Fully integrated inter-channel diversity antenna

Abstract

A printed circuit board (PCB) is provided, the PCB comprising a first outer layer and a second outer layer and an antenna. The antenna is formed as an integral part of the PCB and comprises a first antenna element configured to operate at a first frequency and a second antenna element configured to operate at a second frequency, wherein the first frequency is different from the second frequency, and wherein the second outer layer is free of antenna elements.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to antennas for connected products, such as thermostats. In particular, the invention relates to antennas which are part of printed circuit board (PCB).BACKGROUND OF THE INVENTION

[0002] Connected products generally rely on a wireless link at 2.4GHz using WiFi, Zigbee or similar protocol. A low-cost option providing such connectivity is e.g. a printed antenna. Such antenna provided as a part of a printed circuit board (PCB) occupies a particular area on the PCB which must be free of circuitry and components; minimal clearance from other electrical components and metallic structural parts (display, batteries, etc.) is needed. Another consideration relates to improvements to link reliability, achieved e.g. by channel diversity.

[0003] From the user's perspective, it is preferred to have a display on the device (e.g. a thermostat) which is as large as possible and preferably full size (bezel-less design). This, however, poses additional challenges. In particular, the antenna needs a certain clearance from the display to avoid the display shielding the antenna and thus decreasing reliability of the whole device.

[0004] An example of an existing solution is to provide a bezel gap antenna, which is formed by coupling the RF circuitry to isolated sections of the metallic bezel. However, the bezel gap antenna does not represent the low-cost and fully PCB-integrated antenna solution, because its structure has metallic external parts requiring reliable RF coupling to PCB circuitry.

[0005] Therefore, there is a need for further improvements.SUMMARY OF THE INVENTION

[0006] In a first aspect, a printed circuit board, PCB, is provided, comprising a first outer layer and a second outer layer, the PCB comprising an antenna, the antenna being formed as an integral part of the PCB, the antenna comprising a first antenna element configured to operate at a first frequency and a second antenna element configured to operate at a second frequency, wherein the first frequency is different from the second frequency, wherein the second outer layer is free of antenna elements.

[0007] In embodiments of the first aspect, the PBC may utilize one or more of the following features: The first antenna element may be a λ / 4 slot antenna. The second antenna element may be a quarter-mode substrate-integrated waveguide antenna.

[0008] One of the first and second frequencies may be in the lower-half channels and the other of the first and second frequencies may be in the upper-half channels. One of the first and second frequencies may be in channels 1-5 and the other one of the first and second frequencies may be in channels 10-14. One of the first and second frequencies may be in channel 1 and the other one of the first and second frequencies may be in channel 14.

[0009] The first frequency may be 2400 MHz and the second frequency is 2484 MHz, or the second frequency may be 2400 MHz and the first frequency may be 2484 MHz.

[0010] The PCB may be rectangular, rectangular with rounded edges, square-shaped, square-shaped with rounded edges, trapezoid-shaped, trapezoid-shaped with rounded edges, quadrilateral, quadrilateral with rounded edges. The PCB may be of a shape distinct from a circle, ellipse or oval. If the PCB is quadrilateral or quadrilateral with rounded edges, the quadrilateral may be substantially concave.

[0011] The core thickness may be more than 1 mm, for example 1.5mm, 1.8mm or 2mm.

[0012] A copper layer thickness in the PCB may be between 0.30 µm and 0.40 µm.

[0013] A feeding line for the antenna may be implemented in the first outer layer, or in the second outer layer.

[0014] In a second aspect, a device comprising the PCB of any of the embodiments above is provided. The device may further comprise a bezel-less display.

[0015] In embodiments of the second aspect, the device may be a thermostat. The antenna may be configured to communicate wirelessly with one or more temperature sensors.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a simplified view of a PCB with a fully integrated inter-channel diversity antenna; Figure 2 is a detail of the simplified view of a PCB with fully integrated inter-channel diversity antenna; Figure 3 is a schematic example device which may utilize the fully integrated inter-channel diversity antenna; Figure 4 is a schematic view of a PCB with a fully integrated inter-channel diversity antenna used in device of Fig 3; Figure 5 shows a detail of an example PCB with a fully integrated inter-channel diversity antenna used in device of Fig 3; Figure 6 shows a detail of an example PCB with a fully integrated inter-channel diversity antenna and a display used in device of Fig 3. DETAILED DESCRIPTION

[0017] The below description is for illustration only, and is not intended to be limiting. Various elements of embodiments described below may be combined into new embodiments not explicitly described herein, as appropriate.

[0018] Like reference numbers describe like elements in the drawings.

[0019] For the sake of clarity, in all Figures, only conductive materials are shown. A skilled person will understand that there may be further materials in appropriate places, such as a core, prepreg etc. Some details are given below.

[0020] Figs 1 and 2 show a schematic example of a PCB 101. Similarly, Figs 4-6 show a schematic example of a PCB 301. For clarity, no circuit elements are shown on the PCBs 101, 301 of Figs 1-2 and 4-6, but it will be understood that any number of conventional elements will be accommodated on the PCB 101, 301.

[0021] In the embodiments shown in the Figures, a fully integrated inter-channel diversity antenna 107, 307 is provided in a form of a slot 102, 302 and a cavity 104, 304. There is also a feeding probe assembly 103, 303 associated with the antenna.

[0022] In Figs 1-2, the PCB 101 comprises two outermost layers: a first outer layer 101a and a second outer layer 101b. It will be understood that between these layers, there are further layers (such as prepreg, copper, core). These are not shown in detail in the Figs, for the sake of simplicity. The slot 102 occupies a portion of a first outer layer 101a of the PCB 101 (and possibly one or more underlying layers). The second outer layer 101b which is opposite the first outer layer 101a of the PCB 101 is without any corresponding slot (and possibly one or more layers adjacent the second outer layer 101b are also free of any corresponding slot). There is thus no need for antenna clearance on the second outer layer 101b of the PCB 101, and the whole of the second outer layer 101b of the PCB 101 may be used for circuitry and / or for a display.

[0023] The display (not shown in Figs 1, 2) may be in particular a full-size and / or bezel-less display. The configuration with the slot 102 on one side only (i.e. formed in one of the outer layers only) allows the circuitry and / or the display to have a minimal impact on the antenna 107 performance (minimal shielding of the antenna 107 by the circuitry and / or the display).

[0024] The structure of the antenna 307 of Figs 4-6 is similar to the structure of the antenna 107 of Figs 1-2.

[0025] The structure and position of the slot 302 provided on the PCB 301 of Figs 4-6 is similar to the slot 102 provided on the PCB 101 of Figs 1-2, e.g. in that it is formed in a portion of a first outer layer 301a while the second outer layer 301b is free from any similar slot. The effects and advantages of such position and structure are similar to those described for the slot 102 of Figs 1-2.

[0026] In the example shown in Figs 1 and 2, the cavity 104 is triangular. The cavity 104 is formed by a space which does not contain conductive material between the opposite top layers 101a, 101b (i.e. the space between the opposite top layers 101a, 101b is free of any further conductive material, but may contain e.g. a PCB core and prepreg (not shown)). The cavity 104 is defined by its edges 104a, 104b. The edges 104b are a part of the PCB boundary; the edge 104a is a border where further PCB layers (i.e. other than the opposite top layers 101a, 101b, e.g. a conductive body 108) start. The cavity 104 may be e.g. an isosceles triangle (with the edges 104b of the same length). In the example shown in Figs 4-6, the cavity 304 resembles a triangle except that one of the vertices defining the cavity 304 is rounded, and the side 304b is thus a smooth curve. In a preferred embodiment, the side 304b comprises a rounded vertex and a portion of straight line on either side of the rounded vertex.

[0027] It will be understood that the examples of the Figs are schematic for the sake of clarity. In a PCB with e.g. four layers (excluding the core (substrate)), the slot 102, 302 is formed in a first (outer) layer and a second layer immediately adjacent to the first (outer) layer (i.e., the slot is formed in two layers). The cavity 104, 304 may be formed between second and third layers. Fourth (outer) layer is free of any antenna elements. In this configuration, the second and third layers adjacent to the first and fourth outer layers, respectively, are e.g. copper.

[0028] In an embodiment, the slot 102, 302 has no power supply of its own and is fed from the cavity 104, 304, which in turn is fed by the feeding probe assembly 103, 303.

[0029] The slot 102, 302 may function as a λ / 4 slot antenna. Therefore, the length of the slot is chosen with respect to the intended use (intended wavelength that the slot 102, 302 is designed to work at).

[0030] Similarly, the cavity 104, 304 may function similarly to a quarter-mode substrate-integrated waveguide antenna. Therefore, the dimensions of the cavity, in particular the length of the edges 104a, 104b, 304a, 304b are chosen according to the required wavelength the antenna is to work at. In the embodiment of Figs 4-6, further design considerations may include the curvature of the rounded vertex and / or the length of the straight portions of the edge 304b.

[0031] In an embodiment, it may be advantageous to design the slot 102, 302 and the cavity 104, 304 to work at two close but different wavelengths. For example, in the 2.4 GHz band, the cavity 104, 304 may resonate at the lower end of the band (near 2.4GHz, for example below 2.45 GHz, more particularly below 2.42 GHz) and the slot 102, 302 resonates at upper end of the band (near 2.5GHz, for example above 2.45 GHz, more particularly above 2.48 GHz).

[0032] Fig 3 shows a schematic example of a device 300 which may utilize the PCB as described above (in particular, the PCB 301 shown in Figs 4-6). The device 300 may be for example a wireless thermostat. The device 300 may be any other connected home appliance, a control device for a smart home and the like. The device 300 generally comprises a housing 305 and a front side. A display 306 may be positioned on the front side (i.e. the side intended to be facing the room and / or the user and which provides the user interface). The display 306 may provide a user interface (e.g. sensor readings and / or controls for a room temperature, a zone temperature and the like). The housing 305 may be adapted to be mounted onto a wall or a similar surface and / or it may be adapted to be positioned on a stand (not shown). The display 306 may be positioned such that it covers majority of the front side or even the whole front side of the device 300.

[0033] As shown in Fig 6, in a device 300, the PCB 301 with the fully integrated inter-channel diversity antenna 307 is positioned such that the first outer layer 301a (i.e. the layer comprising the slot 302) is positioned towards the back side of the device and facing away from the display 306. The second outer layer 301b, which does not comprise the slot 302, is positioned against (i.e. facing) the display 306. The housing 305 of the device 300 is not shown in Fig 6.

[0034] The two radiation elements, i.e. the cavity 104, 304 and the slot 102, 302, may advantageously show orthogonal radiation patterns. Such orthogonality enables radiation pattern (channel and / or wavelength) diversity. As described above, the slot 102, 302 and the cavity 104, 304 may be designed such that each of these two radiation elements resonates at a slightly different frequency (as in the examples above; e.g. in upper and lower half of the 2.4 GHz band). In such case, each of the channels thus created is transmitted by different radiation element (respectively by the cavity 104, 304 and the slot 102, 302) with different radiation pattern. Thus inter-channel diversity is ensured, as two distant channels (distinct in frequency) are radiated by a sufficiently orthogonal radiation patterns.

[0035] If provided as a part of a PCB 101, 301, the efficiency of the fully integrated inter-channel diversity antenna 107, 307 is higher than the efficiency of the cavity 104, 304 on its own (without the slot 102, 302). By varying parameters (such as thickness of the respective layers) of the PCB, the efficiency of the antenna 107, 307 may be further increased.

[0036] For example, increasing the thickness of the conductive body 108, 308 (while keeping the other parameters constant) may increase the efficiency of the antenna 107, 307 to above 25% in the whole 2.4 GHz range. In an exemplary embodiment, the core may be 2mm thick, the prepreg may be about 0.2mm, and copper may be about 35µm; such embodiment may show both advantageous efficiency and also advantageous envelope correlation coefficient (discussed below).

[0037] The efficiency of the antenna 307 may be further increased by rounding the edge (as shown in the embodiment of Figs 4-6), even while other parameters are kept (e.g. the core 308 thickness, the thickness of the prepreg etc.).

[0038] The two antenna elements, i.e. the slot 102, 302 and the cavity 104, 304, of the antenna 107, 307 of Figs 1-2 and 4-6 may operate in two different ranges of channels of the 2.4 GHz band. In an embodiment, the antenna 107, 307 may in particular operate simultaneously in the upper and lower halves of the 2.4 GHz band (as outlined above). In an advantageous embodiment, the antenna utilizes two distant channels (for example, channels 1 to 5 and channels 10 to 14, respectively, or channels 1-3 and channels 12-14, respectively, or channels 1 and 14, respectively).

[0039] Generally, to measure the independence of the radiation pattern of two antennas (or two antenna elements, e.g. the slot 102, 302 and the cavity 104, 304 as described above), an envelope correlation coefficient (ECC) is used. It is generally desirable to have the ECC as low as possible (e.g. in a theoretical ideal case, if one antenna is completely horizontally polarized, and the other is completely vertically polarized, the two antennas would have ECC equal to zero, which would make the antennas independent). In practice, embodiments which have the ECC below 0.5 are advantageous. For example, in the embodiment of Figs 1-2, the ECC may be the lowest for the frequency pair 2400 MHz and 2484 MHz (where the ECC may be below 0.4 in certain configurations). As another example, in the embodiment of Figs 4-6, the ECC for the frequency pair may be below 0.35. In the particular configuration of Fig 6 (with the display 306 adjacent to the PCB 301), the ECC for the frequency pair 2400 MHz and 2484 MHz may be below 0.30. An exemplary embodiment may have a design as shown in Fig 6, while the core may be 2mm thick, the prepreg may be about 0.2mm, and copper may be about 35µm; such embodiment may show ECC for the frequency pair 2400 MHz and 2484 MHz as low as 0.28 while keeping efficiency above 25%.

[0040] A relatively low ECC (such as below 0.5 and in particular as described above) allows for channel diversity: connected product using the antenna 107, 307 may switch between channels (e.g. if one channel has a stronger signal, the antenna may switch to this channel). For example, the cavity 104, 304 may operate in a first channel, for example, lower half of channels of operation band (e.g. Wi-Fi band); the slot 102, 302 may operate in a second channel, for example, upper half of channels of operation band, and based on availability of these channels and the strength of signal, the transmission may be effected on either of these channels. Conventionally, such diversity is achieved withing single channel by providing multiple antennas (e.g. two). With the antenna 107, 307, a single antenna suffices. This in turn may lead to a more compact design of the device 300 (e.g. because a single antenna requires less space than multiple antennas). In other words, the antenna 107, 307 described above may behave like a two antennas which allows channel diversity by switching channels in a single antenna body (rather than switching two different antennas within single channel), and this in turn may make the antenna more compact.

[0041] Due to its position on the edge of one side of the PCB 101, 301 (and not, as is conventional, e.g. along the display, in the display frame, occupying both sides of PCB etc.), the antenna 107, 307 may allow minimizing the display frame. In an embodiment, a device incorporating the antenna may allow for a full-size / bezel-less display. Alternatively or in addition, the product may be made smaller, as one side of the PCB is clear of antenna and may be used to accommodate other PCB elements.

[0042] The antenna 107, 307 as described above may be used in particular in devices intended for detached or semi-detached houses (e.g. as compared to terraced houses or blocks of flats) because of better availability of the two particular channels the antenna 107, 307 is configured to operate at.

[0043] The antenna 107, 307 as described above may be more reliable than the existing solutions, e.g. a plurality of bezel gap antennas.

[0044] A PCB the shape of which is based on a square, a rectangle or a trapezoid (possibly with rounded edges, as shown in the example of Figs 4-6) is particularly advantageous.

Examples

Embodiment Construction

[0017]The below description is for illustration only, and is not intended to be limiting. Various elements of embodiments described below may be combined into new embodiments not explicitly described herein, as appropriate.

[0018]Like reference numbers describe like elements in the drawings.

[0019]For the sake of clarity, in all Figures, only conductive materials are shown. A skilled person will understand that there may be further materials in appropriate places, such as a core, prepreg etc. Some details are given below.

[0020]Figs 1 and 2 show a schematic example of a PCB 101. Similarly, Figs 4-6 show a schematic example of a PCB 301. For clarity, no circuit elements are shown on the PCBs 101, 301 of Figs 1-2 and 4-6, but it will be understood that any number of conventional elements will be accommodated on the PCB 101, 301.

[0021]In the embodiments shown in the Figures, a fully integrated inter-channel diversity antenna 107, 307 is provided in a form of a slot 102, 302 and a cavity 1...

FIELD OF THE INVENTION

[0001] The present invention relates to antennas for connected products, such as thermostats. In particular, the invention relates to antennas which are part of printed circuit board (PCB).BACKGROUND OF THE INVENTION

[0002] Connected products generally rely on a wireless link at 2.4GHz using WiFi, Zigbee or similar protocol. A low-cost option providing such connectivity is e.g. a printed antenna. Such antenna provided as a part of a printed circuit board (PCB) occupies a particular area on the PCB which must be free of circuitry and components; minimal clearance from other electrical components and metallic structural parts (display, batteries, etc.) is needed. Another consideration relates to improvements to link reliability, achieved e.g. by channel diversity.

[0003] From the user's perspective, it is preferred to have a display on the device (e.g. a thermostat) which is as large as possible and preferably full size (bezel-less design). This, however, poses additional challenges. In particular, the antenna needs a certain clearance from the display to avoid the display shielding the antenna and thus decreasing reliability of the whole device.

[0004] An example of an existing solution is to provide a bezel gap antenna, which is formed by coupling the RF circuitry to isolated sections of the metallic bezel. However, the bezel gap antenna does not represent the low-cost and fully PCB-integrated antenna solution, because its structure has metallic external parts requiring reliable RF coupling to PCB circuitry.

[0005] Therefore, there is a need for further improvements.SUMMARY OF THE INVENTION

[0006] In a first aspect, a printed circuit board, PCB, is provided, comprising a first outer layer and a second outer layer, the PCB comprising an antenna, the antenna being formed as an integral part of the PCB, the antenna comprising a first antenna element configured to operate at a first frequency and a second antenna element configured to operate at a second frequency, wherein the first frequency is different from the second frequency, wherein the second outer layer is free of antenna elements.

[0007] In embodiments of the first aspect, the PBC may utilize one or more of the following features: The first antenna element may be a λ / 4 slot antenna. The second antenna element may be a quarter-mode substrate-integrated waveguide antenna.

[0008] One of the first and second frequencies may be in the lower-half channels and the other of the first and second frequencies may be in the upper-half channels. One of the first and second frequencies may be in channels 1-5 and the other one of the first and second frequencies may be in channels 10-14. One of the first and second frequencies may be in channel 1 and the other one of the first and second frequencies may be in channel 14.

[0009] The first frequency may be 2400 MHz and the second frequency is 2484 MHz, or the second frequency may be 2400 MHz and the first frequency may be 2484 MHz.

[0010] The PCB may be rectangular, rectangular with rounded edges, square-shaped, square-shaped with rounded edges, trapezoid-shaped, trapezoid-shaped with rounded edges, quadrilateral, quadrilateral with rounded edges. The PCB may be of a shape distinct from a circle, ellipse or oval. If the PCB is quadrilateral or quadrilateral with rounded edges, the quadrilateral may be substantially concave.

[0011] The core thickness may be more than 1 mm, for example 1.5mm, 1.8mm or 2mm.

[0012] A copper layer thickness in the PCB may be between 0.30 µm and 0.40 µm.

[0013] A feeding line for the antenna may be implemented in the first outer layer, or in the second outer layer.

[0014] In a second aspect, a device comprising the PCB of any of the embodiments above is provided. The device may further comprise a bezel-less display.

[0015] In embodiments of the second aspect, the device may be a thermostat. The antenna may be configured to communicate wirelessly with one or more temperature sensors.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a simplified view of a PCB with a fully integrated inter-channel diversity antenna; Figure 2 is a detail of the simplified view of a PCB with fully integrated inter-channel diversity antenna; Figure 3 is a schematic example device which may utilize the fully integrated inter-channel diversity antenna; Figure 4 is a schematic view of a PCB with a fully integrated inter-channel diversity antenna used in device of Fig 3; Figure 5 shows a detail of an example PCB with a fully integrated inter-channel diversity antenna used in device of Fig 3; Figure 6 shows a detail of an example PCB with a fully integrated inter-channel diversity antenna and a display used in device of Fig 3. DETAILED DESCRIPTION

[0017] The below description is for illustration only, and is not intended to be limiting. Various elements of embodiments described below may be combined into new embodiments not explicitly described herein, as appropriate.

[0018] Like reference numbers describe like elements in the drawings.

[0019] For the sake of clarity, in all Figures, only conductive materials are shown. A skilled person will understand that there may be further materials in appropriate places, such as a core, prepreg etc. Some details are given below.

[0020] Figs 1 and 2 show a schematic example of a PCB 101. Similarly, Figs 4-6 show a schematic example of a PCB 301. For clarity, no circuit elements are shown on the PCBs 101, 301 of Figs 1-2 and 4-6, but it will be understood that any number of conventional elements will be accommodated on the PCB 101, 301.

[0021] In the embodiments shown in the Figures, a fully integrated inter-channel diversity antenna 107, 307 is provided in a form of a slot 102, 302 and a cavity 104, 304. There is also a feeding probe assembly 103, 303 associated with the antenna.

[0022] In Figs 1-2, the PCB 101 comprises two outermost layers: a first outer layer 101a and a second outer layer 101b. It will be understood that between these layers, there are further layers (such as prepreg, copper, core). These are not shown in detail in the Figs, for the sake of simplicity. The slot 102 occupies a portion of a first outer layer 101a of the PCB 101 (and possibly one or more underlying layers). The second outer layer 101b which is opposite the first outer layer 101a of the PCB 101 is without any corresponding slot (and possibly one or more layers adjacent the second outer layer 101b are also free of any corresponding slot). There is thus no need for antenna clearance on the second outer layer 101b of the PCB 101, and the whole of the second outer layer 101b of the PCB 101 may be used for circuitry and / or for a display.

[0023] The display (not shown in Figs 1, 2) may be in particular a full-size and / or bezel-less display. The configuration with the slot 102 on one side only (i.e. formed in one of the outer layers only) allows the circuitry and / or the display to have a minimal impact on the antenna 107 performance (minimal shielding of the antenna 107 by the circuitry and / or the display).

[0024] The structure of the antenna 307 of Figs 4-6 is similar to the structure of the antenna 107 of Figs 1-2.

[0025] The structure and position of the slot 302 provided on the PCB 301 of Figs 4-6 is similar to the slot 102 provided on the PCB 101 of Figs 1-2, e.g. in that it is formed in a portion of a first outer layer 301a while the second outer layer 301b is free from any similar slot. The effects and advantages of such position and structure are similar to those described for the slot 102 of Figs 1-2.

[0026] In the example shown in Figs 1 and 2, the cavity 104 is triangular. The cavity 104 is formed by a space which does not contain conductive material between the opposite top layers 101a, 101b (i.e. the space between the opposite top layers 101a, 101b is free of any further conductive material, but may contain e.g. a PCB core and prepreg (not shown)). The cavity 104 is defined by its edges 104a, 104b. The edges 104b are a part of the PCB boundary; the edge 104a is a border where further PCB layers (i.e. other than the opposite top layers 101a, 101b, e.g. a conductive body 108) start. The cavity 104 may be e.g. an isosceles triangle (with the edges 104b of the same length). In the example shown in Figs 4-6, the cavity 304 resembles a triangle except that one of the vertices defining the cavity 304 is rounded, and the side 304b is thus a smooth curve. In a preferred embodiment, the side 304b comprises a rounded vertex and a portion of straight line on either side of the rounded vertex.

[0027] It will be understood that the examples of the Figs are schematic for the sake of clarity. In a PCB with e.g. four layers (excluding the core (substrate)), the slot 102, 302 is formed in a first (outer) layer and a second layer immediately adjacent to the first (outer) layer (i.e., the slot is formed in two layers). The cavity 104, 304 may be formed between second and third layers. Fourth (outer) layer is free of any antenna elements. In this configuration, the second and third layers adjacent to the first and fourth outer layers, respectively, are e.g. copper.

[0028] In an embodiment, the slot 102, 302 has no power supply of its own and is fed from the cavity 104, 304, which in turn is fed by the feeding probe assembly 103, 303.

[0029] The slot 102, 302 may function as a λ / 4 slot antenna. Therefore, the length of the slot is chosen with respect to the intended use (intended wavelength that the slot 102, 302 is designed to work at).

[0030] Similarly, the cavity 104, 304 may function similarly to a quarter-mode substrate-integrated waveguide antenna. Therefore, the dimensions of the cavity, in particular the length of the edges 104a, 104b, 304a, 304b are chosen according to the required wavelength the antenna is to work at. In the embodiment of Figs 4-6, further design considerations may include the curvature of the rounded vertex and / or the length of the straight portions of the edge 304b.

[0031] In an embodiment, it may be advantageous to design the slot 102, 302 and the cavity 104, 304 to work at two close but different wavelengths. For example, in the 2.4 GHz band, the cavity 104, 304 may resonate at the lower end of the band (near 2.4GHz, for example below 2.45 GHz, more particularly below 2.42 GHz) and the slot 102, 302 resonates at upper end of the band (near 2.5GHz, for example above 2.45 GHz, more particularly above 2.48 GHz).

[0032] Fig 3 shows a schematic example of a device 300 which may utilize the PCB as described above (in particular, the PCB 301 shown in Figs 4-6). The device 300 may be for example a wireless thermostat. The device 300 may be any other connected home appliance, a control device for a smart home and the like. The device 300 generally comprises a housing 305 and a front side. A display 306 may be positioned on the front side (i.e. the side intended to be facing the room and / or the user and which provides the user interface). The display 306 may provide a user interface (e.g. sensor readings and / or controls for a room temperature, a zone temperature and the like). The housing 305 may be adapted to be mounted onto a wall or a similar surface and / or it may be adapted to be positioned on a stand (not shown). The display 306 may be positioned such that it covers majority of the front side or even the whole front side of the device 300.

[0033] As shown in Fig 6, in a device 300, the PCB 301 with the fully integrated inter-channel diversity antenna 307 is positioned such that the first outer layer 301a (i.e. the layer comprising the slot 302) is positioned towards the back side of the device and facing away from the display 306. The second outer layer 301b, which does not comprise the slot 302, is positioned against (i.e. facing) the display 306. The housing 305 of the device 300 is not shown in Fig 6.

[0034] The two radiation elements, i.e. the cavity 104, 304 and the slot 102, 302, may advantageously show orthogonal radiation patterns. Such orthogonality enables radiation pattern (channel and / or wavelength) diversity. As described above, the slot 102, 302 and the cavity 104, 304 may be designed such that each of these two radiation elements resonates at a slightly different frequency (as in the examples above; e.g. in upper and lower half of the 2.4 GHz band). In such case, each of the channels thus created is transmitted by different radiation element (respectively by the cavity 104, 304 and the slot 102, 302) with different radiation pattern. Thus inter-channel diversity is ensured, as two distant channels (distinct in frequency) are radiated by a sufficiently orthogonal radiation patterns.

[0035] If provided as a part of a PCB 101, 301, the efficiency of the fully integrated inter-channel diversity antenna 107, 307 is higher than the efficiency of the cavity 104, 304 on its own (without the slot 102, 302). By varying parameters (such as thickness of the respective layers) of the PCB, the efficiency of the antenna 107, 307 may be further increased.

[0036] For example, increasing the thickness of the conductive body 108, 308 (while keeping the other parameters constant) may increase the efficiency of the antenna 107, 307 to above 25% in the whole 2.4 GHz range. In an exemplary embodiment, the core may be 2mm thick, the prepreg may be about 0.2mm, and copper may be about 35µm; such embodiment may show both advantageous efficiency and also advantageous envelope correlation coefficient (discussed below).

[0037] The efficiency of the antenna 307 may be further increased by rounding the edge (as shown in the embodiment of Figs 4-6), even while other parameters are kept (e.g. the core 308 thickness, the thickness of the prepreg etc.).

[0038] The two antenna elements, i.e. the slot 102, 302 and the cavity 104, 304, of the antenna 107, 307 of Figs 1-2 and 4-6 may operate in two different ranges of channels of the 2.4 GHz band. In an embodiment, the antenna 107, 307 may in particular operate simultaneously in the upper and lower halves of the 2.4 GHz band (as outlined above). In an advantageous embodiment, the antenna utilizes two distant channels (for example, channels 1 to 5 and channels 10 to 14, respectively, or channels 1-3 and channels 12-14, respectively, or channels 1 and 14, respectively).

[0039] Generally, to measure the independence of the radiation pattern of two antennas (or two antenna elements, e.g. the slot 102, 302 and the cavity 104, 304 as described above), an envelope correlation coefficient (ECC) is used. It is generally desirable to have the ECC as low as possible (e.g. in a theoretical ideal case, if one antenna is completely horizontally polarized, and the other is completely vertically polarized, the two antennas would have ECC equal to zero, which would make the antennas independent). In practice, embodiments which have the ECC below 0.5 are advantageous. For example, in the embodiment of Figs 1-2, the ECC may be the lowest for the frequency pair 2400 MHz and 2484 MHz (where the ECC may be below 0.4 in certain configurations). As another example, in the embodiment of Figs 4-6, the ECC for the frequency pair may be below 0.35. In the particular configuration of Fig 6 (with the display 306 adjacent to the PCB 301), the ECC for the frequency pair 2400 MHz and 2484 MHz may be below 0.30. An exemplary embodiment may have a design as shown in Fig 6, while the core may be 2mm thick, the prepreg may be about 0.2mm, and copper may be about 35µm; such embodiment may show ECC for the frequency pair 2400 MHz and 2484 MHz as low as 0.28 while keeping efficiency above 25%.

[0040] A relatively low ECC (such as below 0.5 and in particular as described above) allows for channel diversity: connected product using the antenna 107, 307 may switch between channels (e.g. if one channel has a stronger signal, the antenna may switch to this channel). For example, the cavity 104, 304 may operate in a first channel, for example, lower half of channels of operation band (e.g. Wi-Fi band); the slot 102, 302 may operate in a second channel, for example, upper half of channels of operation band, and based on availability of these channels and the strength of signal, the transmission may be effected on either of these channels. Conventionally, such diversity is achieved withing single channel by providing multiple antennas (e.g. two). With the antenna 107, 307, a single antenna suffices. This in turn may lead to a more compact design of the device 300 (e.g. because a single antenna requires less space than multiple antennas). In other words, the antenna 107, 307 described above may behave like a two antennas which allows channel diversity by switching channels in a single antenna body (rather than switching two different antennas within single channel), and this in turn may make the antenna more compact.

[0041] Due to its position on the edge of one side of the PCB 101, 301 (and not, as is conventional, e.g. along the display, in the display frame, occupying both sides of PCB etc.), the antenna 107, 307 may allow minimizing the display frame. In an embodiment, a device incorporating the antenna may allow for a full-size / bezel-less display. Alternatively or in addition, the product may be made smaller, as one side of the PCB is clear of antenna and may be used to accommodate other PCB elements.

[0042] The antenna 107, 307 as described above may be used in particular in devices intended for detached or semi-detached houses (e.g. as compared to terraced houses or blocks of flats) because of better availability of the two particular channels the antenna 107, 307 is configured to operate at.

[0043] The antenna 107, 307 as described above may be more reliable than the existing solutions, e.g. a plurality of bezel gap antennas.

[0044] A PCB the shape of which is based on a square, a rectangle or a trapezoid (possibly with rounded edges, as shown in the example of Figs 4-6) is particularly advantageous.

Examples

Embodiment Construction

[0017]The below description is for illustration only, and is not intended to be limiting. Various elements of embodiments described below may be combined into new embodiments not explicitly described herein, as appropriate.

[0018]Like reference numbers describe like elements in the drawings.

[0019]For the sake of clarity, in all Figures, only conductive materials are shown. A skilled person will understand that there may be further materials in appropriate places, such as a core, prepreg etc. Some details are given below.

[0020]Figs 1 and 2 show a schematic example of a PCB 101. Similarly, Figs 4-6 show a schematic example of a PCB 301. For clarity, no circuit elements are shown on the PCBs 101, 301 of Figs 1-2 and 4-6, but it will be understood that any number of conventional elements will be accommodated on the PCB 101, 301.

[0021]In the embodiments shown in the Figures, a fully integrated inter-channel diversity antenna 107, 307 is provided in a form of a slot 102, 302 and a cavity 1...

Claims

1. A printed circuit board, PCB, comprising a first outer layer and a second outer layer, the PCB comprising an antenna, the antenna being formed as an integral part of the PCB, the antenna comprising a first antenna element configured to operate at a first frequency and a second antenna element configured to operate at a second frequency, wherein the first frequency is different from the second frequency, wherein the second outer layer is free of antenna elements.

2. A printed circuit board of claim 1, wherein the first antenna element is a λ / 4 slot antenna.

3. A printed circuit board of any one of preceding claims, wherein the second antenna element is a quarter-mode substrate-integrated waveguide antenna.

4. A printed circuit board of any one of preceding claims, wherein one of the first and second frequencies is in the lower-half channels and the other of the first and second frequencies is in the upper-half channels.

5. A printed circuit board of claim 4, wherein the first frequency is 2400 MHz and the second frequency is 2484 MHz, or wherein the second frequency is 2400 MHz and the first frequency is 2484 MHz.

6. A printed circuit board of any one of preceding claims, wherein the printed circuit board is rectangular or rectangular with rounded edges.

7. A printed circuit board of any one of preceding claims, wherein the printed circuit board is square-shaped or square-shaped with rounded edges.

8. A printed circuit board of any one of preceding claims, wherein the core thickness is 2mm.

9. A printed circuit board of any one of preceding claims, wherein a copper layer thickness is between 0.30 µm and 0.40 µm.

10. A printed circuit board of any one of preceding claims, wherein a feeding line for the antenna is implemented in the first outer layer, or in the second outer layer.

11. A device comprising the PCB of any one of claims 1 to 10 and further comprising a bezel-less display.

12. A device of claim 11, wherein the device is a thermostat.

13. A device of claim 12, wherein the antenna is configured to communicate wirelessly with one or more temperature sensors.

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