Patent Publication Number: US-2012032862-A1

Title: Antenna arrangement, dielectric substrate, pcb &amp; device

Description:
TECHNICAL FIELD  
     The present invention concerns an antenna arrangement, a dielectric substrate and a printed circuit board (PCB), and a device comprising such an antenna arrangement, dielectric substrate or PCB. 
     BACKGROUND OF THE INVENTION  
     A microstrip or “patch” antenna is usually fabricated by etching an antenna element pattern in a metal trace on one side of an insulating dielectric substrate and providing a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. 
     Portable electronic devices, such as mobile phones, typically include a patch antenna that is connected to electrically conducting tracks or contacts on a printed circuit board by soldering or welding. Manufacturers of such electronic devices are under constant pressure to reduce the physical size, weight and cost of the devices and improve their electrical performance. This low cost requirement dictates that the electronic device and its antenna should be simple and inexpensive to manufacture and assemble, and should occupy as little space as possible. 
     It is also desirable for manufacturers to provide an electronic device with an antenna capable of simultaneously transmitting and/or receiving signals using different wireless communication standards, such as GSM (Global System for Mobile communications), UMTS (Universal Mobile Telecommunications System) and frequencies of 700-960 MHz and 1.7-2.7 GHz, i.e. a multiband antenna. An antenna is therefore often provided with a tuning unit that matches a transceiver with a fixed impedance to a load (feed line and antenna) impedance which is unknown, complex or otherwise does not match, so that the antenna may be used to receive and/or transmit a broad range of frequencies. 
     An antenna&#39;s impedance may be affected by factors, such as how the electronic device containing the antenna is being held (the so-called “head and hand effect”). When users hold their head or hands near an antenna radiator, the antenna is namely detuned, causing mismatch at the intended operating frequency. If a large metallic component, such as a loudspeaker, is placed in the vicinity of an antenna, this may also degrade the performance of the antenna. 
     U.S. Pat. No. 6,650,294 concerns a broadband multi-resonant antenna that utilizes capacitive coupling between multiple conductive plates for compact antenna applications. The number and design of conductive plates may be set to achieve the desired bandwidth. The antenna may be designed for four resonant frequencies and may include three L shaped legs each including a micro-strip conductive plate and connection pin, with configurations approximately parallel to one another. The centre L-shaped leg may be a feed patch with a feed pin connected to a transmitter, receiver, or transceiver. The upper L-shaped leg may be a dual band main patch and ground pin. The dual band main patch may have two different branches with different lengths and areas to handle three of four desired resonant frequencies. The lower L shaped leg may be a parasitic high band patch and ground pin designed to handle one of the two higher desired resonant frequencies. A drawback with such an antenna is that the multilayer structure of the antenna is not easy to manufacture. 
     SUMMARY OF THE INVENTION  
     An object of the invention is to provide an improved antenna arrangement that is suitable for multiband applications. 
     This object is achieved by an antenna arrangement comprising a ground plane, a feeding branch, a first branch and a second branch whereby the first branch is longer than the second branch. The feeding branch is capacitively coupled to the first branch to create a variable capacitance, inductance and/or impedance as a function of frequency which increases the bandwidth. The design and length of the feeding branch and the first branch may be selected to achieve the desired bandwidth and/or the number of distinct transmission frequencies for a particular application. The feeding branch, the first branch and the second branch comprise inductor loading and are arranged in a single plane at a distance from the ground plane. The inductance of the inductor loading is chosen so that a resonance frequency of the antenna arrangement corresponds to an operating frequency thereof or for size reduction, filtering and matching, and antenna efficiency improvement purposes. The inductor loading can therefore be arranged to create multiple resonances with good bandwidth. A multiband antenna arrangement may therefore be realized which may consequently increase the functionality of a device in which it is included. 
     Such a one-layer multiband antenna arrangement has been found to significantly improve the antenna performance, i.e. antenna efficiency and bandwidth, Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS). The antenna arrangement is of compact design and alleviates the head and hand effect even if a metallic component (RF-lossy material), such as a loudspeaker is placed in the vicinity of the antenna arrangement, since the antenna arrangement may be arranged at the bottom of a portable electronic device. Furthermore, such an antenna arrangement requires no matching or switching circuits, which leads to a reduction in manufacturing costs, time and complexity. Having said that, a matching or switching circuit may however be used with the antenna arrangement according to the present invention. 
     According to an embodiment of the invention the feeding branch, the first branch and/or the second branch each comprise a first conducting portion, a second conducting portion and a gap between the first and second conducting portions, whereby a plurality of inductor elements is connected in parallel across the gap. The inductor elements may comprise wire wound elements having at least one coil or chip inductor or any other kind of inductor. It should be noted that the feeding branch, the first branch and the second branch may comprise any number of such conducting portions and gaps. The accompanying claims recite a plurality of inductor elements, since a plurality of inductor elements have been found to substantially improve the performance of an antenna arrangement in a manner in which a single inductor element connected across a gap does not. 
     According to an embodiment of the invention the feeding branch may comprise an L-shaped portion and the first branch may be arranged to substantially follow and surround the end of the L-shaped portion of the feeding branch. 
     According to another embodiment of the invention the antenna arrangement may include capacitive coupling between the feed branch and the second branch. 
     According to a further embodiment of the invention the antenna arrangement is arranged to transmit and/or receive frequencies in one, or more, or all of the following frequency ranges: 700-800 MHz, 824-894 MHz, 880-960 MHz, 1710-1850 MHz, 1820-1990 MHz, 1920-1990 MHz, 1920-2170 MHz, 2500-2700 MHz. 
     According to an embodiment of the invention the antenna arrangement comprises a switching circuit, such as a pin-diode or a micro-electromechanical system (MEMS) switch so that the antenna arrangement may be tuned to more frequency bands. The first branch and/or the second branch may for example be arranged to be switched to a different inductor loading. 
     The present invention also concerns a dielectric substrate or printed circuit board (PCB) that comprises an antenna arrangement according to any of the embodiments of the invention. 
     The present invention further concerns a device that comprises an antenna arrangement, a dielectric substrate or a PCB according to any of the embodiments of the invention. The device may be a portable or non-portable electronic device, such as a telephone, media player, Personal Communications System (PCS) terminal, Personal Data Assistant (PDA), laptop computer, palmtop receiver, camera, television, radar or any appliance that includes a transducer designed to transmit and/or receive radio, television, microwave, telephone and/or radar signals. The antenna arrangement, dielectric substrate and PCB according to the present invention are however intended for use particularly, but not exclusively for high frequency radio equipment. 
     According to an embodiment of the invention the device is a mobile communication device. The mobile communication device may be a mobile telephone, wherein the antenna arrangement is preferably arranged at the bottom of the mobile communication device when it is in use in order to optimize the talk-position performance, including antenna efficiency, TRP, TIS, and Specific Absorption Rate (SAR), Hearing Aids Compatibility (HAC) and unavoidably, to reduce the hand effect. It is however also possible to arrange the antenna arrangement at the top of a mobile communication device. 
     According to an embodiment of the invention the device comprises a chassis and at least part of the antenna arrangement is arranged on part of the chassis of the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended figures where; 
         FIG. 1  shows an antenna arrangement according to an embodiment of the invention, 
         FIGS. 2 &amp; 3  are graphs illustrating frequency responses for an operational antenna arrangement according to an embodiment of the invention, and 
         FIG. 4  shows a device according to an embodiment of the invention. 
     
    
    
     It should be noted that the drawings have not been drawn to scale and that the dimensions of certain features have been exaggerated for the sake of clarity. 
     DETAILED DESCRIPTION OF EMBODIMENTS  
       FIG. 1  shows an on-ground multiband tunable L-loading coupling-fed antenna arrangement  10  according to an embodiment of the invention. The antenna arrangement  10  comprises a ground plane  12 , a feeding branch  14 , a first branch  16 , and a second branch  18  whereby the first branch  16  is longer than the second branch  18 . The feeding branch  14 , the first branch  16  and the second branch  18  are arranged in a single plane at a distance from the ground plane  12  and are arranged to provide resonant frequencies useful for radio communications. Dielectric material (constituting at least part of a dielectric substrate, PCB or part of a device chassis for example) or air may be arranged between the ground plane  12  and the plane containing the feeding branch  14 , the first branch  16  and the second branch  18 . 
     The feeding branch  14  is capacitively coupled to the first branch  16 . The first branch  16  and the second branch  18  may consequently include one or more distinct areas which will be resonant at predetermined desired frequencies that have a wider bandwidth due to the capacitive coupling between the feeding branch  14  and the first branch  16 . 
     The feeding branch  14  comprises inductor loading L 1 , the first branch  16  comprises inductor loading L 2  and L 3  and the second branch  18  comprises inductor loading L 4 . The first branch  16  and the second branch  18  are connected to the ground plane  12  via ground pins for example, and the feeding branch  14  is connected to a feed point  20 , via a feed pin for example, the single feed point  20  being arranged to be connected to a receiver, transmitter or transceiver. The ground pins and feed pin may be arranged to extend substantially perpendicularly to the substrate, PCB or part of the device chassis that supports the antenna arrangement  10  so as to form an L-shape with the first and second branches  16  and  18  and the feeding branch  14 . The branches  14 ,  16  and  18  of the antenna arrangement may for example comprise printed conductive traces formed on the dielectric material of the substrate, PCB, or device chassis part. 
     The first branch  16  comprises a first conducting portion  16   a,  a second conducting portion  16   b  and a gap between the first and second conducting portions  16   a  and  16   b,  whereby a plurality of inductor elements, constituting the inductor loading L 1 , is connected in parallel across the gap. The second branch  18  and the feeding branch  14  are also arranged in such a manner although the feeding branch in the illustrated embodiment comprises two gaps containing inductor loading L 2  and L 3 . The inductor elements may comprise wire wound elements having at least one coil or chip inductor or any other kind of inductor. The conducting portions  16   a,    16   b  may be of any form and may for example comprise a meandering conducting path. 
     The feeding branch  14  in the illustrated embodiment comprises an L-shaped portion and the first branch  16  is arranged to substantially follow and surround the end of the L-shaped portion of the feeding branch  14 , i.e. to have portions that extend along both sides of the L-shaped portion of the feeding branch  14 , around the distal end of the L-shaped portion of the feeding branch  14  and along at least part of the inner side of the L-shaped portion of the feeding branch  14  as shown in  FIG. 1 . 
       FIG. 2  shows a graph illustrating the frequency response for an operational antenna arrangement  10  according to an embodiment of the invention, such as the antenna arrangement  10  illustrated in  FIG. 1 . Frequency is shown on the x-axis and the voltage standing wave ratio (VSWR) is shown on the y-axis. The VSWR is a measure of how well a load is impedance-matched to a source. The value of VSWR is always expressed as a ratio with 1 in the denominator (2:1, 3:1, 10:1, etc.) It is a scalar measurement only (no angle), so although they reflect waves oppositely, a short circuit and an open circuit have the same VSWR value (infinity:1). A perfect impedance match corresponds to a VSWR 1:1, but in practice this is impossible to achieve. Impedance matching means that maximum power transfer from source to load will be obtained. 
     The frequency response shown in  FIG. 1  has three distinct resonance bands with best performance points at  22 ,  24  and  26 . The lowest resonant frequency is at point  22 , at approximately 0.8 GHz, and corresponds to the low frequency resonance band of the first branch  16  and has a VSWR of approximately 1. The two higher resonant frequencies are at points  24  and  26 , at approximately 1.8 GHz and 2.15 GHz respectively, and correspond to the high frequency resonance bands of the second branch  18  and the feeding branch  14  respectively. Such an antenna may therefore be successfully used for broadband applications, for example in a three band mobile telephone. 
     An antenna arrangement  10  according to the present invention may comprise a switching circuit for example to enable the antenna whose frequency response is shown in  FIG. 2  to be operable in more frequency bands. For example, a switching circuit, such as a pin-diode or MEMS switch may be used to switch the inductive coupling, L 1 , on the first branch  16  of the antenna arrangement  10  to another inductor loading, L 5  (not shown) and/or to switch the inductive coupling, L 4 , on the second branch  18  of the antenna arrangement  10  to another inductor loading, L 6  (not shown) for example. 
       FIG. 3  shows the frequency response for an antenna that has five distinct resonance bands with best performance points at  22 ,  24 ,  26  (as shown in  FIG. 2 ),  28  and  30 . The lowest resonant frequencies at points  22  and  28 , at approximately 0.8 GHz and 1 GHz, correspond to the low frequency resonance bands of the first branch  16 . The two higher resonant frequencies at points  24  and  30 , at approximately 1.8 GHz and 2.45 GHz respectively, correspond to the high frequency resonance bands of the second branch  18 , and the high resonant frequency at point  26  corresponds to the high frequency resonance band of the feeding branch  14 . Such an antenna arrangement may therefore be successfully used for broadband applications, for example in a five band mobile telephone. The antenna arrangement according to the present invention is preferably arranged to be used in an 8-band device. 
     Numerous variations for the physical structure and layout of the antenna arrangement according to the present invention are possible in order to achieve various desired broadband applications and performance. For example, the location of the branches and connector pins (ground pings and feed pin) for the antenna arrangement could be varied and still achieve a broadband multiband antenna. It is only necessary that their respective locations, sizes, shapes, and distance relative to the substrate and to one another be set so as to tune the antenna arrangement to the desired frequencies and match the antenna arrangement to a device&#39;s system impedance. Furthermore, the branches can be any shape such as, but not limited to, rectangular, triangle, circular, and they can be two dimensional or three dimensional or have a T or M shape. 
       FIG. 4  shows a device  32  comprising a built-in antenna arrangement (not shown) according to the present invention. The device  32  may be arranged to transmit and/or receive frequencies in one, or more, or all of the following frequency ranges: 700-800 MHz, 824-894 MHz, 880-960 MHz, 1710-1850 MHz, 1820-1990 MHz, 1920-1990 MHz, 1920-2170 MHz, 2500-2700 MHz. 
     According to an embodiment of the invention the antenna arrangement  10  is arranged at the bottom  32   b  of the device  32  when the device is in use. At least part of the antenna arrangement  10  may be arranged on part of a chassis of the device  32 . 
     Further modifications of the invention within the scope of the claims would be apparent to a skilled person.