WO2009004361A1

WO2009004361A1 - Antenna module with adjustable beam and polarisation characteristics

Info

Publication number: WO2009004361A1
Application number: PCT/GB2008/050479
Authority: WO
Inventors: Devis Iellici; Simon Philip Kingsley; Steve Krupa; Michael Gaynor
Original assignee: Antenova Limited
Priority date: 2007-07-03
Filing date: 2008-06-23
Publication date: 2009-01-08
Also published as: TWI493786B; GB0712787D0; GB2450786A; GB2450786B; TW200917567A; GB0811426D0

Abstract

A module (2) adapted for connection to a printed circuit board (PCB) (1) or printed wiring board (PWB) of an electronic communications device, the module comprising an antenna having respective left and right antenna arms (6,7), and the arms being electrically connected to each other by aconnecting circuit (9) configured to apply a variable or adjustable phase difference between the arms and to provide a single external feed connection (11) for the antenna.

Description

ANTENNA MODULE WITH ADJUSTABLE BEAM AND POLARISATION

CHARACTERISTICS

Inventors: D lellici, S P Kingsley, S Krupa, M Gaynor

Embodiments of the present invention relate to an antenna module with adjustable beam and polarisation characteristics, comprising a pair of antenna arms with interconnecting circuitry and an optional integrated radio component.

BACKGROUND

The design of internal antennas for cellular radio terminals and other electrically small radio platforms is well known to be a difficult problem. Firstly, there are many different types of physical structures to consider. Mobile telephone handsets, for example, can be constructed as clamshells, bar phones, flip phones, sliders or swing phones. The connections between the two parts of segmented phones can have a large impact on the antenna performance. Secondly, handsets are getting smaller and at the same time the antenna is being asked to cover more bands. Thirdly, other radios and other antennas may be present in the handset (GPS, Bluetooth™, WLAN, mobile TV, FM radio, etc.) causing coupling and co-sited radio problems. Finally, there is an increasing call for some protocols to use multiple antennas in a handset for diversity or MIMO (multiple input/multiple output) applications. While all these factors lead to an increase in the complexity of the antenna, commercial pressures require the antenna to be ever cheaper and to occupy less volume in the handset. With the bill of materials already pared to a minimum, larger scale integration of components is seen as the way forward to further cost reductions.

Most existing handset antennas are unbalanced designs such as PIFAs (planar inverted F antennas) and monopoles. These types of antenna are small and make effective use of the PCB (printed circuit board) or PWB (printed wiring board) as part of the antenna, but they need extensive customisation for every product because every PCB/PWB is a different shape and size. Antenna customisation is an expensive process that forms a significant part of the cost of a handset and precludes the use of integrated radio antenna modules, as the cost of customising these components would be prohibitive. However, integration of the radio with the antenna is desirable as this would help to reduce both size and cost. Progress towards integrated antennas could be made by the introduction of balanced or quasi-symmetrical antennas demonstrating reduced interaction with the PCB and so requiring less customisation. Unfortunately, balanced and symmetrical antennas are often twice the size of their unbalanced counterparts and also have less bandwidth because they are not using a wide PCB as part of the radiating structure. A further complication is that many types of balanced antenna (dipoles, spiral pairs, etc.) are adversely affected by self-induced image currents when they are placed electrically close to a groundplane. Modern handset PCBs have a full groundplane and the antenna sits at a small fraction of a free-space wavelength above the groundplane.

A problem to be solved is to create an antenna that occupies a small space and requires little or no customisation when installed on many different types of platform, especially when such platforms have a full groundplane. Such an antenna would then make it economically feasible to create radio-antenna modules and thus advance the integration process.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the present invention, there is provided a module adapted for connection to a printed circuit board (PCB) or printed wiring board (PWB) of an electronic communications device, the module comprising an antenna having respective left and right antenna arms, and the arms being electrically connected to each other by a connecting circuit that provides a single external feed connection for the antenna, wherein, when connected to the PCB or PWB and fed with a signal, the antenna and optionally the connecting circuit generate at least a partial image current in a groundplane of the PCB or PWB, wherein the connecting circuit is configured to apply a variable or adjustable phase difference between the arms so as to allow a beam generated by the antenna to be steered, and wherein the connecting circuit is additionally configured to adjust a phase relationship between the arms and the image current so as to create a degree of signal polarisation.

In embodiments of the present invention, a module containing at least an antenna and passive driving circuit, and preferentially with an active radio circuit or RFIC (radio frequency integrated circuit) has been developed. The aforementioned circuit(s) is(are) the connective circuit of the preceding paragraph. The module is small enough for use in a handset and will work over a PCB groundplane. The module may be used as a stand-alone antenna but it has been designed primarily to work with the radio. For simplicity, the antenna and radio may be etched on the same PCB, although this is not a necessary requirement for the invention to work.

The basic concept of the module is shown in Figure 1.

An antenna module of embodiments of the present invention may be mounted as a vertical 'blade' above a horizontal PCB (such as the main PCB of a mobile phone handset) and so occupies minimum PCB space. Furthermore, by including the radio on the module, the main PCB space that the radio would have occupied is also saved. The antenna structure comprises left and right antenna arms and a circuit to connect them so as to provide, for example, a conventional single-ended 50-ohm feed point. The connecting circuit may be passive or active and may connect directly to a radio (when present) or through some appropriate filtering network. An important element of embodiments of the present invention is that this connecting circuit creates an adjustable or variable phase difference between the two arms. There are many ways of creating a variable phase structure but probably the simplest is the bridge circuit shown in Figure 2.

Each of the antenna arms may in turn be fed from the connecting circuit part of the way along the length of the respective antenna arm. This is similar to an elevated feed monopole but with the preferable addition of some spiralling or meandering to reduce the overall length of each arm.

Figure 3 shows a typical configuration. In effect the structure is similar to a pair of elevated-feed grounded monopoles fed by a bridge phase shifting circuit. Other forms of meandered antenna structures have been tested and these work similarly.

The connecting circuit carries out three important functions. Firstly, it creates a matching network so that if the antenna behaves differently in different applications it can be re-matched to the desired single-ended impedance, for example 50 ohms, and onto the correct frequency. The PCB requires no re-design to do this, only the selection of appropriate surface mount components to achieve the correct matching. Secondly, the connecting circuit can be used to control the relative phase of the two antenna arms and their phase with respect to ground. Thirdly, the appropriate choice of phase can be used to modify or improve the polarization state (linear, circular, etc.) of the antenna. Right hand circular polarisation (RHCP) is important in some applications such as when receiving GPS signals. Left hand circular polarisation can also be created.

In the past there have only been a few ways to create RHCP with an electrically small antenna. Such methods include the helix antenna and its variants such as the quadrifilar helix, the microstrip patch with an appropriate feed mechanism and crossed dipole antennas with an appropriate feed mechanism. RHCP is usually created by driving a pair of physically orthogonal structures with two separate RF signals, identical in frequency and amplitude but carrying a 90 degree difference in phase. In embodiments of the present invention, a single linear antenna structure is used but the combination of the current flowing in the antenna and the partial image current flowing on the PCB may be used to create RHCP. This is demonstrated in Figure 4. The phasing of the connecting circuit is an essential part of getting the right phase between the two currents and creating RHCP.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and 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.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which: FIGURE 1 is a perspective view of a first embodiment mounted on a main PCB;

FIGURE 2 is a circuit diagram showing a bridge-type connector circuit;

FIGURE 3 is a schematic elevation view of a further embodiment of the present invention showing how the lengths of the antenna arms can be varied;

FIGURE 4 is a plan view of an embodiment of the present invention mounted on a main PCB and showing the direction of an antenna current and a corresponding image current in the PCB;

FIGURE 5 shows an embodiment of the present invention mounted at an edge of the main PCB in a first configuration; and

FIGURE 6 shows an embodiment of the present invention mounted at an edge of the main PCB in a second configuration.

DETAILED DESCRIPTION

Referring firstly to Figure 1 , there is shown a main PCB 1 of a handset, the PCB 1 including a conductive groundplane (not shown). A module 2 of an embodiment of the present invention comprising a PCB 3 on which is mounted a radio component 4 inside a conductive shielding case 5, and respective left and right hand antenna arms 6, 7 etched onto the PCB 3 is mounted on the main PCB 1 in a substantially perpendicular manner by way of a connector 8, which connects to a single feed point for the antenna arms 6, 7. A connecting circuit 9 (not visible in Figure 1 but located behind the radio component 4) connects the two antenna arms 6, 7 and also connects to the single feed point, which may be configured as a conventional, single-ended 50 ohm feed point.

Figure 2 shows an appropriate form of connecting circuit 9 configured as a bridge circuit comprising a pair of capacitors Ci and C₂, and a pair of inductors L₁ and L₂. The single feed point is located at 1 1 , and the bridge circuit is grounded at 10. A radio transceiver component 4 is connected at 1 1. Each of the left and right hand antenna arms 6, 7 is configured as a PIFA having a ground connection 12. The bridge circuit 9 acts as a phase shifting circuit between the respective antenna arms 6, 7. The antenna arms 6, 7 may have a spiral configuration as shown in order to reduce space, but other configurations may be employed.

Figure 3 is a front elevation view of a module embodying the present invention. The radio component 4 and connecting circuit 9 are not shown only in outline, but the left and right antenna arms 6, 7 are shown in detail. The antenna arms 6, 7 are formed as etched spiral tracks on the PCB 3, as are the ground connections 12. The antenna arms 6, 7 each have a feed point 13, 14 that is connected to the appropriate part of the connecting circuit 9. Each antenna arm 6, 7 is independently adjustable in length by way of the provision of short circuit connections 15 on each arm. The short circuit connections 15 may take the form of pads to which zero ohm resistors may be reflowed during manufacture of the module. Alternatively or in addition, the zero ohm resistors or the like may be electronically switched in and out so as to provide dynamic variation in length of the antenna arms 6, 7. In yet a further embodiment, the effective lengths of the antenna arms 6, 7 may be continuously electronically varied by the insertion of series varactor diodes into the arms 6, 7 or shunt varactor diodes connecting the arms 6, 7 to ground.

Figure 4 shows a module of an embodiment of the present invention (the PCB is indicated at 3) mounted at an edge of a main PCB 1 , substantially perpendicular thereto. A combination of the current 16 flowing in the antenna and the resulting partial image current 17 flowing in the groundplane of the main PCB 1 may be used to create right (or left) hand circular polarisation.

Figures 5 and 6 show two variations in which the module is mounted to an edge of the main PCB 1 without a lower edge of the module PCB 3 actually resting on an upper surface of the main PCB 1. In other words, the module is dropped down relative to the upper surface of the main PCB 1 and hangs from the edge thereof. This has the advantage of reducing the effective height of the vertically-mounted module PCB 3, thereby saving space within a handset casing. In Figure 6, a cut-out 18 is provided at the edge of the main PCB 1 to allow the module to be mounted in the cut-out 18 without projecting beyond the profile of the main PCB 1. This arrangement still allows a partial image current to be created in the groundplane of the main PCB 1 by way of capacitive coupling. CURRENTLY PREFERRED EMBODIMENTS

In a first embodiment the two arms 6, 7 of the antenna are fed with a 180 degree phase shift. This turns the antenna into a structure similar to gamma-fed dipole. The advantage of a dipole, being a fully balanced antenna structure, is that it has the maximum immunity from groundplane effects, such as changes in the size of the groundplane from one application to another. However, it should be noted that the dipole still creates partial image currents in the groundplane and is not completely immune to groundplane effects. The image is only partial because the antenna sits at one edge of the groundplane. (The structure works just as well at the centre of a groundplane where a full image is created, but this is not an efficient location for antenna radiation and is not of interest to most handset manufacturers.) A disadvantage of the dipole is that it is the narrowest in bandwidth of all the possible configurations of this antenna and often has the lowest efficiency.

In a second embodiment the two arms 6, 7 of the antenna are fed with a phase shift other than 180 degrees. This makes the structure unbalanced and it no longer acts as a simple dipole. The combination of this unbalanced structure and its partial image in the groundplane confers some remarkable and unexpected advantages. Firstly, variations in the phase between the two halves of the antenna structure cause a change in the radiation pattern. The changes are marked and can cause the direction of peak radiation to be switched from one side of the main PCB 1 to the other. For example, with a horizontal PCB 1 , as shown in Figure 1 , the module can be made to radiate upwards or downwards depending on the phase setting. The degree of RHCP also changes when the phase is adjusted.

In a third embodiment, one part of the antenna is grounded. This might be achieved with the simple bridge structure by replacing C₂ with a zero-ohm resistor and omitting component L₁. This has the effect of grounding the left hand arm 6 of the structure. The right hand arm 7 continues to be connected to the radio 4 through Ci and any other components that may be introduced to improve matching. In this third embodiment, the right hand arm 7 becomes a driven monopole and the left hand arm 6 becomes a parasitic monopole. This structure might be considered a special case of the second embodiment. The advantage of this arrangement is to create more options in terms of beam position and degree of RHCP. In a fourth embodiment, an electronic switching circuit is used to switch between the first three embodiments and variations thereof. Switching might be accomplished through the use of PIN diodes, MEMs devices and the like. The importance of switching the values in the connecting circuit lies in the consequent switching of the beam position and the antenna beam diversity that this creates. Antenna diversity is an important aspect of many modern radio systems.

In a fifth embodiment, an electronic tuning circuit is used to adjust continuously between the first three embodiments and variations thereof. Tuning might be most simply accomplished by replacing Ci and C₂ with varactor diodes and applying a variable DC voltage to these diodes. Controllable antenna diversity can be created this way.

In a sixth embodiment, an antenna is provided having the same structure as in the previous embodiments, but with the module dropped down the side of the main PCB 1 , see Figure 5. This arrangement still creates a partial image in the groundplane, because of capacitive coupling with the groundplane and all the benefits of the previous embodiments may be realised. The advantage of this arrangement is that it reduces the effective height of the module. The structure can be prevented from projecting beyond the profile of the main PCB 1 by using a cut-out 18, as shown in Figure 6.

In a seventh embodiment, the connector 8 is replaced by other means of attaching the antenna substrate 3 to the main PCB 1. Other means of attachment include mechanically fastening the antenna structure in place and then electrically attaching it to the main PCB 1 via a flexible PCB or by using a MID (Moulded Interconnect Device) process to plate onto the bottom of the structure and reflowing it on to the PCB, or by similar means. In one preferred configuration, the radio 4 being on the antenna PCB 3 means that no RF signals have to pass through the connector 8. Power and digital control signals pass into the module and digitised data passes out. In a second preferred configuration, a connector 8' is provided on the main PCB 1 for an external antenna (such as might be used on an automobile) and RF signals must therefore pass through the connector 8' to the module. In this case a flexible PCB or reflowed MID structure is preferred.

In an eighth embodiment, the two arms 6, 7 of the antenna structure are adjustable in length. The length can be varied in a simple way by shorting the spiral through the reflowing of zero ohm resistors (short circuits) when the module is manufactured. The pads for these zero ohm resistors can be seen in Figure 3. The same result could be achieved actively by electronically switching in and out such short circuits. The effective length of the arms can also be continuously electronically varied by the insertion of series varactor diodes into the arms or shunt varactor diodes connecting the arms to ground. It is not necessary, or always desirable, for the two arms to have the same length. Having physically somewhat unbalanced structures can be as useful as electrically unbalanced signals when controlling the polarisation and beam pattern of the module.

In a ninth embodiment, as shown in Figure 7, the module 2 is mounted on the main PCB 1 with the antenna PCB 3 in a horizontal configuration, substantially parallel to the main PCB 1. The radio component 4 and conductive shielding case 5 are mounted on top of the antenna PCB 3, and the connector 8 is mounted below the antenna PCB 3. This embodiment is useful for thin handsets, since its height is relatively low. Moreover, there is room underneath the antenna PCB 3 for various components (not shown) on the main PCB 1 , thereby allowing efficient use of space.

Embodiments of the present invention have already been used to create RHCP GPS antennas and GPS radio-antenna modules. A linear polarisation version may be used for Bluetooth™ and WLAN applications. Further integration may be achieved by combining GPS and Bluetooth™ functionality onto a single module structure.

Claims

CLAIMS:

1. A module adapted for connection to a printed circuit board (PCB) or printed wiring board (PWB) of an electronic communications device, the module comprising an antenna having respective left and right antenna arms, and the arms being electrically connected to each other by a connecting circuit that provides a single external feed connection for the antenna, wherein, when connected to the PCB or PWB and fed with a signal, the antenna and optionally the connecting circuit generate at least a partial image current in a groundplane of the PCB or PWB, wherein the connecting circuit is configured to apply a variable or adjustable phase difference between the arms so as to allow a beam generated by the antenna to be steered, and wherein the connecting circuit is additionally configured to adjust a phase relationship between the arms and the image current so as to create a degree of signal polarisation.

2. A module as claimed in claim 1 , further comprising an integrated radio component.

3. A module as claimed in any preceding claim, wherein the connecting circuit is a bridge circuit.

4. A module as claimed in any preceding claim, comprising a PCB or PWB substrate.

5. A module as claimed in claim 4, wherein the antenna arms comprise tracks formed, printed or etched on the substrate.

6. A module as claimed in claim 4 or 5 depending from claim 3, wherein the radio component is formed, printed or etched on the substrate.

7. A module as claimed in any one of claims 4 to 6, adapted to be mounted with the substrate generally perpendicular to the PCB or PWB of the electronic communications device.

8. A module as claimed in any preceding claim, wherein the connecting circuit and the antenna are configured such that the partial image current in the groundplane has a direction substantially normal to a current flow direction in the antenna.

9. A module as claimed in claim 8, wherein the antenna, in use, operates with a degree of right or left hand circular polarisation.

10. A module as claimed in any preceding claim, wherein the antenna, in use, operates with a degree of linear polarisation.

1 1. A module as claimed in any preceding claim, wherein the connecting circuit is configured to provide matching between the antenna arms and the feed connection.

12. A module as claimed in any preceding claim, wherein at least one arm of the antenna is a planar inverted-F antenna with a connection to ground.

13. A module as claimed in any preceding claim, wherein means is provided for adjusting an effective length of one or both of the arms of the antenna.

14. A module as claimed in claim 13, wherein the means comprises at least one shorting component.

15. A module as claimed in claim 14, wherein the means comprise a plurality of shorting components which are electronically switchable.

16. A module as claimed in claim 13, wherein the means comprises at least one series varactor diode in at least one of the arms.

17. A module as claimed in claim 13, wherein the means comprises at least one shunt varactor diode between at least one of the arms and ground.

18. A module as claimed in any preceding claim, wherein the connecting circuit is configured to apply a 180 degree phase shift between the arms of the antenna.

19. A module as claimed in any one of claims 1 to 17, wherein the connecting circuit is configured to apply a phase shift other than 180 degrees between the arms of the antenna.

20. A module as claimed in any preceding claim, wherein one of the arms of the antenna is electrically grounded.

21. A module as claimed in claim 20, wherein the grounded arm of the antenna acts as a parasitic antenna and the other arm acts as a driven monopole.

22. A module as claimed in any preceding claim, further comprising switching circuitry adapted selectively to ground one or other of the arms of the antenna and/or to vary a phase shift between the arms of the antenna.

23. A module as claimed in any one of claims 1 to 21 , further comprising electronic tuning circuitry adapted to vary a degree of grounding of one or other of the arms of the antenna and/or to vary a phase shift between the arms of the antenna.

24. A module adapted for connection to a printed circuit board (PCB) or printed wiring board (PWB) of an electronic communications device, substantially as hereinbefore described with reference to or as shown in the accompanying drawings.