Waveguide antenna

Abstract

A waveguide antenna comprising a waveguide body element (10) made of a solid material and a layer (20) of a conductive material covering at least a portion of a surface of the waveguide body element (10) and being provided with at least one aperture (21) for transmitting and / or receiving electromagnetic waves, wherein the waveguide body element (10) is provided with at least one cavity (30) adjacent to the at least one aperture (21), the at least one cavity (30) being open into the at least one aperture (21).

Description

[0001] WAVEGUIDE ANTENNA

[0002] TECHNICAL FIELD

[0003] The present invention relates to a waveguide antenna.

[0004] BACKGROUND

[0005] A waveguide antenna may be constructed of a hollow metal waveguide provided with one or more slots or generally apertures, which can act as the antenna’s radiating elements producing electromagnetic waves propagating into space. A waveguide antenna may function as a transmitting and receiving antenna. Such an antenna is also known as a slotted waveguide antenna or a slot antenna, for example. The hollow metal waveguide may be filled with air. It is also possible to construct a waveguide antenna from a solid-state material, such as silicon or more generally dielectric material, and cover at least a portion of its surface with a metal layer provided with one or more radiation slots.

[0006] A problem related to such solid-state material-based, such as silicon- based, waveguide antenna structures is that they may have a low radiation efficiency.

[0007] BRIEF DESCRIPTION

[0008] An object of the present invention is thus to provide a method and an apparatus for implementing the method so as to overcome the above problem or at least to alleviate the problem. The object of the invention is achieved by an apparatus and a method which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

[0009] The invention is based on the idea of providing a waveguide body element made of a solid material with at least one cavity adjacent to at least one aperture provided in a layer covering at least a portion of a surface of the waveguide body element for transmitting and / or receiving electromagnetic waves.

[0010] An advantage of the solution of the invention is that the radiation efficiency of the waveguide antenna can be improved.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which Figure 1 shows an example of a waveguide antenna structure according to an embodiment;

[0013] Figure 2 shows an example of a waveguide antenna structure according to an embodiment;

[0014] Figure 3 shows an example of a waveguide antenna structure according to an embodiment;

[0015] Figure 4 shows an example of a waveguide antenna structure according to an embodiment;

[0016] Figure 5 shows an example of a waveguide antenna structure according to an embodiment;

[0017] Figure 6 shows an exemplary diagram illustrating radiation efficiency of the waveguide antenna with varied cavity depths according to an embodiment;

[0018] Figure 7 shows an exemplary diagram illustrating reflection coefficient of the waveguide antenna with varied cavity depths according to an embodiment;

[0019] Figure 8 shows an exemplary diagram illustrating radiation efficiency of the waveguide antenna with varied cavity dimensions according to an embodiment;

[0020] Figure 9 shows an exemplary diagram illustrating reflection coefficient of the waveguide antenna with varied cavity dimensions according to an embodiment;

[0021] Figure 10 shows an exemplary diagram illustrating radiation efficiency of the waveguide antenna with varied lengths of the cavity and aperture according to an embodiment;

[0022] Figure 11 shows an exemplary diagram illustrating reflection coefficient of the waveguide antenna with varied lengths of the cavity and aperture according to an embodiment;

[0023] Figure 12 shows an example of a waveguide antenna according to an embodiment;

[0024] Figure 13 shows examples of a waveguide antenna according to embodiments;

[0025] Figure 14 shows an example of a waveguide antenna array according to an embodiment; and

[0026] Figure 15 shows an example of a waveguide antenna array according to an embodiment.

[0027] DETAILED DESCRIPTION The following embodiments are exemplary. Although the description may refer to “an”, “one”, or “some” embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment, for example. Single features of different embodiments may also be combined to provide other embodiments. Generally, all terms and expressions used should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiments. The figures only show components necessary for understanding the various embodiments. The number, shape and / or configuration of the various elements, and generally their implementation, could vary from the examples shown in the figures.

[0028] According to an embodiment, a waveguide antenna comprises a waveguide body element made of a solid material and a layer of a conductive material covering at least a portion of a surface of the waveguide body element and being provided with at least one aperture for transmitting and / or receiving electromagnetic waves.

[0029] Figure 1 is illustrating an example of a waveguide antenna 100 according to an embodiment. Figures 2 and 3 show side views of a portion of the waveguide antenna 100 from two different directions. The waveguide antenna 100 comprises a waveguide body element (substrate) 10 made of a solid material. The solid material may be a mixture of two or more constituent materials, such as a composite material, for example. Moreover, the solid material may be essentially homogeneous, i.e. of uniform composition, or at least partly non-homogeneous, for example. According to an embodiment, the solid material comprises dielectric material (dielectric medium) and / or semiconductor material (semiconductor medium). It may be generally preferable to use a solid material with a low dielectric constant, i.e. a low relative permittivity sr, which represents a permittivity s of the material. According to an embodiment, a preferable range for the relative permittivity srcould be about 3-6, for example. However, a solid material with a high dielectric constant, i.e. a high relative permittivity sr, may also be used, for example. According to an embodiment, the solid material may have relatively high dielectric constant, i.e. a high relative permittivity sr, which could about 5-12. According to an embodiment, the solid material comprises at least silicon (Si). The dielectric constant, i.e. the relative permittivity, srof silicon is approximately 11.7 (at room temperature of 20 °C), for example. Some possible examples of materials with a low permittivity (or relative permittivity) include standard printed circuit board (PCB) materials, liquid crystal polymer (LCP), and quartz, for example. Some possible examples of materials with a high permittivity (or relative permittivity) include low temperature co-fired ceramics (LTCC), alumina, GaAs, InP and (essentially pure) silicon, for example. One advantage related to the use of silicon is that it is potentially easy to fabricate the waveguide body element 10 from silicon. The solid material may be essentially pure silicon or silicon compound or doped silicon, for example. The silicon is a common semiconductor material, which can have resistivity values from low to high. According to an embodiment, high resistivity silicon may be preferably used as the solid material. According to an embodiment, the resistivity ResSi could be ResSi = about 1000 - about 10000 fl-cm. The waveguide body element 10 may also have two or more portions, sections or elements made of different solid materials. The waveguide body element 10 may have at least three rectangular sides 13 extending between a first end 11 and a second end 12 of the waveguide body element 10. In the illustrated example the waveguide body element 10 has (only) four rectangular sides 13 extending between the first end 11 and the second end 12 of the waveguide body element 10 but the number of the sides could be more than four. Each rectangular side 13 could be a quadrilateral, i.e. a four-sided polygon, having four edges (sides) and four corners (vertices) as shown in the illustrated examples. In the illustrated example a length of the body element 10 between the first end 11 and the second end 12, and thus also a length of the sides 13, is noted as lb. Moreover, a width of the body element 10 is noted as Wb and a height of the body element 10 is noted as hb. However, it should be noted that the waveguide antenna 100 could be used in any position and hence term height noted as hb does not necessarily imply height in a vertical direction, for example. The waveguide body element 10 may have generally an elongated shape between the first end 11 and the second end 12 of the waveguide body element 10. Instead of having such generally rectangular shape, the waveguide body element 10 may have a different shape such as a cylindrical form, which extends between the first end 11 and the second end 12. Moreover, the waveguide body element 10 may have a curved shape including one or more curved sections between the first end 11 and the second end 12 of the waveguide body element 10.

[0030] As an example, the waveguide body element 10 may be dimensioned such that e.g. relative to an air-filled rectangular waveguide dimensions, which scale with operational frequency band, the dimensions may be divided by cr, where cris the relative permittivity of the solid material of the waveguide body element 10. For example, for frequencies 220-325 GHz, an air-filled waveguide could have dimensions of a x b = 0.86 mm x 0.43 mm. If the waveguide body is made of silicon (cr=11.7), the respective dimensions could be 0.25 mm x 0.126 mm. The waveguide body element size could be chosen so that the lowest operational frequency is about 1.25...1.28 x cutoff-frequency (fcutoff). The cutoff-frequency fcutoff is where the width of the waveguide is a half wavelength (a = Acutoff / 2). E.g. for the example of 220-325 GHz operational frequency, the cutoff-frequency fcutoff could be about 173.5 GHz. The height b (b corresponding to hb in the figures) of the waveguide body element 10 could be about half of the width a (a corresponding to Wb in the figures), b = about 0.5a. In some cases, the height could be smaller or larger than this but preferably always smaller than the width to avoid higher-order modes, for example. As an example, generally b = 0.2a - 0.8a.

[0031] The waveguide antenna 100 further comprises a layer 20 of a conductive material covering at least a portion of the surface of the waveguide body element 10. According to an embodiment, the conductive material comprises metal material. The metal material may comprise e.g. gold (Au) and / or aluminium (Al). Moreover, the metal material may be a metal alloy, for example. Generally, it may be preferable to use metal material having a high conductivity and low resistance. In case the waveguide body element 10 has three or more, e.g. rectangular, sides 13 extending between the first end 11 and the second end 12 of the waveguide body element 10, the layer 20 of the conductive material may cover at least a portion of the surface of at least one of the sides 13 as also shown in the illustrated example. It is also possible that the layer 20 of the conductive material covers at least a portion of the surface of more than one of the sides 13. The layer 20 of the conductive material may also cover at least a portion of the surface of each one of the sides 13, e.g. such that the layer 20 of the conductive material at least partially surrounds, encases or encapsulates the waveguide body element 10. The layer 20 of the conductive material may be formed as a coating or e.g. as a sheet attached to the surface of the waveguide body element 10 or by any suitable manner depending e.g. on material(s) used and / or the shape of the waveguide body element 10. In the illustrated example a length of the layer 20 is equal to the length lb of the waveguide body element 10 between the first end 11 and the second end 12 and a width of the layer 20 is equal to the width Wb of the body element 10 and hence the layer 20 of the conductive material in the example of Figure 1 essentially covers the top surface of the waveguide body element 10. The lengths and / or widths of the layer 20 and of the waveguide body element 10 could also be different. The thickness of the layer 20 of the conductive material has been noted as ti. The thickness ti of the layer 20 of the conductive material may be selected on the basis of the requirements of the waveguide antenna and / or on the material used therefore, for example. The thickness of the layer 20 of the conductive material may be essentially uniform or non-uniform, i.e. the thickness could vary in different areas of the layer 20 of the conductive material, for instance.

[0032] The layer 20 of the conductive material is provided with at least one aperture 21, such as a slot, for transmitting and / or receiving electromagnetic waves, such as radio waves. The at least one aperture (hole, opening) 21 extends through the layer 20 of the conductive material. The at least one aperture 21 could be provided by e.g. etching through the layer 20 of the conductive material or by any other suitable method. The electromagnetic waves possibly transmitted (radiated, emitted) by at least one aperture 21 may be supplied (guided) to the at least one aperture 21 by the waveguide body element 10. Moreover, the electromagnetic waves possibly received by at least one aperture 21 may be supplied (guided) away from the least one aperture 21 by the waveguide body element 10. The waveguide body element 10 may be suitably connected, either directly or indirectly, to at least one transmitting and / or receiving apparatus (device, arrangement), such as a radio transmitter and / or receiver (not shown in the figures), such that the waveguide antenna 100 can function as an antenna for such a transmitting and / or receiving apparatus. In other words, the waveguide body element 10 can guide electromagnetic waves to be transmitted and originating from a connected transmitting apparatus to the at least one aperture 21 and / or received electromagnetic waves from the at least one aperture 21 to a connected receiving apparatus. Such a connection could be established e.g. via one of the ends 11, 12 of the waveguide body element 10 by means of a suitable interface in a manner known per se, for example. According to an embodiment, a shape of the at least one aperture 21 is a rectangular slot, such as an elongated rectangular slot, in a plane of the layer 20 of the conductive material. This can be seen in Figure 1 and in Figure 2 in which the direction of the view is perpendicular to the plane of the layer 20 of the conductive material. In other words, such a rectangular shape of the at least one aperture 21 could be in particular a quadrilateral, i.e. a four-sided polygon, having four edges (sides) and four corners (vertices) as shown in the illustrated examples. In the illustrated examples a width of the at least one aperture 21 is noted as waand a length of the at least one aperture 21 is noted as la. Generally, the size and shape of the at least one aperture 21 may vary and may be selected on the basis of the requirements for the waveguide antenna, for example. Thus, the shape of the at least one aperture 21 might differ from the example rectangular shape and could be e.g. circular or triangular. Also the ratio of the width waof the at least one aperture 21 and the length laof the at least one aperture 21 may vary as well as its position in the layer 20 of the conductive material and with respect to the waveguide body element 10. Generally, the dimensions of the aperture, i.e., length, width, shape, and / or size thereof, may determine the operating frequency and / or radiation of the waveguide antenna. The aperture size may be e.g. a fraction of the wavelength of a desired operating frequency. Moreover, while in the illustrated examples the length ladirection(i.e. the longitudinal direction) of the at least one aperture 21 is essentially parallel to the length lb direction (i.e. the longitudinal direction) of the waveguide body element 10 it would also be possible that the length ladirection of the at least one aperture 21 is at an angle (> 0°, <180°) with respect to the length lb direction of the waveguide body element 10, for example.

[0033] The waveguide body element 10 is provided with at least one cavity 30 adjacent to the at least one aperture 21 such that the at least one cavity 30 is open into (in communication with) the at least one aperture 21. For example, as shown in the examples of Figures 1 to 3, a cavity 30 (a hole or generally a hollow space) has been formed into (within) the waveguide body element 10 in a location adjacent to the aperture 21 such that the inner space of the cavity 30 opens into the adjacent aperture 21. According to an embodiment, the at least one cavity 30 may be directly open into the at least one aperture 21 as shown in the examples of Figures 1-3. According to an embodiment, the at least one cavity 30 may be directly open only into the at least one aperture 21 as also shown in the examples of Figures 1-3. In other words, the at least one cavity 30 within the waveguide body element 10, if directly open only into the at least one aperture 21, may thus be surrounded by the waveguide body element 10 from all other directions as also shown in the examples of Figures 1-3. As an example, an inner space of one cavity 30 may directly open only into one aperture 21, or into two or more apertures 21, but may be otherwise closed. In the illustrated examples, a length of the at least one cavity 30 is noted as lc, a width of the at least one cavity 30 is noted as wcand a depth (height) inside the body element 10 of the at least one cavity 30 is noted as hc. According to an embodiment, the width wcand length lcof the at least one cavity 30 may be essentially equal to the width waand length laof the respective at least one aperture 21 and may have the shape of the rectangular slot as shown in the examples of Figures 1 to 3. Thus, in the examples of Figures 1 to 3 the aperture 21 and the adjacent cavity 30 together define a uniform space having a width wa=wc, a length la=lcand a height ti+hc. Alternatively, the width wcand / or length lcof the at least one cavity 30 may be different from the width waand / or length laof the respective at least one aperture 21. For example, the width wcand / or length lcof the at least one cavity 30 could greater or smaller than the width waand / or length laof the respective at least one aperture 21. Moreover, the bottom of the cavity 30 may be essentially uniform and parallel to the surface of the waveguide body element 10 around the cavity or the bottom of the cavity 30 may be non-uniform and / or non-parallel, i.e. at an angle, to said surface of the waveguide body element 10, for example. The depth hcof the at least one cavity 30 from the surface of the waveguide body element 10 may be described as an average depth, for example. According to an embodiment, hc< hb. In other words, the depth hcof the at least one cavity 30, such as an average depth, from the surface of the waveguide body element 10 may be smaller than the height hb of the body element 10, wherein the depth hcand the height hb are dimensions parallel to each other, i.e. they are codirectional. According to an embodiment, a ratio between the depth hcof the at least one cavity 30 and the height hb of the body element 10, i.e. hc / hb, may be preferably in a range of 0.16 - 0.64, and more preferably in a range of 0.32 - 0.48, for example. Accordingly, if the body element 10 height hb = 0.125 mm, then the cavity 30 depth hccould preferably be 0.02 mm - 0.08 mm, and more preferably 0.04 mm - 0.06 mm, for example. According to an embodiment, the at least one cavity 30 is at least partly filled with gaseous material, such as air. The at least one cavity 30 could be formed in the waveguide body element 10 by any suitable method, such as micromachining. As an example, deep reactive ion etching micromachining (DR1E) providing highly accurate dimensional control and enabling a batch fabrication could be utilized.

[0034] According to an embodiment, the waveguide antenna 100 further comprises a cover 40 on top the layer 20 of the conductive material, wherein the cover 40 covers at least the at least one aperture 21. Figure 4 illustrates an example, which otherwise essentially corresponds to that of Figure 3 described above, but additionally comprises a cover 40 on top the layer 20 of the conductive material such that the cover 40 covers the aperture 21. In the example the cover 40 extends also further around the aperture 21, and the cover 40 could cover at least one side 13 of the waveguide body element 10 partially or entirely, for example. The cover 40 could comprise one part or portion, or two or more separate parts or portions, for example, suitably attached on the layer 20 of the conductive material. Such a cover 40 may be formed of the same material as the waveguide body element 10, e.g. of a dielectric material, or the cover 40 may be formed of some different material. Such a cover 40 may be generally a thin layer of suitable material or a membrane, for example. The cover 40 could be a layer made of silicon dioxide (SiO2) or polyimide, or a thin silicon membrane, for example. The thickness twof the cover 40 may be suitably selected depending on the characteristics of the waveguide antenna, for example. As an example, the thickness twof the cover 40 is preferably equal to or less than Am / 10, where Amis a wavelength of electromagnetic waves in the material of the cover 40 at a predetermined frequency. Such a predetermined frequency could be e.g. a centre frequency or operating frequency, or another frequency used for dimensioning the waveguide antenna 100 or otherwise based on e.g. an intended use of the waveguide antenna 100, for instance. More preferably, the thickness twof the cover 40 may be: Am / 20 < tw< Am / 10. According to an embodiment, preferably tw< 50 pm, more preferably 1 pm < tw< 50 pm, and most preferably 10 pm < tw< 30 pm. According to an embodiment, the space defined by the aperture 21 and the adjacent cavity 30 may be hermetically closed (sealed) by the cover 40. Consequently, the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by the cover 40, could thus form or constitute a hermetically closed space. In this case the space defined by the aperture 21 and the adjacent cavity 30 may be filled with a gaseous material which could be different than the material possibly surrounding the waveguide antenna 100, for example. As an example, if the waveguide antenna 100 is surrounded by air, the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by means of the cover 40, could be filled with other gaseous material than air. As another example, if the waveguide antenna 100 is surrounded by a vacuum or liquid material, for instance, the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by means of the cover 40, could be filled with gaseous material and the hermetical sealing by means of the cover 40 can prevent the gaseous material from escaping from said space defined by the aperture 21 and the adjacent cavity 30. As a further example, an ambient pressure of the waveguide antenna 100 could differ from a pressure inside the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by means of the cover 40. l.e., the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by means of the cover 40, could contain gaseous material in a different pressure than the pressure of the material possibly surrounding the waveguide antenna 100, for example. It is also possible that there is a vacuum inside the space defined by the aperture 21 and the adjacent cavity 30, when hermetically closed by means of the cover 40, while the waveguide antenna 100 is surrounded by a gaseous material and / or a liquid material, for example.

[0035] While the examples of Figures 1-4 comprise only one aperture 21 and only one cavity 30, there could be a plurality of apertures 21 and / or cavities 30. According to an embodiment, the layer 20 of the conductive material is provided with a plurality of apertures 21 and the waveguide body element 10 is provided with a plurality of individual cavities 30. There may be at least one individual cavity 30 for each one of the apertures 21 such that each such individual cavity 30 is adjacent to and open into the respective aperture 21. Moreover, each such individual cavity 30 may be directly open into the respective aperture 21 or each such individual cavity 30 may be directly open only into the respective aperture 21, for example. It is also possible that two or more apertures 21 share one or more cavities 30 such that each such shared cavity 30 is adjacent to and open into the respective two or more apertures 21. According to an embodiment, each such aperture 21 and respective individual cavity 30, or only some of them, may be covered by the cover 40, for example. Figure 5 shows an example in which the layer 20 of the conductive material is provided with four apertures 21 and the waveguide body element 10 is provided with four respective individual cavities 30, one such cavity 30 for each one of the apertures 21. The number, shape and / or position of such plurality of apertures 21 and respective plurality of individual cavities 30 may vary. Such plurality of apertures may be arranged in a predetermined configuration to form an array antenna (antenna array), for example. As an example, two or more apertures 21 and respective individual cavities 30 could be arranged in at least one row (line) extending parallel to the longitudinal direction of the waveguide body element 10. According to an embodiment, the spacing of the apertures 21, and respective individual cavities 30, in the longitudinal direction of the waveguide body element 10, could be A, e.g. for broadside radiation if arranged on the same side of the waveguide 100. According to another embodiment, e.g. if arranged on the opposite sides, the spacing of the apertures 21 and respective individual cavities 30 could be A / 2.

[0036] According to an embodiment, an average depth hcof the at least one cavity 30 from the surface of the waveguide body element 10 is preferably in a range of 0.07A - 0.27A, more preferably in a range of 0.15A - 0.22A, and most preferably in a range of 0.17A - 0.2A, where A is a wavelength of electromagnetic waves in the waveguide body element 10 ata predetermined frequency. However, said average depth of the at least one cavity 30 could also be outside of these exemplary ranges, for example. Such a predetermined frequency could be e.g. a centre frequency or operating frequency, or another frequency used for dimensioning the waveguide antenna 100 or otherwise based on e.g. an intended use of the waveguide antenna 100, for instance. For example, if the waveguide body element 10 is made of silicon, A = Asi = o / nsi where Ao is the wavelength in vacuum and ns; is the refractive index of silicon. The length laof the at least one aperture 21may be about half wavelength in length, la= A / 2, at a desired operational frequency, and preferably within a range of 0.5A - 1A, for example. Generally, preferably the following two conditions should be met to obtain a high radiation efficiency of the antenna: the depth of the cavity 30 in the solid material, e.g. silicon, should be high enough for an efficient radiation of the electromagnetic waves by the antenna but the cavity 30 shouldn't disturb the electromagnetic field in the waveguide too much. Such a compromise can be reached with cavities with defined dimensions, for example. The size of the at least one aperture 21 and the respective at least one cavity 30 could be determined using electromagnetic simulations, for example.

[0037] As an example, with a waveguide body element 10 made of silicon and having a width 0.25 mm (O.27Ao) and height 0.125 mm (O.13Ao), the possible dimensions for the cavity 30 for predetermined frequency of 320 GHz could be as follows: length lc= la= 0.29 mm (0.3 lAo, l.O7As0, width wc= wa= 0.03 mm (O.O3Ao, O.llAsi) and height hc= 0.05 mm (O.O5Ao, O.18As0, where Ao= 0.94 mm, si= 0.27 mm. According to an embodiment, generally length lc= la= 0.25 - 0.35Ao. According to an embodiment, generally width wc= wa= 0.02 - O.O4Ao.

[0038] Figure 6 illustrates an example in which the depth h (corresponding to he) of a single cavity 30 from the surface of the waveguide body element 10 is varied between 5 pm and 100 pm, and also without any cavity, and the resulting effect on the radiation efficiency. As can be seen, a frequency of the peak of the radiation efficiency of the antenna is shifted when the depth of the cavity is decreased or increased from the optimal value of 50 pm in the example. Figure 7 illustrates corresponding variation of a reflection coefficient Sn when the depth h of the exemplary cavity 30 from the surface of the waveguide body element 10 is varied between 5 pm and 100 pm, and also without any cavity. In the example, only about 4% radiation efficiency can be obtained with the antenna without any cavity 30 while about 55-65% radiation efficiency can be reached with cavity 30 depth h between 0.04 mm - 0.06 mm, for example. Thus, as can be seen, the radiation efficiency of electromagnetic waves from the at least one aperture can be even substantially increased by the at least one cavity 30.

[0039] Figure 8 illustrates another example in which the relative size of the cavity 30 is varied with respect to the size of the aperture 21. The size of the aperture 21 in the example is fixed. In the example, parameter A indicates the difference between the length lcof the cavity 30 and the length laof the aperture 21 as well as the difference between the width wcof the cavity 30 and the width waof the aperture 21. A positive value of A in the example indicates that said dimensions of the cavity 30 are larger than the respective dimensions of the aperture, and vice versa. As can be seen, in the example the frequency of the peak of the radiation efficiency is shifted when the dimensions (length and width) of the cavity with respect to the dimensions of the aperture 21 are changed bigger and smaller. Figure 9 illustrates corresponding variation in the resulting reflection coefficient Sn of the antenna. It can thus be observed that generally with a larger cavity the effective permittivity decreases causing a higher resonance frequency. And with a smaller cavity the effective permittivity increases causing a lower resonance frequency. Consequently, the highest radiation efficiency may be reached when the cavity 30 has the same length and width as the respective aperture 21.

[0040] Figure 10 illustrates another example in which the length lcof the cavity 30 and length lathe aperture 21 is varied such that the length lcof the cavity 30 is kept equal to the length lathe aperture 21. In the example, 1 = lc= laand the depth of the cavity 30 is 50 pm. As can be seen, a frequency of the peak of the radiation efficiency of the antenna is shifted when the length 1 is decreased or increased from the optimal value (optimal back-short position of the exemplary waveguide) of 370 pm in the example. Figure 11 illustrates corresponding variation of the reflection coefficient Sn when the length 1 is varied between 250 pm and 490 pm similarly to Figure 10. It can thus be observed that generally with a longer length of the aperture 21 and the respective cavity 30 the resonance frequency is lower while with a shorter length of the aperture 21 and the respective cavity 30 the resonance frequency is higher.

[0041] The waveguide antenna 100 according to any one of the embodiments described herein could be used in connection with any application, apparatus or system in which an antenna is used. Some examples include e.g. radar systems, cellular networks, Bluetooth systems and devices, Wi-Fi systems and devices, satellite communication systems, and generally various wireless communication links or systems. In addition, further examples include e.g. portable devices or mobile devices, automotive systems, microwave systems and devices and loT (Internet of Things) systems and devices, for instance. Moreover, e.g. RFID (Radio Frequency Identification) systems may utilise waveguide antennas for tracking and identification purposes, for example. According to an embodiment, the waveguide antenna 100 may be configured to operate in a frequency or frequencies over 100 GHz, and preferably over 200 GHz, e.g. at least up to 1000 GHz.

[0042] Figure 12 illustrates an example of a waveguide antenna according to an embodiment. The example antenna comprises 8 apertures 21 and respective cavities 30. In Figure 12 example (a) illustrates a whole structure and a zoomed view of an RF ground-signal-ground (GSG) transition. Example (b) illustrates the antenna with zoomed view of two apertures 21. Example (c) illustrates a cross section of the two apertures 21 showing the respective cavities 30. Main parameters e.g. for a 300 GHz design could be aperture and cavity length 1 = 0.29 mm, antenna element separation s = 0.36 mm, GSG transition slot length d = 0.09 mm, and cavity depth c = 0.05 mm. The total length of the example antenna is 8.5 mm.

[0043] According to an embodiment, the waveguide antenna 100 comprises one or more interfaces, or feeds, via which the waveguide antenna 100 may be connected to a transmitter and / or a receiver. According to an embodiment, when the layer 20 of the conductive material of the waveguide antenna 100 is provided with a plurality of apertures 21, and the waveguide body element 10 may be provided with a plurality of respective individual cavities 30, as described in the examples herein, the one or more such interfaces, or feeds, of the waveguide antenna 100 may thus be common to the plurality of the apertures 21. Example a) in Figure 13 illustrates an example of a waveguide antenna 100 comprising only one feed which is common to all the apertures 21 of the waveguide antenna 100. The single feed may be arranged in one of the ends of the waveguide body element 10, e.g. in one of the longitudinal ends 11, 12 thereof as illustrated in the figure. In other words, e.g. one of the ends, or another portion ofthe waveguide body element 10 may be configured to function as the feed. Such a single feed could be implemented e.g. as a short-circuit termination or a matched load termination. Example b) in Figure 13 illustrates an example of a waveguide antenna 100 comprising two feeds, e.g. one in each of the longitudinal ends 11, 12 of the waveguide body element 10, common to all the apertures 21 of the waveguide antenna 100. The number of the feeds could be more than two. In the examples, the number of the apertures 21 is four but the number could be generally two or more. The number of cavities 30 could be the same as the number of the apertures 21 or vary according to the embodiments described herein, for example.

[0044] According to an embodiment, a waveguide antenna array comprises two or more waveguide antennas 100. According to an embodiment, a waveguide antenna array comprises two or more waveguide antennas 100 connected in parallel. According to an embodiment, the two or more waveguide antennas 100 may be physically arranged in parallel. According to an embodiment, a waveguide antenna array could comprise a feed arrangement, such as a power division network, configured to connect one or more feeds of the waveguide antenna array to the feeds of the two or more waveguide antennas 100. A power division network can split an RF signal from one feed to multiple waveguides, for example. Figure 14 illustrates an example of a waveguide antenna array comprising four waveguide antennas 100 connected in parallel. Moreover, the example waveguide antenna array comprises (only) one (common) feed which is connected to the respective feeds of the waveguide antennas 100 via a feed arrangement 200. The feed arrangement 200 could comprise one or more waveguides or waveguide sections, for example, and could be implemented in any manner known per se. Figure 15 illustrates another example of a waveguide antenna array comprising four waveguide antennas 100 connected in parallel. In the example of Figure 15, the example waveguide antenna array comprises two (common) feeds which are connected to the respective feeds of the waveguide antennas 100 via the feed arrangement 200. In the example the feed arrangement 200 thus comprises two separate portions, such as two separate power division networks, for example.

[0045] According to an embodiment, a method for manufacturing a waveguide antenna comprises providing a waveguide body element 10 of a solid material, forming at least one cavity 30 in the waveguide body element 10, and forming a layer 20 of a conductive material to cover a portion of a surface of the waveguide body element 10, the layer 20 being provided with at least one aperture 21 for transmitting and / or receiving electromagnetic waves, wherein the at least one aperture 21 is adjacent to the at least one cavity 30 in the waveguide body element 10 such that the at least one cavity 30 is open into the at least one aperture 21. Generally, the proposed solution according to the various embodiments described herein can increase an antenna efficiency, in particular the radiation efficiency, even in order of magnitude. It can be implemented with a dense integration due to potentially small size of the waveguide antenna, for example. As an example, in case of antenna arrays, the array elements, e.g. individual apertures, may be placed with e.g. a Ao / 2 separation. With air-filled waveguides such a dense arrangement of the array elements may be difficult to achieve. However, with a waveguide antenna comprising a waveguide body element made of a solid material, according to any of the embodiments described herein, it may be much easier to implement due to down-scaling of the waveguide size with respect to high permittivity, for instance. Moreover, the proposed solution according to the various embodiments described herein can be implemented with a simple fabrication process, for example.

[0046] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

CLAIMS1. A waveguide antenna, comprising: a waveguide body element (10) made of a solid material; and a layer (20) of a conductive material covering at least a portion of a surface of the waveguide body element (10) and being provided with at least one aperture (21) for transmitting and / or receiving electromagnetic waves, wherein the waveguide body element (10) is provided with at least one cavity (30) adjacent to the at least one aperture (21), the at least one cavity being open into the at least one aperture.

2. A waveguide antenna as claimed in claim 1, wherein the at least one cavity (30) is directly open into the at least one aperture (21) or the at least one cavity (30) is directly open only into the at least one aperture (21).

3. A waveguide antenna as claimed in claim 1 or 2, wherein the layer (20) of the conductive material is provided with a plurality of apertures (21) and wherein the waveguide body element (10) is provided with at least one individual cavity (30) for each one of the apertures (21), wherein each individual cavity (30) is adjacent to and open into the respective aperture (21).

4. A waveguide antenna as claimed in claim 3, wherein the plurality of apertures (21) is arranged in a predetermined configuration.

5. A waveguide antenna as claimed in any one of claims 1-4, wherein a shape of the at least one aperture (21) is a rectangular slot in a plane of the layer (20) of the conductive material.

6. A waveguide antenna as claimed in claim 5, wherein a width and length of the at least one cavity (30) are essentially equal to a width and length of the at least one aperture (21) having the shape of the rectangular slot.

7. A waveguide antenna as claimed in any one of claims 1-6, wherein a depth of the at least one cavity (30) from the surface of the waveguide body element (10) is smaller than a height of the body element (10), wherein the depth of the at least one cavity (30) and the height of the body element are dimensions parallel to each other.

8. A waveguide antenna as claimed in any one of claims 1-7, wherein an average depth of the at least one cavity (30) from the surface of the waveguide body element (10) is preferably in a range of 0.07A - 0.27A, more preferably in a range of 0.15A - 0.22A, and most preferably in a range of 0.17A - 0.2A, where A is a wavelength of electromagnetic waves in the waveguide body element at a predetermined frequency.

9. A waveguide antenna as claimed in any one of claims 1-8, wherein the waveguide body element (10) has at least three rectangular sides (13) extending between a first end (11) and a second end (12) of the waveguide body element (10).

10. A waveguide antenna as claimed in claim 9, wherein the layer (20) of the conductive material covers at least a portion of the surface of at least one of the sides (13) of the waveguide body element.

11. A waveguide antenna as claimed in any one of claims 1-10, wherein the solid material comprises dielectric material and / or semiconductor material.

12. A waveguide antenna as claimed in claim 11, wherein the solid material comprises at least silicon.

13. A waveguide antenna as claimed in any one of claims 1-12, wherein the conductive material comprises metal material and / or the at least one cavity (30) is filled with gaseous material.

14. A waveguide antenna as claimed in any one of claims 1-13, further comprising a cover (40) on top the layer (20) of the conductive material, wherein the cover (40) covers at least the at least one aperture (21).

15. A method for manufacturing a waveguide antenna, the method comprising: providing a waveguide body element (10) of a solid material; forming at least one cavity (30) in the waveguide body element;forming a layer (20) of a conductive material to cover a portion of a surface of the waveguide body element (10), the layer (20) being provided with at least one aperture (21) for transmitting and / or receiving electromagnetic waves, wherein the at least one aperture (21) is adjacent to the at least one cavity (30) in the waveguide body element (10) such that the at least one cavity (30) is open into the at least one aperture (21).

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