APPLICATIONS

Field of the Invention

[0001] The present invention generally relates to wireless communications, and more particularly to a wideband dielectric resonator antenna for K _u -band applications.

Background of the Invention

[0002] For wireless communication systems, antenna is one of the most crucial parts because the antenna is the only structure for interfacing between a guiding device and the free-space surrounding the systems. FIG 1 shows the functional block diagram of a conventional RF front end in which an antenna is used together with low noise amplifier, mixer and band pass filter to build a complete microwave system. The antennas suitable for current modern wireless communications systems such as radar have to be not only compact but also high gain and wideband.

[0003] As time goes on, current frequency spectrum allocated for public usage cannot be sustained since the increasing number of users will result in signal interception and jamming. Consequently, new frequency spectrums are needed to be explored, and K _u band is one of them. The K _u band is an abbreviation of a K under band and consists of a portion of the overall K band family in the microwave spectrum. The frequency spectrum of the K _u band ranges from 12 GHz to 18 GHz, which is particularly utilized for radar applications, terrestrial communications and fixed-satellite services. Due to the high frequency of K„ band, the conductor loss of conventional metallic antennas becomes severe and the efficiency of the antennas is reduced significantly. Therefore, for microwave point to point and out door high speed link for Ku band applications, a wide bandwidth, lightweight, low profile, low cost and high performance directional antenna is essentially required.

[0004] The recent advances in material development have led to revolutionary changes in wireless communication technology. One of them is the development of dielectric oxide ceramics that have transformed the microwave wireless communication industry by reducing the size, cost and performance of antennas. This new antenna technology is known as dielectric resonator antenna (DRA). DRAs are known as miniaturized antennas of ceramics or another dielectric medium for microwave frequencies. When materials have a high dielectric constant are used, furthermore a compact, miniaturized structure may be achieved. DRA is highly flexible, easily being assembled with any latest technology by changing the size, form as well as dielectric constant of material. DRA is able to be excited with various feeding mechanisms that lead to different mode excitations.

[0005] DRA can be configured in an array format so as to achieve high bandwidth and high gain as well. At Ku-band, DRA array is useful since it has potential to replace conventional parabolic antenna that is normally being used in this particular band. Parabolic antenna is typically heavy and big in size, occupying a lot of space, and causes high conduction loss. However, by using DRA array, the size of antenna can be miniaturized and the weight can be reduced.

[0006] In fact, low-profile and small antenna is recommended for any communication system that is based on wireless device to operate, including mobile, military, media and medical systems. For instance, in radar technology, small antenna is essential to reduce the weight of the radar, enabling smooth mobility of the rotators for driving the compact and small antennas. In addition, conventional Yagi Uda antenna that can easily be found over the roof of each house is characterized by its big size, easily susceptible to damage and has many branches on either side. Hence, it is reasonable and practical to replace this antenna with an efficient, small and low-profile antenna while still maintaining its performance.

[0007] Many different wireless standards are available and another standard will emerge in the future for the next generation of communication devices. Demand for the wireless devices that can support multiple wireless standards keeps on increasing, requiring that the same wireless device can support different frequency bands, therefore increasing the functionality of the devices. The use of multiple antennas to cover multiple bands increases the cost and space. Hence, one solution for this problem is to have an antenna that can cover multiple band operations such as WLAN at 2.5 GHz, GPRS at 1.5575 GHz and many more. [0008] Therefore, there is an imperative need for an efficient, small and low-profile wideband antenna for wireless communications.

Summary of the Invention

[0009] One aspect of the present invention provides a wideband dielectric resonator antenna for Ku-band applications. In one embodiment, the dielectric resonator antenna comprises a substrate made from electrically non-constructive material, a microstrip line embedded in the substrate, where the microstrip line is made from electrically conductive material, a RF connector electrically coupled with one end of the microstrip line, and two dielectric resonator elements disposed sequentially onto the microstrip line, forming a co- planar configuration, wherein power is fed through the RF connector and the electromagnetic energy is coupled to the dielectric resonator elements through the direct microstrip line contact, wherein the amount of coupling is controlled by adjusting the spacing between the dielectric resonator elements and the length of the line underneath each dielectric resonator element, and wherein the voltage standing wave ratio (VSWR) of the input port can be improved by adjusting the positions of the dielectric resonator elements with respect to the open end of the microstrip line.

[0010] In another embodiment of the wideband dielectric resonator antenna, the dielectric resonator elements are made from dielectric ZrSnTiO materials.

[0011] In a further embodiment of the wideband dielectric resonator antenna, the dielectric resonator elements are cylindrical.

[0012] In yet a further embodiment of the wideband dielectric resonator antenna, the dielectric resonator elements are attached to the microstrip line by silicon glue.

[0013] In yet another embodiment of the wideband dielectric resonator antenna, the microstrip line length and width are 49.5 mm and 2.18 mm, respectively; the dielectric constant, ε _Γ , of the substrate is 2.4 with a thickness of 0.762 mm and a size of 40 mm x 49.5 mm; and the two cylindrical dielectric resonator elements with the same radius of 5 mm and height of 2.98 mm are positioned at distances di = 16.5 mm and di = 43.0 mm from the RF connector to obtain the optimum coupling.

[0014] Another aspect of the present invention provides a process for design and fabrication of a wideband dielectric resonator antenna for Ku-band applications. In one embodiment, the process comprises modeling of the wideband dielectric resonator antenna (DRA) by using 3D Computer Simulation Technology (CST) on the placement of two dielectric resonator elements plus variation of dielectric properties to get optimum performance of the DRA, fabricating of DRA by using solid state reaction method, characterizing of dielectric properties of the fabricated DRA by using Hakki-Coleman method, wherein the dielectric properties include dielectric constant, tan loss and temperature coefficient of resonant frequency, and testing the DRA on the parameters of S- parameter, input impedance, bandwidth and radiation pattern.

[0015] The objectives and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings.

Brief Description of the Drawings [0016] Preferred embodiments according to the present invention will now be described with reference to the Figures, in which like reference numerals denote like elements.

[0017] FIG 1 shows the functional block diagram of a conventional RF front end.

[0018] FIG 2 shows an illustrative view of a DRA device with a plurality of dielectric resonator elements connected by probes and configured in a planar format.

[0019] FIG 3 shows the geometry of an exemplary wideband DRA device in accordance with one embodiment of the present invention.

[0020] FIG 4 shows the simulated and measured return losses of the wideband

DRA device shown in FIG 3 within the range of 10 GHz to 14 GHz.

[0021] FIG 5 shows the simulated gain at resonant frequencies of the DRA as shown in FIG 3(a).

[0022] FIG 6 shows the simulated and measured E-plane and H-plane radiation patterns of the DRA as shown in FIG 3(a). Detailed Description of the Invention

[0023] The present invention may be understood more readily by reference to the following detailed description of certain embodiments of the invention.

[0024] Throughout this application, where publications are referenced, the disclosures of these publications are hereby incorporated by reference, in their entireties, into this application in order to more fully describe the state of art to which this invention pertains.

[0025] The present invention provides a wideband DRA. At high frequency, the only loss for a DRA is due to the imperfect dielectric material, which can be very small in practice. In order to achieve high gain and directivity, which are the fundamental requirements in the microwave point to point application, the dielectric resonator elements of a DRA can be arrayed either in linear or planar array as shown in the FIG 2, where the dielectric resonator elements are connected by probes. Single dielectric element antenna is normally associated with low gain and omni directional radiation pattern. However, when dielectric elements are arranged in such a way where every beam generated from the single dielectric can be combined together, high directional DRA can be produced.

[0026] Dielectric array antenna can be designed to control its radiation characteristics by properly selecting the phase and/or amplitude distribution between the elements. In fact, the principle of scanning arrays, where the maximum of the array pattern can be pointed in different directions, is based primarily on control of the phase excitation of the elements. In an array of identical elements, there are five controls that can be used to shape the overall pattern of the antenna, including the geometrical configuration of the overall array (linear, circular, rectangular, spherical, etc), the relative displacement between the elements, the excitation amplitude of the individual elements, the excitation phase of the individual elements and the relative pattern of the individual elements. For the design and study of DRA arrays, the spacing of 0.5λ _ο between dielectric elements is used since it contributes to the directional pattern. Additionally, the position of dielectric elements in planar array produce more directional pattern as compared with linear array configuration.

[0027] Now referring to FIG 3, there is provided the geometry of an exemplary wideband DRA device in accordance with one embodiment of the present invention. FIG 3(a) shows the simulated structure and FIG 3(b) shows the fabricated structure according to the design of the simulated structure as shown in FIG 3(a). As shown in FIG 3(b), the wideband DRA 1 comprises a substrate 2, a RF connector 3, a microstrip line 4 and two dielectric resonators 5. The microstrip line 4 is embedded in the substrate 2 and electrically coupled with the RF connector 3, and the two dielectric resonator elements are configured to be deposited on the microstrip line 4 and form a. planar array. The microstrip line 4 is used as the transmission line at the expense of probe and slot feeding, conferring the simplicity to the DRA 1. The power is fed through the RF connector 3 and the electromagnetic energy is coupled to the dielectric resonators 5 through the direct microstrip line contact. The amount of coupling is controlled by adjusting the spacing between the dielectric resonator elements and the length of the line underneath each dielectric resonator element. The substrate is made from electrically non-conductive materials; the microstrip line from electrically conductive materials; and the dielectric resonator element from dielectric ZrSnTiO materials.

[0028] One advantage of the DRA configuration of the present invention is that the voltage standing wave ratio (VSWR) of the input port can be improved by adjusting the position of the dielectric resonators (DRs) with respect to the open end of the microstrip line. This is very convenient because matching can be performed without introducing an external matching network, which would increase the cost and complexity of an antenna.

[0029] In one actual fabrication of the DRA as shown in FIG 3(b), the microstrip transmission line length and width were 49.5 mm and 2.18 mm, respectively. The dielectric constant, ε _Γ , of the substrate was 2.4 with a thickness of 0.762 mm, and the overall circuit was 40 mm x 49.5 mm. Two cylindrical dielectric resonator elements with the same radius of 5 mm and height of 2.98 mm were positioned at distances d; = 16.5 mm and c¼ = 43.0 mm from the input port to obtain the optimum coupling.

[0030] FIG 4 shows the simulated and measured return losses of the DRA as shown in FIG 3 and fabricated as above specified within the range of 10 GHz to 14 GHz. It can be noted that the measured resonant frequency experienced upward shift around (1 1.92 GHz - 1 1.23 GHz) 690 MHz. Both of the results have wide bandwidth due to the existence of two resonant frequencies which are adjacent to each other to produce broad bandwidth. Otherwise, only dual band instead of broad band can be obtained. The - 10 dB return loss bandwidth starts at 10.99 GHz and stop at 12.19 GHz and the difference is 1.19 GHz or 10.29 %. The measured bandwidth is 1.09 GHz or 8.87 %. The differences between the measurement and simulation result are associated closely with the properties of dielectric material, dimension of the DRA as well as external factors such as the cable and RF connector.

[0031] FIG 5 shows the simulated gain at resonant frequencies of the DRA as shown in FIG 3(a). It can clearly show that at 1 1.23 GHz and 1 1.82 GHz, gain is high with 6.20 dB and 5.92 dB, respectively. The present of second dielectric resonator has enhanced the gain, in addition to the characteristic of ZrSnTi0 ₂ material which has high quality factor of 5000. This contributes to the low dielectric loss.

[0032] FIG 6 shows the simulated and measured (a) E-plane and (b) H-plane normalized radiation patterns at 1 1.9 GHz. The measured and simulated patterns are quite similar to each other with many lobes at different angles. It is observed that this DRA is a type of quasi omni directional antenna. For the measured H-plane, radiation below the ground plane occurs because of the signal bounce back from the surrounding object resulting in forming side lobe. In theory, there is no radiation below the ground plane as shown in the simulated H-plane as ground plane acts as a reflector to reflect the entire signal above. For this particular DRA, dielectric resonator is made from ceramic material known as zirconium tin titanate (ZrSnTiO). The preparation of ZrSnTiO is done by using solid state reaction and characterized by the classic Hakki and Coleman method. The value of dielectric constant and quality factor are 37.1 and 5000@ 10 GHz, respectively and the application of this resonator ranging from 1.8 GHz to 30 GHz. All the above figures indicate that this DRA has wide bandwidth and high gain, thus suitable for application in the _u -band.

[0033] The present invention also provides a process for design and fabrication of the wideband DRA. The process comprises modeling, fabricating, characterizing and testing.

[0034] In one embodiment, the modeling of DRA can be done by using 3D CST

Microwave Studio version 2009. The design of the antenna was started with the simulation of the antenna by using 3D simulation software known as Computer Simulation Technology (CST). Extensive simulation on the placement of Dielectric Resonator plus variation of dielectric properties was conducted. Optimization was done to get optimum performance of the DRA. [0035] In one embodiment, the fabrication of dielectric resonators can be done by using conventional solid state reaction method. The fabrication of the dielectric resonator from various composition of the dielectric material was carried out by using conventional solid state reaction techniques. In solid state reaction, the process starts from mixing to sintering process.

[0036] In one embodiment, the characterization of dielectric properties of the fabricated dielectric resonators was carried out by using Hakki-Coleman method modified by Courtney. The essential properties of dielectric resonator need to be characterized are dielectric constant, tan loss and temperature coefficient of resonant frequency. From the result, the quality of the DR produced from the solid state reaction can be determined. Fabrication of DR is redone in case the DR produced not satisfied with the desired requirement.

[0037] In one embodiment, the DRA testing is done after dielectric resonators are attached to the PCB board by using silicon glue. The important parameters of the antenna such as S-parameter, input impedance, bandwidth and radiation pattern are tested. Network analyzer is used to determine S-parameter while radiation pattern is tested in the anechoic chamber. Comparison result between the simulated and measured output is also done to observe any dissimilarities of the result. On-field test is also conducted involving the point to point wireless hub.

[0038] To advance the technology of these materials, it is extremely important to accurately measure their properties of dielectric constant, tangent loss and temperature coefficient of resonant frequency. This advancement accelerated the development of new materials. These characteristics were obtained by measuring the microwave dielectric properties of low-loss materials using Kobayashi's method of a dielectric rod resonator short circuited at both ends by two parallel conducting plates.

[0039] In this invention, Computer Simulation Technology (CST) was used for the modeling and dielectric resonator fabrication involved conventional solid state reaction technique. Antenna configuration of DRA consists of two dielectric resonators in co-planar configurations which are directly coupled by microstripline. Two resonant frequencies represent each dielectric resonator. The idea is that when there have multiple dielectric resonators, many resonant frequencies can be produced resulting in wide bandwidth. This invention gives flexibility on account of its ability to tune the frequency for either wideband or dual band operation. Approximately, 10 % impedance bandwidth increased at Ku Band was noticed in this invention. The field pattern show directional beam pattern with high gain of 6.2 dB. This antenna was tested and it best operated at Ku-band. This type of antenna has a big potential in many applications that requires small space such as for anti-collision system, ground penetrating radar and satellite.

[0040] The present invention provides the design of a DRA for Ku-band application. The operating frequency of this DRA is around K _u -band which makes it suitable in practical application for radar system, terrestrial communication and fixed- satellite services, particularly. The present invention also provides the design of a wideband DRA by using two ZrSnTiO dielectric resonator elements. Combination of these dielectric resonator produce wide bandwidth of DRA for around 10.29 %. The position of ZrSnTiO dielectric resonator elements at distances di = 16.5 mm and d ₂ = 43.0 mm from the input port which producing optimum coupling of DRA.

[0041] The present invention has many advantages. One is surface wave elimination. The surface waves are not supported by the DRA array, therefore, the scan blind problem that exists in large microstrip antenna array when the scanning is at low elevation angles will not be of concern in the DRA arrays. One of the problems in large microstrip antenna phased arrays is the scan blind effect when the main beam is scanned to low elevation angles. The signal is completely lost due to the mutual coupling in the microstrip array. That causes the radar screen to be blank, which is considered as blindness for the radar.

[0042] Another advantage is high antenna efficiency and capability. The DRA is made from low-loss dielectric material with low dissipation loss. Therefore, it can handle high power, thus enhancing the covering range of the DRA. Since, the dissipation loss is too small, no cooling is required for the antenna, which decrease the operation cost and simplify the antenna design. In contrast with patch antenna, vivaldi antenna and the rest, all of them suffer from high dissipation loss since they are mostly fabricated from the conducting material (copper). This low dissipation loss associated with DRA contributes to the low radiation quality factor and lead to the high radiation efficiency.

[0043] Another advantage is superior bandwidth enhancement. By using multiple dielectric resonators, for instance dual resonators, each resonator can be tuned more or less independently by changing the position, allowing for a great deal of design flexibility. Additionally, DRA's bandwidth enhancement can also be realized by lowering the inherent Q-factor of the resonator and using external matching networks. Existing antenna technologies do not have such kind of variety to increase the bandwidth. With wide frequency band, frequency hoping is possible within large bandwidth, which minimizes possible jamming to the applications. Together with high permittivity material, dielectric resonator can be made small, thus contribute to the size reduction of any system application.

[0044] While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrative and that the invention scope is not so limited. Alternative embodiments of the present invention will become apparent to those having ordinary skill in the art to which the present invention pertains. Such alternate embodiments are considered to be encompassed within the scope of the present invention. Accordingly, the scope of the present invention is defined by the appended claims and is supported by the foregoing description.