CN111293419A - Compact LTE antenna arrangement - Google Patents

Abstract

The invention discloses a compact LTE antenna arrangement. A portable or wearable communication device is disclosed. The portable or wearable communication device comprises a metal case, a battery and circuitry assembly and at least one antenna element, wherein the metal case has a metal side wall configured to support the screen element on one side and a back cover on the other side; the battery and the circuit assembly are mounted on a main board contained in a metal shell; at least one antenna element supports wireless communication. At least one of the antenna elements comprises a monopole defined by a segment of the sidewall bounded by the dielectric slot.

Description

Compact LTE antenna arrangement

The present invention relates to a compact Long Term Evolution (LTE) antenna arrangement, particularly but not exclusively for implementation in a wearable mobile communication device such as a smart watch.

Background

Compact or miniaturized computing and telecommunication devices, especially those worn on the body such as smartwatches, have recently become very popular. Many manufacturers have products on the market and each manufacturer seeks to provide more aesthetic designs and more communication functions, which are characteristic of flagship products on the market.

As with high-end electronic devices such as tablet and notebook computers, the design of small or wearable devices such as watches is evolving towards metal cases and large screens that occupy a large portion of the dead space on the front of the device, leaving only a very narrow bezel. As with the production of electronic devices, such designs on miniature or wearable devices present significant problems in transmitting and receiving the required signals for providing the wireless services required by the user. For example, the compact arrangement of electronic circuit boards, touch screens, and lithium ion batteries packaged in metal foils provides a number of radio frequency-blocking (RF-blocking) structures in the interior space of the device.

Still further problems with miniaturized wearable devices are limitations, i.e. the space of any antenna supporting wireless services is more limited than in tablet or laptop computers, and the bottom part on the housing can be located close to the human body, creating problems with this surface to serve the reception and transmission of radio frequency signals.

US 2018/0048057 a1 and US 2018/0048058 a1 both of the apple company describe a smart watch device having a metal case with a metal side wall. The antenna radiating element is formed by a capacitively coupled trace in a stack of components on, for example, a display screen, a touch screen, a motherboard perimeter, or a back cover. The metal can serves as a common defined ground for all devices in the assembly stack.

This approach of using a metal housing as a common ground means that the antenna elements are confined to a specific radio-frequency-transparent (RF-transparent) window for signal ingress and egress. This limitation reduces the efficiency of the antenna.

Drawings

Fig. 1a and 1b are perspective views of a typical smart watch design.

Fig. 2a and 2b show a typical internal layout of a current generation of smart watches.

Fig. 3 a-3 c show some solutions of the prior art.

Fig. 4 shows an exemplary metal case with the top display element, battery, main board and back cover removed.

Fig. 5a and 5b show examples where the shell arrangement is divided into 2 elements (RE1-RE2) and 4 elements (RE1-RE4), respectively.

Figure 6 shows an example where the radiating element is suitably fed and grounded to provide the antenna function.

Fig. 7 shows an example of achieving a wide range of low frequencies of the low frequency band by switching between different capacitances using a Controlled Matching Circuit (CMC).

Fig. 8 shows an exemplary embodiment of a CMC.

FIG. 9 illustrates a low-band analog S-parameter response of a coupled monopole antenna arrangement according to an embodiment

Fig. 10 shows the complete simulated response of the LTE antenna.

Fig. 11 shows the analog isolation between two antenna elements.

Fig. 12 shows a shell radiating element arrangement according to a second embodiment.

Fig. 13a and 13b show examples of a mating shaped back cover for each form factor.

Fig. 14 shows a perspective view of an underside watch with a transparent back cover.

Fig. 15 shows a simulated S-parameter response of a low-band LTE antenna design according to the second embodiment.

Fig. 16 shows the efficiency of the low-band antenna according to the second embodiment.

Fig. 17 shows a perspective view of the rear part of a watch according to a third embodiment.

Fig. 18 shows a simulated S-parameter response of an LTE low-band antenna according to the third embodiment.

Fig. 19 shows the simulated efficiency of the LTE low band antenna according to the third embodiment.

Fig. 1a and 1b show perspective views of a typical smart watch design, illustrating the form factor of such a design having a circular or substantially rectangular case, as shown in fig. 1a and 1b, respectively.

The metal housing (1) accommodates a screen element (2) and has a frame (3) on the front side. Wrist straps (4) are attached to the distal and proximal faces to allow the user to comfortably wear the device. There may also be a convex element (5) attached to one of the sides to enable control of the watch function.

A generally rectangular shell form factor (fig. 1b) has clearly defined sides for the left and right sides, and distal and proximal sides to which the wristband is attached.

A typical internal layout of a current generation of smart watches is summarized in fig. 2a and 2b, in which a cross-section of the device is shown.

The cross-sectional view in fig. 2a has the screen element (2), the shell (1) and the bottom cover (13) on top. The bottom cover may have a sensor package (14) or other structure, such as a sim card tray or wireless charging unit, wherein the sensor package (14) is used to measure a physical characteristic of the user when in close proximity to the wearer's skin.

Inside the housing arrangement there is a battery (11) and a motherboard (12), wherein the motherboard (12) contains the processor, memory and all control circuitry required for the functioning of the device. The battery and the main board are essentially metal components and therefore act as a large ground plane or radio-frequency-blocking element with respect to the antenna element located in the housing. Similarly, the screen element (2) is either a simple IPS LCD (In-Plane Switching Liquid Crystal Display) with a metal rear shell or a touch screen device. Both display components also act as important ground planes or radio-frequency-blocking elements for the internal antenna.

It should be noted that the internal arrangement of components in the current generation of smart watches includes: batteries arranged above the main board (fig. 2a), and batteries also arranged below the main board (fig. 2 b).

The shaded area (15) represents the available space for arranging any antenna components. The prior art solutions are limited to a small window around the edge of the display screen, or a radio-transparent area in the back cover, e.g. where the sensor package is located, or the back cover may be non-metallic. Such prior art solutions are shown in fig. 3 a-3 c.

Fig. 3a shows a prior art loop or open loop antenna (20) element that is positioned around the battery and has sufficient viewing angle to show the edges of the element so that the signal can be effectively passed into and out of the housing. It should be noted that this type of solution is only really feasible when the size of the battery or the main board is designed such that the antenna loop can be accommodated and also have a sufficient view of the screen edges for efficient operation. Similarly, fig. 3b shows another prior art design in which the ring or loop antenna element is located within a screen mat (21) and has a radio frequency view into and out of the housing at the edge of the display screen glass. Fig. 3c shows an antenna element (22) utilizing a radio frequency transparent region associated with a sensor package located on the back cover.

The limitations provided by each of the prior art locations that provide a restrictive or narrow radio-transparent window or allow signals to be transmitted out of the back cover adversely affect the efficiency of the antenna.

Embodiments of the present disclosure seek to address the shortcomings of the described prior art.

Brief summary of the disclosure

Embodiments of the present invention use a metal shell to form the antenna radiating element. Fig. 4 shows an exemplary metal case with the top display element, battery, main board and back cover removed.

There is no internal component, screen or bottom cover, and we are shown the remaining metal side shells. The metal element may functionally serve as one or more antenna Radiating Elements (RE). The metal element can be divided into radiating elements of different lengths by using a dielectric slot (30) located along the periphery. Examples of such arrangements are shown in fig. 5a and 5 b.

In fig. 5a and 5b, for illustrative purposes, the shell arrangement is divided into 2 elements (RE1-RE2) (fig. 5a) and 4 elements (RE1-RE4) (fig. 5b), each element having an arbitrary length. It should be noted, however, that the slots may be located at positions required to produce the desired number of radiating elements and the desired length.

Embodiments of the present invention allow flexibility in the location where the radiating element is fed or grounded. The use of metal case sides enables both the feed point and the ground point to use the battery foil covering (battery foil covering), the bottom surface of the screen, or the motherboard as a large ground plane. The ground connection may be realized by a wire, a flexible printed circuit board (Flex-PCB) or a stamped metal element. Figure 6 illustrates in more detail the principles and flexibility provided by embodiments of the present invention.

In both examples in fig. 6, including circular and substantially rectangular housing structures, the radiating element is suitably fed and grounded to provide the antenna function.

Once the screen, back cover and internal components are removed, the remaining cover structure may have an arcuate profile, a straight profile, a generally c-shaped or bracketed profile, or other profiles, which will be the shape of the radiating element.

Not all antenna elements defined by the notches need to be driven; some may simply remain floating or grounded. Such passive elements may be coupled to adjacent driven antenna elements to provide further benefits, such as broadening the response by coupling or modifying the response by forming a loop coupling to ground.

First embodiment

In a first exemplary embodiment, using the techniques and methods described above, the watch case may be used to cover the primary LTE band required to operate in the 4G wireless service band.

The frequency range for the low frequency band of LTE is approximately 820-960MHz, and the mid/high frequency band is approximately 1.7-2.7 GHz. These frequency ranges can be achieved by using the monopole and PIFA elements shown in fig. 6. A wide range of low frequencies of the low frequency band is achieved by switching between different capacitances using a Controlled Matching Circuit (CMC), and this is illustrated in more detail in fig. 7.

One end of the monopole (RE1) is fed through a large central ground plane. The other end of the monopole (RE1) is connected to a plurality of different capacitors or passive networks through a Controlled Matching Circuit (CMC) (40). This makes the electrical length of the monopole element dependent on which low frequency band is desired.

Fig. 8 shows an exemplary embodiment of the CMC (40) in which the SP4T radio frequency switch (50) selectively connects the end of the monopole (RE4) to one of four different capacitors or passive networks and then to the center ground plane. The monopoles formed by RE4 are also mutually coupled to RE1 to produce a longer length of conductor to assist the low frequency band, in this case the shell has 4 slots. The monopole may also be a longer segment without a slot incorporating RE4 and RE 1. However, this will affect the tuning of the mid-high band.

A PIFA antenna is a tuned or resonant PIFA element that covers the frequency bands required for GPS, bluetooth and WiFi (1.5-2.4GHz and 5GHz), hereinafter referred to as a 3in1(3 in one) PIFA antenna. The antenna is fed at a feed point 2 and is grounded to a large central ground plane through a ground point.

Fig. 9 shows the low-band analog S-parameter response of the coupled monopole (RE4, RE1) antenna arrangement described in this embodiment. The results clearly show that the radio frequency switching state of the CMC produces a favorable resonance over the 820-. These five states include 1, where the switch is connected to ground and then each of the 4 tuning capacitors is turned on into the circuit.

Fig. 10 shows the complete simulated response of an LTE antenna, including the response of the low band (handover) and the fixed medium and high band. The mid-high band response is always present at the port, independent of the state of the CMC, or coupling with the top element (RE 1).

FIG. 11 shows the analog isolation between two antenna elements, a1 monopole formed by RE4 and RE 1; and 3in1PIFA elements. The worst isolation in the simulation is indicated as-14.3 dB.

Second embodiment

The second exemplary embodiment uses the case for LTE mid/high band and 3in1 antennas, but instead uses a non-metallic area on the back case for low band LTE antennas.

Fig. 12 shows a shell radiating element arrangement according to this second embodiment.

The LTE high band radiating element (RE1) is fed through feed point 1 and resonates or feeds through a matching circuit. This arrangement uses a large central ground plane as a counterpoise to operate as a monopole antenna. The 3in1 antenna element is formed on the opposite side of the housing and is in the form of a Planar Inverted F Antenna (PIFA). The PIFA antenna is fed from a feed point 2 and has a ground portion (ground pin) located on a large central ground plane.

The LTE low band antenna is formed on the back case of the watch. As shown in fig. 13a and 13b, for each form factor, there is a cooperatively shaped back cover.

In fig. 13a, the cover may be metal or plastic and would have snap-in edges (snap-lip) or threads (50) to secure the back cover to the housing frame. In fig. 13b, the back cover may also have built-in or very close components (features), which components (51) may include windows, sensor packages or wireless charging components, such as coils. These components will occupy a portion of the available space on the back cover and may also affect the radio frequency response of the antenna elements located thereon. When placing the antenna on the back cover, other metal parts from the main board next to the back cover, such as sim card trays, must also be considered.

In this embodiment it is proposed to attach a Planar Inverted F Antenna (PIFA) to the back cover. In this example, the shape of the antenna is generally U-shaped, but may be any geometric or meander line shape that accommodates components on the back cover. In this case, the sim card tray and wireless charging coil must be avoided.

Fig. 14 shows a perspective view of an underside watch with a transparent back cover to provide details of the back. The arrangement comprises a suitably shaped PIFA antenna (75) which is very close to, or adhered to, or part of the back cover, depending on the antenna structure. The antenna may be fabricated onto the back shell according to metal stamping, flexible PCB, LDS or other direct metallization techniques. The PIFA is fed through a feeding point (72) and grounded through a grounding point (73); both directly from the large central ground plane formed by the motherboard, screen housing or battery foil elements, or from all elements if grounded together. This central ground plane element acts as a counterpoise for operation of the PIFA element.

A suitable shape for the PIFA antenna (75) is one that does not obscure any sensor package or other structure, such as the wireless charging coil unit (71) or sim card tray (74), and provides the appropriate electrical length to resonate or perform at the desired frequency band by matching.

A surprising feature of this arrangement is that the PIFA on the back cover appears to be insensitive to the performance (i.e., efficiency) of the antenna with respect to the metal components immediately adjacent to the back cover. The metal components are properly grounded and they only affect the matching, which is a more easily solved problem that is solved by using the proper passive circuit in place to satisfy the required response.

Fig. 15 shows a simulated S-parameter response of the proposed low-band LTE antenna design described in this second embodiment.

The plot of the S-parameter shows two distinct wide resonances with a suitable response between 824MHz and 960 MHz.

Fig. 16 shows the efficiency of the low-band antenna according to this second embodiment. It can be seen that the efficiency is higher than-10 dB, even very close to the metal element.

It should also be noted that the low band antenna elements on the back cover may also support the desired mid/high bands by appropriate tuning and/or matching circuitry.

Third embodiment

A third embodiment of the present invention is similar to the second embodiment in that both the mid/high LTE band and 3in1 antennas use a housing element for their operation, but the LTE low band antenna is formed on the back housing using a ground loop design. Fig. 17 shows this third embodiment in more detail by using a perspective view of the back of the watch, which has a transparent shell to show the components of the back.

The antenna in this embodiment is a generally U-shaped monopole element (75) with an additional bend (76) that folds the distal end back on itself to produce the appropriate electrical length required. The antenna is fed at the proximal end (72) and grounded at the distal end at the end of the additional bend (73). The substantially U-shaped antenna element (75) is designed and shaped so as to avoid crossing any metallic elements next to or embedded in the back cover. Such as a sim card reader (74), a wireless charging coil (71), or other electronic device, such as a sensor package.

It should also be noted that this antenna, positioned at the back cover, and the previous embodiments, will send out signals mainly through the base of the watch, and will therefore have some interaction with the wearer's wrist. Another surprising aspect of this and the previous embodiments is that if the distance between the back cover LTE antenna layers is arranged by the thickness of the back cover or by the arrangement of the component layers in the housing, the antenna-wrist interaction can be used to increase the efficiency instead of decreasing the efficiency.

The antenna elements may be metal stamped, made from a flexible PCB, or embedded directly into the back shell by LDS or similar direct metallization techniques.

Fig. 18 shows simulated S-parameters of the LTE low-band antenna according to this third embodiment. With proper matching, the resonance provides support for the low LTE band from 700MHz up to 960MHz, which is an improvement over the bandwidth obtained in the second embodiment.

Fig. 19 shows the simulated efficiency of the LTE low band antenna according to this third embodiment. The efficiency is higher than-14 dB for the whole band, with lower frequencies occurring at the band limits (e.g., low and high frequencies). These results are sufficient to meet the performance requirements of a smart watch antenna.

All embodiments in the present invention do not rely on the particular order of the stacks of internal components as in the prior art. Our feed and ground points can be taken from the nearest available point, such as the screen back case, battery foil, or motherboard, to reduce the flex PCB or wiring requirements within the watch case. Furthermore, the use of the housing sidewall elements as radiating elements and bottom antennas means that we are also not limited by the size of components such as the screen or motherboard, and we do not rely on a small rf-transparent path through internal components and away from the edge of the screen as in the prior art.

Throughout the description and claims of this specification, the words "comprise" and "comprise", and variations thereof, mean "including but not limited to", and it is not intended to (and does not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not limited to the details of any of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims (19)

1. A portable or wearable communication device, comprising:

i) a metal case including a metal sidewall configured to support the screen member at one side and a rear cover at the other side;

ii) a battery and circuit assembly mounted on a motherboard contained within the metal case;

iii) at least one antenna element supporting wireless communication;

wherein the at least one antenna element comprises a monopole antenna defined by a segment of the sidewall bounded by a dielectric slot.

2. The apparatus of claim 1, wherein a section of the sidewall is provided with a feed point at one end and a tuning circuit at the other end.

3. The device of any preceding claim, wherein a portion of the screen element, the motherboard, the battery and circuit assembly together form a common ground plane.

4. A device as claimed in claim 3 when dependent on claim 2, wherein the tuning circuit and feed point are mounted on the common ground plane.

5. The apparatus of claim 1, wherein the monopole antenna is configured to couple with one or more other segments of the housing sidewall defined by a dielectric slot.

6. The apparatus of claim 5, wherein the coupling is to increase an electrical length of the antenna element.

7. The apparatus of claim 5, wherein the coupling is to provide a broadband effect on a response of the antenna element.

8. The apparatus of claim 5, wherein the coupling and the tuning circuit provide a low-band frequency response.

9. The apparatus of claim 2, wherein the tuning circuit comprises an RF switch configured to switch between two or more passive elements, such as capacitors, and optionally directly to ground, in order to provide tuning by changing the electrical length of the antenna element.

10. The device of claim 1, wherein another segment of the sidewall, also defined by a dielectric slot, forms a PIFA antenna for operation in GPS, bluetooth and/or WiFi bands.

11. A device as claimed in claim 10 when dependent on claim 3, wherein the PIFA is fed from and grounded to the common ground plane.

12. The apparatus of claim 1, wherein the metal sidewall is at least one of curved, straight, or bracketed.

13. The apparatus of claim 1, wherein the metal shell has a generally circular or generally rectangular shape.

14. Device according to any one of the preceding claims, in particular a smart watch.

15. The device of claim 1, wherein the monopole antenna covers LTE mid-band and high-band.

16. The apparatus defined in claim 15 wherein the back cover comprises a dielectric material and wherein a second monopole antenna is formed on the dielectric material of the back cover to cover an LTE low band.

17. The apparatus of claim 16, wherein the second monopole antenna is selected from the group consisting of an IFA, a PIFA, a ground loop, a meander line, and a coupling loop.

18. The apparatus of claim 17, wherein the rear cover, the motherboard, the battery, and circuit components together form a common ground plane, and wherein the second monopole is fed from and grounded to the common ground plane.

19. A device as claimed in claim 16, 17 or 18, wherein the second monopole antenna is formed by metal stamping on the dielectric material of the back cover, a flexible pcb (fpc), laser direct write (LDS), or by another direct metallization technique.

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