INTRODUCTION

[0001] Electronic devices rely on wireless connectivity to an increasing number of resources, requiring operation on many frequency bands. The very compact nature of the equipment design, together with requirements for low weight and low cost, result in stringent design constraints for the antennas needed to provide the requisite radio services.

[0002] Both cost and size can often be reduced if a single antenna is able to operate on multiple frequency bands. Multi-band operation is of particular advantage when the associated radio transmitter/receiver chip is able to operate on multiple bands.

[0003] The present invention extends the application of loop and notch antennas to multiple frequency bands.

BACKGROUND

[0004] The use of loop and notch antennas is well known, but the operation of these antennas is generally restricted to a single frequency band.

[0005] A notch antenna formed in an edge of an aircraft wing is known from Burberry, R.A.; "Electrically Small Antennas"; IEEE Colloquium on Electrically Small Antennas; 23 ^rd October 1990; pp 1-5.

[0006] Also known, for example from "Electrically small loop antenna using the MNG ground plane structure" by Joong-Kwan Kim, Yong-Jin Kim and Hong-Min Lee, IEEE Antennas and Propagation Society International Symposium, 2008. AP-S 2008, pp 1-4, is a loop antenna that has very small dimensions in terms of the operating wavelength, and is suitable for incorporation into the groundplane of a printed circuit board. While such arrangements are capable of operating over a single wide frequency band, they are not capable of operation in separate widely spaced frequency bands, being perhaps an octave or more apart.

[0007] Figure 1 shows a typical notch antenna in which a printed circuit substrate having a continuous area of copper groundplane 1 on at least one side is provided with a loop antenna formed by an aperture 2 and closed by a conductor 3 in series with a tuning capacitor 4. The loop is excited by a feed conductive member 5. The feed member 5 is connected to the groundplane 1 at its extremity 6 and is fed from an attached transmitter or receiver across a gap at 7. The position of the feed conductor 5 and the area embraced inside it are design parameters that can be selected to optimise the impedance bandwidth and the efficiency of the antenna.

[0008] The designations "notch antenna" and "loop antenna" are somewhat arbitrary. A classical loop is a magnetic dipole, having a closed current path around its periphery. A classical notch is a quarter wavelength long, but may be loaded by a capacitance at its open end. The antennas of the present invention are hybrid structures whose characteristics depend on the value of the tuning capacitance placed across their open- circuit ends. A notch having a tuning capacitor with a low reactance across its open end may be regarded as a form of loop.

[0009] Niamien, M.A.C. et al.; "A Compact Dual-Band Notch Antenna for Wireless Multistandard Terminals"; IEEE Antennas and Wreless Propagation Letters, Vol. 11 ; 2012; pp 877-880 discloses a capacitively-loaded notch antenna that makes use of a single notch and an impedance matching network to provide dual-band operation.

[0010] The arrangement described by Niamien et al is an open-circuit quarter-wave notch or slot having a capacitive stub provided between its edges at a position between the feed line and the short-circuit end of the notch. The present invention does not employ such a capacitive stub and enables the use of a much shorter notch (12mm x 7mm compared with Niamien's 36mm x 6mm). Despite its smaller dimensions the impedance bandwidth demonstrated in the lower operating band is much wider than that obtained by Niamien's substantially larger arrangement.

[0011] The dependence of the bandwidth and efficiency of small antennas on currents flowing in their associated groundplanes has received a great deal of study. Vainikainnen et al.; "Resonator-based analysis of the combination of mobile handset antenna and chassis"; IEEE Trans AP; vol. 50; No 10; Oct. 2002; pp. 1433-1444 showed the dependence of bandwidth on the dimensions of the groundplane and the present inventor, Collins, B.S.; "Improving the RF performance of clamshell handsets"; IEEE International Workshop on Antenna Technology (iWAT 2006); pp. 265-268 showed simulations of the excitation of the groundplane modes that account for this behaviour. Antennas for handsets and other small devices are typically monopoles or PIFAs physically positioned at the end of the groundplane. These are unbalanced antennas that we may regard as end-exciting the groundplane at its high impedance point. With the extension of the frequency bands in use for mobile phone services, the design of these antennas has developed to allow the coverage of multiple bands; a branched PIFA on a 100-mm long platform will typically cover 824-960 MHz and 1710-2170 MHz.

[0012] As the dimensions allowed for the antenna are reduced, the Q-factor of the antenna increases and the gain/bandwidth performance is reduced. What is not obvious is the limit for the dimensions of the exciting device - generally regarded as the antenna - and the performance of the platform as a whole.

[0013] In addition to the more usual monopoles, PIFAs, and their derivatives, antennas positioned at the end of the groundplane have included magnetic dipole antennas (MDAs) and isolated 'islands' used to drive the groundplane. Examples include included antennas for the UHF-TV band (J. Holopainen, Antenna for handheld DVB terminal, MSc Thesis, Helsinki University of Technology, 2005) and antennas for various single mobile radio and other bands (J. Anguera, A. Andujar and C. Garcia, Multiband and small coplanar antenna system for wireless handheld devices, IEEE Trans AP, in press, DOI: 10.1109/TAP.2013.2253297).

BRIEF SUMMARY OF THE DISCLOSURE

[0014] The present application is directed to a class of capacitively-loaded antennas intermediate between loops and notches. These are intrinsically current-drivers and perform best when placed away from the ends of the host platform. Notch antennas have a long history of application in the HF and VHF bands on aircraft and trains, but they are usually regarded as having a high Q and a correspondingly narrow bandwidths. A capacitively-loaded notch can be regarded as a configuration intermediate between a loop (in which the loading capacitance C is effectively very large) and a notch (in which C = 0). For given loop dimensions the resonant frequency falls as C is increased.

[0015] Antennas for mobile handsets and M2M platforms typically operate in two groups of operating frequency bands; this requirement is usually addressed by using branched monopoles or branched PIFAs, in which long and short radiating elements, serving the lower and upper frequency bands are excited in parallel.

[0016] Viewed from a first aspect, there is provided a multi-band antenna device comprising an electrically conductive groundplane having at least first and second apertures formed therein, each aperture having at least first and second opposed edges, a feed structure configured to feed an RF signal to the first and second apertures in series, and at least one electrically conductive strip extending into or across the first aperture from the first edge towards the second edge and including or providing a first tuning capacitance between the first and second edges, wherein a first antenna having a first operating frequency is defined by a loop comprising a perimeter of the first aperture and the electrically conductive strip, and wherein a second antenna having a second operating frequency is defined by a loop comprising a perimeter of the second aperture. [0017] The second aperture may also be provided with at least one electrically conductive strip extending into or across the second aperture from the first edge towards the second edge and including or providing a second tuning capacitance between the first and second edges.

[0018] The first and/or second aperture may be formed at an edge of the groundplane so as to take the form of a notch with a mouth portion at the edge of the groundplane. The at least one electrically conductive strip, which may include a discrete capacitor such as a chip capacitor or may have a portion disposed generally parallel to the edge of the aperture to provide the necessary tuning capacitance, may be provided across the mouth of the notch.

[0019] The first and second opposed edges of the first and/or second aperture may be substantially parallel. The first and/or the second aperture may be substantially rectangular.

[0020] The first and second apertures may have substantially equal dimensions, in which case the operating frequencies of the first and second antennas are determined by the choice of capacitive component in the electrically conductive strip.

[0021] Alternatively, the first and second apertures may be differently dimensioned, for example with different lengths and/or widths, so as to allow operation at respective first and second frequencies.

[0022] The first and second apertures may be located generally next to each other, or one may be nested inside the other, for example by way of an appropriately configured conductive strip.

[0023] In some embodiments, the first aperture may be configured as an aperture wholly contained within the conductive groundplane (i.e. without a mouth portion at the edge of the groundplane), and the second aperture may be configured as a smaller, narrower aperture having a mouth portion defined by an edge of the first aperture. A capacitor may be connected across the mouth portion of the second aperture.

[0024] The feed structure may be configured as an open-circuit transmission line stub, and may be configured to have a different width across the first aperture than across the second aperture so as to allow the impedance bandwidth to be optimized at each operating frequency. Other feed structures may be used as appropriate.

[0025] Viewed from a second aspect, there is provided a multi-band antenna device comprising an electrically conductive groundplane having an aperture formed therein, the aperture having at least first and second opposed edges, a feed structure configured to feed an RF signal to the aperture, and at least one electrically conductive strip extending into or across the aperture from the first edge towards the second edge and including or providing a tuning capacitance between the first and second edges, wherein a first antenna having a first operating frequency is defined by a loop comprising a perimeter of the aperture and the electrically conductive strip, and wherein a second antenna having a second operating frequency is defined by the loop acting in combination with a series reactance contributed by the feed structure.

[0026] Preferred features of the first aspect apply equally to the second aspect as the context allows.

[0027] Embodiments of the present invention provide for the use of at least one resonant loop or notch radiating element excited by a feed structure fed from a single connection to an external circuit.

[0028] Certain embodiments are particularly useful for use as antennas for devices that are worn on the human body, such as wearable computing devices worn on the wrist or on other body parts. This is because embodiments of the present invention are relatively resistant to detuning and loss caused by proximity to a user's body.

[0029] Accordingly, embodiments of the present invention may be configured as a wearable strap, such as a wrist strip, arm strap or leg strap. The antenna device and groundplane may be incorporated into the strap. Optionally, an inner surface of the strap may be lined with foam or some other appropriate dielectric material to maintain a suitable separation between the antenna/groundplane and the user's body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a prior art notch antenna;

Figure 2 shows an embodiment comprising two differently-dimensioned loop antennas having different operating frequencies;

Figure 3 shows an embodiment comprising two similarly-dimensioned loop antennas having different operating frequencies;

Figure 4 shows an alternative embodiment comprising two differently- dimensioned loop antennas having different operating frequencies;

Figure 5 shows a further alternative embodiment comprising two differently- dimensioned loop antennas having different operating frequencies; Figure 6 shows an embodiment with a smaller loop nested within a larger loop; Figure 7 shows a prior art notch antenna;

Figure 8 shows a pair of notch antennas of the type shown in Figure 7, the notches being differently dimensioned;

Figure 9 shows an embodiment of the present invention comprising one notch and one loop antenna;

Figure 10 shows an embodiment comprising one notch embedded within one loop;

Figure 11 shows an embodiment comprising one notch and two loop antennas; Figure 12 shows an embodiment with an alternatively-configured capacitive loading;

Figure 13 shows an alternative embodiment with a single notch;

Figures 14 and 15 show variations of the embodiment of Figure 13;

Figure 16 shows a prior art slot antenna;

Figures 17 to 19 show alternative embodiments comprising a closed perimeter aperture formed away from an edge of a groundplane;

Figure 20 shows a variant of the Figure 2 embodiment;

Figure 21 shows a single notch antenna;

Figure 22 shows a first experimental embodiment in detail;

Figures 23 and 24 show efficiency plots for the Figure 22 embodiment;

Figures 25 and 26 show radiation patterns for the Figure 22 embodiment;

Figure 27 shows a second experimental embodiment in detail;

Figure 28 shows an efficiency plot for the Figure 27 embodiment; and

Figure 29 shows a Smith chart plot for the Figure 27 embodiment.

DETAILED DESCRIPTION

[0031] Figure 2 shows an embodiment of the present invention comprising two loop antennas having different operating frequencies. The multi-band antenna includes a conductive groundplane 1 forming part of a printed circuit board, with first and second apertures or notches 1 1 , 12 formed at an edge 10 of the groundplane 1. A first loop comprises the aperture 11 in association with the conductive element 13 and tuning capacitor 15, while a second loop comprises the aperture 12 in association with the conductive element 14 and the tuning capacitor 16. A feed conductor 17 is located on a different layer of the printed circuit board from the groundplane 1 and extends across mouth portions of both apertures 1 1 , 12, forming a microstrip line from an input port 17 and terminating in an open or short circuit at 18. The feed conductor 17 may be straight and aligned parallel with the bottom of the apertures 1 1 , 12 as shown, or may be bent or angled in order to separately optimize the excitation of each loop. The width of the feed conductor 17 may be constant throughout its length or it may be provided with regions having different widths, computed or derived by experiment to optimize the impedance bandwidth of the antenna in each operating frequency band.

[0032] Figure 3 shows an embodiment in which the dimensions of the apertures 1 1 and 12 are equal and the different tuned frequencies of the loops are determined solely by the choice of the values of the capacitors 15 and 16. It has been shown that it is possible to cover the unlicensed ISM frequency bands used for wireless local area networks (2.4- 2.85GHz and 4.8-5.8GHz) using this arrangement, with total antenna dimensions of 7mm x 9mm.

[0033] Figure 4 shows an alternative arrangement applicable for large frequency separations between the operating bands in which two loops have different lengths and widths. In this example the feed conductor 17 is bent through a right angle; this geometry provides considerable freedom of choice of the individual excitations of the two loops. Figure 5 shows a further implementation in which the feed 17 is arranged from the closed end of one of the loops. This can be chosen for reasons of compatibility with the physical layout of other components sharing the same circuit board, or to provide simple adjustment of the feed 17 arrangement during optimization.

[0034] Figure 6 shows an embodiment in which a smaller loop 20 is nested within the area occupied by a larger loop 21.

[0035] In a loop antenna the resonant frequency is generally determined by the inductance of the conductors from which the loop is formed and the capacitance across any gaps in the conductors forming the loop. In the format shown in Figure 1 , the inductance is predominantly provided by the narrow conductive strip 3 closing the aperture in the groundplane 1. The resonant frequency is determined by this inductance in series with the tuning capacitance 4 combined with the length of the internal perimeter of the loop formed in the groundplane. An alternative form of prior art antenna comprises a simple notch 40 formed in a groundplane 1 as shown in Figure 7, where the length of the aperture 40 is chosen to make the antenna self-resonant at the desired operating frequency. [0036] Figure 8 shows a combination of unloaded notch antennas 50, 51 , while Figure 9 shows a combination of a loop 50 and a notch 52 in accordance with an embodiment of the invention.

[0037] Figure 10 shows an embodiment in which a notch 55 is set within a loop element 56.

[0038] Figure 11 shows a combination of one notch 50 and two loop elements 52, 53 excited by a common feedline 17. The loop elements 52, 53 are in the form of a pair of adjacent apertures having conductive strips 13, 14 with capacitive components 15, 16 across their mouth portions at the edge 10 of the groundplane 1.

[0039] Figure 12 shows a notch antenna 50 and an adjacent loop antenna 52 excited by a common feed structure 17 in which a loading capacitance 57 is provided at a point within the area of the loop 52.

[0040] Figure 13 shows an embodiment in which only a single notch or loop structure 60 is used. The lower frequency resonance is created by the combined operation of the notch 60 together with the series reactance created by the extended open-circuit feedline 17. The upper frequency resonance is controlled by the dimensions of the notch 60 together with value of the tuning capacitance 15 positioned at the end of the conductive element 13 across the mouth of the notch 60.

[0041] Figure 14 shows an embodiment similar to that of Figure 13, but in which the tuning capacitor 15 is replaced by a printed line or structure 65 which creates a capacitance to the groundplane 1 and an edge of the notch 60.

[0042] Figure 15 shows an embodiment similar to that of Figure 14, but in which the open-circuit feedline 17 is bent in order to conserve space on the groundplane 1. In a further alternative, the feedline 17 could be terminated using a discrete capacitor having the value required to effect tuning of the lower frequency resonance to the required frequency.

[0043] In all arrangements the dimensions of the loop or notch are frequently chosen to balance requirements for high radiation efficiency and low VSWR with the need to conserve space on a small crowded platform. The required physical dimensions of the loops/notches are dependent on the dimensions of the groundplane in which the at least one loop or notch is cut, as well as the bandwidths over which operation is required.

[0044] The application of the invention need not be constrained to an arrangement of one or two loops or notches, but may be extended to three or more radiating structures. [0045] In each of the arrangements illustrated the tuning capacitors may comprise one or more discrete physical components or may be provided by conductive structures formed on the circuit board that supports the antenna. The location of the at least one tuning capacitor along the conductive element is not critical, although the choice of its position may change the capacitance value required to tune resonance to a specified frequency. The conductive element may be positioned across the end of the aperture formed in the groundplane as illustrated in Figures 1 to 6, 9 to 1 1 and 13 to 15 but it may also be positioned within the aperture as shown in Figure 12.

[0046] In place of tuning capacitors having fixed values as shown in the exemplary embodiments above, it is possible to tune one or more of the resonant loops/notches by the use of capacitors whose effective capacitance can be varied by means of an external signal, allowing adjustment of the tuned frequency and operating frequency band. Such variable capacitors may also be used to terminate the open circuit end of the feedline 17. Suitable components for this purpose include switched capacitors, variable-capacitance diodes or digitally controlled variable capacitors.

[0047] While the exemplary embodiments shown in Figures 2 to 15 are placed on the outer edge 10 of the groundplane 1 , some embodiments may comprise apertures formed within the groundplane, having no opening at its edge.

[0048] In Figure 16, there is shown a groundplane 1 with an aperture 60 having a continuous perimeter, and a feed 17 which causes the aperture 60 to radiate. This is a known type of slot antenna, where the length of the slot or aperture 60 is typically half a wavelength.

[0049] In Figure 17, the perimeter of the radiating aperture 60 is penetrated by a further aperture 70, having the effect of increasing the perimeter and inductance of the aperture 60 and reducing the resonant frequency thereof. The aperture 70 may be shaped and oriented in any convenient manner, may be positioned at any convenient location around the perimeter of the aperture 60 and may be formed or meandered to reduce the space occupied by the whole arrangement.

[0050] In Figure 18, a capacitor 71 is placed across the junction between the aperture 60 and the aperture 70 to increase the total effective inductance, further reducing the resonant frequency of the aperture 60.

[0051] An embodiment is shown in Figure 19, where the aperture 60 is connected to a second aperture 70 by way of a capacitor 71. The capacitor 71 may be fixed or may be variable in value to permit tuning of the resonant frequency. [0052] The effective value of the variable capacitors may be controlled using an algorithm implemented on a microcontroller which may be integrated with the associated radio apparatus.

[0053] Some specific experimental results will now be described in detail.

[0054] Referring to Figure 20, two separate notches 1 1 , 12 were used, fed in series by a common feedline 17. This arrangement has a large number of independent dimensions (degrees of freedom) - a situation that can usually be exploited by the antenna designer. These include the width, depth and separation between the two notches, as well as the loading capacitances C1 and C2, the position and Z ₀ of the feedline and its terminating capacitance.

[0055] A single notch 11 , embedded in a groundplane 1 , is shown in Figure 21. The dimensions chosen were of the order of 0.1λ x 0.05A, and the notch 1 1 was excited by means of a microstrip line 17 passing across the short dimension of the notch 11 and terminated as a capacitive open circuit stub. The resonant frequency of the antenna was adjusted by capacitive loading of the open end of the notch 1 1 and the distributed capacitance terminating the feedline. Loading of the notch 1 1 was variously realized by using a chip capacitor C1 or by arranging a narrow, and often extended, gap between the two sides of the notch at or near its open end. With no loading capacitance the antenna forms a classical notch, while if the capacitance is large the antenna becomes a classical loop. With the chosen values of capacitance the antenna has characteristics intermediate between these forms.

[0056] The antennas of Figures 20 and 21 were constructed on 0.8mm thick FR4 with the groundplane and notch on one face and the feed on the other face.

[0057] Typical loop antennas are fed by means of a small loop contained within the main radiating loop; by choosing the right relationship between the areas of the two loops, the resistive component of the input impedance is arranged to be 50 ohms at resonance.

Notches are fed across their narrow dimension, if possible at a position chosen to provide

R _in = 50 ohms. In its simplest form, the antenna comprises a capacitively-loaded notch cut in the groundplane and fed by a microstrip line passing across it at a position chosen to yield R _in = 50 ohms at resonance. The unfed end of the feed line extends beyond the edge of the notch and is terminated in an open circuit, the length of overlap being chosen to provide the required operating frequency and bandwidth.

[0058] In order to obtain operation on non-contiguous frequency bands, two loaded notches were positioned close together and fed by a single microstrip line passing across both notches, feeding them in series. The most significant modification made to these basic schemes was the use of closely-spaced PCB conductors to provide the loading capacitances; these were simple to adjust, although they may have contributed some loss that could be avoided in a production design.

[0059] To ensure that the measured results were influenced as little as possible by the feed cable, the coaxial input connector was positioned near the mid-point of the PCB and a coaxial choke was used to suppress currents on the cable outer. In practice it was found that even without the choke, touching the cable with a hand had little influence on the measured input impedance.

[0060] The most surprising result found during the course of this work was that it was possible to obtain a very satisfactory dual-band response from a single notch fed in the manner described.

[0061] Experimental work began with the series fed, dual notch configuration shown in Figure 22. By optimizing the feed structure and the capacitive loading arrangement, this provided a measured terminal efficiency greater than 50% over almost all the bands 824- 960 MHz and 1710-2170 MHz. The very large number of dimensions needed to specify its geometry is indicative of the large number of degrees of freedom that are available in the design of this apparently simple antenna. A copper capacitive loading strip (indicated by the dashed rectangle) is 17.1 mm long and overlaps the groundplane by 6.0mm at its right hand end. The feedline and loading strip are on the opposite face of the 0.8mm FR4 PCB to the groundplane and notches. The chip capacitor has a value of 1 pF

[0062] The overall dimensions of this antenna were 18 mm x 13 mm (0.05A x 0.034A at 824 MHz). Its efficiency, shown in Figure 23, was limited by its impedance bandwidth, which could probably be extended by further optimization and the use of an input matching circuit. By extending its overall dimensions to 23 mm x 23 mm it proved possible to extend the useful bandwidth (efficiency >50%) of a dual notch to 730-960 MHz and 1700- 2700MHz as shown in Figure 24. Radiation patterns of this antennas are shown in Figures 25 and 26, with Figure 25 showing polarization sum radiation patterns at 725MHz and 960MHz, and Figure 26 showing polarization sum radiation patterns at 1700MHz, 2200MHz and 2700MHz. In each case, the PCB lies in the x-y plane with its long axis along the 0/180 degree axis. Dual notches of generally similar configuration can be designed to cover band combinations such as GPS/WiFi (2.4 GHz), and WiFi 2.4/5 GHz.

[0063] The radiation patterns in Figures 25 and 26 are plotted for the total power in both polarizations. It will be seen that even in the high band the patterns display only two significant notches, these being in the plane of the PCB. They are not as deep as would be obtained from typical end-mounted PIFAs. [0064] A single loaded notch antenna is also capable of providing operation in two noncontiguous frequency bands. An example of this is shown in Figure 27, with measured terminal efficiency in Figure 28. The feed track is 2.5mm wide except for the section across the notch, which is 1.3mm wide. The low band efficiency of this antenna is very high and could be improved by some re-positioning of the optimum frequency. The efficiency at the edges of the low band is almost the same as the reflection loss caused by the band-edge VSWR; dissipative losses appear to be very small. High-band efficiency may have been reduced by dissipative loss caused by the very narrow capacitive loading gaps and could be improved by using one or more chip capacitors in their place. Figure 29 shows a Smith chart plot of the impedance of the single notch pentaband antenna of Figure 27 at the coaxial input connector with no added matching network.

[0065] As with most small antennas on electrically small platforms, some antennas described in the present application operate by driving current in the host PCB. They operate best when placed near the centre of a long edge of a groundplane (for example 133mm x 60mm). As the antenna is moved towards the corner of the PCB the impedance bandwidth and efficiency of the antenna both fall. In the configurations discussed here, the antenna operates as a low-impedance current driver. By contrast, conventional end- mounted PIFAs and monopoles act as high impedance electric-field drivers and are most effective when placed on the (high impedance) ends of a groundplane of the dimensions used.

[0066] A further interesting difference between these antennas, which can be regarded as magnetic dipoles, and PIFAs/monopoles is their detuning behaviour. The resonant frequency of a PI FA or monopole is typically reduced when approached by the user's body, the effect being caused by additional capacitive loading of the resonant element. By contrast, when a loop antenna is approached by a parallel conducting plane, its resonant frequency increases because the conducting plane acts as a short-circuited turn, reducing the inductance of the loop and causing a consequent increase in resonant frequency. This characteristic is easily demonstrated for the antennas described. If the loading capacitance is very small (effectively a classical notch), the capacitive effect of an approaching conductor dominates and the resonant frequency falls. As the loading capacitance is increased, the antenna behaves more like a loop so there will be a 'sweet spot' where the behaviour lies between the two and the resonant frequency is little affected. This does not imply that no loss is created by the approach of a user's body, but its effects are likely to be less severe than with a conventional PI FA or monopole.

[0067] As with any embedded antenna, radiation depends on the excitation of groundplane currents, so the design of the groundplane must be carried out with this function in mind. Continuous flood groundplanes are preferably provided on both faces of the PCB, bonded together with vias at regular intervals around their perimeters. Small components may be mounted through apertures in the groundplane, but large components should be covered with screening cans to allow currents to flow continuously in the groundplanes. This practice not only optimises the efficiency and bandwidth of the antennas, but also reduces unwanted coupling that can induce noise into receiving systems.

[0068] The radiating system characteristic of both notch and PI FA antennas on small platforms combines a small (implicitly high-Q) exciting device coupled to a larger, low-Q radiating PCB. Such a system usually has a combined Q given by:

1/Q = 1/Q1 + 1/Q2. (1)

[0069] In the case of these embedded antennas it is unclear whether this applies, and there seems to be no recognised expression for the minimum dimensions (and maximum Q) of the 'antenna'.

[0070] It has been demonstrated that in combination with a hybrid capacitively/inductively coupled input line, small embedded loaded-notch antennas are capable of providing usefully wide bandwidths and high efficiency in two non-contiguous frequency ranges.

[0071] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do 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.

[0072] 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 restricted to the details of any 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.

[0073] 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.