TITLE

COMPACT DIELECTRIC SLAB-MODE ANTENNA

FIELD OF THE INVENTION

[0001] The present invention relates to an antenna More specifically, the present invention relates to a dielectric slab-mode antenna

BACKGROUND OF THE INVENTION

[0002] Low-loss, directive antennas are needed for future wideband millimeter wave (mmW) communications in the non-licensed 60-GHz-band It was shown in references [1]-[3] that indoor wireless transmission of data at gigabit rate is strongly dependent on directive antenna technology Furthermore, since the generation of electromagnetic energy in this frequency range is costly and battery power in mobile devices is limited, such low-loss directive antennas should be as efficient as possible As part of a future commercial product, the antenna also has to be compact and capable of being integrated, light-weight, and cheap to manufacture using planar lithographic fabrication techniques and established material technologies

[0003] Currently used antennas in comparable frequency ranges of the order of 50 GHz or above for military and space applications most often use metal waveguide technologies and corresponding horn antennas This approach provides good performance but fails to meet with the requirements of compact design, light weight and low production cost necessary for commercial success

[0004] For this reason, planar antennas became very popular in the microwave range up to 30 GHz Such planar antennas have to be arranged in arrays in order to obtain a certain directivity Although this concept works at

lower microwave frequencies, it is not easily transferable to the mmW range, because conductor losses in the inevitable complex feeding network rise quickly with frequency.

[0005] Special antennas that comprise focusing parts, e.g. lenses, have been designed to achieve directive antennas. However, these designs are not planar and the design effort and manufacture costs are high.

[0006] One planar end-fire antenna became very popular due to its wide bandwidth: the Vivaldi antenna [4]. It is basically a tapered slot antenna whose radiation pattern can be improved by a more complex and expensive multi-layer design [5]. A difficulty in connection with the Vivaldi antenna is the transition between the feeding waveguide structure (usually microstrip or coplanar waveguide) and slot line. For good performance, the substrate should be extremely thin at mmW frequencies, especially when high-permittivity substrates are used, e.g. ε/εo = ε _r > 6. Frequently used high-permittivity substrates with good mmW performance like alumina, sapphire, or semiconductors including silicon and gallium arsenide, generally induce a field trapping effect due to the high refractive index contrast between the material and free space. Instead of being radiated, a big part of the electromagnetic energy is reflected, which results in increased losses and deteriorated radiation patterns.

SUMMARY OF THE INVENTION

[0007] To overcome the above-mentioned problems of the prior realizations, the present invention is concerned with a compact dielectric slab- mode antenna comprising:

an electrically conductive ground body defining a ground plane, the ground plane having a proximal end portion and a curved distal end portion;

a dielectric slab having a grounded proximal end portion applied to the proximal plane portion of the ground plane and an ungrounded distal end portion forming a cantilever;

a surface wave source operatively connected to the grounded proximal end portion of the dielectric slab to launch surface waves in the dielectric slab;

wherein the curved distal end portion of the ground plane end defines a gradual transition from the grounded proximal end portion to the ungrounded distal end portion of the dielectric slab.

[0008] The present invention is also concerned with a compact dielectric slab-mode antenna comprising:

an electrically conductive ground body defining a ground plane, the conductive ground body having a proximal end and a distal end;

a dielectric slab laid on the ground plane, the dielectric slab being in the form of a flat planar substrate having a proximal end and a distal end; and

a surface wave source comprising an input ending in a slot dipole acting as a coupling probe to a metallized patch operatively connected to the proximal end of the dielectric slab to launch surface waves in the

dielectric slab and at least one metallized back-short via placed in contact with the metallized patch;

wherein the distal end of at least one of the conductive ground body and the dielectric slab is tapered so as to reduce wave reflection and/or to achieve a desired directivity.

[0009] The present invention is further concerned with a compact dielectric slab-mode antenna comprising:

an electrically conductive ground body defining a ground plane, the conductive ground body having a proximal end and a distal end;

a dielectric slab laid on the ground plane, the dielectric slab being in the form of a flat planar substrate having a proximal end and a distal end; and

a surface wave source comprising a waveguide formed by at least two spaced apart rows of metallized vias located within the dielectric slab, in a direction from the proximal end to the distal end of the dielectric slab, conductively connected to a pair of metallic ground planes positioned on opposite faces of the dielectric slab, and at least two spaced apart metallized back-short vias conductively connected to the pair of metallic ground planes, whereby a portion of the dielectric slab located between the at least two spaced apart rows of metallized vias forms an input;

wherein the distal end of at least one of the conductive ground body and the dielectric slab is tapered so as to reduce wave reflection and/or to achieve a desired directivity.

[0010] As used in this specification and claim(s), the words

"comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "include" and "includes") or "containing" (and any form of containing, such as "contain" and "contains"), are inclusive or open- ended and do not exclude additional, unrecited elements or process steps.

[0011] The foregoing and other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the appended drawings:

[0013] Figure 1 is a schematic perspective view of a compact dielectric slab-mode antenna according to a first illustrative embodiment of the present invention;

[0014] Figure 2 is a schematic perspective view of the electrical fields propagated in the horizontal plane at a lower slab surface of the compact dielectric slab-mode antenna of Figure 1 ;

[0015] Figure 3 is a schematic perspective view of the compact dielectric slab-mode antenna of Figure 1 to which was added a planar dielectric lens;

[0016] Figure 4 is a schematic perspective view of the intensity of the electrical fields propagated in the horizontal plane at a lower slab surface of the compact dielectric slab-mode antenna of Figure 3;

[0017] Figure 5 is a schematic perspective view of the intensity of the electrical fields propagated in the vertical plane in the center of the compact dielectric slab-mode antenna of Figure 3;

[0018] Figure 6 is a schematic perspective view of a compact dielectric slab-mode antenna according to a second illustrative embodiment of the present invention;

[0019] Figure 7 is a schematic perspective view of a compact dielectric slab-mode antenna according to a third illustrative embodiment of the present invention;

[0020] Figure 8 is a schematic perspective view of a compact dielectric slab-mode antenna according to a fourth illustrative embodiment of the present invention;

[0021] Figures 9a, 9b and 9c are schematic perspective views of examples of coplanar waveguide (CPW) slab-mode launchers;

[0022] Figure 10 is a schematic perspective view of a modified CPW slab-mode launcher;

[0023] Figure 11 is a schematic perspective view of an example of a substrate integrated waveguide (SIW) launcher; and

[0024] Figure 12 is an exploded schematic perspective view of a cross section of a SIW launcher waveguide taken along axis XII — XM of Figure 11.

DETAILED DESCRIPTION

[0025] The illustrative embodiments of the present invention are concerned with a compact dielectric slab-mode antenna suitable for printed- circuit fabrication. The antenna is generally in the form of a dielectric slab-mode end-fire antenna comprising an electrically conductive ground body with a dielectric slab laid on one of its faces and a suitable source to supply a captured surface-guided electromagnetic wave for propagation in the grounded dielectric slab. Due to its dimensions (dielectric slab thickness) and assembly, the compact dielectric slab-mode antenna is advantageously suited for communication applications using frequencies of 24 GHz or above, but is not limited to that particular range of frequencies.

[0026] The compact dielectric slab-mode antenna is also well suited for wireless gigabit communication applications, for example in the unlicensed 60 GHz band. This includes, but is not limited to, short-haul, high capacity wireless data links and wireless local or personal area networks (WLANs / WPANs), last mile or radio-over-fiber mobile transceivers and temporary setups for broadcasting in high definition quality for special events. Other applications include, mobile transceivers and sensors, low cost antenna arrays for imaging systems and spatial power combining and short or medium range radar systems (used, for example, in the automotive industry).

[0027] Directive antennas such as compact dielectric slab-mode antennas are also useful for indoor communication applications because the

signal delay spread is kept small in order to transmit at high data rates. Directive antennas also increase the range in outdoor environments.

[0028] Referring to Figure 1 , there is shown a first illustrative embodiment of the compact dielectric slab-mode antenna, which is identified by the reference 10. To overcome the above discussed drawback of the prior realizations, the compact dielectric slab-mode antenna 10 is provided with a dielectric medium, having a coplanar waveguide input, as a wave guiding structure in the form of a generally thin rectangular dielectric slab 12 laid on one face of an electrically conductive ground body 14 presenting the general form of a parallelepiped. It is to be understood that the dielectric slab 12 may also be of a shape different from rectangular, for example a trapezoid, of dimensions such that the surface wave propagation is not obstructed. One face of the ground body 14 defines a ground plane 17 with a proximal end portion and a curved distal end portion 15. At its proximal end 16, the dielectric slab 12 generally has dimensions corresponding to those of the ground plane 17, although this is not a requirement. Also, the dielectric slab 12 comprises a grounded proximal end portion 11 applied to the proximal end portion of the ground plane 17. However, at the distal end 18, the dielectric slab 12 has generally the same length or is longer than the ground plane 17 curved distal end portion 15 to form a cantilever ungrounded distal end portion 13.

[0029] It is then possible to achieve very low loss while keeping a simple planar, compact, low-cost slab design. The curved distal end portion 15 of the electrically conductive ground body 14 acts as a gradual transition from the grounded proximal end portion 11 of the dielectric slab 12 to its ungrounded distal end portion 13, the guided wave being radiated into free space when it reaches the distal end 18 of the dielectric slab 12. Thus, reflections at the distal end 18 of the dielectric slab 12 are small due to weak guidance in the ungrounded slab portion 13; the larger portion of the guided fields being in the surrounding air, not in the dielectric slab 12.

[0030] The design of the compact dielectric slab-mode antenna 10 is based on the dielectric slab 12. Conductor losses are kept at a minimum, losses mainly depend on the material of the dielectric slab 12. Materials that possess the lowest dielectric loss in the mmW range are often high permittivity materials like alumina (ceramics) and sapphire as well as silicon and gallium arsenide (semiconductors). The high permittivity substrate used as the dielectric slab 12 can also serve as a carrier for flip-chip mounted monolithic mmW integrated circuits (MMICs) and other microwave circuitry. If a semiconductor material is used, direct monolithic fabrication of active devices on the substrate may be possible. A relative convenient substrate thickness can be chosen for the dielectric slab 12 even at high mmW frequencies, for example 300 μm to 400 μm at 94 GHz. This solves the problem of thin wafer / substrate handling, which is a major cost factor in the fabrication of mmW components.

[0031] As for the curved ground body 14, it may be fabricated in a cost-efficient way by plastic injection molding and electroplating, forming the ground plane 17, and may be part of a housing of a communication product.

[0032] Optionally, the dielectric slab 12 may be separated from the ground plane 17 by a thin insulation film or air gap for reduced conductor losses. The film may consist of a low-permittivity dielectric material with small dissipation factor, for example a material based on polytetrafluoroethylene (PTFE).

[0033] A planar surface wave source 20, which includes a directive wave launcher 21 and a waveguide input 22 is operatively connected to the dielectric slab 12 at its proximal end 16. The directive wave launcher 21 enables the efficient excitation of a captured surface-guided electromagnetic wave for propagation through the grounded slab portion 11 , while the waveguide input 22

establishes a connection compatible with modern MMICs, which will find widespread use in future commercial mmW products.

[0034] An example of a directive wave launcher 21 that may be used is the coplanar waveguide (CPW) slab-mode launcher. Alternatively, a substrate integrated waveguide (SIW) launcher may also be used. Both the CPW slab- mode launcher and the SIW launcher will be detailed further below.

[0035] However, these are not the only options, the planar surface wave source 20 may also be a pillbox antenna design, as known from references [6] and [7], as well as any other source capable of efficiently exciting a slab-mode propagated wave.

[0036] As illustrated in Figure 2, the surface waves 31 generated in the dielectric slab 12 of Figure 1 propagate through the grounded slab portion 11. The directive wave launcher 21 alone radiates nearly cylindrical surface waves 31 in a wide angle, with the ground plane 17 being the only conductor. No field singularities exist, as known, for example, from other planar waveguide technologies like microstrip or coplanar waveguide. This fact and the extensive field distribution leads to a significant reduction of conductor loss, thus making the compact dielectric slab-mode antenna 10 suitable for use at high frequencies in the mmW range and above, e.g. sub-mmW range. As previously mentioned, an optional insulation film or air gap between the dielectric slab 12 and the ground plane 17 leads to even better conductor loss properties, because the induced surface currents in the ground plane 17 are lower.

[0037] Referring now to Figure 3, an optional planar dielectric lens 19 may be placed on top of the dielectric slab 12 in order to focus the guided wave to achieve higher gain. The planar dielectric lens 19 may consist, for example

and as illustrated in Figure 3, of a circular region of increased thickness made of the same material as that of the dielectric slab 12 or be part of it.

[0038] As illustrated in Figure 4, the surface waves 33 generated in the dielectric slab 12 of Figure 3 propagate through the grounded slab portion 11 provided with the planar dielectric lens 19, with the ground plane 17 being the only conductor. Again, no field singularities exist, as known, for example, from other planar waveguide technologies like microstrip or coplanar waveguide. By locally increasing the thickness of the dielectric slab 12, and thus locally slowing down surface wave 33 propagation, the planar dielectric lens 19 produces an effect of focalization of the fields. This may be observed by most of the intensity of the surface waves 33 propagating in directional beam 30.

[0039] A variety of beam shapes and width 30 can be obtained in this manner, depending on the shape, width and thickness of the planar dielectric lens 19, as well as its distance from the wave source 20. An arrangement of multiple lenses is also feasible for radiation beam shaping. Although a discoidal lens is easy to fabricate, the thickness of the lens may be increased gradually from its edges in order to achieve lower reflections.

[0040] The electric field component 32, illustrated in Figure 5, which is perpendicular to the plane of the dielectric slab 12, i.e. transverse magnetic mode, yields relatively weak guidance. When the propagating surface waves 33 reach the distal end 18 of the dielectric slab 12, they are therefore radiated into free space without strong reflection. The large vertical field extension at the distal end 18 produces a large effective vertical antenna aperture and thus increased directivity in the E-plane, which can be controlled by the thickness of the dielectric slab 12. The E-plane beam width can also be controlled by gradually tapering the width of the dielectric slab 12 (similar to dielectric rod antennas). While the surface waves 31 are well confined in the grounded slab

portion 11 (see Figure 2), the fields extend much further into the surrounding air through the ungrounded slab portion 13.

[0041] Due to the abrupt termination of the dielectric slab 12 in air, not all the power is radiated, but a part of it is reflected (which also entails radiation and scattering in unwanted directions). Although the level of reflection is usually low (-25 dB to -20 dB), the scattered fields can deteriorate the overall radiation pattern.

[0042] Accordingly, in order to decrease those reflections, a quarter- wave anti-reflection layer with lower permittivity can be added at the distal end 18 of the dielectric slab 12, which significantly reduces the reflection level and scattering. Alternatively, since fabrication of such an added layer of different permittivity may be difficult and costly, simple thinning of the distal end 18 of the dielectric slab 12 may also be used for achieving a similar result. This may take the form of a smooth taper at the distal end 18 of the dielectric slab 12 (see reference [8]).

[0043] Referring to Figure 6, there is shown a second illustrative embodiment of the compact dielectric slab-mode antenna, which is identified by the reference 40. In this illustrative embodiment, the conductive ground body 44 does not comprise a curved ground plane similar to ground plane 17 of the compact dielectric slab-mode antenna 10 of Figure 1. However, if the dielectric slab 42 terminates abruptly, a high level of reflection and scattering occurs due to the tightly bound surface wave on the grounded dielectric slab 42. This would deteriorate the radiation pattern. The high level of reflection and scattering may be addressed by providing the dielectric slab 42 with a thinning taper 45 at its distal end 48.

[0044] Referring to Figure 7, there is shown a third illustrative embodiment of the compact dielectric slab-mode antenna, which is identified by the reference 50. In this illustrative example, the conductive ground body 54 does not comprise a curved ground plane and the dielectric slab 52 is provided with a taper 55 having an irregular pattern such as, for example, a zig-zag pattern, at its distal end 58 in order to avoid reflections and scattering.

[0045] Referring to Figure 8, there is shown a fourth illustrative embodiment of the compact dielectric slab-mode antenna, which is identified by the reference 60. In this illustrative example, the conductive ground body 64 does not comprise a curved ground plane and etched metallic radiation elements 65 are fabricated on top of the dielectric slab 62, yielding a linear array antenna or leaky-wave antenna. However, a drawback from this illustrative embodiment is the presence of frequency-scanning of the beam.

[0046] It is to be understood that dielectric slabs 42, 52 and 62 may optionally be separated from their respective ground bodies 44, 54 and 64 by a thin insulation film or air gap, as previously described, for reduced conductor losses.

CPW slab-mode launcher

[0047] Referring to Figure 9a, a first example of the directive wave launcher 21 is illustrated by CPW slab-mode launcher 121. The CPW slab- mode launcher 121 includes an input 132, which ends in a slot dipole 134. The slot dipole 134 acts as a coupling probe to a patch resonator 136. The latter is formed by a rectangular metallized patch on the upper side of the dielectric slab 12 (see Figure 1).

[0048] In use, an electromagnetic wave fed by the CPW line is coupled through the slot dipole 134 to the patch resonator 136. Coupling also occurs from the patch resonator 136 to the grounded dielectric slab portion 11 (see Figure 1), so that a guided surface wave is excited. Two back-short vias 138a and 138b are placed at the back side of the patch resonator 136 in order to achieve directional excitation. A narrow substrate channel 139 is left in the center to support the CPW feed line and is of a narrow width so that the electromagnetic fields cannot leak through.

[0049] A possible placement of a MMIC is identified by dotted lines

140 in the case where a flip-chip mounting is used. Flip-chip means that the raw chip, the so-called die, is turned upside down for connection to a waveguide on a substrate. Such a connection is advantageous because it has very low loss due to the short line lengths. In addition, if the back-short vias 138a and 138b are filled completely, they can be used as effective heat sinks to ground, which is desirable for power amplifiers. The compatibility with MMICs is inherently assured by the input 132 of the CPW slab-mode launcher 121.

[0050] Referring to Figure 10, a modified CPW slab-mode launcher

121 ' may be positioned on the grounded dielectric slab portion 11 (see Figure 1) so as to leave a space 148 between the proximal end 16 of the dielectric slab 12 and the back-short vias 138a and 138b, which space 148 can serve as a carrier for other circuits such as, for example, MMICs or microwave circuits (not shown). In this case, the modified CPW slab-mode launcher 121 ' is similar to the CPW slab-mode launcher 121 of Figure 9a with the possible exception of the input 132' which can continue through the vias 138a and 138b in order to connect to other circuits that can be accommodated on the same substrate, e.g. dielectric slab 12.: Thus, the compact dielectric slab-mode antenna 10 is not connected externally but becomes part of the circuit module, which makes the compact dielectric slab-mode antenna 10 suitable for integration.

[0051] Although efficient, the CPW slab-mode launcher 121 requires metallized vias 138a and 138b which sometimes are difficult to fabricate or just incompatible with the other steps in manufacturing. A second example of the directive wave launcher 21 is presented in Figure 9b, for which the CPW slab- mode launcher 221 comprises a metallized continuous back-short 238, which may extend a portion or the whole width of the proximal end 16 of the dielectric slab 12 (see Figure 1). The CPW slab-mode launcher 221 also includes an input 232, which ends in a slot dipole 234. The slot dipole 234 acts as a coupling probe to a patch resonator 236. It is to be noted that since the back- short 238 is continuous, the CPW slab-mode launcher 221 does not have a substrate channel and thus the slot dipole 234 is placed farther within the patch resonator 236.

[0052] Alternatively, a third example of the directive wave launcher 21 is presented in Figure 9c, for which the CPW slab-mode launcher 321 also comprises a metallized continuous back-short 338 but includes an input 332, which ends in an inverted slot dipole 334 that acts as a coupling probe to a patch resonator 336.

[0053] The positioning of the slot dipoles 234 and 334 may be selected according to the desired application and for ease of coupling with the CPW line. Performance and bandwidth of the CPW slab-mode launchers 221 and 321 are comparable to the CPW slab-mode launcher 121 , but the requirements for fabrication tolerances are somewhat more relaxed.

SIW launcher

[0054] Referring to Figure 11 , a fourth example of the directive wave launcher 21 is illustrated by SIW launcher 421. The SIW launcher 421 includes a waveguide 422 having an input 432 and a pair of metallic ground planes 436a

and 436b (not shown in Figure 11 ) positioned on the upper face and the under face, respectively, of the dielectric slab 12 (see Figure 1 ). The upper face metallic ground plane 436a forms a patch resonator equivalent to the patch resonators 136, 236 and 336 of Figures 9a, 9b and 9c, respectively, and the under face metallic ground plane 436b can be separate from or part of the ground plane 17.

[0055] Referring now to Figure 12, there is shown an exploded cross sectional view of the waveguide 422, which is an integrated version of the standard rectangular hollow metal waveguide that can be integrated into a dielectric substrate, such as the dielectric slab 12, by creating two rows 441 , 442 of metallized vias 440 conductively connected between the upper face 436a and under face 436b metallic ground planes located on opposite faces of the dielectric slab 12. The wave guidance effect is very similar to a standard waveguide, but the SIW waveguide 422 is smaller (due to the increased substrate permittivity compared to air), much cheaper, and can be integrated with other circuits on the same substrate. The loss properties are slightly worse than that of the rectangular hollow metal waveguide, but much better than those of other integrated waveguides like microstrip or coplanar waveguide (CPW).

[0056] In the case where the dielectric slab 12 is separated from the ground plane 17 by a thin insulation film or air gap, the under face metallic ground plane 436b will either be separate from the ground plane 17 or the metallized vias 440 will be designed to go through the insulation film or air gap such that they are conductively connected with the ground plane 17.

[0057] Such SIW launcher 421 has low-loss properties in the millimeter-wave range and therefore is well-suited as a feed line for compact dielectric slab-mode antenna 10 of Figure 1.

[0058] Also, because of its basic design, high-performance passive components like filters, directional couplers, and antennas can be designed by persons skilled in the art in a very similar way as known from conventional metal waveguide. An SIW band pass filter can, for example, directly follow the dielectric slab-mode antenna 10 incorporating a SIW waveguide input 132.

[0059] It is to be understood that the invention is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The invention is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the present invention has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature of the subject invention as defined in the appended claims.

REFERENCES:

[1] Smulders, P. F. M., Vervuurt, G.J.A.P., "Influence of antenna radiation patterns on MM-wave indoor radio channels," Int'l Conf. on Universial Personal Communications, vol. 2, 1993, pp. 631-635.

[2] Manabe, T., Miura, Y., lhara, T., "Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz," IEEE J. SeI. Areas Commun., vol. 14, no. 3, pp. 441-448, Apr. 1996.

[3] Emrick, R. M., Volakis, J. L., "Antenna requirements for short range high speed wireless systems operating at millimeter-wave frequencies," in 2006 IEEE MTT-S Int. Microwave Symp. Dig., pp. 974-977.

[4] Gibson, P. J., "The Vivaldi Aerial," in Proc. 9 ^th European Microwave Conference, 1979, pp. 101-105.

[5] Langley, J. D. S., Hall, P. S., Newham, P., "Balanced antipodal Vivaldi antenna for wide bandwidth phased arrays," IEE Proc. - Microwave Antennas Propagat., vol. 143, no. 2, pp. 97-102, Apr. 1996.

[6] Miller, L. S., "Compact microwave antenna suitable for printed-circuit fabrication," U.S. patent no. 5,486,837, Jan. 23, 1996.

[7] Teshirogi, T., Kawahara, Y., Hidai, T., Yamamoto, A., "Dielectric leaky wave antenna having mono-layer structure," U.S. patent no. 6,597,323, JuI. 22, 2003.

[8] Whitman, G. M., Pinthong, C, Wan-Yu Chen, Schwering, F. K., "Rigorous TE solution to the dielectric wedge antenna fed by a slab waveguide," IEEE006 IEEE Trans. Microwave Theory Tech., vol. 54, no. 1 , pp. 101- 114, Jan. 2006.