FSL) may include a metal ground plane on the YIG bonded to a carrier substrate prior to grinding the YIG to a taper. This may allow for a relatively simple manufacturing process that may reduce costs. After grinding the YIG to tapered thickness, a microstrip center conductor may be patterned and aligned according to the resulting thickness. This configuration achieves low loss and strong limiting while also supporting wideband (e.g., 2-18 GHz) operation.

[0028] In embodiments, the microstrip ground plane may not require alignment. The microstrip pattern is aligned to the YIG thickness after YIG fabrication, which may reduce the required tolerance on absolute thickness during YIG polishing. Some embodiments may be compatible with surface mount packages with integrated bias magnets.

[0029] The stripline embodiment provides improved confinement characteristics, allowing for narrower transmission lines to maintain a 50 ohm impedance.

[0030] In some embodiments, the magnetic substrate material may include a ferrite material, such as, for example, yttrium iron garnet (YIG), single crystal yttrium iron garnet (SC-YIG), polycrystalline yttrium iron garnet (PC-YIG), hexagonal ferrite, calcium vanadium garnet (CVG), lithium ferrite, or nickel zinc ferrite. The material supporting the transmission line bend may include any non-magnetic material, such as a ceramic material. Any suitable non-magnetic material may be used.

[0031] Those skilled in the art will appreciate that the concepts described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects as illustrative rather than limiting of the concepts described herein. The scope of the concepts is therefore indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced within the scope of the concepts.

Claims

1. A frequency selective limiter (FSL), comprising: a substrate including a magnetic material and having opposing first and second surfaces; a substrate tapered from a first thickness to a second thickness less than the first thickness; a transmission line disposed relative to the first surface of the substrate; the transmission line having segments and bends; the segments are generally parallel to one another; each segment traverses the substrate over a constant thickness of the substrate; A transmission line; The FSL comprises:

2. a first one of the segments being wider than a second one of the segments; 2. The FSL of claim 1.

3. each of the segments having a constant width across the substrate; 2. The FSL of claim 1.

4. a first one of the segments, the first one having the widest width, traverses the substrate at a location where the thickness of the substrate is greater than any of the other segments; 2. The FSL of claim 1.

5. As the thickness of the substrate decreases, the thickness of each adjacent segment also decreases.

2. The FSL of claim 1.

6. the substrate comprises a yttrium iron garnet (YIG) material; 2. The FSL of claim 1.

7. The FSL further comprises: a non-magnetic substrate supporting the bend in the transmission line; 2. The FSL of claim 1.

8. the transmission line comprises a microstrip configuration; 2. The FSL of claim 1.

9. the transmission line comprises a stripline configuration; 2. The FSL of claim 1.

10. different ones of the segments provide different ranges of power attenuation; 2. The FSL of claim 1.

11. The FSL further comprises: a magnetic field source providing a constant bias magnetic field substantially parallel to the RF magnetic field in the magnetic material; 2. The FSL of claim 1.

12. The FSL further comprises: a magnetic field source providing a constant bias magnetic field substantially perpendicular to the RF magnetic field in the magnetic material; 2. The FSL of claim 1.

13. 1. A method for providing a frequency selective limiter (FSL), comprising: Using a substrate comprising a magnetic material and having opposing first and second surfaces; tapering the substrate from a first thickness to a second thickness less than the first thickness; disposing a transmission line relative to the first surface of the substrate; the transmission line having segments and bends; the segments are generally parallel to one another; each segment traversing the substrate over a constant thickness of the substrate; A method comprising:

14. a first one of the segments being wider than a second one of the segments; The method of claim 13.

15. each of the segments having a constant width across the substrate; The method of claim 13.

16. a first one of the segments, the first one having the widest width, traverses the substrate at a location where the thickness of the substrate is greater than any of the other segments; The method of claim 13.

17. As the thickness of the substrate decreases, the thickness of each adjacent segment also decreases. The method of claim 13.

18. the substrate comprises a yttrium iron garnet (YIG) material; The method of claim 13.

19. The method further comprises: using a non-magnetic substrate to support the bend in the transmission line; The method of claim 13, comprising:

20. different ones of the segments provide different ranges of power attenuation; The method of claim 13.

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