WAVEGUIDES

Abstract

An electronic device comprises a waveguide block defining a cavity therein. The device has a monolithic microwave or millimetre-wave integrated circuit device positioned at least partially in the cavity. The integrated circuit device comprises a dielectric substrate and a metal foil layer that extends outwards from an external edge of the dielectric substrate. The metal foil layer and the dielectric substrate define a through hole, wherein a first edge of the through hole is an edge of the metal foil layer and defines an end of the elongate waveguide channel, and wherein the metal foil layer at least partly determines both a length and a width of an elongate waveguide channel within the cavity.

Claims

1. An electronic device comprising: a waveguide block defining a cavity therein; and a monolithic microwave or millimetre-wave integrated circuit device positioned at least partially in the cavity, wherein: the monolithic microwave or millimetre-wave integrated circuit device comprises a dielectric substrate and a metal foil layer that extends outwards from an external edge of the dielectric substrate; the metal foil layer and the dielectric substrate define a through hole, wherein a first edge of the through hole is an edge of the metal foil layer and defines an end of an elongate waveguide channel within the cavity; and the metal foil layer at least partly determines both a length and a width of the elongate waveguide channel.

2. The electronic device of claim 1, wherein the metal foil layer defines at least one edge of the elongate waveguide channel.

3. The electronic device of claim 1, wherein the cavity comprises an elongate cavity having a first length and a first width, the elongate waveguide channel being located within the elongate cavity and having a second length and a second width, wherein the second length is less than the first length and wherein the second width is less than the first width.

4. The electronic device of claim 1, wherein the metal foil layer is fastened or bonded to the dielectric substrate and to the waveguide block.

5. The electronic device of claim 1, wherein the waveguide block comprises a first portion and a second portion defining the cavity therein therebetween, and wherein the metal foil layer is clamped between the first and second portions of the waveguide block so as to provide mechanical support to the dielectric substrate.

6. (canceled)

7. (canceled)

8. The electronic device of claim 1, wherein the through hole is a closed hole completely surrounded by the metal foil layer and by the dielectric substrate.

9. (canceled)

10. (canceled)

11. (canceled)

12. The electronic device of claim 1, wherein the dielectric substrate is substantially planar.

13. The electronic device of claim 1, wherein the dielectric substrate comprises a gallium arsenide substrate.

14. (canceled)

15. (canceled)

16. A monolithic microwave or millimetre-wave integrated circuit device for use in a waveguide block that defines a cavity, wherein: the monolithic microwave or millimetre-wave integrated circuit device comprises a dielectric substrate and a metal foil layer that extends outwards from an external edge of the dielectric substrate; 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 or millimetre-wave integrated circuit device is situated at least partially within the cavity of the waveguide block; and the metal foil layer and the dielectric substrate are shaped to define a through hole, wherein a first edge of the through hole is an edge of the metal foil layer for defining an end of the elongate waveguide channel.

17. The integrated circuit device of claim 16, wherein the metal foil layer is shaped to define at least one edge of the elongate waveguide channel.

18. The integrated circuit device of claim 16, wherein the dielectric substrate is elongate and wherein the metal foil is shaped such that the waveguide channel is elongate along an axis substantially perpendicular to an axis of the dielectric substrate.

19. The integrated circuit device of claim 16, wherein the metal foil layer and the dielectric substrate are shaped so that the through hole is framed in part by the metal foil layer, in part by the dielectric substrate, and in part by the waveguide block.

20. The integrated circuit device of claim 16, wherein the through hole is a closed hole completely surrounded by the metal foil layer and by the dielectric substrate.

21. The integrated circuit device of claim 16, wherein a majority of a circumference of the through hole is framed by the metal foil layer, and wherein a further portion of the circumference of the through hole is framed by the dielectric substrate.

22. The integrated circuit device of claim 16, wherein the through hole has a second edge for defining a first side edge of the elongate waveguide channel, and a third edge for defining a second side edge of the elongate waveguide channel, wherein the second and third edges are edges of the metal foil layer.

23. The integrated circuit device of claim 22, wherein the through hole is a rectangular hole and has a fourth edge that is an edge of the dielectric substrate.

24. The integrated circuit device of claim 16, wherein the dielectric substrate is part of a microstrip.

25. The integrated circuit device of claim 16, wherein the substrate carries an integrated circuit comprising at least one active component.

26. The integrated circuit device of claim 25, wherein the integrated circuit device comprises at least one of a mixer, a filter, an amplifier, a multiplier or a frequency divider.

27. The integrated circuit device of claim 16, wherein the metal foil layer comprises a gold foil layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Certain embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0043] FIG. 1 is a schematic drawing of a conventional MMIC device in a waveguide cavity;

[0044] FIG. 2 is a graph illustrating a consistency issue associated with the device of FIG. 1;

[0045] FIG. 3 is a schematic drawing of a MMIC device in a waveguide cavity in accordance with an embodiment of the present invention;

[0046] FIG. 4 is a further schematic drawing of the MMIC device of FIG. 3 from a further viewing angle;

[0047] FIG. 5 is the same view as FIG. 4 but with a through hole highlighted;

[0048] FIG. 6a is a simulated electromagnetic-field plot for a conventional MMIC design;

[0049] FIG. 6b is a simulated electromagnetic-field plot for the MMIC device of FIG. 3;

[0050] FIG. 7 is a graph illustrating an improvement in the consistency associated with the device of FIG. 3; and

[0051] FIG. 8 is a further graph illustrating an improvement in the consistency associated with the device of FIG. 3.

DETAILED DESCRIPTION

[0052] FIG. 1 is a schematic drawing of an electronic device 2 of conventional design comprising a waveguide block 4, in which a MMIC device 6 is positioned within a waveguide cavity 8. This particular device 2 is a frequency doubler circuit. The substrate of the MMIC device 6 provides a probe 9, a set of bias filters 10, and a diode 11, located within the waveguide cavity 8. The diode 11 could be discrete or monolithically integrated with the MMIC device 6. Those skilled in the art will appreciate that frequency doubler 2 generates an output signal at twice the frequency of the input signal due to the non-linear properties of the diode 11, where the output power is the product of the input power applied and the circuit conversion efficiency.

[0053] 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.

[0054] 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 FIG. 1, there is a discrepancy between the dimensions and location of the waveguide cavity 8, denoted by solid lines filled with dotted shading, and the ideal cavity 12 denoted by the dashed lines, i.e. the intended cavity according to a modelled waveguide design. This discrepancy arises due to machining errors. Machining the cavity 8 is relatively difficult, and higher operating frequencies require tighter machining tolerances.

[0055] 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.

[0056] 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.

[0057] FIG. 2 is a graph illustrating a consistency issue associated with the frequency doubler device of FIG. 1. Shown on the graph are plots of the output power vs output frequency, at a constant 25 mW input power, of four different conventional devices—labelled circuits 1-4— similar to the device 2 shown in FIG. 1. As can be seen from these plots, the performance of the four different devices is inconsistent across the devices. This inconsistency can, at least in part, be attributed to machining errors as described above.

[0058] FIG. 3 is a schematic drawing of an electronic device 130 comprising a MMIC device 100 in a waveguide cavity 102 in accordance with an embodiment of the present invention. FIG. 4 is a further schematic drawing of the electronic device 130 of FIG. 3 from a further viewing angle.

[0059] As with the device 2 of FIG. 1, in the device 130 of FIG. 3 the waveguide block 104 is formed from upper and lower portions, split in the E-plane, that, when assembled, have opposing complementary faces which come into contact with one another to form a single block 104.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Similarly to the MMIC microstrip device 6 of FIG. 1, the MMIC device 100 of FIG. 3 provides a diode 106 integrated within the waveguide cavity 102, where the diode 106 is carried by the MMIC device 100. The device 100 comprises a dielectric substrate 108 which, in this particular example, is a gallium arsenide (GaAs) substrate. The GaAs substrate 108 carries the diode 106, which may be formed on the substrate 108 using known deposition techniques.

[0064] However, unlike the MMIC device 6 of FIG. 1, the MMIC device 100 of FIG. 3 is provided with a metal foil layer 110 that extends from the substrate 108. This metal foil layer 110 is, in this embodiment, gold. Gold is preferred due to its high conductivity and because it is relatively inert under atmospheric conditions. This gold foil layer 110 extends laterally from the substrate 108 of the MMIC device 100 in various directions and is ‘sandwiched’ between the upper and lower waveguide blocks when assembled. The foil is approximately 1 to 3 microns thick. The foil layer 110 in this example comprises three distinct portions 110a, 110b, 110c which act as mechanical supports that hold the substrate 108 in a fixed position within the waveguide cavity 102. The foil layer 110 is grounded electrically to the waveguide block 104.

[0065] 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.

[0066] 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.

[0067] FIG. 5 highlights the rectangular through hole 140 within the cavity 102 that is defined by the dielectric substrate 108 and the portions 112a, 112b, 112c of the gold foil layer 110. A straight edge of the semi-circular region 112a defines a first edge 141 of the through hole 140. A straight edge of the first rectangular region 112b defines a second edge 142 of the through hole 140. A straight edge of the second rectangular region 112c defines a third edge 143 of the through hole 140, opposite the second edge 142. A straight edge of the dielectric substrate 108 defines a fourth edge 144 of the through hole 140, opposite the first edge 141. The first edge 141 defines an end of the elongate waveguide channel within the cavity 102a, while the second edge 142 and third edge 143 define respective side edges for the waveguide channel.

[0068] FIGS. 6a & 6b illustrate how the inclusion of the foil 110 perturbs the electromagnetic fields. The contours in FIG. 6a show simulated electric field strengths for a shorted waveguide section at an end of a waveguide channel that does not have any foil protruding from the waveguide backshort—e.g., similar to the output waveguide channel 8a in the conventional device 2 of FIG. 1. The contours in FIG. 6b show simulated electric field strengths for a shorted waveguide section of the device 130 of FIG. 3, which has a region 112 of the gold foil 110 protruding into the waveguide cavity 102 from the waveguide backshort. It can be seen that the inclusion of the foil 110 causes the electric field to be compressed, compared with the foil-less conventional design. This demonstrates how the presence of the foil 110, and its dimensions, can strongly affect the electrical properties of the waveguide structure 104.

[0069] FIG. 7 is a graph illustrating an improvement in the consistency associated with devices 130 manufactured to the design of FIG. 3. Shown on the graph are plots of the measured output power vs output frequency, at a constant 40 mW input power, of two devices both constructed as per the design of FIG. 3.

[0070] 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 FIG. 2, corresponding to the conventional device 2 of FIG. 1.

[0071] FIG. 8 is a further graph illustrating an improvement in the consistency associated with the device 130 of FIG. 3. Shown on the graph are plots of the output power vs input power performance of the two devices, for an operating frequency of 320 GHz. As can be seen from this graph, the two devices are consistent in terms of the relationship between their output power to input power transfer functions.

[0072] 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.

[0073] 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.