GB2552828A

GB2552828A - A compact broadband circularly polarized crossed dipole antenna for GNSS applications

Info

Publication number: GB2552828A
Application number: GB1613835.6A
Authority: GB
Inventors: Huang Yi; Song Chaoyun
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-08-12
Filing date: 2016-08-12
Publication date: 2018-02-14
Also published as: GB201613835D0

Abstract

A compact broadband circularly polarised crossed dipole antenna arrangement 100, 101, for GNSS and GPS systems, comprising a pair of cross-dipoles 200 & 201, 202 & 203, on each side of a dielectric substrate layer, a vacant-quarter printed ring 400, 401, (VQPR) feeding structure on each side of the substrate layer, and near-field coupled parasitic (NFCP) elements 300, 301, 302, 303, on each side of the substrate layer. The antenna feed structure generates circularly polarized radiation at the desired frequency bands. The arms of the crossed-dipole are an elliptical loop shape. The use of an elliptical loop as a radiator reduces the dimensions of the antenna as a whole, and allows a broad CP and impedance bandwidth. The parasitic elements are preferably arc shaped, and are sited in the corners of the substrate. The NFCP parasitic elements are not electrically connected to the antenna, but are printed on both sides of the substrate and coupled to the antenna radiators.

Description

(71) Applicant(s):

Yi Huang

The University of Liverpool,

Dept of electrical Eng & Electron,

The University of Liverpool, LIVERPOOL, L69 3GJ, United Kingdom

Chaoyun Song

Department of Electrical Eng & Electron,

The University of Liverpool, LIVERPOOL, L69 3GJ, United Kingdom (72) Inventor(s):

Yi Huang Chaoyun Song (74) Agent and/or Address for Service:

Yi Huang

The University of Liverpool,

Dept of electrical Eng & Electron,

The University of Liverpool, LIVERPOOL, L69 3GJ, United Kingdom (51) INT CL:

H01Q 9/16 (2006.01) H01Q 1/38 (2006.01)

H01Q 21/24 (2006.01) (56) Documents Cited:

GB 2532727 A EP 2262058 A1

JPH04291806

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION [ONLINE], VOL. 59, NO. 1, JANUARY 2011, J-W Baik et al, Broadband Circularly Polarized Crossed Dipole With Parasitic Loop Resonators and Its Arrays, Available from: http://ieeexplore.ieee.org/ document/5617237/ [Accessed 30 January 2017], pages 80-88

IEEE Transactions on Antennas and Propagation [online], DO110.1109/TAP.2016.2633226, dated 2/12/2016 Son Xuat Ta et al, Compact CrossedDipole Antennas Loaded With Near-Field Resonant Parasitic Elements, Available from: http:// ieeexplore.ieee.org/document/7765125/ [Accessed 30/01/2017]

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION [online] VOL. 55, No. 4, April 2007, SH Wi et al, Wideband Microstrip Patch Antenna With U-Shaped Parasitic Elements, Available from:http:// ieeexplore.ieee.org/document/4148087/ [Accessed 7 February 2017], pages 1196-1199

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS [online] VOL. 13, 2014, Y. He et al, A Wideband Circularly Polarized Cross-Dipole Antenna, Available from: http://ieeexplore.ieee.org/ document/6705593/ [Accessed 30/01/2017], pages 67-70 (58) Field of Search:

INT CL H01Q Other: WPI, EPODOC (54) Title of the Invention: A compact broadband circularly polarized crossed dipole antenna for GNSS applications

Abstract Title: Circularly polarized cross-dipole antenna with parasitic elements (57) A compact broadband circularly polarised crossed dipole antenna arrangement 100, 101, for GNSS and GPS systems, comprising a pair of cross-dipoles 200 & 201, 202 & 203, on each side of a dielectric substrate layer, a vacant-quarter printed ring 400, 401, (VQPR) feeding structure on each side of the substrate layer, and nearfield coupled parasitic (NFCP) elements 300, 301,302, 303, on each side of the substrate layer. The antenna feed structure generates circularly polarized radiation at the desired frequency bands. The arms of the crosseddipole are an elliptical loop shape. The use of an elliptical loop as a radiator reduces the dimensions of the antenna as a whole, and allows a broad CP and impedance bandwidth. The parasitic elements are preferably arc shaped, and are sited in the corners of the substrate. The NFCP parasitic elements are not electrically connected to the antenna, but are printed on both sides of the substrate and coupled to the antenna radiators.

Fig. 1 Front (a) and back (b) views of the compact broadband CP crossed-dipole antenna.

1/6

300

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Fig. 2 Top (a) and bottom (b) 3D prospective views of the compact broadband CP crossed-dipole antenna.

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530 . 3 Side view of the compact broadband CP crossed-dipole antenna.

210

Fig. 4 Geometry of the egg-shaped elliptical loop radiator.

4/6

411

Fig. 5 Geometry of the vacant-quarter-printed ring feeding structure on the top plane of the antenna.

W3

Fig. 6 Geometry of the vacant-quarter-printed ring feeding structure on the bottom plane of the antenna.

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310

Fig. 7 Geometry of the arc-shaped near-field coupled parasitic element.

Frequency (GHz)

Fig. 8 Simulated and measured reflection coefficient (Si 1) in dB of the antenna.

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Fig. 9 Simulated axial ratio in dB of the antenna.

Fig. 10 Simulated realized gain in dB of the antenna

A Compact Broadband Circularly Polarized Crossed Dipole Antenna for GNSS Applications

DESCRIPTION

1. Background

A circularly polarized (CP) antenna is defined as an antenna which can generate a circularly polarized electromagnetic wave. This means that there are two orthogonal currents on the antenna with the same amplitude and a 90-degree phase difference. There are two types of circular polarization: one is the right-hand circular polarization (RHCP) and the other is the left-hand circular polarization (LHCP). CP antennas are now widely used in wireless communication systems such as the Global Position System (GPS) and satellite communication systems. A growing number of literatures on antennas with CP have emerged owing to their ability to reduce multipath propagation or Faraday rotation effects and to improve the flexibility in antenna orientation constrains. The CP feature is characterized by the axial ratio (AR) of antennas in practice. For a CP antenna, the AR is expected to be less than 3 dB at the operational frequencies, along with other requirements such as its reflection coefficient (Sn) should be less than -10 dB. To generate a CP radiation, two orthogonal currents with the same amplitude and a 90-degree phase difference should be generated on the antenna. As described in [US patent in 2013, US8350771], this can be achieved by using two orthogonal feeding ports or feeding networks in a conventional antenna system. Some examples can be found from such as [J. H. Han and N. H. Myung, “Novel feed network for circular polarization antenna diversity”, IEEE

Antennas and Wireless Propag. Lett., vol. 13, pp. 979-982, 2014] and [X. Jiang, Z. Zhang, Y. Li, and Z. Feng, “A wideband dual-polarized slot antenna,” IEEE Antennas Wireless Propag. Lett. vol. 12, pp. 1010-1013, 2013], However, by offsetting the feed location of the antenna as described in [US patent in 2013, US 20130321214], or cutting the corners of a conventional patch antenna as discussed in [US patent in 2003, US 6606061], a single-feed system can also generate two orthogonal currents with the same amplitude but a 90-degree phase difference, some designs have been proposed using these ideas [S. C. Wen and C. Yu, “A novel CP antenna for UHF RFID handheld reader,” IEEE Antennas Propag. Mag., vol. 55, no. 4, pp. 128-137, Aug. 2013; and Z. B. Wang, S. J. Fang , S. Q. Fu and S. L. Jia Single-fed broadband circularly polarized stacked patch antenna with horizontally meandered strip for universal UHF RFID applications IEEE Trans. Microw. Theory Tech., vol. 59, no. 4, pp. 1066-1073, 201 ]. Moreover, some antennas are particularly suitable for generating circularly polarized waves such as the circular patch antennas, helical antennas and spiral antennas [S. Lee, J. Woo, M. Ryu and H. Shin, Corrugated circular microstrip patch antennas for miniaturization, Electron. Lett. vol.38, no.6, pp.262-263, 2002; P. K. Shumaker, C. C. H. Ho and K. B. Smith Printed half-wavelength quadrifilar helix antenna for GPS marine applications, Electron. Lett. vol. 32, no. 3, pp. 153-154, 1996, and S. G. Mao, J. C. Yeh, and S. L. Chen, “Ultra-wideband circularly polarized spiral antenna using integrated balun with application to time-domain target detection,” IEEE

Trans. Antennas Propag., vol. 57, no. 7, pp. 1914-1920, Jul. 2009],

Thus, CP antennas are widely used for applications such as satellite communication and navigation systems. The global navigation satellite systems (GNSS) have progressed significantly for the last few decades, and are providing a wide range of positioning, navigating, and informational functions and activities. For all these applications, GNSS receivers are required which are ranging from relatively simple, consumer-oriented, handheld units to highly sophisticated airborne and marine vessel equipment. In addition to the well-developed GPS, there are some other similar systems which are not yet fully developed or implemented but will become major competitors of the GPS soon. They are the European Galileo, Russian’s GLONASS, and Chinese Beidou (Compass). They all use CP antennas in order to combat the Faraday rotation effect of the ionosphere. To avoid interference, additional frequency bands are allocated for GNSS use. As a result, GNSS transmitting and receiving electronics, including antennas, should work at these frequency bands.

The frequency bands for the GPS are L1: 1575.42 MHz, L2: 1227.6 MHz, L3: 1381.05 MHz, L4: 1379.913 MHz and L5: 1176.45 GHz. Single-band GPS receivers for civil use typically work at L1 band while the dual-band GPS receivers work at L1 and L2 and are used by military. L3 - L5 bands have been used for special applications such as the nuclear detonation detection, additional ionospheric correction, and civilian safety-of life signal reception. There has been a lot of research on GNSS antennas. But most of them are for single band (L1) operation, and some for dualband (L1 and L2) operation. Most existing commercial small L1/L2 GNSS/GPS antennas have relatively narrow 10 MHz bandwidths that are not adequate for supporting the bandwidth required for advanced GPS coding schemes. There is an increasing demand for multiband or broadband CP antennas to cover not only the GPS frequency bands, but also the Galileo or GLONASS or Beidou frequency bands.

This has been a main reason for this invention. Another main reason is that there are special requirements on the antenna size and weight for these GNSS based applications (in addition to the polarization and frequency bands). In addition to being able to receive a greater number of GNSS channels and having wider channel bandwidths, many GNSS applications require antennas to be small in size in order to fit into the desired device packaging. The size must be as small as possible and the weight has to be as light as possible since they are often carried by people (such as soldier) or mounted on vehicles in many cases. As described in [US patent in 2014, US 20140247194], vehicle-mounted antennas are designed to accommodate vehicle motion, which can include movement in six degrees of freedom as well as translations along axes. Some interesting designs can be found from such as [US patent in 2011, US 8686899] and [Z. X. Liang, Y. X. Li, and Y. L. Long, “Multiband monopole mobile phone antenna with circular polarization for GNSS application,” IEEE Trans. Antennas Propag., vol. 62, no. 4, pp. 1910-1917, Jan. 2014], A US patent in 2014 [US 20140210678] has indicated that, the miniaturization of GPS antennas can be achieved by using high dielectric loading material. The effective wavelength of the antenna can be significantly reduced. But the trade-off is a decrease of the radiation efficiency and total efficiency of the antenna [O. Leisten, J. C. Vardaxoglou, P. McEvoy, R. Seager and A. Wingfield “Miniaturized dielectrically-loaded quadrifilar antenna for global positioning system (GPS)” Electron. Lett. vol. 37, no. 22, pp. 1321-1322, 2001 and M. Chen and C. Chen A compact dual-band GPS antenna design IEEE Antennas Wireless Propag. Lett. vol. 12, pp. 245-248, 2013], Inductive loading and capacitive loading are additional approaches for antenna miniaturization, as described in US patent in 2011 [US 20110012788], This can be achieved by adding a meander line in the antenna structure, cutting a slot in the antenna structure, or folding the main radiator of the antenna that can increase the inductance or capacitance of the antenna. The surface current length is increased. The dimension of radiator can be reduced without increasing the dielectric constant of the substrate or loading material [S. X. Ta, H. Choo, I. Park and R. W. Ziolkowski, Multi-band, wide-beam, circularly polarized, cross, asymmetrically barbed dipole antennas for GPS applications IEEE Trans. Antennas Propag., vol. 61, no. 11, pp. 5771-5775, 2013],

The cross dipole antenna is a nature selection for CP antennas since it is very easy to generate two orthogonal currents with the same amplitude and a 90-degree phase difference. It also offers many other attractive features such as an omnidirectional radiation pattern, a simple structure, a reasonable bandwidth, and low-cost. Many designs and patents are already published [US Patent US8325101], Recently, a very interesting cross dipole antenna was proposed by [Y. J. He, W. He, and H.

Wong, “A wideband circularly polarized cross-dipole Antenna,” IEEE Antennas and Wireless Propag. Lett. vol. 13, pp. 67-70, 2014], A new feeding structure was introduced by using a vacant-quarter printed ring (VQPR) as a 90-degree phase delay line between the dipole pair. The CP bandwidth is broadened due to the broadband feature of the configuration. Both the Right Hand Circular Polarization (RHCP) and Left Hand Circular Polarization (LHCP) can be generated at two sides of the antenna separately.

There is a demand for CP antennas having a wide impedance bandwidth as well as a broad CP bandwidth that can cover all the known GNSS frequency bands. Also, the antenna is expected to be of low profile, light weight and compact size so that it can be used in portable applications.

2. The Invention

This invention presents a novel compact broadband circularly polarized crossed-dipole antenna for GNSS applications. Disclosed herein is an exemplary antenna structure adapted to provide broadband coverage comprising a dielectric substrate layer and two conducting layers printed on both sides of the substrate. Embodiments of the antenna are adapted to utilize both crossed-dipole radiators and near-field coupled parasitic (NFCP) elements to produce wide bandwidth and achieve antenna miniaturization. An embodiment is also disclosed that further comprises a 90degree phase delay feeding structure between the dipole pair to generate circularly polarized radiation field for the antenna. The feeding structure is a particular vacantquarter-printed ring (VQPR) structure that can configure two dipole elements in a single port feed system and create CP radiation field. An additional embodiment of the invention is comprised of an egg-shaped elliptical loop structure for the crossed-dipole radiators of the antenna. The antenna could achieve very wide CP bandwidth and a significant reduction of the dimension by using such elliptical loop structure radiators. The use of the elliptical loop as a radiator for the crossed-dipole in the present invention is a very novel concept that can improve the CP performance of a conventional dipole antenna in terms of the CP bandwidth as well as the impedance bandwidth. An exemplary embodiment may also include an arc-shaped parasitic element for the antenna. The parasitic elements are not electrically connected to the antenna, but they are printed on both sides of the substrate and coupled to the antenna radiators. The overall dimension of the antenna can be significantly reduced by using these NFCP elements, for example, the electrical length of the antenna could be reduced from the length of a conventional resonant dipole (1/2 wavelength) to the length about 1/4 wavelength. The miniaturization of this invention is a novel capacitive coupling approach. The concept and design in accordance to the present invention can be easily modified by tuning the size of the elliptical loop radiators and the size of the arc-shaped NFCP elements to cover other frequencies.

In an exemplary embodiment of the invention, a compact broadband CP crosseddipole antenna is proposed using the aforementioned novel features and concepts in accordance to the present invention. The present antenna covers the entire GPS L1 L5 bands and Galileo E1, E5, and E6 bands from 1.16 GHz to 1.88 GHz for the reflection coefficient (Sn) < -10 dB. The CP bandwidth of the antenna is also relatively broad that covers from 1.24 GHz to 1.86 GHz for the axial ratio < 3 dB. More importantly, the antenna could be printed on a low cost printed circuit board (PCB), such as FP4 with a relative permittivity of 4.4 and a thickness of 1.6 mm. Its overall dimension of the antenna is about 64 χ 64 χ 1.6 mm³, which is only about 0.247A χ 0.247A χ 0.006A (where A is the free space wavelength of the lowest resonate frequency 1.164 GHz). Among the existing antenna designs in the literature and current available products on the market, the present invention has probably achieved the widest impedance and CP bandwidth (when compared with the antennas with a similar size), and may have achieved the smallest dimension for antennas covering the same frequency band.

In addition to the novel features and advantages mentioned above, other benefits are apparent from the following descriptions of the drawings and exemplary embodiments.

Figure 1(a) is a front view illustration of an exemplary embodiment of an antenna in accordance to the present invention;

Figure 1(b) is a back view illustration of an exemplary embodiment of an antenna in accordance to the present invention;

Figure 2(a) is the top of the 3D prospective view illustration of the embodiment of Fig.

1(a);

Figure 2(a) is the bottom of the 3D prospective view illustration of the embodiment of

Fig. 1(b);

Figure 3 is a side view illustration of the embodiment of Figs. 2(a) and (b);

Figure 4 is a detailed illustration of an exemplary embodiment of an egg-shaped elliptical loop radiator in accordance to the present invention;

Figure 5 is a detailed illustration of an exemplary embodiment of a vacant-quarterprinted ring feeding structure on the top plane of the antenna in accordance to the present invention;

Figure 6 is a detailed illustration of an exemplary embodiment of a vacant-quarterprinted ring feeding structure on the bottom plane of the antenna in accordance to the present invention;

Figure 7 is a detailed illustration of an exemplary embodiment of an arc-shaped near-field coupled parasitic element in accordance to the present invention;

Figure 8 is a graph of simulated and measured reflection coefficient with respect to frequency for an exemplary embodiment;

Figure 9 is a graph of simulated axial ratio with respect to frequency for an exemplary embodiment;

Figure 10 is a graph of simulated realized gain with respect to frequency for an exemplary embodiment;

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Exemplary embodiments of the present invention are directed to a compact broadband CP antenna design. For example, one embodiment of the antenna may be configured to be 34.3 mm in length and 24.4 mm in width. In one example, the size of the antenna is only about 0.247A in GPS L5 band. In an exemplary embodiment, broadband coverage may be achieved by using the elliptical loop radiator for the dipole and capacitive coupling parasitic element for the antenna.

Referring to Figs. 1 (a) and (b), an exemplary embodiment of the antenna 100,101 according to the present invention may comprise a pair of dipoles with four identical arms 200, 201, 202, 203 printed on both sides of the antenna. The two dipoles are orthogonal to each other and each dipole is fed by using a special vacant-quarterprinted ring (VQPR) structure 400, 401 that can generate a 90-degree phase delay between the dipole pair. More particularly, the current from the feed port firstly travels to the initial dipole 200, 203, and then passing through the VQPR structure and flows into the secondary dipole 201, 202. In a specific frequency range, the phase of the secondary dipole 201,202 can be delayed by 90 degrees. In this scenario, the crosseddipole may have the current with the same amplitude (due to the identical arms) and a 90-degree phase difference, and therefore the antenna may be of circular polarization. In addition, the embodiment ofthe antenna 100,101 according to the present invention may comprise four parasitic elements 300, 301, 302, 303. Each element is in an arcshaped structure. The parasitic elements are not electrically connected to the dipoles in the present invention, but they are deployed on the four corners of the PCB and printed on both sides of the antenna. Each parasitic element is coupled to the antenna radiator (on the other side) through the substrate. The coupling between the antenna radiator and the parasitic element is capacitive coupling. Thus the resonant frequency of the antenna can be shifted down to lower frequency, or in other words, the dimension of the antenna can be significantly reduced by using these parasitic elements. The antenna may be fabricated using a low cost FR4 substrate with a relative permittivity of 4.4 and a thickness of 1.6 mm. The copper layers for antenna printing may have a thickness of 0.035 mm. The antenna may be fed by using a 50 Ω coaxial cable, where the inner conductor of the cable 500 is fed to the metal on the top plane of the antenna and the outer conductor 501 is connected to the bottom metal.

Figs. 2 (a) and (b) show the 3D prospective views of the embodiment of the antenna 120, 121 as shown in Fig. 1. It can be seen that the structure of the arms (radiator) of the dipole 220, 221, 222, 223 is an egg-shaped elliptical loop. This is a novel feature in the present invention that can control the current path on the radiator. The current may travel in a complete circle (from 0 to 360 degrees) on the loop structure. In this scenario, the CP performance of the antenna could be improved by using such elliptical loop structure for the radiator. More particularly, there could have more current paths (at different frequencies) that may have the same amplitude and 90-degree phase delay. In addition, the loop shape radiator can improve the impedance matching of the antenna at low frequencies, thus the size of the antenna in the present invention can be reduced by using the novel elliptical loop radiator for the dipole arms. In addition, it io is clearly seen that the parasitic elements 320, 321, 322, 323 are coupled to the radiators at both sides of the antenna. The coaxial cable 520 is orthogonal to the PCB and fed to the VQPR structure 420, 421 at the top and bottom planes of the antenna in the present invention. Similarly, Fig. 3 is a side view of the embodiment of the antenna in the present invention. It is apparent that the parasitic elements 330, 331 are not connected to the radiators of the antenna 230,231, the VQPRs 430,431 are electrically connected to the arms of the dipole 230, 231 and fed by the coaxial cable 530.

In an exemplary embodiment of the invention, at least four conducting dipole arms may serve as the radiators of the antenna. An egg-shaped elliptical loop structure 210 may be used by the arm and a detailed illustration of the geometry of the shape is depicted in Fig. 4. The major parameters that may affect the performance should be the length (L1) and height (H1) of the loop as well as the width (W1) of the conducting strip (i.e. copper). The lowest resonant frequency of the antenna can be controlled by modifying the length of the loop, or in other words, the dimension of the antenna is mainly determined by the value of L1. Meanwhile, the impedance bandwidth and CP bandwidth of the antenna are dependent on the height of the loop. More particularly, a crossed-dipole with a ‘fatter’ radiator (larger value of H1) may have a broader impedance and CP bandwidth. Moreover, the width of the strip can affect the impedance matching performance of the antenna. A smaller reflection coefficient can be achieved by tuning the value of W1. As an example, the antenna in accordance to the present invention may have W1 = 0.7 mm, H1 = 24.4 mm, and L1 = 34.3 mm.

In the embodiment of the present invention, at least two VQPR structure may be used to link the dipole pair and produce CP radiation for the antenna. Fig. 5 shows the detailed illustration of the geometry of the VQPR structure 412 on the top plane of the antenna. It may consist of two portions that include a VQPR 410 and a rectangular patch 411 respectively. The rectangular patch can make the antenna easily fed to the inner conductor of the coaxial cable 510. Thus the length (H2) and width (W2) of the rectangular patch 411 may affect the matching performance of the antenna, they should be optimized and tuned using electromagnetic simulation software such as the CST in the design. The frequency for CP performance is determined by the radius (R1) of the VQPR, since the circumference of the VQPR is equivalent to a quarter wavelength at the desired frequency. The width of the conducting strip (W3) for the VQPR will affect the CP bandwidth as well as the matching performance of the antenna in the present invention. Thus it should be optimized in the design using the CST software. As an example, the antenna in accordance to the present invention may have

H2 = 7.6 mm, W2 = 6 mm, R1 = 7 mm, and W3 = 1.5 mm. In addition, the inner conductor of the feeding coaxial cable may have a diameter D1 = 1 mm. Similarly, Fig. 6 is a detailed illustration of the VQPR 415 used on the bottom plane of the antenna. It can link the two dipole arms at the bottom layer of the PCB and generate CP radiation. It still consists of a VQPR 413 and a rectangular patch 414 and has the same dimension as the VQPR 412 on the top plane. However, one major difference is that the rectangular patch 414 in this VQPR should be electrically connected to the outer conductor of the coaxial cable 511. Thus, the antenna in accordance to the present invention may have H3 = 7.6 mm, W4 = 6 mm, R2 = 7 mm, and W5 = 1.5 mm.

Parasitic elements are used in the present invention to reduce the size of the antenna. Fig. 7 shows the detailed geometry of the parasitic element in the embodiment of the present invention. An arc-shaped structure 310 is designed for the parasitic element, where the length (L2) and height (H4) of the arc could be the major parameters that may affect the performance. The width of the conducting strip (W6) of the arc can affect the impedance of this strip. The parasitic elements are coupled to the elliptical loop radiator on both sides of the PCB. It is a novel concept for capacitive coupling that can reduce the size of the antenna. As an example, the antenna in accordance to the present invention may have W6 = 1 mm, H4 = 13.9 mm, and L2 = 27.9 mm. In an exemplary embodiment, when the disclosed design steps are performed to design an embodiment of the invention optimized to operate at the entire GPS L1- L5 and Galileo E1, E5 and E6 bands using the FR4 board. A prototype antenna was fabricated to verify the antenna performance. The overall dimension of the antenna is 64 χ 64 χ 1.6 mm³, which is only about 0.247A χ 0.247A χ 0.006A (A is the free space wavelength at the lowest frequency :1.164 GHz, GPS L5).

The simulated and measured reflection coefficient (Sn) of the antenna in accordance to the present invention are shown in Fig. 8. It is found that the antenna covers a wide bandwidth from 1.16 to 1.9 GHz for Sn < -10 dB. At GPS L1 band (1.575 GHz), the value of Si 1 is as low as -30 dB that shows an excellent impedance matching performance. The measured results are well-agreed with the predicted performance. It demonstrates that the antenna in the present invention has indeed covered the desired GPS and Galileo bands with relatively good performance. The simulated axial ratio of the antenna in the present invention is shown in Fig. 9 against frequency. It can be seen that the CP bandwidth of the antenna is from 1.24 to 1.87 GHz for axial ratio is less than 3 dB. The value of axial ratio over the bandwidth of interest is less than 4.5 dB in all cases. This shows that the proposed antenna has a very wide CP bandwidth and a broad impedance with a compact size. The novel features such as the elliptical loop radiator, VQPR feed structure, and arc-shaped parasitic element have indeed improved the antenna performance and reduced the antenna size. The simulated realized gain of the antenna is shown in Fig. 10 as a function of frequency. It can be seen that the average gain over the broadband is about 2 dBi. The antenna in the present invention is a dipole-type antenna with bidirectional radiation pattern and a wide half-power-beamwidth. A conducting ground plane reflector can be placed below the antenna to produce a unidirectional radiation pattern and a higher realized gain (up to dBi). While the space between the antenna and the reflector could be about the quarter wavelength (64 mm) of the lowest resonant frequency (1.164 GHz). For a lowprofile configuration, a broadband artificial magnetic conductor (AMC) plane that covers the frequency band of interest could be used to replace the conducting ground plane. In this way, the overall height of the antenna in the present invention with a reflector can be lower than 20 mm. Due to the wide bandwidth and compact size of the antenna in the present invention, it can not only be used in the conventional GNSS applications and wireless communications, but also be used in many portable applications such as mounted on the soldier’s body or mounted on a vehicle for navigation applications.

Any embodiment of the present invention may include any of the optional or preferred features of the other embodiments of the present invention. The exemplary embodiments herein disclosed are not intended to be exhaustive or to unnecessarily limit the scope of the invention. The exemplary embodiments were chosen and described in order to explain the principles of the present invention so that others skilled in the art may practice the invention. Having shown and described exemplary embodiments of the present invention, those skilled in the art will realize that many variations and modifications may be made to the described invention. Many of those variations and modifications will provide the same result and fall within the spirit of the claimed invention. It is the intention, therefore, to limit the invention only as indicated by the scope of the claims.

Claims

CLAIMS The claims are:

1. An antenna comprising:

a dielectric substrate layer; and a pair of cross dipoles on both sides of the substrate layer; and a pair of vacant-quarter-printed ring on both sides of the substrate layer; and four near-field coupled parasitic elements on both sides of the substrate layer;

wherein the antenna is adapted to provide broadband coverage and antenna miniaturization using the crossed-dipole and parasitic elements.

2. The materials to make the dipoles of claim 1 are any printed circuit board.

3. The pair of cross dipoles of claim 1 wherein the crossed-dipole may have at least four identical dipole arms.

4. The dipole arm of claim 3 wherein the arm may have an egg-shaped elliptical loop structure.

5. The egg-shaped elliptical loop structure of claim 4 wherein the loop is made by conducting copper strip. The loop may have a height such as 24.4 mm and a length of 34.3 mm.

6. The pair of vacant-quarter-printed ring of claim 1 wherein the ring may have a radius of such as 7 mm and a width of 1.5 mm.

7. The dipole arms of claim 3 are linked by the vacant-quarter-printed rings of claim 6 on both sides of the substrate of claim 2 to produce 90-degree phase difference between the dipole pair.

8. The near-field coupled parasitic elements of claim 1 wherein the parasitic elements are not electrically connected to the antenna and the elements are deployed in the corners and printed on both sides of the substrate.

9. The near-field coupled parasitic elements of claim 8 may have an arc-shaped structure with a length of 27.9 mm and a height of 13.9 mm.

10. The antenna of claim 1 may have an operating bandwidth from 1.16 to 1.87

GHz for reflection coefficient < -10 dB.

11. The antenna of claim 1 may have a CP bandwidth from 1.24 to 1.87 GHz for axial ratio < 3 dB.

12. The concept of using the egg-shaped elliptical loop structure of claim 5 as the dipole radiators may improve the impedance bandwidth and CP bandwidth of the antenna.

13. The concept of using the vacant-quarter-printed ring of claim 6 as the feeding structure may improve the CP performance of the antenna.

14. The concept of using the near-field coupled parasitic elements of claim 9 may reduce the antenna dimension.

15. The antenna of claim 1 using the aforementioned novel features and concepts may have very wide impedance and CP bandwidth and also have a compact size and low profile.

Intellectual

Property

Office

Application No: Claims searched:

GB1613835.6

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