Patent Application
20220376375
The present invention relates to waveguide devices, in particular to waveguide devices for use in microwave and millimetre-wave (terahertz) systems.
A Monolithic Microwave Integrated Circuit, or MMIC (sometimes pronounced “mimic”), is a type of integrated circuit (IC) device that operates at microwave or terahertz frequencies (e.g., in frequency bands between approximately 300 MHz and 3 THz). These devices may provide functions such as high-frequency mixing, frequency multiplication, direct detection, power amplification, low-noise amplification, and high-frequency switching and have applications in fields such as radar, telecommunications, and remote sensing (e.g. Earth and Space sensing).
Before MMICs were developed, only discrete-component devices were used in the art. Such discrete-component devices are typically semiconductor-based in which the active components, e.g. diodes, are soldered to a substrate, typically quartz or aluminium nitride. However, the assembly of these devices is generally difficult and often results in alignment errors which generally leads to a relatively wide scatter in the results that they achieve. They may also have poor thermal properties which may also contribute to poor performance.
In order to overcome these issues, integrated devices have been used in which the diode(s) are integrated on a substrate during fabrication. This can provide improvements in the alignment between the diode(s) and the microstrip matching networks typically employed by such devices. Integrated devices may also provide for easier assembly, an improved thermal layout, and an improved consistency of the results.
The substrate may be gallium arsenide or a substrate transfer to silicon, aluminium nitride, silicon dioxide, etc.
MMIC devices are typically placed in a cavity within a waveguide block—e.g. as a suspended microstrip. However, high precision machining of waveguide blocks is difficult and expensive. In particular, as the operating frequency increases from microwave to terahertz frequencies, the dimensions of the waveguide and cavity become smaller, thus requiring tighter tolerances in order to achieve a desired performance. For example, with an operating frequency of 300 GHz, a machining tolerance of as little as ±10 μm can result in significant performance variability, both in terms of the tuned frequency and the impedance of the cavity.
When viewed from a first aspect, the present invention provides an electronic device comprising:
When viewed from a second aspect, the present invention provides a monolithic microwave or millimetre-wave integrated circuit device for use in a waveguide block that defines a cavity, wherein:
More generally, when viewed from another aspect, the present invention provides an electronic device comprising:
When viewed from a further aspect, the present invention provides a monolithic microwave or millimetre-wave integrated circuit device for use in a waveguide block that defines a cavity, wherein the integrated circuit device comprises a dielectric substrate and a metal foil layer that extends outwards from an external edge of the dielectric substrate; and wherein the metal foil layer is shaped to determine, at least partly, both a length and a width of an elongate waveguide channel within the cavity, when the monolithic microwave integrated circuit device is situated at least partially within the cavity of the waveguide block.
Thus it will be appreciated that the present invention provides an improved MMIC device that, once placed in the cavity, intrinsically defines a channel length and channel width of a waveguide channel within the cavity, thereby controlling the electromagnetic wave propagation characteristics of the cavity. The channel length and width are both determined, at least in part, by a metal foil layer, instead of depending on the cavity alone to determine the dimensions of a waveguide channel. This can make accurately controlling the waveguide parameters easier, reducing the design and fabrication burden associated with tight tolerance requirements, because it is generally easier to fabricate the metal foil layer to meet a desired tolerance than it is to fabricate a waveguide block to the same tolerance. In particular, it may allow both the frequency response and the impedance of the device to be controlled more easily and accurately than in known devices. It may therefore be possible, in some instances, to fabricate the waveguide block with a looser tolerance on the cavity dimensions than would otherwise be required, because the metal foil of the MMIC that sits within the cavity determines the effective channel length and the effective channel width of the electronic device.
The dielectric substrate and the metal foil layer may be fabricated in a common fabrication process. The alignment of the foil layer with other elements of the MMIC device can thus be determined by a semiconductor manufacturing process and so be highly accurate, thereby enabling a very accurate alignment between the MMIC device and the waveguide channel.
The metal foil layer may define the length of the waveguide channel by being configured (e.g. shaped) to define an end of the waveguide channel. The metal foil layer may define the width of the waveguide channel by being configured (e.g. shaped) to provide at least one edge of the waveguide channel. In some embodiments, the foil layer may provide two edges of the waveguide channel, which may be opposite edges.
The cavity in the waveguide block may comprise an elongate cavity (which may be only a portion of a larger cavity) having a first length and a first width. It may be defined by one or more walls, which may be planar or curved. The elongate cavity may have a rectangular cross-section (which may be constant along the first length, although this is not essential). It may be closed at one end. The waveguide channel may be within the elongate cavity. The waveguide channel defined at least partly by the foil layer may have a second length and a second width. The second length may be less than the first length, and the second width may be less than the first width. The lengths may be determined relative to a point on the dielectric substrate, or any other convenient point. The lengths may be maximum or minimum or average (e.g., mean) lengths along an axis of the elongate channel. The widths may be maximum or minimum or average (e.g., mean) widths over the respective lengths. The widths may be determined perpendicular to an axis of the elongate channel—i.e. perpendicular to the lengths. The MMIC may be substantially planar, and the widths may be determined parallel with a plane of the MMIC device.
Moreover, since the metal foil layer extends from the dielectric substrate, and is preferably bonded to the dielectric substrate, the alignment of the elongate waveguide channel relative to the dielectric substrate can be accurately controlled and is less sensitive to the exact positioning of the MMIC within the waveguide block. The metal foil layer, when clamped between the two halves of the waveguide block, may hold the substrate in position.
Thus, some embodiments provide an electronic device comprising:
Typically, the channel length of a closed-ended waveguide cavity influences the ‘tuned’ frequency of the cavity. It is known for a waveguide block to provide a ‘backshort’ in order to set the channel length to a desired value. However, in accordance with certain embodiments of the present invention, the foil layer advantageously provides a backshort that is integrated as part of the MMIC device itself. The backshort may define the end of the elongate waveguide channel. The waveguide block itself need not then act as a backshort, as is typically the case with arrangements known in the art per se. The waveguide cross-section and termination distance (defined by the backshort) can be important for determining how the device behaves.
The impedance of a waveguide channel typically depends on the width of the channel. The metal foil may determine an effective width for the elongate waveguide channel within the waveguide cavity. Moreover, the metal foil may effectively confine the electromagnetic fields beyond the edges of the foil, i.e. away from the walls of the waveguide cavity. The impedance of the waveguide channel may thus be partly or wholly defined by the shape of the metal foil, rather than wholly by the dimensions of the waveguide cavity itself. This therefore allows the machining tolerance of the cavity width to be relaxed compared to that of conventional arrangements.
The waveguide block may be conductive (e.g. comprising metal), although in some embodiments it could be dielectric. It may comprise a first portion (or shell) and a second portion (or shell) which, when brought together, define the cavity. An electric field may be confined by a conductor short-circuiting the first and second portions of the waveguide block. The metal foil layer may terminate the elongate cavity at a point in space required so as to efficiently or optimally reflect EM energy back toward a probe for collecting the EM energy (e.g. a probe of the MMIC device). The reflected EM energy may superimpose (i.e. combine) in-phase with the incident wave, setting up a standing wave (i.e. spatially constant) which imposes a particular impedance at a given point in the circuit or transforms one impedance to another within the circuit.
The metal foil layer may comprise one or more distinct foil sections which may be physically separated from each other. Some or all of the foil layer (e.g. one or more foil section) may be electrically connected to the waveguide block, or otherwise grounded. The foil layer may be substantially planar, or planar over a majority of its surface by area, when assembled within the waveguide block. It may be planar away from the dielectric substrate, but may, in some embodiments, curve out of this plane adjacent or touching the dielectric substrate. Any suitable metal may be used for the foil, as the function is achieved due to the conductive properties of the metal foil. In some embodiments the metal foil layer comprises a gold foil layer. Gold may be preferred because of its relatively high conductivity and malleability compared to other metals and because it is relatively inert under atmospheric conditions, making it easier to handle during fabrication.
The metal foil layer may provide mechanical support to the dielectric substrate. It may be fastened or bonded to the dielectric substrate. It may also be fastened or bonded to the waveguide block (e.g. chemically, or by friction). The metal foil layer may extend from at least two edges of the dielectric substrate—e.g., with respective foil sections extending in opposite directions.
While it is possible that, in some embodiments, a second edge of the elongate waveguide channel is defined by a face of the waveguide block, in other embodiments the metal foil layer is further configured (e.g. shaped) to define a second edge of the elongate waveguide channel. The second edge may be parallel to the first edge. In this way, the effective width of the waveguide channel may advantageously be determined wholly by the shape of the metal foil layer, and need not depend on the precision of the cavity machining at all.
The metal foil layer and dielectric substrate may define a through hole. Such an arrangement conveniently enables the foil layer to provide one or more edges that may determine the width and length of the waveguide channel, while facilitating a precise fabrication alignment between the foil layer and the substrate from which the foil extends. The through hole may be framed by the metal foil layer around a majority of the circumference of the hole—e.g. around three sides of a rectangular hole. The hole may be framed by the dielectric substrate along a portion of its circumference—e.g., around a fourth side of a rectangular hole. While the through hole may be framed in part by the waveguide block, preferably the through hole is a closed hole, completely surrounded by the metal foil layer and the dielectric substrate. The through hole may be elongate. It may be rectangular. A first edge of the through hole may define the end of the elongate waveguide channel. A second edge of the through hole may define the first side edge of the elongate waveguide channel. The first and second edges of the hole may be perpendicular. A third edge of the through hole may define the second side edge of the elongate waveguide channel. The second and third edges of the hole may be parallel. Any or all of the first, second and third edges may be edges of the foil layer. A fourth edge may be an edge of the dielectric substrate. Any of the edges may be straight edges.
More generally, the metal foil may comprise an edge which determines the length of the elongate waveguide channel. The edge may be suspended within the cavity. It may span the cavity. It may be a straight edge. The ability to determine the shape of this edge—e.g. to provide a straight edge—can be advantageous over conventional designs in which the shape of the end of a waveguide channel may be constrained by the machining used to create the cavity—e.g. constrained to be semi-circular with a fixed or minimum radius. This may allow better control over the electromagnetic field within the waveguide channel.
The metal foil layer may act as a finline waveguide within the cavity. The foil layer may cause a perturbation of electromagnetic fields which may define the effective width, and hence impedance, of the waveguide channel.
The cavity may comprise a plurality of elongate cavities. The waveguide block may define one or more waveguide channels along one or more elongate cavities. The waveguide channel whose length and width are determined by the metal foil layer may adjoin or be a continuation of a waveguide channel whose width is defined by faces of the waveguide block and which may be wider than the first width defined by the metal foil layer.
The dielectric substrate may be shaped in order to fit partly or wholly within the waveguide cavity. In at least some embodiments, the substrate is planar or substantially planar. In a set of such embodiments, the substrate is elongate, having a substrate length along a device direction and a substrate width substantially perpendicular to the device direction. The metal foil may be shaped such that the elongate waveguide channel has an axis substantially perpendicular to an axis of the dielectric substrate.
In preferred embodiments, the substrate comprises a gallium arsenide substrate. Gallium arsenide (GaAs) may be preferred over silicon (Si) due to its higher device (transistor) speed which is beneficial for high-frequency applications.
In some embodiments, the substrate carries an integrated circuit. The integrated circuit may form only a portion of larger electrical circuit. In a preferred set of such embodiments, the integrated circuit comprises at least one active component. These one or more active components may comprise one or more diodes and/or transistors. The active component may be arranged to receive a signal from along the waveguide channel, or to output a signal along the waveguide channel. The integrated circuit may comprise a mixer, a filter, an amplifier, a multiplier, a frequency divider, a detector, a duplexer, a diplexer, an oscillator, etc.
Certain embodiments of the present invention will now be described with reference to the accompanying drawings, in which:
The waveguide block 4 is formed from upper and lower portions, split in the E-plane (the plane containing the electric field vector), which have been brought together to define the cavity 8.
The waveguide cavity 8, defined by surfaces of the waveguide block 4, acts as a waveguide channel for guiding microwave or millimetre-wave signals through the device 2. In this example, the cavity 8 includes an output waveguide channel 8a and an input waveguide channel 8b, at right angles to each other. As can be seen in
Due to this discrepancy between the actual cavity 8 and the ideal cavity 12, the waveguide termination does not have the intended dimension, relative to the position of the MMIC device 6, resulting in improper tuned frequency for the device 2. Similarly, the impedance of the waveguide depends on the width of the cavity, which also does not have the intended value.
By contrast, the metal foil provided in accordance with embodiments of the present invention sets an effective channel width and backshort position within the waveguide cavity, such that the impedance and tuned frequency are defined by the metal foil, rather than by the dimensions of the waveguide cavity itself. This therefore allows the machining tolerance of the cavity width to be relaxed compared to that of conventional arrangements.
As with the device 2 of
These two portions define the cavity 102 between them and are otherwise in physical and electrical contact with one another across their opposing faces. The cavity 102 includes an output cavity portion 102a and an input cavity portion 102b, at right angles to each other. These cavities 102a, 102b generally have rectangular cross-sections, which are of constant width in the vicinity of the MMIC device 100, apart from a circularly tapering end portion of the input cavity 102a. This circular taper is caused by the cylindrical machine tool used to form the cavity 102; its shape may be determined by a minimum radius of the cutter. The waveguide block 104 is, at least in this example, machined from an aluminium alloy, however it will be appreciated that other materials such as copper, brass, etc. may be used instead.
Rectangular waveguides support propagating modes in frequency bands determined from their physical dimensions. The dimensions of the waveguide determine the propagation characteristics and electrical properties, notably the impedance, of the waves supported in the waveguide.
The output cavity 102a has a constant width of W1 along most of a length L1, adjacent the MMIC device 100, and a width of less than W1 within the tapered end portion. The length L1 is here measured from an edge of the dielectric substrate 108 to the end of the tapered end portion of the cavity 102a. In some embodiments, L1 may be approximately 1 mm, while W1 may be approximately 0.3 mm, although the dimensions may vary according to desired design parameters. As will be explained in further detail below, the MMIC device 100 allows for these parameters to be greater than they should be for the desired waveguide tuned frequency and impedance. This lessens the need for such tight tolerances in the process used to machine the cavity 102 in the waveguide block 104. Thus this length L1 and width W1 are both greater than an intended length and width for which the total waveguide assembly is designed.
Similarly to the MMIC microstrip device 6 of
However, unlike the MMIC device 6 of
A region 112 of the gold foil portion 110a extends into the cavity 102a, parallel to the E-plane. This region 112 of the gold foil 110 causes a perturbation of the electromagnetic field which determines the effective length and impedance of an elongate waveguide channel within the cavity 102a. In particular, a region 112a shaped like a rectangle joined to a semicircle (the shape of which is partly defined by the straight walls and the curved tapering end wall of the cavity 102a) is suspended within the cavity 102a and spans the width of the cavity 102a. It has a free edge 113 which spans a width W2 of the cavity 102a. The region 112a acts as a backshort for a longer channel within the cavity 102, which reduces the effective maximum length of the channel by L1 minus L2, i.e. the electromagnetic wave is prevented from propagating in the semi-circular region 112a and the backshort in the cavity 102a is formed with length L2. Additionally, a first rectangular region 112b, of size L2 by (W1−W2)/2, protrudes from, and runs parallel to, a first side wall of the cavity 102a, while a second rectangular region 112c, also of size L2 by (W1−W2)/2, protrudes from, and runs parallel to, an opposite side wall of the cavity 102a. These rectangular regions 112b, 112c set the effective width of the waveguide channel, where the foil 112b, 112c is present, at a width W2, which is less than the width W1 of the machined cavity 102a. Thus the foil layer 110 both shortens and narrows the effective length and width of the cavity 102a to desired values.
In this way, the portion 112 of the gold foil layer 110 is what sets the effective length L2 and width W2 of the cavity with regard to electromagnetic waves propagating through the waveguide. As the gold foil 110 may be defined lithographically, this length L2 and width W2 are easier to control than the dimensions L1, W1 of the machined cavity, thus allowing a more precise resultant waveguide channel without the stringent machining tolerance requirements that would be imposed when attempting to use conventional techniques.
As can be seen from these plots, the two different devices are relatively consistent, as the plots are far closer in values than those shown in
Thus it will be appreciated by those skilled in the art that embodiments of the present invention provide an improved MMIC device that allows for simpler and more accurate control of the tuned frequency and impedance characteristics of a waveguide channel, rather than relying on precise machining of the waveguide cavity itself. As the channel length and width are both controlled by the metal foil layer, the design and fabrication burden associated with tight tolerance requirements are reduced.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that the embodiments described in detail are not limiting on the scope of the claimed invention, which is defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1915109.1 | Oct 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/052614 | 10/16/2020 | WO |
