GB2453160A

GB2453160A - Patch antenna with slots

Info

Publication number: GB2453160A
Application number: GB0718929A
Authority: GB
Inventors: Maksim Berezin; Michael Astanovsky; Ovadia Grossman
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2007-09-28
Filing date: 2007-09-28
Publication date: 2009-04-01
Anticipated expiration: 2027-09-28
Also published as: GB0718929D0; GB2453160B; WO2009042393A1

Abstract

A patch antenna comprises a dielectric substrate 101 on which there is a resonant patch 107 formed with at least two slots 117, 119. The patch 107 may be formed on a circuit board type substrate, such as FR4. A microstrip feed 113 may be arranged on the same surface 103 of the substrate 101 as the patch 107 such that it is in direct contact with an edge 108 of the patch 107. An earth connection 114 and a signal connection 116 may be made to the said microstrip feed 113. The patch 107 may be directly driven while the slots 117, 119 may be driven to resonance by electromagnetic coupling arrangements. The patch 107 may have radiating edges 106, 108 and non-radiating edges 102, 104. The slots 117, 119 may be arranged with a short open ended portion propagating into the patch from respective non-radiating edges 102, 104 with a larger slot portion running parallel with the said edges. Specific dimensions associated with the location and slot parameters may be used to obtain desired operational characteristics. A conductive ground frame 200 may be arranged with a separation layer from the substrate 101 to obtain the desired antenna resonance performance. The antenna provides a compact, broadband or multi-band antenna for mobile devices.

Description

TITLE: RADIO FREQUENCY ANTENNA

TECHNICAL FIELD

The technical field relates generally to a radio

frequency (RF) antenna. In particular, the technical

field relates to a patch antenna for use in RF

transmission and reception in a mobile communication terminal. I0

BACKGROUND

RF antennas, also known as RF resonators or RF radiators, are devices that provide a transformation of an RF electromagnetic signal having a frequency in an operational frequency band in which the antenna shows an electrical resonance. An RF signal that is bound, e.g. travelling along a conducting transmission line extending from an RF transmitter to the antenna, may be transformed by the antenna into one that is radiated and sent through space to a distant RF terminal.

Conversely, an RF signal that is a radiated signal sent from a distant terminal may be picked up by the antenna and transformed into a bound electromagnetic signal that may delivered to an RF receiver. In many applications, e.g. in communication terminals which are portable or mobile stations, the same antenna may be employed for both transmission and reception of radiated RF signals. Often, the transmitter and receiver of an RF communication terminal are combined in a common transceiver unit. Further, such a transceiver unit may be connected to the antenna by a common transmision line that delivers both transmitted and received bound RF signals.

Antennas of various kinds are known for use in use in RF terminals, particularly mobile communication terminals. Examples of the different kinds include monopole and dipole antennas, chip antennas, inverted F' (PIF) antennas and patch antennas.

Patch antennas are becoming widely used in communication termnials, especially mobile terminals because they can be produced by popular rnicrostrip printed circuit technology. A patch antenna usually comprises a conducting patch deposited on a first face of a dielectric substrate such as a printed circuit board. The antenna also comprises a further conducting layer, e.g. usually deposited on a second surface of the substrate, acting as a ground plane.

Patch antennas are known to have a relatively narrow operational bandwidth. Various techniques are known in the art to increase the bandwidth. These techniques include: (I) reducing the permittivity of the substrate dielectric; (ii) using a substrate having an increased thickness; (iii) using a patch having an increased width between its non-radiative edges; (iv) employing one or more additional parasitic elements in the same plane as the patch or in another plane in a stacked arrangement; (v) creating an aperture coupling RF feed for the patch; and (vi) using a patch having a U-slot.

None of the techniques known for increasing the bandwidth of a patch antenna is entirely satisfactory.

Frequently, there are space or size restrictions in the design of the antenna where it is to be incorporated in a communication terminal, especially a mobile terminal, and these restrictions rule out some of the known techniques. Furthermore, some of the known techniques require a relatively complex fabrication process or are relatively expensive to apply, or both.

Thus, there exists a need for a patch antenna, especially for use in a mobile communication terminal, which addresses at least some of the shortcomings of past and present patch antennas.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The accompanying drawings, in which like reference numerals refer to identical or functionally similar items thr.oughout the separate views which, together with the detailed description below, are incorporated in and form part of this patent specification and serve to further illustrate various embodiments of concepts that include the claimed invention, and to explain various principles and advantages of those embodiments.

In the accompanying drawings: FIG. 1 is a front view of a patch antenna embodying the invention.

FIG. 2 is a transverse cross-sectional end view of the antenna of FIG. 1.

FIG. 3 is a rear view of the antenna of FIG. 1.

FIG. 4 is an enlarged front view of part of the antenna of FIG. 1 showing more detail of a slot of the antenna.

FIG. 5 is an enlarged front view of another part of the antenna of FIG. 1 showing more detail of another slot of the antenna.

FIG. 6 is an enlarged front view of another part of the antenna of FIG. 1 showing more detail of an RF feed arrangement of the antenna.

Skilled artisans will appreciate that items shown in the drawings are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

For example, the dimensions of some of the items may be exaggerated relative to other items to assist understanding of various embodiments. In addition, the description and drawings do not necessarily require the order illustrated. Apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the various embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood items that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments.

DETAILED DESCRIPTION

Generally speaking, pursuant to the various embodiments to be described, there is provided an improved radio frequency (RF) patch antenna including a dielectric substrate and, on a first face of the dielectric substrate: (i) an electrically conducting half wavelength resonating patch having at least two quarter wavelength resonating elongate slots formed in the patch; and (ii) a conducting feed arrangement comprising a microstrip feed conductor galvanically connected to the patch to provide feed of RE' signals to and from the patch and the at least two slots.

The improved RF patch antenna may be operable to radiate or pick up RF signals having a frequency corresponding to a resonant frequency of the patch and a resonant frequency of the slots. The RF signals may have a frequency in an enhanced operational frequency band which includes the resonant frequency of the patch and the resonant frequency of the slots. Alternatively, the RF signals may have frequencies in separate operational frequency bands including a first band which includes the resonant frequency of the patch and a second band which includes the resonant frequency of the slots.

The conducting patch may have a shape which is or approximates to a rectangle providing in operation radiative edges and non-radiative edges. Each of the slots may beneficially have a first section which is substantially parallel to one of the radiative edges and a second section which is substantially parallel to one of the non-radiative edges. The microstrip feed conductor may be galvanically connected to the patch at or adjacent to one of the radiative edges of the patch.

The improved patch antenna may beneficially have an enhanced operational bandwidth, or alternatively a plurality of operational frequency bands, without introducing the disadvantages of the prior art. The additional resonance giving the enhanced bandwidth or additional band may be provided by slot radiators provided by the slots without increasing the overall space occupied by the improved antenna since the slots may be provided in the patch and a single feed conductor in the conducting feed arrangement may be employed for delivery of RF signals to or from both the patch and the slots. The location and orientation of the slots may be selected, as described in more detail later, to permit efficient delivery of signals by electromagnetic coupling to and from the slots.

Those skilled in the art will appreciate that these recognized advantages and other advantages described herein are merely illustrative and are not meant to be a complete rendering of all of the advantages of the various embodiments of the invention.

Referring now to the accompanying drawings, in particular FIGS. 1 to 3, there is shown a patch antenna embodying the invention. FIG. 1 is a front view of the antenna 100. FIG. 2 is a transverse cross-sectional end view of the antenna 100 as seen in a plane defined by the line 2-2 in FIG. 1. FIG. 3 is a rear view of the antenna 100.

For convenience of reference only, in the embodiments to be described with reference to the drawings the expression vertical', or extending vertically', refers to items such as the line 2-2 which are shown as being vertical in FIG. 1. The expression horizontal', or extending horizontally', refers to items which are shown as horizontal in FIG. 1. Items extending at an angle between vertical and horizontal as shown in FIG. 1 are referred to herein as diagonal', or extending diagonally'.

The patch antenna 100 includes a dielectric substrate 101 and a conducting frame (chassis) 200 which is electrically connected to ground. The substrate 101 has a front face 103 which carries conducting components bonded thereto, including a conducting patch 107 and a conducting layer 118 of a conducting feed arrangement 113. The substrate 101 may be fixed to and supported on the frame 200 by a known support structure (which is omitted for the purposes of simplicity and clarity).

The substrate 101 may be made of a known solid dielectric material. Conveniently, the dielectric material may be a material employed in the art for making boards for printed circuits. A well known example of such a material is a board produced from the glass fibre reinforced epoxy resin known by the industry standard name FR4. Such a board typically has for example a low dielectric loss (tan ö) of about 0.01 and a high relative permittivity (er) of about 4.4 at frequencies of between about 1 MHz and about 1 GHz. The board employed may be supplied with a conducting layer such as copper already bonded to its front face in a known manner. The conducting patch 107 and the conducting layer 118 may be formed from the conducting layer in a known manner, e.g. by selective etching or machining.

As shown in FIG. 2, the conducting frame 200 includes a conducting ground layer 202 and side walls 207 and 209 extending from the ground layer 202 substantially perpendicular to the ground layer 202.

The conducting ground layer 202 has a rear face 201 and a front face 203. The front face 203 faces the substrate 101 and is substantially parallel to the front face 103 (including the conducting patch 107) of the substrate 101. An air separation layer 205 separates the substrate 101 and the conducting ground layer 202. The patch 107 is thereby separated from a ground plane provided by the ground layer 202 by a dielectric medium comprising two dielectric layers of uniform thickness, namely the substrate 101 and the air separation layer 205. The air separation layer 205 suitably reduces the effective permittivity of the combined dielectric material to facilitate design of the patch antenna 100.

The side walls 207 and 209 have an influence over the radiation pattern of the patch antenna 100. The radiation pattern can have a more pronounced directivity with the side walls 207 and 209 present.

However, the side walls 207 and 209 also have an influence over the bandwidth of the patch antenna 100; the bandwidth is slightly reduced with the side walls 207 and 209 present.

The conducting patch 107, in conjunction with the ground plane provided by the ground layer 202 and the dielectric medium separating them, is adapted to provide a half wavelength patch antenna. The conducting patch 107 has radiative edges between which an electrical resonance is established. The radiative edges have a main separation which is equivalent to a half wavelength at a centre frequency of the resonance, as described in more detail later. The conducting patch 107 has a shape which approximates to a rectangle, the patch 107 having a cut away section 115 in one corner.

The conducting patch 107 has a first side 102 and a second side 104 which both extend horizontally, parallel to and close to the respective horizontal side edges of the substrate 101. The sides 102 and 104 of the conducting patch 107 provide in operation non-radiative edges of the conducting patch 107. The conducting patch 107 has a first end 108 and a second end 106 which provide in operation radiative edges of the conducting patch 107. The side 102 and the side 104 of the conducting patch 107 extend between the end 108 and the end 106 of the conducting patch 107.

There is a space 111 between a first end 112 of the front face 103 and the first end 108 of the conducting patch 107. The front face 103 of the substrate 101 is exposed in the space 111. The conducting layer 118 of the conducting feed arrangement 113 is bonded to the front face 103 in the space 111.

The conducting feed arrangement 113 also includes connectors 114 and 116, such as conducting pins, which extend through the substrate 101 to provide electrical connections to the conducting layer 118. The conducting layer 118 of the feed arrangement 113 is galvanically connected to the conducting patch 107 at a feed edge at the end 108 of the conducting patch 107. The conducting feed arrangement 113, which serves to deliver RF signals to and from the conducting patch 107, is described in more detail later with reference to FIGS. 3 and 6.

The second end 106 of the conducting patch 107 may conveniently be close to a second end 110 of the front face 103 of the substrate 101 as shown in FIG. 1 to provide maximal practical coverage of the front face 103 at the second end 110 by the conducting patch 107, in order to maximize the length of the conducting patch 107 between its radiative edges provided respectively at the ends 106 and 108.

The cut away section 115 is in a corner of the conducting patch 107 between the first side 102 and the first end 108. By having the cut away section 115, the length of the conducting patch 107 measured horizontally along the first side 102 of the conducting patch 107 is shorter than the length of the conducting patch 107 measured horizontally along the second side 104. This allows part of the space 111 adjacent to the cut away section 115 to be enlarged in order to accommodate the conducting layer 118.

A first elongate slot 117 and a second elongate slot 119 are formed in the conducting patch 107 thereby exposing dielectric material of the substrate 101 in the slots 117 and 119. The slots 117 and 119 provide, in conjunction with the ground plane provided by the conducting frame 200 and the dielectric medium provided by the substrate 101 and the air separation layer 205, quarter wavelength slot radiators. Each of the slots 117 and 119 has an electrical length which is equivalent to a quarter wavelength (in air) at a centre frequency of resonance of the slot radiator.

Thus, the antenna 100 includes a combination of Ci) a patch radiator comprising the conducting patch 107; and (ii) two slot radiators comprising the slots 117 and 119. The length of the slots 117 and 119 may be selected so that a centre frequency of resonance of the slot radiators is offset from the centre frequency of resonance of the patch radiator. The antenna 100 may thereby have a broadened resonance band compared with that of the conducting patch 107 without the slots 117 and 119. The slots 117 and 119 and their operation as a slot radiators working together with the patch radiator comprising the conducting patch 107 are described in more detail later, particularly with reference to FIGS. 4 and 5.

In operation of the antenna 100, RF signals to be radiated by the antenna 100 in a transmission mode of operation are delivered from an RF transmitter (not shown) via the conducting feed arrangement 113.

Similarly, RF signals picked up by the antenna 100 in a reception mode of operation are delivered via the conducting feed arrangement 113 to an RF receiver (not shown) . The transmitter and receiver may for example be incorporated in a mobile communication terminal such as a portable radio terminal. The delivery of an RF signal from the transmitter to the conducting feed arrangement 113, as well as from the conducting feed arrangement 113 to the receiver, may be provided by a known transmission line, such as a coaxial cable. Generally, the transmission line comprises a live conductor, e.g. the inner conductor of a coaxial cable, carrying the RF signal, and a shield conductor, e.g. the outer conductor of a coaxial cable, connected to ground.

A conductor which in operation is to be the live conductor of a transmission line may conveniently be connected to the conducting layer 118 of the conducting feed arrangement 113 through the substrate 101 and through the air separation layer 205. An example of such a connection arrangement is illustrated in FIG. 3.

The transmission line from the RF transmitter in this example comprises a coaxial cable 303 having an inner or live conductor 305, an insulating sleeve 309 covering the inner conductor 305, an outer ground shielding conductor 311, e.g. in a braided form, carried on an outer surface of the insulating sleeve 309 and an outer insulating sleeve 315. A hollow portion 301 is formed in the conducting frame 200 (in the ground layer 202) . A contact 307 insulated from the conducting frame 200 is optionally provided in the hollow portion 301. The inner conductor 305 of the coaxial cable 303 may be bonded to the contact 307, e.g. by soldering, to make galvanic connection with the contact 307. The inner conductor 305 is insulated from the conducting frame 200 by the insulating sleeve 309 and the hollow portion 301. The hollow portion 301 including the contact 307 where present, may conveniently be sited directly behind the connector 114 (FIG. 1). The contact 307 where present is galvanically connected to the connector 114, e.g. by a conducting pin soldered at one end to the connector 114.

Alternatively, the connector 114 may be provided by an end portion of the inner conductor 305 so that the inner conductor 305 is fitted through the conducting layer 202, the air separation layer 205 and the substrate 101 without use of the contact 107.

The connector 114 is thus a conducting member which passes through the air separation layer 205 and the substrate 101 from the hollow portion 301, e.g. in a direction generally perpendicular to the faces 103 and 201, and provides contact with the conducting layer 118 of the conducting feed arrangement 113 at a contact region at an end of the connector 114 as shown in FIG. 1, thereby galvanically connecting the inner conductor 305 of the coaxial cable to the conducting layer 118 on the face 103.

The connector 116 makes galvanic contact with the conducting layer 118 on the face 103 at a contact region at an end of the connector 116 as shown in FIG. 1. The connector 116 is a conducting member which passes through the substrate 101 and the air separation layer 205, e.g. in a direction generally perpendicular to the faces 103 and 201. The connector 116 has a galvanic connection (not shown) to ground at the ground layer 202 of the conducting frame 200. The connector 116 thus provides a galvanic connection of the conducting layer 118 of the feed arrangement 113 to the ground plane provided by the ground layer 202. The purpose of this connection to ground is described later with reference to FIG. 6.

Although an end of the connector 114 is shown in FIG. 1 (and in FIG. 6) to indicate a contact region at which the connector 114 contacts the conducting layer 118, the end may be covered by the conducting layer 118 in the making of the galvanic contact between the connector 114 and the conducting layer 118. Similarly, although an end of the connector 116 is shown in FIG. 1 (and in FIG. 6) the end may be covered by the conducting layer 118.

FIG. 4 is an enlarged front view of part of the antenna 100 of FIG. 1 showing more detail of the slot 119 formed in the conducting patch 107. The slot 119 has a first end 401, which is open at a gap in the side 104 of the conducting patch 107 close to a vertical end edge 402 at the end 108 of the conducting patch 107.

The slot 119 extends from the first end 401 to a second end 404 of the slot 119 which is closed inside the conducting patch 107. The slot 119 includes a short first section 403 which extends vertically from the first end 401 of the slot 119 close to and substantially parallel to the end edge 402 of the conducting patch 107. The slot 119 includes a longer second section 405 which extends horizontally from the first section 403 close to and substantially parallel to the side 104 of the conducting patch 107.

A uniform separation distance Dl is maintained between the second section 405 of the slot 119 and the side 104 of the conducting patch 107. Selection of the distance Dl is described later.

The first section 403 of the slot 119 is located at a separation distance D2 from the end edge 402 of the conducting patch 107. Selection of the distance D2 is described later.

The slot 119 has a width which is substantially uniform along its entire length including the first 16 -S.

section 403 and the second section 405. Selection of the width is described later.

FIG. 5 is an enlarged front view of part of the antenna 100 of FIG. 1 showing more detail of the slot 117 formed in the conducting patch 107. The slot 117 has a first end 502, which is open at a gap in the side 102 of the conducting patch 107 close to a vertical end edge 501 at the end 108 of the conducting patch 107 in the cut away section 115. The slot 117 extends to a second end 504 which is closed inside the conducting patch 107. The slot 117 includes a short first section 503 which extends vertically from the first end 502 of the slot 117 close to and substantially parallel to the end edge 501. The slot 117 includes a longer second section 505 which extends horizontally from the first section 503 close to and substantially parallel to the side 102 of the conducting patch 107. The slot 117 also includes a third section 507 which also extends horizontally as a continuation of the second section 505, close to and substantially parallel to the side 102.

The slot 117 has a first width which is substantially uniform along the first section 503 and the second section 505 and a second width which is substantially uniform along the third section 507. The first width of the slot 117 may conveniently be substantially the same as the width of the slot 119.

The second width of the slot 117 is less than the first width of the slot 117. Selection of the first width and the second width is described in more detail later.

Each of the second section 505 and the third section 507 of the slot 117 is maintained a constant separation distance from the side 102 of the conducting patch 107. The constant distance may conveniently be the distance Dl referred to earlier. Its selection is described later.

The first section 503 of the slot 117 is located a separation distance D3 from the end edge 501 of the conducting patch 107. Selection of the distance D3 is described later.

FIG. 6 is an enlarged front view of the conducting feed arrangement 113. The arrangement 113 includes the conducting layer 118 bonded to the face 103 of the substrate 101 (FIG. 1) . The conducting layer 118 is a shaped layer which may be formed of the same conducting material as that employed to form the conducting patch 107. The connector 114, which as noted earlier is to be galvanically connected to, or an end portion of, a conductor which is to be a live conductor of a transmission line (such as the inner conductor 305 of the coaxial cable 303), makes galvanic contact with the conducting layer 118 in a contact region at an end of the connector 114 as shown in FIG. 6. The contact region is located in a vertically extending strip section 609 of the conducting layer 118. The conducting layer 118 includes a rectangular section 601 for providing galvanic connection to the conducting patch 107 at the feed edge 120 (FIG. 1) . The rectangular section 601 is galvanically connected to the strip section 609 by a vertical strip section 603, a horizontal strip section 605 and a diagonal strip section 607. The sections 609, 607, 605, 603 and 601 of the conducting layer 118 together provide a live microstrip feed conductor from the connector 114 to the conducting patch 107 and have shapes and dimensions which are selected to give a suitable feed impedance transformation between the impedance, e.g. of 50 ohms (as widely used in the art), of a connected transmission line, such as the coaxial cable 303, and the input impedance of the conducting patch 107. In particular, it is to be noted that the impedance transformation provided by the conducting layer 118 between the connection 114 and the conducting patch 107 is obtained by selective features in the conducting layer 118, namely changes in strip direction and changes in strip width between each of the strips 609, 607, 605, 603 and 601. The strip width increases in steps from a smallest width in the strip 609 to a largest width in the strip 601.

The conducting layer 118 of the conducting feed arrangement 113 thus provides a feed conductor between the live connector 114 and the feed edge 120 (FIG. 1) of the conducting patch 107 of RF signals into and out of the slotted patch comprising the conducting patch 107 and the slots 117 and 119. The conducting layer 118 is a single feed conductor, advantageously provided in a microstrip form coplanar with the conducting patch 107. This allows dielectric losses in the antenna 100 to be minimized. Furthermore, as noted earlier, the conducting layer 118 of the feed arrangement 113, the conducting patch 107 and the slots 117 and 119 may advantageously be formed together from a single conducting patch on the same face, i.e. the front face 103, of the substrate 101, thereby beneficially simplifying and reducing the cost of manufacturing procedures.

The connector 116, which as noted earlier is to be connected to ground, such as via the conducting frame 200 at its ground layer 202, makes a galvanic contact with the conducting layer 118 of the arrangement 113 in a galvanic contact region at the end of the connector 116 shown in FIG. 6. The contact region is located in a horizontally extending strip section 619. The strip section 619 is galvanically connected to the live contact region at the end of the connector 114 in the strip section 609 by a vertical strip section 617, a horizontal strip section 615 and a diagonal strip section 613. The strip sections 619, 617, 615, 613 and 609 have dimensions such that they provide, together with the connection 116, a conductor having an effective electrical length between the live contact region provided by the end of the connector 114 and the ground plane presented by the inner surface 203 of the ground layer 202 which is equivalent to a quarter wavelength in air of a resonance of the antenna at its centre frequency of operation. The purpose of this quarter wavelength conductor is to provide a conducting path to ground for any unusual unwanted current spikes, e.g. due to lightning strikes on the antenna 100.

The conducting layer 118 of the feed arrangement 113 and the conducting patch 107 may be formed of a single continuous conducting layer on the face 103 of the substrate 101. In this case, the feed edge 120 shown in FIG. 1 is to be considered as a notional edge between the conducting patch 113 and the conducting patch 107 from which RF signals are launched into or received from the conducting patch 107.

Operation of the antenna 100, including the patch radiator provided by the conducting patch 107 and the slot radiators provided by the slots 117 and 119, and selection of related design parameters, will now be described in more detail.

From known theory, it can be shown that the conducting patch 107, together with the conducting frame 200 and the dielectric medium of the substrate 101 and the air separation layer 205, provides a half wave patch radiator which has an effective electrical length L which is given by: L=> where 2,is the wavelength of radiation produced in air by the patch radiator at the centre frequency of its resonance band and Creff is the effective combined relative permittivity of the dielectric medium referred to above. A target operational centre frequency of the resonance band of the patch radiator can be obtained by selecting a physical length approximately equal to the effective electrical length L which gives the corresponding wavelength X. As an illustrative example, a target centre frequency of from about 720 MHz to about 730 MHz is required for Broadband Wireless Access (BWA) for high-speed data, Voice over IP (VoIP) and multimedia services. For example, a target centre frequency of 722 MHz can be obtained by selecting the physical length of the conducting patch 107 (which approximates to L) to be about 163 mm and the width of the conducting patch 107 to be about 109 mm.

As noted earlier, the slots 117 and 119 provide, together with the conducting frame 200 and the dielectric medium of the substrate 101 and the air separation layer 205, dual slot radiators. Each of the slots 117 and 119 has an effective electrical length equivalent to a quarter wavelength at a centre frequency of a resonance of the slot radiators, which is a resonance additional to the resonance of the patch radiator described above. RF signals for transmission are delivered to the slots 117 and 119 (as well as to the conducting patch 107) from the conducting feed arrangement 113. The delivery to the slots 117 and 119 is by electromagnetic coupling. RF signals picked up for reception are delivered from the slots 117 and 119 (as well as from the conducting patch 107) . The delivery from the slots 117 and 119 is also by electromagnetic coupling.

In particular, in a transmission mode, an input RF signal having a frequency corresponding to the resonance band of the slot radiator of each of the slots 117 and 119 is delivered into the conducting layer 118 from the connector 114. The transformation of impedance provided by the conduction layer 118 (as described earlier) allows the signal to be received by the conducting patch 107 with minimal losses. Suitable

electromagnetic fields are developed between the

radiating edges provided by the ends 106 and 108 of the conducting patch 107 and the ground plane provided by the ground layer 202 via the dielectric medium between them as described above. These electromagnetic fields provide feeding of the slot radiators of the slots 117 and 119 by electromagnetic coupling.

As noted earlier, the purpose of the slot radiators provided by the slots 117 and 119, is to create a resonance additional to that of the main resonance of the patch radiator comprising by the conducting patch 107. The additional resonance may be designed to have a centre frequency given by (f0+1M) or (f-Af), where f0 is the centre frequency of the main resonance provided by the patch radiator and M is the difference in frequency between the centre frequency of the main resonance of the conducting patch 107 and the centre frequency of the additional resonance of the slots 117 and 119. The combined antenna 100 comprising the patch radiator and the slot radiators may beneficially have an increased overall bandwidth BW given approximately by the following expression: BW = BW + BWs where BW is the bandwidth of the patch radiator and BW is the bandwidth of the slot radiators. The overall bandwidth BW is approximately equal to Lf multiplied by two. As an illustrative example, if the combined antenna 100 has the operational centre frequency of about 722 MHz, it may have an overall resonance bandwidth BW of at least about 48 MHz including frequencies in the range from about 698 MHz to about 746 MHz. This may beneficially give an illustrative bandwidth improvement of about 20 per cent compared with an unslotted patch antenna.

In some applications, the resonance provided by the slot radiators may be selected to be sufficiently offset from that of the patch radiator so that separate operational frequency bands are obtained. Such separation may be employed in a known manner to give transmission and reception of different RF signals in the separate bands.

It is to be noted that dual slot radiators provided by the slots 117 and 119 having elongate sections adjacent to opposite non-radiative edges of the conducting patch 107, namely the sides 102 and 104, allows suitable symmetry to be obtained in the resulting radiation pattern of the antenna 100. In principle, one or more further slots (not shown) may be included in the conducting patch 107.

As noted earlier, the second section 405 of the slot 119 and the second section 505 and the third section 507 of the slot 117 have an orientation which is selected to be parallel to, and at a location selected to be close to, the respective sides 104 and 102 of the conducting patch 107 which in operation provide non-radiating edges of the conducting patch 107. This is so that the centre frequency of the resonance of the patch radiator is not substantially changed by the presence of the slots 117 and 119. The distance Dl maintained between: (1) the side 104 of the conducting patch 107 and the second section 405 of the slot 119; and between (ii) the side 102 of the conducting patch 107 and the second section 505 and the third section 507 of the slot 117; may be not greater than about 0.02 times Xo, where A0 is the wavelength in air of radiation at a centre frequency of the required resonance band, e.g. 722 MHz as described above.

Illustratively, the distance Dl is selected to be about 0.01 times A0 or less.

In an illustrative example to give the target frequency of 722 MHz referred to earlier, A0 is about 415 mm and the distance Dl is about 4 mm (0.01 times A0).

The first end 108 of the conducting patch 107 has in operation a radiative edge which has a first portion at the end edge 402 and a second portion at the end edge 501. The first and second portions of that radiative edge are not in line with one another, but are parallel to one another in a stepped relationship, as a result of providing the cut away section 115. The first sections 403 and 503 respectively of the slots 119 and 117 are located close to and parallel to the respective radiative edge portions at the end edge 401 and the end edge 402 in order to maximize the feeding efficiency by electromagnetic coupling and the radiation efficiency of the slots 117 and 119. The first section 403 of the slot 119 has a length which is selected to be equal to the sum of about Dl plus about half of the width of the first section 403. The second section 503 of the slot 117 also has a length which is selected to be equal to the sum of about Dl plus about half of the width of the first section 403. The length of the first section 403 and of the first section 503 may be not greater than a length equivalent to about 0.02X0. Illustratively, the length of the first section 403 and of the first section 503 is equivalent to about O.O1A0 or less, where Ao is the wavelength in air of radiation at a centre frequency of a required resonance band, e.g. about 722 MHz as described above.

Each of: (1) the distance D2 between the first section 403 of the slot 119 and the first radiative edge portion at the end edge 402 of the conducting patch 107; and (ii) the distance D3 between the first section 503 of the slot 117 and the second radiative edge portion at the end edge 501 of the conducting patch 107; is selected to be not greater than about 0.03X0. The distance D3 is selected to be less than the distance D2 to compensate for effects caused by the presence of the cut away section 115. The magnitude of electromagnetic fields in the corner of the conducting patch 107 in the cut away section 115 is less than for a corner without a cut away section, e.g. between the end edge 402 and the side 104, so a compensation is needed for suitable electromagnetic coupling to feeding of the slot radiator of the slot 117. For example, the distance D3 may be selected to be not greater than about 0.03A0 and the distance D3 may be selected to be not greater than about 0.OlX0. Illustratively, the distance D2 may be selected to be about 0.025 times Xo and the distance D3 may be selected to be about 0.006 times Xo, where Xo is as defined above. In an illustrative example to give the target frequency of 722 MHz referred to earlier, A0 is about 415 mm, the distance D2 is about 10 mm (0.025 times A0) and the distance D3 is about 2.5 mm (0.006 times Ao).

In another embodiment, if the distances D2 and D3 are less than the values specified above (0.025 times A0 and 0.006 times A0 respectively), so that the radiation efficiency of the slot radiators provided by the slots 117 and 119 is increased, the antenna 100 may provide in combination: (i) a patch radiator; and (ii) slot radiators; which have two different radiation polarizations in the different resonance bands described earlier with similar values of radiation efficiency for each of these bands. The patch radiator and the slot radiators may in this case still be operated using a single feed system comprising the conducting feed arrangement 113 as described earlier.

This allows the antenna 100 to operate in a known manner with different RF signals having the same or similar frequencies but with polarization diversity.

The slot 119 has a shape which is selected so that the length of the second section 405 of the slot 119 which is parallel to the non-radiative edge provided by the side 104 of the conducting patch 107, can be maximized. Similarly, the slot 117 has a shape which is selected so that the combined length of the second section 505 and the third section 507 of the slot 119 which are parallel to the non-radiative edge provided by the side 102 of the conducting patch 107, can be maximized.

In another embodiment, the slot 119 and the slot 117 could be replaced by slots (not shown) having a shape which includes multiple sections parallel to the horizontal sides of the conducting patch 107, although the combined electrical length of all sections in each slot is selected to be about a half wavelength for the centre frequency in air of the resonance band for each slot.

The width of each of the slots 117 and 119 is a function of a coefficient V which increases as the width decreases. The coefficient V is given by: v w where W is width of the slots and 2 is the wavelength of radiation provided in air by the slot radiator provided by the slot at its centre frequency. The coefficient V and an effective electrical length I of the slot are related by the following expression:

I-4*i/

where CrJr is the effective relative permittivity of the dielectric material occupying the space between the sides of the slot, a combination of air and dielectric material of the substrate 101, and * indicates multiplication. For a slot having an infinitesimal width, the coefficient V is equal to one. For slots having a finite width the coefficient V is less than one. As an illustrative example, the average width of the slot 119 and the average width of the slot 117 in its first section 503 and its second section 505 may be selected to be about 1 mm (0.0025X) or less for operation at a slot radiator having a centre frequency of 704 MHz.

As noted earlier, the second width of the slot 117 in the third section 507 is less than the width of the slot 117 in the first section 503 and the second section 505 of the slot 117. This reduction of the width in the third section 107 enables the influence of the cut away portion 115 on the slot radiator 117 to be compensated for. The width in the third section 107 may be not greater than about half of that of the second section 505. As an illustrative example, the average width in the third section 507 may be selected to be about 0.3 mm (0.0007X5) or less for operation at a centre frequency of 704 MHz.

In the foregoing specification, specific

embodiments have been described. However, one of ordinary skill in the art will appreciate that various modifications and changes can be made without departing from the scope of the invention as set forth in the accompanying claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this patent application and all equivalents of those claims as issued.

Moreover in this document, relational terms such as first' and second', front' and rear', and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

The terms comprises', comprising', has', having', includes', including', contains', containing' or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes or contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by comprises...a', has a', includes...a', or contains...a' does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, contains the element. The terms a' and an' are defined as one or more unless explicitly stated otherwise herein. The terms substantially', essentially', approximately', about' or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%, of a stated value.

The accompanying Abstract of the Disclosure is

provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may lie in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter. 32 p

Claims

1. A radio frequency (RF) patch antenna including a dielectric substrate and, on a first face of the dielectric substrate: (1) an electrically conducting half wavelength resonating patch having at least two quarter wavelength resonating elongate slots formed in the patch; and (ii) a conducting feed arrangement comprising a microstrip feed conductor galvanically connected to the patch to provide feed of RF signals to and from the patch and the at least two slots.

2. An RF patch antenna according to claim 1 which is operable to radiate or pick up RF signals having frequencies corresponding to a resonant frequency of the patch and a resonant frequency of the slots.

3. An RF patch antenna according to claim 2 which is operable to radiate or pick up RF signals having frequencies in an enhanced operational frequency band which includes the resonant frequency of the patch and the resonant frequency of the slots.

4. An RF patch antenna according to claim 2 which is operable to radiate or pick up RF signals having frequencies in separate operational frequency bands including a first band which includes the resonant frequency of the patch and a second band which includes the resonant frequency of the slots.

5. An RF patch antenna according to any one of the preceding claims wherein the patch has in operation radiative edges and non-radiative edges and a first one of the slots has at least one section which is substantially parallel to at least a first one of the non-radiative edges and a second one of the slots has at least one section which is substantially parallel to at least a second one of the non-radiative edges.

6. An RF patch antenna according to claim 5 wherein the patch has a shape which is or approximates to a rectangle and the radiative edges are at ends of the patch and the non-radiative edges are substantially parallel edges at sides of the patch.

7. An RF patch antenna according to claim 6 wherein the feed conductor is galvanically connected to the patch at a first end of the patch.

8. An RF patch antenna according to claim 7 wherein each of the slots is operable to receive RF signals for radiation from the slot, or to deliver RF signals picked up by the slot, by electromagnetic coupling.

9. An RF patch antenna according to claim 8 wherein a first one of the slots includes a first section which is substantially parallel to a radiative edge of the patch at a first end of the patch and the second slot includes a first section which is substantially parallel to a radiative edge of the patch at the first end of the patch.

10. An RF patch antenna according to claim 9 wherein the first section of the first slot extends from an open end of the slot at a gap in the first non-radiative edge of the patch and the first section of the second slot extends from an open end of the slot at a gap in the second non-radiative edge of the patch.

11. An RF patch antenna according to claim 9 or claim 10, wherein the first slot has a second section longer than the first section and substantially parallel to a first non-radiative edge of the patch; and the second slot has a second section longer than the first section and substantially parallel to a second non-radiative edge of the patch.

12. An RF patch antenna according to any one of claims 9 to 11 wherein the first section of the first slot is located a distance D3 from a first portion of the first radiative edge and the first section of the second slot is located a distance D2 from a second portion of the first radiative edge, the distance D3 being less than the distance D2.

13. An RF patch antenna according to claim 12 and wherein the patch has a shape which approximates to a rectangle and has, in a corner region between the first portion of the first radiative edge and the first non-radiative edge of the patch, a cut away section to provide an enlarged space on the first face of the substrate to accommodate the conducting feed arrangement.

14. An RF patch antenna according to claim 12 or claim 13 wherein the distance D2 is not greater than about 0.03A0 and the distance D3 is not greater than about 0. 01Xo.

15. An RF patch antenna according to claim 14 wherein the distance D2 is less than about O.025A0 and the distance D3 is less than about O.OO6X0, and the antenna is operable to radiate or pick up a first RF signal by resonance of the patch and a second RF signal by resonance of the first and second slots, the first and second signals having different radiation polarizations.

16. An RF patch antenna according to any one of claims 11 to 15 wherein the second section of at least one of the slots is a located a distance Dl from one of the non-radiative edges, the distance Dl being not greater than about O.O1A0, where X0 is the wavelength in air at a centre frequency of operation of the antenna.

17. An RF patch antenna according to any one of the preceding claims wherein each of the slots has at least a section having an average width which is not greater than about O.OO25X, where A is the wavelength in air of slot radiators provided by the slots at a centre frequency of operation of the slot radiators.

18. An RF patch antenna according to any one of claims 11 to 17 wherein the second section of the first slot has a first width and the first slot includes a third section having a second width less than the first width.

19. An RF patch antenna according to claim 18 wherein the first width is not greater than about O.OO25A and the second width is not greater than about O.0007A5, where X is the wavelength in air of radiation at a centre frequency of operation of slot radiators provided by the first and second slots.

20. An RF patch antenna according to any one of the preceding claims including a conducting ground layer, the ground layer being separated from the conducting patch by dielectric material including dielectric material of the substrate.

21. An RF patch antenna according to claim 20 including a conducting frame including the ground layer, the ground layer being separated from the substrate by an air separation layer.

22. An RF patch antenna according to claim 21 wherein the conducting frame includes conducting side walls substantially perpendicular to the ground layer.

23. An RF patch antenna according to any one of the preceding claims wherein the ground layer has a surface area greater than that of the conducting patch.

24. An RF patch antenna according to any one of the preceding claims wherein the dielectric material of the substrate comprises a glass fibre reinforced epoxy resin material.

25. An RF patch antenna according to any one of the preceding claims wherein the conducting feed arrangement includes a connector at which an RF signal is deliverable to the microstrip feed conductor.

26. An RF patch antenna according to claim 25 including a conducting ground layer separated from the conducting patch by dielectric material including dielectric material of the substrate and an air separation layer and wherein the connector extends through the substrate and the air separation layer and galvanically connects the microstrip feed conductor to a transmission line.

27. An RF patch antenna according to claim 25 or claim 26 wherein the conducting feed arrangement includes a quarter wavelength connection from the connector to the ground layer.

28. An RF patch antenna according to any one of claims 20 to 27 including a further connector extending through the substrate and the air separation layer and galvanically connecting the quarter wavelength connection to the ground layer.

29. An RF patch antenna according to any one of the preceding claims and substantially as herein described with reference to any one or more of the accompanying drawings.