AU784452B2 - Dual band antenna - Google Patents

Description

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P/00/011 28/5/91 Regula Von 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: DUAL BAND ANTENNA The following statement is a full description of this invention, including the best method of performing it known to us 1 Dual Band Antenna Field Of The Invention The present invention relates to antenna devices, and, more particularly to dual band antenna devices adapted for mounting on glass or similar dielectric surfaces.

The invention has been developed primarily for use in PCS, CDMA, TDMA, AMPS, GSM and wireless LAN and ISM telecommunication systems and will be described herein after with respect to those applications. However, the invention is not limited to that particular field of use and is also applicable to in-vehicle and other portable and stationary applications, and other telecommunications systems.

Background Art Vehicle mounted antenna devices of various sorts have been used to receive UHF and other band signals for many years. One known device utilises external whip antennas which are capacitively or inductively linked to a coupling unit inside the glass, which in turn is linked to a cellular phone or other transmitting and/or receiving apparatus.

Another known device involves a generally planar antenna adhered to the inside of the window. Most previously known devices were designed to function with only a single frequency band for example, the prevailing cellular telephone frequency, typically 800 900 MHz.

Increasingly, however, demand exists for an antenna which is capable of dual band operation. One aspect of this demand relates to dual band GSM telephone standards, which operate on 900 and 1800 MHz in Australia, most of 6 2 Europe and much of Asia. In addition, some nations (such as the USA and Canada and some countries in Asia) also operate cellular telephony in the 800 MHz and 1900 MHz bands. Such cellular telephony systems include PCS, TDMA, CDMA and AMPS Systems.

Furthermore, other frequencies are either now in use or proposed for use.

For example, the recently launched "3G" or Third Generation mobile network operates in the 1900 to 2200 MHz frequency range and is rapidly being deployed in large cities to address increasing consumer bandwidth needs.

Some dual band vehicle and non-vehicle mounted antenna devices have been proposed, providing varying degrees of suitability. However, the dual bands to which the antenna is resonant are generally related, for example, as multiples or harmonics. It is important to appreciate that in many of these applications it is necessary not just to receive but also to transmit.

Typically, known dual band devices have operated by exciting two resonant frequencies by means of either a single feed or a power divider/phase shifter combining the frequencies into a single port.

Mobile telephone users who seek to maximize the performance of their mobile telephones can employ externally mounted antennas to overcome issues of vehicle cabin shielding, wherein the cabin of the motor vehicle cabin effectively blocks or shields the mobile telephone from receiving and transmitting a signal.

The use of an externally mounted antenna significantly boosts mobile telephone performance in the field and with higher frequencies now employed or envisaged, the resultant level of cabin shielding from signals at these frequencies will increase.

(t 3 The use of mobile telephones continues to expand and the performance of these devices with the use of an external antenna is severely restricted, with cabin shielding by motor vehicles contributing a shielding effect of greater than in the case of 900 MHz applications, more than 12 dB in the case of applications in the 1800-1900 MHz band and, it is anticipated, even higher levels of shielding as the introduction of the 2.1 GHz (nominal) "3G" services come into use worldwide. Therefore, the use of externally mounted antennas is expected to increase markedly.

This increase will be further amplified by the high level of public concern over levels of exposure to RF emissions from mobile telephones. In the case of many users, a choice is made to minimize their own exposure (or that of employees or family) by ensuring that all of the RF power from the phone is effectively transferred to the exterior of the vehicle by the use of a "hands free" kit and an appropriate external antenna.

The most common of vehicle mounted cellular antennas in the marketplace are glass mounted antennas whereby the antenna radiator (whip section) is mounted externally on the vehicle and the RF energy is coupled to and from this radiator via a coupling box which is located inside the vehicle.

The prior art includes a number of variations, all of which provide single band coverage but do not properly provide for the coupling of two, significantly separated and not necessarily related bands of frequencies from, for example, the inside of the vehicle to the outside.

A further issue with many existing dual band devices is that they are relatively complicated and expensive. Some known antennas have used planar t 4 or similar circuits which are inherently broadband, however, they display inefficiency in the field with the antennas exhibiting limited market acceptance.

For example, PCB slot antennas in their conventional form and at low-microwave frequencies generally require a large ground plane, and in most base station antenna applications, this is not an issue as physical size is rarely a major concern to designers.

In mobile antennas however this is not the case, as the visual impact of a large, full sized ground plane would be cumbersome, unattractive and enjoy limited consumer or industry acceptance.

Dual band antennas for cellular telephone engineering are widely discussed in the literature and references are provided below. However, the majority of the literature refers specifically to the cellular base station product rather than to mobile applications.

In terms of dual band antenna matching and pattern manipulation, the base station antenna design approach is a relatively mature technique whereas for glass mounted mobile antenna designs, the majority of the focus has historically been based on achieving an adequate match, with little or no focus on the overall performance of the product in the field. As a result, many of the so called dual band mobile antennas in the market exhibit inefficient performance in one or other of the target bands.

In addition to the abovementioned single band prior art antennas, some prior art also exists for multiple band coverage substrate mounted cellular antennas. Reference is made to the following prior art documents as examples: US Patent No. 5343214 in the name of The Allen Telecom Group, Inc.; Australian Patent No. 645084 in the name of Panorama Antennas Ltd.; US Patent No. 4328799 in the name of Avanti Research and Development Inc.; US Patent No. 4621243 in the name of Harada Kogyo Kabushiki Kaisha; and W096/38873 and US Patent No. 6054953 in the name of Allgon AB.

In general, however, the art in these antennae have been inefficient over two unrelated bands. They employ a coupling on a single band (generally the lower of the two bands) and the upper band, while matched within the coupling band for resonance, is not efficiently coupled and radiated.

The result in practice, for example during transmission of an RF signal, is that the prior art exhibits unsatisfactory coupling and performance in the upper band of operation. It can be the case that the RF energy of the upper band is radiated directly from the coupling box or from the actual feeder cable rather than passed on to and subsequently radiated by a whip element which is mounted externally.

S' Summary of the Invention It is an object of the present invention to provide an effective dual band antenna. A further object of the present invention is to provide an interface 20 element for use in facilitating the coupling of RF radiation intermediate h an RF circuit and a radiating element.

According to a first aspect of the invention there is provided an interface element for use in a dual band RF antenna, the interface element selectively disposable in the near field of an RF transmitting circuit on a first side and an adjacent RF radiator on a second side, the interface element including a patch element having at least two notches disposed thereon wherein the dimensions of the patch element and notches are predetermined to provide for the patch element to be substantially tuned to the lower frequency of the dual band and the notches to be substantially tuned to the upper frequency of the dual band.

Preferably, a dielectric substrate in the form of glass is disposed intermediate the interface element and the RF transmitting circuit.

Preferably, the interface element includes mounting means for receiving the RF radiator.

Preferably also, the interface element is formed from a brass plate having threaded apertures to receive screws for mounting the RF radiator thereto.

A protective coating is preferably disposed about the interface element and the RF radiator when mounted together.

Preferably, the RF radiator is a dual band whip antenna including two coils, one coil being substantially tuned to the upper frequency and the other coil being substantially tuned to the lower frequency. This dual coil whip radiator is preferably designed to deliver 3dB gain in both the upper and the lower frequency bands.

In other preferred forms, the RF radiator is a dual band whip antenna including a single coil, the coil being substantially tuned to the upper frequency and the overall length of the single coil antenna being substantially tuned to the lower frequency. This single coil whip radiator is designed to deliver unity gain in both the upper and the lower frequency bands.

According to another aspect of the invention there is provided a dual band RF antenna including: a coupling module for disposal on one side of a dielectric substrate and including: a two sided printed circuit board (PCB) having: a substantially elliptical slot forming a closed path disposed on the first side so as to be adjacent the dielectric substrate; a matching circuit including a strip line RF feed element ooo* 8 [PAGES 8-10 ARE INTENTIONALLY BLANK] 11 disposed on the second side of the PCB; a plurality of tuning elements extending from the first side of the PCB to the second, the tuning elements having predetermined composition, displacement and size so as to selectively control the localised dielectric behaviour of the PCB; and RF input/output means in communication with the strip line feed element; a shielding member disposed adjacent the matching circuit and having predetermined dimensions corresponding to the dimensions of the elliptical slot; adhesive means for affixing the coupling module onto the one side of the dielectric substrate; an interface element for disposal on a second side of the dielectric substrate and including a patch element having at least two notches disposed thereon wherein the dimensions of the patch element and notches are predetermined to provide for the patch element to be substantially tuned to the lower frequency of the dual band and the notches to be substantially tuned to the upper frequency of the dual band; and an RF radiator disposed adjacent the interface element.

Preferably, the dimensions and composition of the strip line RF feed element are predetermined so as to provide a predetermined input impedance at the RF input/output means and the RF input/output means is a coaxial connector or strip line junction.

In preferred embodiments of the invention, the matching circuit is of a 12 predetermined shape and disposed about the tuning elements on the second side of the PCB wherein the tuning elements are metallic pins. However, in alternative embodiments of the invention, the tuning elements are formed by conductively coating a hole extending through the PCB material. The conductive holes are of a predetermined cross-section which is preferably constant through the PCB.

Preferably also, the PCB material is selected from the group including, but not limited to, reinforced fibreglass material (one such form being known in the art as PTFE based material, tetrafunctional epoxy/glass rigid laminate, low loss silicon based substrate materials and plastic/metal laminate material.

Preferably, the adhesive means is double sided tape and the shielding member is a metallic plate composed of brass.

In other embodiments, the dual band RF antenna includes a box-like dielectric cover including a first and second major face wherein the shielding member is mounted adjacent to the inside of one major face and the PCB element is mounted adjacent the other major face wherein the substrate is a glass onto which the first major face is adhered.

Preferably, the interface element includes mounting means for receiving the RF radiator.

In other preferred forms, the interface element is a formed brass plate having threaded apertures to receive screws for mounting the RF radiator thereto.

Preferably, a protective coating is disposed about the interface element and the RF radiator when mounted; wherein the RF radiator is a dual band radiating whip antenna including two coils, one coil being substantially tuned to the upper frequency and the other coil being substantially tuned to the lower 13 frequency. Preferably also, the dual coil RF radiator provides a 3dB gain to each of the frequency bands.

In other preferred embodiments, a protective coating is disposed about the interface element and the RF radiator when mounted; wherein the Rf radiator is a dual band radiating whip antenna including a single coil, this coil being substantially tuned to the upper frequency and the overall length of the single coil whip section being substantially tuned to the lower frequency. Preferrably also, the single coil RF radiator provides a unity (0dB) gain to each of the frequency bands.

It is important to note that mobile telephone applications in the current and emerging marketplace extend well beyond the scope of mobile voice telephony as mobile telephones are increasingly providing a wider range of services and find use in data specific applications including mobile internet connectivity, data transfer and other services. Furthermore, the invention has only been explicitly described with reference to the current Australian GSM telecommunications frequencies, however, it may also be reduced such that the dual frequencies provided are, for example, the 900MHz GSM band and a 2200MHz 3G band or a 2.4GHz (nominal) wireless LAN and ISM band.

The principles of annular slot antennas are a well known in the art and are particularly common in satellite and airborne applications because of their low profile. They typically provide medium gain, omnidirectional performance for a single frequency or single band of frequencies. The simplest form of such an antenna consists of an extended thin flat sheet of metal with the slot adapted to radiate electromagnetic radiation.

14 The slot is excited by a voltage source such as a balanced parallel transmission line connected to the opposite edges of the slot, or a coaxial line. A typical bandwidth of a slot antenna might be as much as one octave but not more.

In one form they can typically consist of a circuit board with simply a connector fitted to the board and a radome covering the circuit board. The circuit board has a ground plane on one side of the board. The slot element is cut into the ground plane which is from where the radiating wave is propagated.

The slot element according to preferred embodiments of the invention is elliptical with its diameter (both inside and outside and, amongst other things, the ratio between the two) determining the frequency of operation of the slot antenna element.

In general terms, the resonant frequency of a circular annular slot antenna is determined by xg 27R n where R is the median radius of the slot, n is an integer and ?g is the wavelength on the microstrip line.

The elliptical slot element may also be termed "the coupling antenna" and its design is controlled by reference to Figure 6 and the well established criteria wherein the equation for an ellipse is given by: x 2 a 2 y 2 /b 2 1; r+r'=2a a 2 b 2 c 2 where r and r' are a function of the wavelength on the microstrip line Xg and the integer n. It is noteworthy that the design of the elliptical element is well known and not itself considered "new" in the art. Rather, the elliptical slot is simply a single element of the dual band antenna according to preferred embodiments of the invention. That is, the combination of the individual elements within the dual band antenna address the objects of the invention.

The design of the elliptical slot and the shorting pins provided on the PCB is arrived at by considering the antenna as a whole, including the interface element which, in preferred embodiments of the invention, is e-shaped for mounting on one side of the dielectric substrate, the radiating element and the "environmental" characteristics of the other components. These characteristics include the casing, the mounting tapes and the plastic used in the mounting foot itself. The design arrived at is one which takes into account the impact which each element of the device has on the overall functionality and response wherein each element provides a loading of some form and this has to be considered in the total antenna design.

In practice, it has been found that one particular geometry and/or componentry results in the tuning of the frequency bands of interest in the dual band antenna but this geometry could be altered significantly in order to take into account the impact of a change in any one element of the antenna. For example, 16 providing a substitute bonding tape to adhere the device to the dielectric substrate will generally provide a different dielectric effect and some perturbations to the geometry will be required.

Accordingly, the geometry of the elliptical element, tuning elements and interface element may be altered depending upon the components employed or target design frequencies. For example, a change in the binding means or material, housing material or dimensions, or even the dielectric insulator used as the substrate of the printed circuit board may alter the response of the antenna.

Equally, an alternative geometry may be arrived at in accordance with preferred embodiments of the present invention but with a different geometry. That is, there is no inherent ratio at play with respect to the elliptical slot element, interface element or the shorting pins and the bands over which the dual band antenna may operate. The slot element, shorting pins, patch element and other circuit elements all have an effect on the tuning, and it is the combined load of all of the elements of the device which results in the desired tuning response.

Preferred embodiments of the present invention have a wide range of possible applications. For example, embodiments of the dual band device described and illustrated herein can be used to allow a single transceiver or cellular telephone to operate in both the 900 MHz and 1800 MHz cellular telephone bands but a similar derivative of the device in a dual band form could be used to allow a single antenna to operate on any two other operational bands such as CDMA/AMPS/D-AMPS 800 MHz frequencies, PCS (1900 MHz band), UHF mobile radio, or indeed in other frequency bands not described here.

For details of specific aspects of dimensions and design, reference is 17 made to standard citations dealing with these topics which include, for example: 1. Li, Method of moment analysis of electrically large circular-loop antenna: Nonuniform currents, IEEE Proc.-Microw. Antennas Propag,. Vol 146, No. 6, December 1999.

2. Hsien, Inset microstrip line fed dual frequency circular microstrip antenna and its application to a two element dual frequency microstrip array" IEEE Proc.-Microw. Antennas Propag,. Vol 146, No. 5, October 1999.

3. Mohamed Sanad, Compact Internal Multiband Microstrip Antennas for Portable GPS, PCS, Cellular and Satellite Phones, Microwave Journal, vol 47, August 1999.

4. W.R. Deal, Planar Integrated Antenna Technology, Microwave Journal, vol 46, no. 1, pp. 22-32, July 1999.

Palit, Design and development of wideband microstrip antenna, IEEE Proceedings,. vol 146, no. 1, pp. 35-39, February 1999.

6. Yongxi Qian, A microstrip patch antenna using novel photonic band-gap structures, Microwave Journal, vol 40, no. 1, January 1999.

7. Jasik, "Annular slot,"Antenna Engineering handbook, second edition, pp.

8/12-8/15, 1984.

8. Jean-Francois Zurcher, Microstrip antennas, Broadband patch antennas, pp. 19-40, 1995.

9. Fujimoto, Essential techniques in mobile antenna systems design, Mobile antenna systems handbook, pp. 17-111, 1994.

K. Y. See, Rigorous approach to modeling electromagnetic radiation from finite-size printed circuits structures, IEEE Proceedings, vol 146,no.1, pp. 29-34, i.

18 February 1999.

11. L. Zaid Kossiavas, Dual-frequency and broadband antennas with stacked quarter wavelength elements, IEEE transaction, vol 47, no. 4, pp. 654-658, April 1999.

12. John Kraus, "Slot antenna, "Antennas, second edition, pp. 624-628, 1988.

Description Of The Figures Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which: Figure 1 is a plan view of a matching circuit according to one aspect of the invention; Figure 2 is a plan view of one side of an RF circuit according to another aspect of the invention; Figure 3 is a plan view of a matching circuit on the other side of the RF circuit of Fig. 2; Figure 4 is an isometric view of a coupling module according to a further aspect of the invention; Figure 5 is a side view of an assembled dual band antenna device according to another aspect of the invention; and Figure 6 is an illustration of an ellipse whose parameters control the design of the elliptical slot of the one side of the RF circuit of Figure 2.

Detailed Description of the Preferred Embodiments Referring to Figs.1 and 5, there is illustrated an interface element 10 for use in a dual band RF antenna 50. In the embodiment of the invention described hereinafter, the dual bands refer to the 900MHz and 1800 MHZ GSM bands currently employed widely in Australia. It is to be noted, however, that in other embodiments of the invention not described the dual bands are any combination GSM, PDS, TDMA, CDMA, AMPS and/or wireless LAN and ISM bands.

Interface element 10 includes a plate-like metallic patch element 11 in the form of a brass plate having at least two notches 12 disposed thereon. In operation, interface element 10 is selectively disposable in the near field of an RF transmitting circuit on a first side of element 10 and adjacent an RF radiator on the other.

In the embodiment illustrated in Fig. 5, element 10 is illustrated as having an RF radiator 52 in the form of a dual coil whip antenna adjacent one side and a dielectric substrate 51 in the form of a vehicle window disposed on the other side.

The substrate can be any dielectric material, however, it will be described with respect to a vehicle window, being the main application for preferred embodiments of the invention. Adjacent the other side of substrate 51 is disposed a coupling module 40 having an RF transmitting circuit. Element 10, RF radiator 52 and coupling module 40 are substantially aligned and element 10 is disposed in the near field of the RF circuit in coupling module The dimensions of the patch element are predetermined for any given pair bands and largely depend on the composition of element 10 and materials in the environment. The patch element 11 is dimensionally chosen so as to be substantially tuned to the lower frequency of the dual bands, 900Mhz in the present case. Furthermore, the notches 12 are disposed so as to be substantially tuned to the higher of the dual bands, 1800MHz presently.

The notch geometry is chosen to allow the coupling of both bands (dual band coupling) with minimal impedance mismatch in either of the two desired bands. This is achieved by removing a portion of the surface area of element in a pre-determined geometry, in order to provide a good match over both of the intended operational bands of interest. In the present preferred embodiment, the polarization planes and broadside radiation characteristics of the coupling circuit remain largely similar in both of the bands of interest in the geometry which has been arrived at.

In some embodiments of the invention not illustrated, the interface element is mountable to substrate 51 by means of an adhesive such as double-sided tape. In such embodiments, element 10 includes threaded apertures predisposed on the plate for receiving screws to mount RF antenna 52 thereto. Alternatively, element 10 and antenna 52 are mountable by means of an epoxy adhesive or double-sided tape.

Once RF antenna 52 is mounted to interface element 10, a protective coating, for example, a heat shrink plastic, may be applied about their conjoint to provide environmental protection.

The precise location and shape of notches 12 is dependant on the tuning required and the specific intended application. The patch element 11 and notches 12 employed in some preferred embodiments of the invention may be altered geometrically whilst achieving largely the same result. The nature of element 10 is that patch 11 and notches 12 provide a loading and are generally dependent on a specific application. It has been found that a particular geometry and/or componentry results in the tuning of the frequency bands of interest. For example, providing a substitute bonding tape to adhere the device to a surface 21 will generally provide a different dielectric effect and some small perturbations to the geometry will be required.

Equally, an alternative geometry for patch element 11 and/or notches 12 may be arrived at in accordance with preferred embodiments. That is, there is no inherent ratio at play between the patch element and the notches, and the bands over which interface element 10 may operate. The patch and notches each have an independent effect on the tuning and it is the combined load provided by the patches and other elements which results in the desired dual tuning response.

The principle of operation of dual band devices will now be described in general terms. As is the case in preferred embodiments, the power to the radiating element of a slot antenna is typically fed by a strip line or microstrip.

The strip line employs a ground plane on the upper side of the board as its own ground reference and its central, active element is conducted along the other side of the circuit board. The central feed element extends past or through the slot element coupling energy into the slot and thus propagating radiation of the antenna. In other words, the strip line must extend on its separate plane to intersect the volume defined by the slot element in its respective plane.

The strip line active element is not physically connected in any other way to the slot, and the coupling of the energy into the radiating slot is simply an RF phenomena based on tuning the circuits to make this possible.

The length of the strip line element underneath the slot and indeed other dimensional characteristics of this element will have a substantial bearing on the effective frequency of the slot element and efficiency of energy coupling into that slot element. The theory of slot antennas is well known in the art of antenna 22 design, and so the calculations will not be described in detail, but the interested reader is referred to the standard documents cited above.

In these arrangements, the coaxial connector or strip line junction is usually fitted to one side of the board and the strip line element referred to earlier conducts RF energy to the feed point of the slot antenna.

Reference is now also made to Figs. 2 and 3 where there is respectively illustrated the top and bottom sides 20 and 30 of a printed circuit board having an RF circuit for use in a dual band antenna preferably operating on the 900MHz and 1800MHz GSM bands.

The RF circuit is formed on a PCB composed of a reinforced fibreglass material generally known in the art as FR4. Alternatively, the PCB may be composed from PTFE based materials, tetrafunctional epoxy/glass rigid laminate, plastic/metal laminate, low loss silicon based substrate materials or any other suitable material.

Fig. 2 illustrates the top side of the PCB circuit 20 in which a substantially elliptical slot 22 is formed from masking material 21 in the form of a metallic coating. Slot 22 forms a closed path and is selectively disposable adjacent RF radiating element 52, with or without the presence of substrate 51.

Fig. 3 illustrates the other side of the PCB 30 which includes an RF matching circuit 31 of predetermined geometry.

The RF circuit further includes a plurality of tuning elements 23 extending from one side of the PCB to the other. Tuning elements 23 are preferably metallic pins of predetermined composition and size and control the localised dielectric behaviour of the PCB. In the embodiment illustrated, conductive metal 23 pins 23 are disposed substantially perpendicularly through the PCB. However, in alternative embodiments of the invention not illustrated, the tuning elements are formed by conductively coating a hole extending through the PCB material. The conductive holes are of a predetermined cross-section which is preferably constant through the PCB.

In a space about the pins (or conductive holes), the localised dielectric properties are modified sufficiently by the presence of the pins to allow the RF circuit disposed on the PCB to be more efficiently tuned to the 900MHz and 1800MHz frequency bands of interest. Small perturbations in the geometry and placement of the pins will alter the localised dielectric properties of the PCB to vary the efficiency of the RF circuit in those frequency bands.

The use of shorting pins in microstrips is a known art, however, not in the design of dual band antennas. The pins are more commonly used in the upper microwave bands at frequencies greater than 25 GHz for example.

Shorting pins are commonly used in these upper microwave bands to reduce the level of surface waves. They are also a common feature in lower band RF based circuit board construction to reduce the overall size of the circuit board which is carrying an RF component. Presently, the use of the shorting pins has been necessary in order to reduce the frequency of operation to meet the target design bands.

In preferred embodiments of the invention, the dimensions of the microstrip antenna 20, wherein the elliptical annular slot which is constructed on the PCB, have been reduced by loading the antenna with a plurality of shorting pins. The resonant frequency is altered significantly by the position and dimensions of these pins.

The number and placement of the shorting pins is modeled as an inductance parallel to a resonant LC-circuit. The designers place the shorting pins and then view the total circuit, for example, via computer modeling. The modeling allows the designers to view the new, altered resonance mode, including the impact of the shorting pins, resulting from an increased inductance due to the pins being in series with the static capacitance of the microstrip antenna.

The placement and radius of each of the shorting pins is critical and has a significant effect on the resonance of the entire circuit. By placing the pins at the corners and edges of the PCB, the lowest possible resonant frequency can be obtained. Conversely, increasing the radius of the individual pins lowers the inductive component provided by each pin, resulting in a higher resonant frequency.

The placement of the shorting pins is critical and in preferred embodiments has been arrived at largely on the basis of "trial and error" with the pins being placed, and then the circuit modeled, this process being repeated until the desired operational characteristics are obtained.

It is quite possible that by placing the pins in alternate locations a similar total circuit could be arrived at, so the actual geometry of the pin placement is considered "non critical". In a preferred embodiment, one particular combination and geometry of pin placements is arrived at to meet the required design criteria for the bands of interest. However, it is possible that another such geometry could result in a similar overall result.

Moreover, to tune the device for other bands of interest (for example to cover the US PCS and AMPS/CDMA bands or "3G" mobile telephony bands) an alternative geometry would be necessary, but this alternative geometry would be simply a derivative of the same invention.

Matching circuit 30 further includes a strip line feed element 32 for driving the elliptical slot 22 at one of two desired bands by means of RF induction between the strip-line feed 32, matching circuit 31 and the elliptical slot.

Strip line feed 32 is of predetermined composition and dimensions to provide, in combination with an input/output means, a desired impedance at the strip line feed. In the present embodiment, the impedance is 50n and a coaxial connector is employed to connect the matching circuit to an input or output signal.

In other embodiments of the invention, a strip line junction is employed instead of the coaxial connector.

It is to be noted that the dimensions of the matching circuit are dependent on environmental factors such as, for example, PCB type and the number and arrangement of tuning elements 23.

Referring also to Fig. 4, there is illustrated a coupling module 40 for encasing the RF circuit of Figs. 2 and 3. Module 40 is selectively disposable adjacent one side of dielectric substrate 51 having an interface element 10 and an RF antenna 52 on the other.

Module 40 includes the RF circuit mounted therein with PCB circuit disposed at one side of the module adjacent substrate 51 and matching circuit disposed facing the other way.

An electromagnetic shield 41 is disposed adjacent the matching circuit to 26 minimise the propagation of RF radiation from circuit 20 in the direction of matching circuit 30. Shield 41 is in the form of a brass plate having predetermined dimensions corresponding to the size of elliptical slot 22. That is, shield 41 is of similar same surface area as the elliptical slot.

Module 40 further includes a dielectric casing 42. The casing is selectively mountable to substrate 51 at the end which circuit 20 is facing, for example, by means of epoxy materials or double-sided tape.

The outer casing is preferably made from ABS plastic material. Suitable materials include ASTALAC ABS with type number ASTALAC Z48 and ASTALOY ALLOY with type number ASTALOY M150. Furthermore, the double-sided tape material may be a polyurethane foam attachment tape with high-performance acrylic on both sides. This is preferably a closed-cell polyurethane tape with acrylic adhesive on both sides. Such a foam is energy dissipating and highly conformable, which makes it especially useful for applications involving mismatched surfaces and extreme temperatures. Any tape selected should provide excellent aging properties and environmental resistance against weathering, extreme temperatures, UV exposure, oxidisation and ozone.

Referring again to Fig. 5, there is illustrated a dual band RF antenna including a coupling module 40 as described above, and having an input/output means in the form of a coaxial connector (not illustrated) for connection to, for example, a mobile telephone. Coupling module 40 is disposed adjacent substrate 51 by means of double-sided tape such that RF circuit 20 is adjacent the substrate and circuit 30 is facing away from the substrate with shield 41 disposed adjacent the matching circuit.

27 In substantial alignment with coupling module 40, interface element 10 is fixedly disposed on the other side of substrate 51 by means of adhesive doublesided tape. RF antenna 52 is fixedly attached to interface element 10 by means of screw engagement wherein antenna 52 and element 10 are also substantially aligned.

Similarly to the above description, antenna 52 is a dual coil dual band whip antenna operating in the 900MHz and 1800 MHz bands. In antenna 52, one coil is substantially tuned to the lower frequency band and the other coil is substantially tuned to the higher frequency band. In this embodiment, antenna 52 provides a 3dB gain to both the 900MHz and 1800MHz frequency bands.

Similarly to the above description, antenna 52 could alternatively be a single coil dual whip band antenna operating in the 900MHz and 1800MHz bands. In this alternative dual band whip antenna the coil is substantially tuned to the upper frequency band and the overall length of the whip antenna is substantially tuned to the lower frequency band. In this embodiment, antenna 52 provides a unity (0dB) gain to both the 900MHz and 1800MHz frequency bands.

Energy can be coupled to antenna 52 in a number of ways including a strip line feed 32 such as the kind employed in preferred embodiments of the invention. Such a strip line feed typically includes a strip line with its reference ground connected to the matching circuit 20 side of the PCB. An RF signal applied to strip line 32 induces a corresponding RF signal in the elliptical slot circuit The RF signal induced at the elliptical slot circuit is radiated generally away from the ground plane and across the substrate wherein it encounters the 28 interface element 10. Element 10 acts to facilitate the more efficient transfer of RF energy from circuit 20 to antenna 52.

Similarly, when antenna 50 is employed as a receiver, RF energy from antenna 52 is more efficiently propagated through interface element 10 through substrate 51 and to the elliptical slot circuit 20. This RF energy excites a corresponding signal across the strip line 32.

The applications for preferred embodiments of the invention are extensive in mobile applications where the antenna might be used for cellular telephony, two way radio applications and also in fixed applications where the antenna might find use as an antenna used for in-building reticulation of radio frequencies for cellular telephone and other applications. Further, the combination of the invention with GPS and other similar future technologies will extend the possible applications for the invention in both mobile and fixed installations which might be required either in the current or future RF environment.

It is emphasised that the properties of the PCB, tape and casing need to be taken into account in the design process, as they will affect the resonant frequency of the antenna. The resonant frequency may shift 20 MHz or more in one or more of the intended operational bands depending on the materials chosen and the proximity of these materials to the radiating element of the antenna device.

It will be appreciated that the present invention is capable of implementation in various ways, and that the implementation described is intended only to be illustrative and exhaustive. In particular, it is intended that a GPS satellite geo-location antenna may be added to the antenna device in order 29 to combine the functionality of a GPS antenna and a cellular telephone antenna in a single housing.

Although the invention has been described with reference to specific examples, it will be apparent to those skilled in the art that the invention may be embodied in many other forms.

Claims (29)

1. An interface element for use in a dual band RF antenna, wherein the interface element is selectively disposable in the near field of an RF transmitting circuit on a first side and an adjacent RF radiator on a second side, the interface element including a patch element having at least two notches disposed thereon wherein the dimensions of the patch element and notches are predetermined to provide for the patch element to be substantially tuned to the lower frequency of the dual band and the notches to be substantially tuned to the upper frequency of the dual band.

2. An interface element according to claim 1, wherein a dielectric substrate in the form of glass is disposed intermediate the interface element and the RF transmitting circuit.

3. An interface element according to claim 1 or 2, wherein the interface element includes mounting means for receiving the RF radiator. 15

4. An interface element according to claim 3, wherein the interface element is formed from a brass plate having threaded apertures to receive screws for mounting the RF radiator thereto.

5. An interface element according to claim 3 to 4, wherein a protective coating is disposed about the interface element and the RF radiator when mounted together. Soo

6. An interface element according to any one of the preceding claims, wherein the RF radiator is a dual band whip antenna including two coils, one coil being substantially tuned to the upper frequency and the other coil being substantially tuned to the lower frequency.

7. An interface element according to any one of claims 1 to 5, wherein the RF radiator is a dual band whip antenna including a single. coil, the coil being substantially tuned to the upper frequency and the overall length of the RF radiator being substantially tuned to the lower frequency.

8. A dual band RF antenna, said antenna including: a coupling module for disposal on one side of a dielectric substrate and including: a two-sided printed circuit board (PCB) having: a substantially elliptical slot forming a closed path disposed on the first side so as to be adjacent the dielectric substrate; a matching circuit including a strip line RF feed element disposed on the second side of the PCB; a plurality of tuning elements extending from the first side of the PCB to the second, the tuning elements having predetermined composition, displacement and size so as to selectively control the localised dielectric behaviour of the PCB; and 15 RF input/output means in communication with the strip line S feed element; a shielding member disposed adjacent the matching circuit and having predetermined dimensions corresponding to the dimensions of the S"elliptical slot; adhesive means for affixing the coupling module onto the one side of the dielectric substrate; an interface element for disposal on a second side of the dielectric substrate and including a patch element having at least two notches disposed thereon wherein the dimensions of the patch element and the notches are predetermined to provide for the patch element to be substantially tuned to the lower frequency of the dual band and the notches to be substantially tuned to the upper frequency of the dual band; and an RF radiator disposed adjacent the interface element.

9. A dual band RF antenna according to claim 8, wherein the dimensions and composition of the strip line RF feed element are predetermined so as to provide 32 a predetermined input impedance at the RF input/output means and the RF input/output means is a coaxial connector or strip line junction.

A dual band RF antenna according to claim 8 or 9, wherein the matching circuit is of a predetermined shape and disposed about the tuning elements on the second side of the PCB.

11. A dual band RF antenna according to any one of claims 8 to 10, wherein the tuning elements are metallic pins.

12. A dual band RF antenna according to any one of claims 8 to 10, wherein the tuning elements are conductively coated holes extending through the PCB material.

13. A dual band RF antenna according to claim 12, wherein the conductively coated holes are of a predetermined cross-section.

14. A dual band RF antenna according to claim 13, wherein the cross-section of the conductively coated holes is substantially constant through the PCB. 9• S 15

15. A dual band RF antenna according to any one of claims 12 to 14, wherein S- the conductively coated holes are shorting pins. e.g. 9

16. A dual band RF antenna according to any one of claims 8 to 15, wherein the PCB is composed of material selected from the group including: reinforced fibreglass material, PTFE based material, tetrafunctional epoxy/glass rigid 9.99 20 laminate, low loss silicon based substrate material and plastic/metal laminate materials.

17. A dual band RF antenna according to any one of claims 8 to 16, wherein the adhesive means is double sided tape or an epoxy resin.

18. A dual band RF antenna according to any one of claim 8 to 17, wherein the shielding member is a metallic plate. 33

19. A dual band RF antenna according to claim 18, wherein the metallic plate is composed of brass.

A dual band RF antenna according to any one of claims 8 to 19, the antenna further including a box-like dielectric cover including a first and second major face wherein the shielding member is mounted adjacent to the inside of one major face and the PCB element is mounted adjacent to the other major face wherein the substrate is a glass onto which the first major face is adhered.

21. A dual band RF antenna according to any one of claim 8 to 20, wherein the interface element includes mounting means for receiving the RF radiator.

22. A dual band RF antenna according to claim 21, wherein the interface element is a formed brass plate having threaded apertures to receive screws for mounting the RF radiator thereto.

23. A dual band RF antenna according to claim 21 to 22, wherein a protective coating is disposed about the interface element and the RF radiator when 15 mounted together. *d

24. A dual band RF antenna according to any one of claims 8 to 23, wherein the RF radiator is a dual band whip antenna including two coils, one coil being substantially tuned to the upper frequency and the other coil being substantially tuned to the lower frequency. lilt

25. A dual band RF antenna according to claim 24, wherein the dual coil RF radiator provides a 3dB gain to each of the frequency bands.

26. A dual band RF antenna according to any one of claim 8 to 23, wherein the RF radiator is a dual band whip antenna including a single coil, the coil being substantially tuned to the upper frequency and the overall length of the single coil antenna being substantially tuned to the lower frequency. 34

27. A dual band RF antenna according to claim 26, wherein the single coil RF radiator provides a unity (0dB) gain to each of the frequency bands.

28. An interface element for use in a dual band RF antenna substantially as herein described with reference to any of the embodiments illustrated in the accompanying drawings.

29. A dual band RF antenna substantially as herein described with reference to any of the embodiments illustrated in the accompanying drawings. DATED this 17th day of January 2006 RF INDUSTRIES PTY LIMITED 4€ WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA S.P PNF/SWE i 0T