WO2014011119A1

WO2014011119A1 - Antenna enhancing structure for improving the performance of an antenna loaded thereon, antenna device and method of fabricating thereof

Info

Publication number: WO2014011119A1
Application number: PCT/SG2013/000292
Authority: WO
Inventors: Pui Yi LAU; Zhining Chen; Xianming Qing
Original assignee: Agency For Science, Technology And Research
Priority date: 2012-07-11
Filing date: 2013-07-11
Publication date: 2014-01-16

Abstract

An antenna enhancing structure is provided for improving the performance of an antenna loaded thereon. The structure includes a first array of metallic patches, and second array of metallic patches, wherein the first array and the second array are separated by a dielectric medium, and the first array and the second array are configured with respect to each other such that the metallic patches in the first array are offset from the metallic patches in the second array along a plane of the first array. There is also provided an antenna device having the antenna enhancing structure and a method of fabricating thereof.

Description

ANTENNA ENHANCING STRUCTURE FOR IMPROVING THE PERFORMANCE OF AN ANTENNA LOADED THEREON, ANTENNA

DEVICE AND METHOD OF FABRICATING THEREOF

FIELD OF INVENTION

The present invention generally relates to an antenna. More particularly, the present invention relates to an antenna enhancing structure for improving the performance of an antenna loaded thereon, an antenna device having an antenna loaded on the antenna enhancing structure, and a method of fabricating thereof.

BACKGROUND Metamaterials depict a new paradigm in electromagnetic science and technology as they can be engineered to produce electromagnetic properties that cannot be found in natural materials. Conventional antennas have been disclosed with improved

radiated power. However, although the gain may be increased, the antenna bandwidth is typically narrow. It may be possible to increase the bandwidth and gain by increasing the thickness/profile of the antenna. However, this approach would increase the size of the antenna and thus would be a problem if a low profile antenna is desired.

A need therefore exists to provide an antenna device having a low profile while also featuring a wide bandwidth and a high gain. It is against this background that the present invention has been developed.

SUMMARY The present invention seeks to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice. According to a first aspect of the present invention, there is provided an antenna enhancing structure for improving the performance of an antenna loaded thereon, the structure comprising:

a first array of metallic patches, and

a second array of metallic patches, wherein

the first array and the second array are separated by a dielectric medium, and

the first array and the second array are configured with respect to each other such that the metallic patches in the first array are offset from the metallic patches in the second array along a plane of the first array.

Preferably, at least a majority of the metallic patches in the first array each has a central axis that is offset from a center axis of a corresponding metallic patch in the second array in a direction parallel to the first or second array.

Preferably, the corresponding metallic patch in the second array of a metallic patch in the first array is a metallic patch in the second array which is opposing or closest to said metallic patch in the first array.

In an embodiment, the dielectric medium is a dielectric substrate, and the first array is formed on a first side of the dielectric substrate and the second array is formed on a second side of the dielectric substrate opposing the first side. In another embodiment, the dielectric medium is an air medium.

Preferably, each pair of adjacent metallic patches in the first array has a first gap therebetween, and each pair of adjacent metallic patches in the second array has a second gap therebetween, and wherein the first gap and the second gap each has a width in the range of about 0.001 λ to about 0.06A, where λ is a center operating frequency of the antenna. Preferably, the metallic patches in the first array and the second array each has a width in the range of about 0.04Λ to about 0.15λ, where λ is a center operating frequency of the antenna. In an embodiment, the metallic patches in the first array each has a first planar size and the metallic patches of the second array each has a second planar size, and the first planar size and the second planar size are substantially the same.

In another embodiment, wherein the metallic patches of the first array each has a first planar size and the metallic patches of the second array each has a second planar size, and the first planar size and the second planar size are different.

Preferably, the metallic patches of the first and second arrays are generally square in shape.

According to a second aspect of the present invention, there is provided an antenna device comprising:

the antenna enhancing structure according to the first aspect of the present invention described hereinbefore; and

an antenna loaded on the antenna enhancing structure, and a feed line for transmitting an electric signal to the antenna.

Preferably, the antenna comprises a dipole-type antenna. Preferably, the feed line has an inverted "L" shape and comprises at least a first portion and a second portion extending substantially perpendicular to the first portion.

Preferably, the antenna comprises an antenna dipole having two opposing antenna elements, and one of the two antenna elements has a side wall connected to a ground plane, and the first portion of the feed line extends substantially parallel to the side wall so as to form a parallel coupling line for transmitting an electric signal to the second portion, and the second portion couples the electric signal to the other of the two opposing antenna elements. Preferably, the feed line comprises a coaxial cable and a bridge feed, and the antenna comprises an antenna dipole having two opposing antenna elements, and wherein one of the two opposing antenna elements is connected to an outer conductor of the coaxial cable to the ground and the other of the two opposing antenna elements is connected to a central conductor of the coaxial cable, via the bridge feed, for receiving an electric signal.

Preferably, the bridge feed comprises a cut-out portion for enhancing isolation of the antenna dipole.

According to a third aspect of the present invention, there is provided an antenna system comprising:

a plurality of antenna devices according to the second aspect of the present invention described hereinbefore, and

a power divider for distributing an input power to the plurality of antenna devices at a predetermined ratio.

Preferably, the power divider comprises:

a node portion including a plurality of nodes connected in series, each node having a substantially oval shape;

an input portion for receiving an input power; and

a plurality of output portions for outputting the received power. Preferably, the node portion comprises a slit for controlling a predetermined ratio that the input power is divided amongst the plurality of output portions to the respective antenna devices.

According to a fourth aspect of the present invention, there is a method of fabricating an antenna enhancing structure for improving the performance of an antenna loaded thereon, the method comprising:

forming a first array of metallic patches,

forming a second array of metallic patches, and

separating the first array and the second array by a dielectric medium, wherein the first array and the second array is configured with respect to each other such that the metallic patches in the first array are offset from the metallic patches in the second array along a plane of the first array. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Fig. 1A depicts a schematic top view of an antenna enhancing structure according to an exemplary embodiment of the present invention;

Fig. 1B depicts a schematic cross-sectional side view of the antenna enhancing structure;

Fig. 2 depicts a schematic top view of an antenna enhancing structure 100 according to another exemplary embodiment of the present invention; Fig. 3A depicts an exemplary single-layer HPPS according to an exemplary embodiment of the present invention;

Fig. 3B depicts an exemplary multi-layered HPPS according to an exemplary embodiment of the present invention;

Fig. 4A depicts a graph of the permittivity of the antenna enhancing structure over a frequency range;

Fig. 4B depicts a graph of the reflection phase of the antenna enhancing structure over a frequency range;

Fig. 4C depicts a graph of the simulated and measured results of the reflection phase of the antenna enhancing structure over a frequency range; Fig. 5A depicts a schematic top view of an exemplary antenna device according to a first embodiment of the present invention;

Fig. 5B depicts a schematic cross-sectional side view of the antenna device of the first embodiment;

Fig. 6 depicts current distribution diagrams of a conventional simple dipole antenna and the antenna device 500 of the first embodiment over a complete frequency cycle at 1/4 wavelength intervals;

'^'- ^{:; '}¾H-'^''.

Fig. 7A depicts a graph comparing the return loss (S11) of the antenna device according to the first embodiment against conventional simple dipole antennas;

Fig. 7B depicts a graph comparing the antenna gain of the antenna device according to the first embodiment against conventional simple dipole antennas;

Fig. 8 depicts a graph comparing the return loss (S11) of the antenna device according to the first embodiment with different gap widths and conventional simple dipole antennas;

Fig. 9A depicts a schematic top view of an exemplary antenna device according to a second embodiment of the present invention;

Fig. 9B depicts a schematic cross-sectional side view of the antenna device of the second embodiment;

Fig. 9C depicts a schematic top view of a pair of bowtie antennas of the second embodiment; Fig. 9D depicts an exemplary dimension of the bowtie antenna;

Fig. 10A depicts a schematic top view of an antenna device according to a third exemplary embodiment of the present invention; Fig. 10B depicts a schematic perspective view of the antenna device of the third embodiment;

Fig. 10C depicts a schematic cross-sectional side view of the antenna device of the third embodiment;

Fig. 10D depicts schematic diagrams of the first and second probe feeds of the third embodiment; Fig. 11 A depicts a schematic top view of the antenna device according to a fourth embodiment of the present invention;

Fig. 11 B depicts a schematic perspective view of the antenna device according to the fourth embodiment;

Fig. 11C depicts a schematic cross-sectional side view of the antenna device of the fourth embodiment;

Fig. 11 D depicts an antenna system according to an embodiment with an array of antenna devices of the fourth embodiment;

Fig. 11 E depicts a wideband microstrip power divider for power distribution amongst four antenna devices of the fourth embodiment; Fig. 12A depicts a schematic top perspective view of an antenna device according to a fifth embodiment of the present invention;

Fig. 12B depicts a schematic cross-sectional side view of the antenna device of the fifth embodiment;

Figs. 12C to 12E depict close-up perspective views of the connection of the coaxial cables to the respective ring dipoles; and Fig. 13 depicts a diagram illustrating a method of fabricating an antenna enhancing structure according to an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention seek to provide an antenna device having a low profile while also featuring a wide bandwidth and a high gain. In particular, an antenna enhancing structure is provided for improving the performance of an antenna loaded thereon. Details of the antenna enhancing structure according to exemplary embodiments of the present invention will now be described.

Fig. 1A depicts a schematic top view and Fig. 1 B depicts a schematic cross-sectional side view of an antenna enhancing structure 100 according to an exemplary embodiment of the present invention. As shown in Figs. 1A and 1B, the antenna enhancing structure 100 comprises a first array 104 (e.g., an upper or top array) of metallic patches 105 and a second array 108 (e.g., a lower or bottom array) of metallic patches 109 separated or spaced apart by a dielectric medium 112. The metallic patches 105, 109 in the first and second arrays 104, 108 are configured or arranged periodically or in an ordered pattern. Therefore, the first and second arrays 104, 108 each constitutes a high permittivity periodic structure (HPPS), which is an example of a metamaterial because it is an artificial structure that possesses electromagnetic properties different from a natural material. The dielectric medium 112 may be a dielectric substrate or an air medium. For example, the dielectric substrate can be a printed circuit board (PCB) or other supporting materials such as wood, paper, glass, plastic and so on. A PCB may be preferred due to its suitability and low cost. Therefore, exemplary antenna enhancing structures 100 may be described hereinafter having a dielectric medium 112 made of a PCB. However, it will be appreciated to a person skilled in the art that the dielectric medium 112 is not limited to a PCB and the present invention encompasses any other types of dielectric medium. The metallic patches 105, 109 can be made of any high conductivity metals such as, but not limited to, Copper (Cu) or Gold (Au). In the exemplary embodiment, the metallic patches 105, 109 are generally square in shape. In other embodiments, the metallic patches 105, 109 may have other shapes such as rectangular, triangular, hexagonal or circular shape. In the exemplary embodiment, the first array 104 and the second array 108 are configured or arranged with respect to each other such that the metallic patches 105 of the first array 04 are offset along a plane of the first array from the metallic patches 109 of the second array 105. That is, at least a majority of the metallic patches 105 in the first array 104 are offset from the metallic patches 109 in the second array 105 with respect to an axis 114 perpendicular to the first array 104 or second array 108. In the example of Fig. 1 B, a center axis 115 of a metallic patch 105 in the first array 104 is offset from a center axis 116 of a corresponding metallic patch 109 in the second array 108 in a direction 117 parallel to the first or second array 104, 108. The metallic patch 109 in the second array 108 corresponding to a metallic patch 105 in the first array 104 may be defined as the metallic patch 109 in the second array 108 which is opposing (i.e., in the perpendicular axis 114) and/or closest (e.g., measured from the respective center axis) to the metallic patch 105 in the first array 104, and vice versa. Therefore, in the example of Figs. 1A and 1B, the metallic patch in the first array 104 denoted as 105a has one or more corresponding metallic patches in the second array 108 denoted as 109a, 109b, 109c and/or 109d (since the metallic patches 109a, 109b, 109c and 109d are all opposing and equidistant to the metallic patch 104a). In the exemplary embodiment, each pair of adjacent metallic patches 105, 109 has a gap (g) therebetween. The gap between each pair of adjacent metallic patches 105 in the first array 104 may be referred to as the first gap 120, and the gap between each pair of adjacent metallic patches 109 in the second array 108 may be referred to as the second gap 124. As can be seen from Fig. 1A, there exists a plurality of intersections 128 throughout the first array 104 where the respective first gaps 120 converge. Similarly, there exists a plurality of intersections (cannot be seen in Fig. 1A as they are blocked by the first array 104) throughout the second array 108 where the respective second gaps 124 converge. Therefore, in the example where the metallic patches 105, 109 has a square shape as shown in Fig. 1A, the first and second gaps 120, 124 each comprises a plurality of first (e.g., horizontal) and second (e.g., vertical) gaps, and the intersections 128 will be at where the horizontal and vertical gaps meet. Furthermore, in this exemplary embodiment, the metallic patches 105, 109 in each of the first and second arrays 104, 108 are configured into straight rows and columns as depicted in Fig. 1A. As described above, the first array 104 and the second array 108 are configured or arranged with respect to each other such that the metallic patches 105 of the first array 104 are offset along a plane of the first array from the metallic patches 109 of the second array 105. Therefore, in the example shown in Fig. 1A, the first gaps 120 of the first array 104 are offset along a plane of the first array from the corresponding second gaps 124 of the second array 108 (i.e., the first gaps are diagonally aligned/offset from the corresponding second gaps with respect to the perpendicular axis 1 4). The second gap 124 in the second array 108 corresponding to a first gap 120 in the first array 04 may be defined as the second gap 124 in the second array 108 which is diagonally opposing and/or closest to the first gap 120 in the first array 104, and vice versa. For example, with reference to Fig. 1 B, the first gap 120a has corresponding second gap(s) denoted as 124a and/or 124b. In the exemplary embodiment of Fig. 1 , each metallic patch 105 of the first array 104 and each metallic patch 109 of the second array 108 have the same planar size (i.e., width/ length (P)). Therefore, in the exemplary embodiment, the first array 104 is configured or arranged with respect to the second array 108 such that each metallic patch 105 of the first array 104 is offset along the plane of the first array 104 from its corresponding metallic patch(es) 109 of the second array 105. Preferably, as shown in Fig. 1A, each metallic patch 105 of the first array 104 is substantially centered over a corresponding intersection of the second gaps 124 in the second array 108. In other words, each metallic patch 105 of the first array 104 is offset from the corresponding metallic patch 109 of the second array 108 by about P₀ where P₀ = P/2 (i.e., offset by half the width/length of the metallic patch).

In another embodiment, the metallic patches 105 of the first array 104 each has a first planar size and the metallic patches 109 of the second array 108 each has a second planar size, whereby the first planar size and the second planar size are different. For example, Fig. 2 depicts a schematic top view of an antenna enhancing structure 100 whereby the metallic patches 105 of the first array 104 have a smaller planar size than the metallic patches of the second array 108. As can be seen from Fig. 2, the first array 104 and the second array 108 are configured or arranged with respect to each other such that the metallic patches 105 of the first array 104 are offset along a plane of the first array 104 from the metallic patches 109 of the second array 105. By configuring the first array 104 to have a different metallic patch size than those of the second array 108, the radiation frequency bandwidth of the antenna can be improved. For example, the first array 104 having a smaller metallic patch size improves the upper radiation frequency band of the antenna while the second array having a larger metallic patch size improves the lower radiation frequency band of the antenna.

In the embodiment where the dielectric medium 112 is a dielectric substrate such as a PCB, the first array 104 is formed on a first side (e.g., top or upper surface) 140 of the dielectric substrate 112 and the second array 108 is formed on a second side 142 (e.g., bottom or lower surface) of the dielectric substrate 112 opposing the first side 140. The antenna enhancing structure 100 as shown in Figs. 1A and 1B can be referred to as a double-layer HPPS (i.e., the structure 100 comprises two arrays 104, 108 of metallic patches). This double-layer HPPS may also be formed by combining (i.e., stacking) two single-layer HPPS together. An exemplary single-layer HPPS 300 is shown in Fig. 3A. Furthermore, in other embodiments, a multi-layered HPPS 320 may be constructed by stacking multiple single or double-layer HPPS together as illustrated in Fig. 3B. In Fig. 3B, a multiple-layer HPPS 320 is constructed by stacking a 1^st to an n ^h single or double layer HPPS together such that the multiple-layer HPPS 320 has a first and second arrays (e.g., top and bottom arrays) 104, 108 of metallic patches and one or more intermediate arrays 322 of metallic patches therebetween whereby each pair of adjacent arrays of metallic patches are separated by a dielectric medium 112.

The configuration of the antenna enhancing structure 100 as described above according to embodiments of the present invention (in particular the first and second arrays 104, 108 configured so as to be offset from each other) has been found to enhance the performance of an antenna loaded thereon. In particular, the antenna enhancing structure 100, 200 features high permittivity and a consistent reflection phase (i.e., within an acceptable range) over a wider frequency bandwidth, thereby making it suitable for a wideband, low-profile antenna design with a high gain and radiation efficiency.

In embodiments of the present invention, the width/length of the metallic patches 105, 109 is preferably in the range of about 0.04A to about 0.15λ, and more preferably about 0.05Λ to about 0.8λ, where λ is the wavelength at the center operating frequency of the antenna. The width of the gap (g) between a pair of adjacent metallic patches is preferably in the range of about 0.001 λ to about 0.06Λ, and more preferably in the range of about 0.001 λ to about 0.02A. Of the above range of dimensions, in general, the smaller the planar size of the metallic patches, the smaller the width of the gaps is required. Therefore, the width of the gaps depends on the planar size of the metallic patches, although this correlation is not necessary fixed or linear. The above range of dimensions has been found to produce better enhancement effects on the antenna. However, it will be appreciated to a person skilled in the art that the present invention is not limited to the above described ranges and other dimensions may also be appropriate for various purposes.

For better understanding of the present invention, exemplary antenna enhancing structures 100 having specific dimensions or geometry will be described hereinafter by way of examples only. Furthermore, various types of antenna loaded on the antenna enhancing structure 100 will also be described according to exemplary embodiments of the present invention. It will be appreciated to a person skilled in the art that any specific dimensions described hereinafter are merely provided to aid the understanding of the present invention, and the present invention is not limited to the specific dimensions described.

The antenna enhancing structure 100 shown in Figs. 1A and 1B will now be described in further details with exemplary dimensions according to an embodiment of the present invention to demonstrate its electromagnetic properties. In this example, the first and second arrays 104, 108 of metallic patches 105, 109 are printed on a PCB 112 (e.g., a low cost FR-4), and the antenna enhancing structure 100 is designed for an antenna having operating frequency in the range from about 1.5GHz to 12GHz. In this example, the lowest operating frequency of 1.5GHz was used for calculating the wavelength (λ) since the antenna enhancing structure 100 has an ultra wideband, where A=c/f and c is the speed of light in vacuum (i.e. ~3x 10⁸m/s). The thickness of the PCB 1 2 is 0.008Λ (1.6mm) and the dielectric constant ε_Γ is 4.4. The planar size of the antenna enhancing structure 100 is 1.5λ x 1.5λ (300mm * 300mm). The metallic patches 105, 109 of the first and second arrays 104, 108 are each square in shape with a width/length (P) measuring about 0.03A (6 mm). The gap (g) between each pair of adjacent metallic patches 105, 109 is about 0.005A (1 mm). The first and second arrays (e.g., top and bottom arrays) 104, 108 are offset or displaced by P₀=P/2 (or 0.015λ) from each other. Accordingly, the first array 104 and the second array 108 are configured or arranged with respect to each other such that the metallic patches 105 of the first array 104 are offset along a plane of the first array from the metallic patches 109 of the second array 105. In this example, the number of metallic patches 105 in the first array 104 and the number of metallic patches 109 in the second array 108 are 1 1 x 1 1 and 12x 12, respectively.

The antenna enhancing structure 100 with the above exemplary dimensions was measured in free-space using horn antennas to demonstrate its properties. This is a well-established measurement method in the field of antennas and can be set up using horn antennas and a network analyzer. Free space measurement is suitable for wideband structures since the bandwidth of the set up is limited only by the bandwidth of the transmitter and receiver. Figs. 4A and 4B depict the measured results of the antenna enhancing structure 100 and show that the permittivity of the structure 100 is above 30 from 2GHz to 5GHz while the refraction index is maintained at around 6. Fig. 4C shows the simulated and measured results of the reflection phase of the antenna enhancing structure 100. It can be seen that the variation in the reflection phase from 2GHz to 5 GHz is less than 30 degree, which demonstrates the improvement in the antenna radiation bandwidth.

Various types of antenna loaded on the antenna enhancing structure 100 will now be described according to exemplary embodiments of the present invention. It will be appreciated to a person skilled in the art that they are provided for better understanding of the present invention, but the present invention is not limited to the specific type of antennas described herein. Various other types of antenna which can be loaded on the antenna enhancing structure 00 are within the scope of the present invention.

Fig. 5A depicts a schematic top view of an exemplary antenna device 500 according to a first embodiment of the present invention. This exemplary antenna device 500 has a low profile and comprises a dipole antenna 502 loaded on an antenna enhancing structure 100 over a ground plane 504. The dipole antenna 502 is excited by a 50-ohms coaxial cable 510 which extends from the ground plane 504 through a cut-out portion 511 of the antenna enhancing structure 100 and towards the dipole antenna 502. For symmetric properties, the cut-out portion 511 is preferably at substantially a center portion of the antenna enhancing structure 100. However, this is not necessary if symmetric properties are not required. The thickness (H₂) of the antenna device 500 is 0.088A (where λ is the wavelength at the centre operating frequency of the antenna device 500). This is significantly thinner than a conventional antenna device having comparable performance which will typically require a thickness of 0.25A or more. The antenna device 500 has also been found to provide a wide operating bandwidth of about 22%.

Fig. 5B depicts a schematic cross-sectional side view of the antenna device 500. As shown, the dipole antenna 502 is fed by the coaxial cable 510. In particular, the outer conductor 512 of the coaxial cable 510 is connected to the ground plane 504 at one end and to one of the two opposing antenna elements at the other end such that the antenna element connected thereto is grounded. The central conductor 514 of the coaxial cable 510 is extended to connect to the other of the two opposing antenna elements such that the antenna element connected thereto receives an electric signal.

In this example, the center operating frequency of the antenna device 500 is designed at 1.95 GHz. Each antenna element of the dipole antenna 502 has a length (L) of 0.094A (16 mm) and a width (W) of 0.012λ (2 mm). The total height (H₂) of the antenna is 0.088A (15 mm), and the height Hi of the first array 104 from the ground plane 504 is 0.083A (14.2mm). The first and second arrays 104, 108 are formed by periodic square metallic patches 105, 109 having a width/length (P) of 0.05A (8.5 mm) (i.e., the metallic patches are about 8.5mm x 8.5mm) with a gap (g) between a pair of adjacent metallic patches being about 0.008A (1.4 mm). The number of metallic patches in the first array 104 and the second array 108 are 7x7 and 8x8, respectively. The size (G) of the square ground plane 504 is 0.735A*0.735A (125mm * 125 mm). The dielectric constant (ε_Γ) of the FR-4 PCB used in this example is 4.4. As shown in Fig. 5B, there is disposed another dielectric substrate layer 516 over the antenna enhancing structure 100. This can simplify the manufacturing process as the dipole antenna 502 can simply be disposed on the additional dielectric substrate layer 516. Alternatively, the additional dielectric substrate layer 516 is not provided, and therefore the dipole antenna 502 and the antenna enhancing structure 100 are simply separated by an air medium.

The exemplary geometry of the antenna device 500 described above is summarised in Table 1 below. Parameters P Po G 9 H H, H₂ L Li W

Unit 8.5 / 4.25 / 125 / 1.4 / 13.4 / 14.2 / 15 / 16 / 5 / 2 /

(mm/λ) 0.05 0.025 0.735 0.008 0.079 0.083 0.088 0.094 0.029 0.012

Table 1 - Exemplary geometry of the antenna device 500

An experiment was conducted to compare the differences in performance between a conventional simple dipole antenna (i.e., without the antenna enhancing structure 100) and the antenna device 500 described above (i.e., simple dipole antenna 502 integrated with the antenna enhancing structure 100). Fig. 6 illustrates current distribution diagrams of the conventional simple dipole antenna and the antenna device 500 over a complete frequency cycle at 1/4 wavelength intervals. By comparing the current distribution diagrams in Fig. 6, it can be clearly observed that the antenna enhancing structure 100 significantly enhances the antenna radiation over a larger effective radiation area.

Figs. 7A and 7B illustrate further exemplary performance comparisons between the antenna device 500 described above against conventional simple dipole antennas. In particular, the antenna device 500 is compared against a conventional simple dipole antenna loaded on a substrate having a dielectric constant (ε_Γ) of 4.4 (hereinafter conventional antenna device E4.4) and a conventional simple dipole loaded on a substrate having a dielectric constant (ε_Γ) of 36 (hereinafter conventional antenna device E36). Fig. 7A plots the return loss (i.e., S11 of the S-parameters for the antenna) and Fig. 7B plots the antenna gain (dBi) for the above-mentioned three antenna devices over the frequency range of 2 GHz to 5 GHz. From Fig. 7A, it can be observed that the return loss for the conventional antenna device E4.4 performed the worst (with only about 10% of the frequency range performing better than the -10dB reference (typical industrial reference)). On the other hand, the return loss for the conventional antenna device E36 performed the best (with about 70% of the frequency range performing better than the - 10dB reference). However, referring to Fig. 7B, it can be observed that the conventional antenna device E36 has a narrow gain bandwidth of about 22% from 2.2GHz to 2.75GHz with a peak gain of 7dBi only. On the other hand, the antenna device 500 demonstrated high gain over a significantly wider frequency range of 45% from 2.6GHz to 4.1GHz with a peak gain of 9.3dB^'i, which is 2.3dBi higher than the conventional antenna device E36. Therefore, this demonstrates that the antenna enhancing structure 100 is capable of improving the performance of an antenna loaded thereon, for example, the wide bandwidth and high gain obtained by the antenna device 500 while having a low profile.

As described above, the width of the gap (g) between a pair of adjacent metallic patches 105, 109 in the first and second arrays 104, 108 is preferably in the range of about 0.001 λ to about 0.06A, and more preferably in the range of about 0.001 λ to about 0.02A. Fig. 8 depicts a return loss graph for different antenna devices to compare their performance with respect to different gap widths. In particular, the following antenna devices were compared: simple dipole antenna device with an air dielectric medium (and without the antenna enhancing structure 100), simple dipole antenna device with a conventional PCB dielectric substrate (and without the antenna enhancing structure 100), and simple dipole antenna devices each respectively integrated with an antenna enhancing structure 100 having a gap width of 0.001 λ (0.1mm), 0.01 λ (1mm), 0.02A (2mm), 0.03A (3mm) and 0.06A (6mm). In this comparison, the size of metallic patches in the first and second arrays is maintained at 0.06A x 0.06A (6mm x 6mm) and the dielectric substrate has a dielectric constant (ε_Γ) of 4.4. From Fig. 8, it can be observed that the return loss of the antenna devices integrated with the antenna enhancing structure 100 of different gap widths all generally performed better than the conventional devices without the antenna enhancing structure 100. Amongst the antenna devices with the antenna enhancing structure 100, gap widths in the range of 0.001 A to 0.02A showed better return loss than gap widths higher than 0.02A. Fig. 9A depicts a schematic top view of an exemplary antenna device 900 according to a second embodiment of the present invention. The exemplary antenna device 900 comprises a pair of bowtie antennas 902 loaded on an antenna enhancing structure 100 over a ground plane 904. This results in a low profile dual-polarization bowtie antenna device 900. In this example, the center operating frequency of the antenna device 900 is designed at 5.4 GHz (4.8 GHz to 6 GHz) with dual polarization (±45°).

Fig. 9B depicts a schematic cross-sectional side view of the antenna device 900, and Fig. 9C depicts a schematic top view of the pair of bowtie antennas 902. As shown, the pair of bowtie antennas 902 comprises an upper bowtie dipole 905 and a lower bowtie dipole 906, and each comprising two opposing antenna elements. The upper bowtie dipole 905 and the lower bowtie dipole 906 are each respectively fed by a first and a second coaxial cable 910, 912. The first and second coaxial cables 910, 912 each has an outer conductor connected to the ground plane 904 and a central conductor for transmitting an electric signal. Therefore, for the upper bowtie dipole 905, one of the two opposing antenna elements is connected to the outer conductor of the first coaxial cable 910 so as to be grounded, and the other of the two opposing antenna elements is connected to the central conductor so as to receive an electric signal. The lower bowtie dipole 906 is connected to the second coaxial cable 912 in the same manner.

Fig. 9D illustrates an exemplary dimension of the bowtie antenna 905/906. The bowtie antenna 905/906 has a length (L) of 4.7mm and a Width (W-,) of 3mm. The total height (H₂) of the antenna is 0.09A (5mm), whereas the height (Hi) of the first array 104 from the ground plane 804 is 0.08A (4.5mm). The first and second arrays 104, 108 are formed by periodic square metallic patches having a width/length of about 0.057A (3.2 mm) (i.e., the metallic patches are about 3.2 mm x 3.2 mm) with a gap (g) between adjacent metallic patches being about 0.5 mm (0.001 λ). The number of metallic patches 105, 109 in the first and second arrays 104, 108 are 9x9 and 10x10, respectively. The size (G) of the square ground plane 904 is 0.9λ*0.9λ (50 mm * 50 mm). The dielectric constant (ε_Γ) of the dielectric substrate is 4.4. The exemplary geometry of the antenna device 900 described above is summarised in Table 2 below.

Table 2 - Exemplary geometry of the antenna device 900

The antenna device 900 according to the second embodiment was found to achieve a wide operating bandwidth of 28% with gain of larger than 7 dBi. Moreover, the isolation between the pair of bowtie antennas 902 is more than 30dB.

Fig. 10A depicts a schematic top view and Fig. 10B depicts a schematic perspective view of an antenna device 1000 according to a third exemplary embodiment of the present invention. In this embodiment, a dual-polarization dipole antenna 1002 is loaded on the antenna enhancing structure 100 over a ground plane 1004. The dual-polarization dipole antenna 1002 comprises a first planar dipole 1010 and a second planar dipole 1014, each comprising two opposing planar radiators. Therefore, as shown in Figs. 10A and 10B, the dual-polarization dipole antenna 1002 comprises four planar radiators in four quadrants, respectively. The four planar radiators each has a curved or arched side wall 1026 at an inner corner portion extending to the ground plate 1004 such that the side walls 1026 are shorted to the ground. The curved side wall 1026 extending in a direction generally perpendicular to a plane of the radiator. Therefore, the four planar radiators together form a circular channel at the center portion of the dipole antenna 1002 through which a first and a second probe feed 1020, 1022 extend from the ground plane 1004. Therefore, the antenna enhancing structure 100 has a cut-out portion at substantially a center portion thereof through which the side walls 1026 and the probe feeds 1020, 1022 extend.

Fig. 10C depicts a schematic cross-sectional side view of the antenna device 1000, and Fig. 10D depicts schematic diagrams of the first and second probe feeds 1020, 1022 in further detail. The first probe feed 1020 is configured to excite the first planar dipole 1010 and the second probe feed 1022 is configured to excite the second planar dipole 1014. As shown in Figs. 10C and 10D, each of the first and second probe feeds 1020, 1022 has a generally "P shape (generally inverted "L" shape). Each probe feed 1020, 1022 comprises a first portion 1030, 1036 extending from an SMA connector 1040 mounted below the ground plane 1004 in a manner substantially parallel to the side walls 1026 (e.g. vertically) of a planar radiator (e.g., the left planar radiator shown in Fig. 10C), a second portion 1032, 1038 extending substantially perpendicular from the first portion (e.g., horizontally) towards the opposing planar radiator (e.g., the right planar radiator shown in Fig. 10C), and a third portion 1034, 1040 extending substantially perpendicularly from the second portion towards the ground plane 1004 (e.g., vertically). With this configuration, the first portion 1030, 1036, together with corresponding shorted side wall 1026 of a planar radiator acts as a microstrip line with 50 ohms characteristic impedance which transmit an electric signal from the SMA connector 1040 to the second portion 1032, 1038. The second portion 1032, 1038 functions to couple electrical energy to the opposing planar radiator.

In this exemplary embodiment, the second portion 1038 of second probe feed 1020 crosses under the second portion 1032 of the first probe feed 1020 (in a substantially perpendicular manner). Therefore, as shown in Figure 10D, the second portion 1038 of the second probe feed 1022 has a lowered portion 1042 so as to enhance isolation from the first probe feed 1020. In this example, the center operating frequency of the antenna 1000 is designed at 2.2 GHz (1.7 GHz to 2.7 GHz). The width (W) of the shorted dipole antenna is 0.147A (20mm) and the vertical side wall 1026 has an arc-length ff of 15mm. The total height (H₂) of the antenna device 1000 is 18 mm (0.132λ), and the height (H-i) of the first array 104 from the ground plane 1004 is 17 mm (0.125λ). The first and second arrays 104, 108 are formed by periodic square metallic patches 105, 109 having width/length (P) of about 0.063A (8.5mm) with a gap (g) between a pair of adjacent metallic patches being about 0.011λ (1.5mm). The number of metallic patches in the first array 104 and the second array 108 are 8x 0 and 9x11 , respectively, but truncated three patches at each outer corner as shown in Figs. 10A and 10B. The size (G) of the square ground plane is 0.91A x 0.91A (125mm 125 mm). The dielectric constant (ε_Γ) of the FR-4 PCB 112 is of 4.4 with thickness (t) of 0.011λ (1.52mm).

The exemplary geometry of the antenna device 1000 is summarised in Table 3 below.

Table 3 - Exemplary geometry of the antenna device 1000

The antenna device 1000 according to the third embodiment was found to achieve a wide operating bandwidth of 44% with gain larger than 8dBi. Fig. 11A depicts a schematic top view of the antenna device 1100 and Fig. 1 B depicts a schematic perspective view of the antenna device 1 00 according to a fourth embodiment of the present invention. In this embodiment, a double-layer planar dipole (or dual-arm dipole) 1102 is loaded on the antenna enhancing structure 100 over a ground plane 1104. The double-layer planar dipole 1102 comprises a lower antenna dipole 1106 and an upper antenna dipole 1108, each comprising two opposing planar radiators. The two opposing planar radiators of the upper antenna dipole 1108 are supported on the respective two opposing planar radiators of the lower antenna dipole 1106 via a pair of supporting arms 1112. One of the planar radiators of the lower antenna dipole 1106 has a side strip 1113 extending towards and connected to the ground plane 1104 so as to form a shorted side strip 1113. The upper and lower antenna dipoles 1106, 1108 are generally rectangular in shape. The upper antenna dipole 1108 has a smaller planar size than the lower antenna dipole 1106.

Fig. 11C depicts a schematic cross-sectional side view of the antenna device 1100. As shown, the double-layer planar dipole 1102 is excited by a "Γ" shaped (generally inverted "L" shape) feed line or probe feed 1116 in a similar manner as described in the third embodiment, but except that the feed line is connected directly to one of the two opposing planar radiators of the lower antenna dipole 1106 (e.g., the lower right radiator as shown in Fig. 11C). More specifically, the feed line 116 has a first portion 1120 extending in a substantially parallel manner (i.e., substantially vertical) to the shorted strip 1113 of one of the planar radiators (e.g., the lower left planar radiator as shown in Fig. 11C), a second portion 1122 extending substantially perpendicularly from the first portion 1120 (i.e., substantially horizontal) towards the opposing planar radiator (e.g., the lower right radiator as shown in Fig. 11C) so as to be connected thereto. The feed line 1116 has one end connected to an SMA connector 1 18 mounted below the ground plane 1104. With this configuration, the first portion 1120 of the feed line 1116 together with the shorted side strip 1113 functions as a parallel couple line, which transmits electrical signal from the SMA launcher 1118 to the second portion 1122. The second portion 1122 of the feed line 1116 functions to transmit the electrical energy to the planar radiator connected thereto as shown in Fig. 11C. In this embodiment, the center operating frequency of the antenna device 1100 is designed at 2.2 GHz (1.7GHz to 2.7GHz). For example, this frequency range is suitable to cover 2G/3G/LTE systems. The lower antenna dipole 1106 has a width of 0.284λ (38.6mm), and a length (L,) of 0.432λ (58.8mm). One of the radiators of the lower antenna dipole 1106 is short-circuited to the ground plane 1104 with a length H₂ of 0.143λ (19.5mm), where λ=ο/ί and c is the speed of light in vacuum (i.e., ~3x 10⁸m/s). The upper antenna dipole 1108 has a width (W₂) of 0.239λ (32.5mm), a length (L₂) of 0.299λ (40.65mm) and a height (Η·,) of 0.136λ (18.5mm). The dimensions (G_w x G_L) of the ground plane 1104 are 0.551λ by 1.250λ (75mm ^χ 150mm). The first and second 5 arrays 104, 108 are printed on both sides of a FR-4 PCB with a dielectric constant (ε_Γ) of 4.3 and thickness (t) of 1.52mm0.011\. The square metallic patch has a width/length (P) of 0.048A (6.5 mm) with a gap (g) between a pair of adjacent metallic patches being about 0.007A (1mm). The first array 104 is offset from the second array 108 by 0.028Λ or 3.75mm (i.e., (P+g)/2). The number of metallic patches in the first array 104 and the 10 second array 108 are 8x18 and 9x19, respectively.

The exemplary geometry of the antenna device 1100 is summarised in Table 4 below.

a e - xemplary geometry o t e antenna dev ce 1100

Ί5

In an embodiment, an antenna system 1150 is formed comprising an array of antenna device 1100, a feeding network and a folded ground plane 1154. An exemplary antenna system 1150 may comprise an array of four antenna devices 1100 as shown in Fig. 1D. The exemplary antenna system 1150 (e.g., measuring 300 mm x 150 mm x 38mm) at 20 1.8GHz exhibits the broadside radiation gain of more than 12 dBi over the frequency range of 1.8-2.8 GHz. The antenna system 1150 was found to exhibit good electric characteristics such as low back lope, low cross polarization and sympatric radiation patterns. Furthermore, the antenna system 1150 was found to provide a wide bandwidth of more than 50% with stable radiation.

25

According to an embodiment, the feeding network comprises a wideband microstrip power divider 1160 as illustrated in Fig. 11E for power distribution amongst the four antenna devices 1100. The powder divider 1160 comprises a plurality of divider elements 1162 and is designed with an uneven power distribution for side-lobe reduction. To distribute power to the four antenna devices 1100, the power divider 1160 comprises a network of three divider elements 1162 as shown in Fig. 11E. It will be appreciated to a person skilled in the art that other numbers of divider elements may be provided depending on the number of antenna devices 1000 in the antenna system 1150.

Each divider element 1162 has a node portion 1164 comprising a plurality of nodes 1165, 1166 connected in series, each node 1165, 1166 having a substantially oval shape or cross-section. In a preferred embodiment, the node portion 1164 comprises two nodes 1165, 1166 arranged in series as shown in Fig. 11E. In this case, the node portion 1164 generally has a shape of the numeral "8", and more specially, a compressed "8" shape (compressed in the longitudinal direction). According to other embodiments, more than two nodes are arranged in series to further enhance the bandwidth of the power divider 1160.

Referring to Fig. 11E, the shape of the node portion 1164 provides a wider bandwidth while minimising the size of the divider element 1162. The node portion 1164 has an input portion 1167 for receiving an input power and two output portions 1168 which output power to two antenna devices 1100, respectively, each having an amount determined based on the node portion 1164. In particular, the node portion 1164 has a separation or slit 1170 at an upper portion 1172 and an intermediate portion 1174 thereof for dividing the input power at a desired or predetermined ratio to the two output portions 1168. By adjusting the slit 1170 towards the left or the right, the input power can be distributed accordingly amongst the two output portions 1168 at a predetermined ratio. For example, if 40% power is needed to be divided to the left output portion, then the slit 1170 is adjusted to the left side so that the length of the left side is shorter and about 40% of the overall length of the node portion 1164 (i.e., the "8" shape). Preferably, the upper portion 1172 of the node portion 1164 is thinner than the lower side 1176 for enhancing the operating bandwidth.

For example, the overall length of the node portion 64 can be 1/8λ while conventional power dividers such as Wilkinson type are 1/4λ. Therefore, the power divider 1160 is significantly minimised compared with conventional power dividers. Fig. 12A depicts a schematic top perspective view of the antenna device 1200 according to a fifth exemplary embodiment of the present invention. In this embodiment, a pair of square ring dipoles 1202, 1203 is loaded on the antenna enhancing structure 100 over a ground plane 1204. This results in a low profile dual-polarization square-ring dipole antenna device 1200.

Fig. 12B depicts a schematic cross-sectional side view of the antenna device 1200. Each ring dipole 1202, 1203 comprising two opposing ring elements is excited by a coaxial cable 1210, 1212 connected to the ground plane 1204. Figs. 12C to 12E depict close-up views of the connection of the coaxial cables 1210, 1212 to the respective ring dipoles 1202, 1203. For ring dipole 1202, an outer conductor 1214 of the coaxial cable 1212 is connected to the ground plane 1204 at one end and connected to one of the two opposing ring elements at the other end such that the antenna element connected thereto is grounded. A central conductor 1216 of the coaxial cable is connected to the other of the two opposing ring elements, via a bridge feed 1218, such that the antenna element connected thereto receives an electric signal. In particular, the bridge feed 1218 extends between the two opposing ring elements and is connected to the central conductor 1216 at one end (but not connected to the ring element thereat) and connected to the other of the two opposing ring elements at the other end. The ring dipole 1203 is connected to the coaxial cable 1210 in the same manner.

In an embodiment, the bridge feed 1218 crossing over the underlying bridge feed 1220 (with a 90° rotation) has a slot or a cut-out portion 1220 for enhancing the isolation of the pair of ring dipoles 1202, 1203.

In an example, the center operating frequency of the antenna is designed at 2.3 GHz from 1.5GHz to 3.1GHz. The square ring element has a width(W)/length(L) of about 0.17λ (23mm) and a thickness (t) of about 0.015λ (2mm), where λ is the wavelength at 2.3 GHz. The gap or separation of adjacent ring elements is 3mm. The total height (H) of the antenna is 0.13Λ (18mm), and the height (Η·,) of the first array 104 from the ground plane 1204 is 0.1λ (14.2mm). The square metallic patches of the first array 104 has a width/length (P1 ) of 0.065A (8.5mm) with a gap (g1) between a pair of adjacent metallic patches being 0.001 λ (1.4mm). The square metallic patches of the second array 108 has a width/length (P2) of Ο.Οδλ (10.5mm) with a gap (g2) between a pair of adjacent metallic patches being 0.01A (1.5mm). The height (H₂) of the second array 108 from the ground plane 1204 is 0.06λ (9mm). The number of elements on the top layer HPPS and bottom layer HPPS is 7x7 and 6x6, respectively.

The size (G) of the square ground plane 1204 is 0.95 λ*0.95 λ (125mm x125 mm). The dielectric constant (ε_Γ) of the FR4 PCB used is 4.3.

Figure 13 depicts a flow chart 1300 illustrating a method for fabricating the antenna enhancing structure 100 as described hereinbefore. The method 1300 comprises forming 1302 a first array 104 of metallic patches, forming 1304 a second array 108 of metallic patches, and separating 1306 the first array 104 and the second array 108 by a dielectric medium 112. In particular, the first array 104 and the second array 108 are configured with respect to each other such that the metallic patches in the first array 104 are offset from the metallic patches in the second array 108 along a plane of the first array 104. It will be appreciated to a person skilled in the art that the steps recited in the above method 1300 may be executed in any order and are not limited to the order presented. For example, the first and second arrays 104, 108 may be printed on opposing sides of a dielectric substrate (e.g., PCB) 112, and thus are separated from one another. As another example, alternatively, the metallic patches in the first and second arrays 104, 108 may be formed by etching the metallic layers on opposing sides of the dielectric substrate 112.

Accordingly, embodiments of the present invention described herein advantageously provide an antenna enhancing structure 100 for improving the performance of an antenna loaded thereon. As a result, various types of antenna devices can be realised with a low profile while having a wide bandwidth and a high gain.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. An antenna enhancing structure for improving the performance of an antenna loaded thereon, the structure comprising:

a first array of metallic patches, and

a second array of metallic patches, wherein

the first array and the second array are separated by a dielectric medium, and

2. The antenna enhancing structure according to claim 1 , wherein at least a majority of the metallic patches in the first array each has a central axis that is offset from a center axis of a corresponding metallic patch in the second array in a direction parallel to the first or second array.

3. The antenna enhancing structure according to claim 2, wherein the corresponding metallic patch in the second array of a metallic patch in the first array is a metallic patch in the second array which is opposing or closest to said metallic patch in the first array.

4. The structure according to any one of claims 1 to 3, wherein the dielectric medium is a dielectric substrate, and the first array is formed on a first side of the dielectric substrate and the second array is formed on a second side of the dielectric substrate opposing the first side.

5. The structure according to any one of claims 1 to 3, wherein the dielectric medium is an air medium.

6. The structure according to any one of claims 1 to 5, wherein each pair of adjacent metallic patches in the first array has a first gap therebetween, and each pair of adjacent metallic patches in the second array has a second gap therebetween, and wherein the first gap and the second gap each has a width in the range of about 0.001 λ to about 0.06A, where λ is a center operating frequency of the antenna.

7. The structure according to any one of claims 1 to 6, wherein the metallic patches in the first array and the second array each has a width in the range of about 0.04A to about 0.15A, where λ is a center operating frequency of the antenna.

8. The structure according to any one of claims 1 to 7, wherein the metallic patches in the first array each has a first planar size and the metallic patches of the second array each has a second planar size, and the first planar size and the second planar size are substantially the same.

9. The structure according to any one of claims 1 to 7, wherein the metallic patches of the first array each has a first planar size and the metallic patches of the second array each has a second planar size, and the first planar size and the second planar size are different.

10. The structure according to any one of claims 1 to 9, wherein the metallic patches of the first and second arrays are generally square in shape.

11. An antenna device comprising:

the antenna enhancing structure according to any one of claims 1 to

10; and

12. The antenna device according to claim 11 , wherein the antenna comprises a dipole-type antenna. 13. The antenna device according to claim 11 or 12, wherein the feed line has an inverted "L" shape and comprises at least a first portion and a second portion extending substantially perpendicular to the first portion.

14. The antenna device according to claim 13, wherein the antenna comprises an antenna dipole having two opposing antenna elements, and one of the two antenna elements has a side wall connected to a ground plane, and the first portion of the feed line extends substantially parallel to the side wall so as to form a parallel coupling line for transmitting an electric signal to the second portion, and the second portion couples the electric signal to the other of the two opposing antenna elements. 5. The antenna device according to claim 11 or 12, wherein the feed line comprises a coaxial cable and a bridge feed, and the antenna comprises an antenna dipole having two opposing antenna elements, and wherein one of the two opposing antenna elements is connected to an outer conductor of the coaxial cable to the ground and the other of the two opposing antenna elements is connected to a central conductor of the coaxial cable, via the bridge feed, for receiving an electric signal.

16. The antenna device according to claim 5, wherein the bridge feed comprises a cut-out portion for enhancing isolation of the antenna dipole. 17. An antenna system comprising:

a plurality of antenna devices according to any one of claims 11 to 16, and a power divider for distributing an input power to the plurality of antenna devices at a predetermined ratio. 18. The antenna system according to claim 17, wherein the power divider comprises:

a node portion including a plurality of nodes connected in series, each node having a substantially oval shape,

an input portion for receiving an input power;

and a plurality of output portions for outputting the received power.

19. The antenna system according to claim 18, wherein the node portion comprises a slit for controlling a predetermined ratio that the input power is divided amongst the plurality of output portions to the respective antenna devices.

20. A method of fabricating an antenna enhancing structure for improving the performance of an antenna loaded thereon, the method comprising:

forming a first array of metallic patches,

forming a second array of metallic patches, and

separating the first array and the second array by a dielectric medium, wherein the first array and the second array is configured with respect to each other such that the metallic patches in the first array are offset from the metallic patches in the second array along a plane of the first array.