Patent Publication Number: US-7595758-B2

Title: Compact DTV receiving antenna

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a digital-television receiving antenna, and more particularly, to a compact digital-television receiving antenna. 
   2. Description of the Prior Art 
   With rapid development of wireless communication technology, wireless communication applications are more and more popular. Performances of the wireless communication applications are highly related to volumes and functions of antennas thereof. Since analog signals transmitted by analog communication systems are easily interfered during wireless transmission, digital communication systems are being substituted for the analog communication systems. For example, a digital television (DTV) system can perform digital signal processing to discard noise generated during broadcasting, so that the DTV system can prevent snowflakes, ghost images, and increase image quality in comparison with an analog TV system, which follows NTSC (National Television Standard Committee) standard. In addition, digital signals can be compressed to increase the efficiency of frequency utilization. Now, the DTV system has been developed in three main standards, DVB (Digital Video Broadcasting) by European Broadcast Union (EBU), ATSC (Advanced Television Systems Committee) by US, and ISDB (Integrated Services Digital Broadcasting) by Japan. 
   Plug-and-play (P&amp;P) devices, such as USB (universal serial bus) devices, combining DTV tuners are greatly demanded. Using such devices, DTV signals can be received, demodulated, and transmitted to a desktop or notebook through a USB interface, so that a user can enjoy DTV programs through the desktop or notebook anytime and anywhere. In the prior art, most P&amp;P DTV receivers are connected to external receiving antennas through external wires, which is inconvenient for using. TW patent No. M270,510 discloses a DTV receiving antenna, which functions with a large length and is inconvenient for using. TW patent No. M269,583 discloses another DTV receiving antenna, which is formed as a helix structure and requires high production cost. 
   SUMMARY OF THE INVENTION 
   It is therefore a primary objective of the claimed invention to provide a compact digital television receiving antenna. 
   According to the claimed invention, a digital television receiving antenna comprises a first radiating element and a second radiating element electronically connected to the first radiating element. The second radiating element is foldable, and comprises a wide radiating metal plate, and a narrow radiating metal strip, wherein one end of the narrow radiating metal strip is a feeding point insulated from the first radiating element with a predefined distance, and the other end of the narrow radiating metal strip is electronically connected to the wide radiating metal plate. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a schematic diagram of an antenna in accordance with an embodiment of the present invention. 
       FIG. 2  illustrates a schematic diagram of the antenna shown in  FIG. 1  in a non-operating state. 
       FIG. 3  illustrates a schematic diagram of measured return loss of the antenna shown in  FIG. 1 . 
       FIG. 4  illustrates a schematic diagram of a radiation pattern of the antenna shown in  FIG. 1  at 570 MHz. 
       FIG. 5  illustrates a schematic diagram of radiation efficiencies of the antenna shown in  FIG. 1 . 
       FIG. 6  illustrates a schematic diagram of an antenna in accordance with an embodiment of the present invention. 
       FIG. 7  illustrates a schematic diagram of an antenna in accordance with an embodiment of the present invention. 
       FIG. 8  illustrates a schematic diagram of an antenna in accordance with an embodiment of the present invention. 
       FIG. 9  illustrates a schematic diagram of measured return loss of the antenna shown in  FIG. 8 . 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 1 , which illustrates a schematic diagram of an antenna  1  in accordance with an embodiment of the present invention. The antenna  1  includes a first radiating element  11  and a second radiating element  12 . The first radiating element  11  is made of metal with a rectangular shape, and utilized for forming a system ground of a plug and play (ex. USB) device. A flare angle is formed between the second radiating element  12  and the first radiating element  11 . The second radiating element  12  includes a wide radiating metal plate  121  and a bar-shaped narrow radiating metal strip  122 . The width of the narrow radiating metal strip  122  is smaller than 3 mm. One end of the narrow radiating metal strip  122  is a feeding point  13  of the antenna  1 , while the other end is electronically connected to the wide radiating metal plate  121 . The feeding point  13  and an edge  111  of the first radiating element  11  are separated with a predefined distance d smaller than 5 mm. The flare angle is in a range of 45° to 180°. In the present invention, the bar-shaped narrow radiating metal strip  122  is used for increasing the inductance of the antenna  1 . In this case, the current will reach its maximum value more rapidly than the original path does. Thus, the resonance frequency of the antenna  1  can be decreased so as to compact the size of the antenna  1 , and the height of the antenna  1  after opening up can be decreased. Moreover, the wide radiating metal plate  121  is used for making the excited surface current more uniform, which further decreases the resonance frequency and improves the impedance bandwidth of the antenna. 
     FIG. 2  illustrates a schematic diagram of the antenna  1  in a non-operating state, in which the flare angle is zero. In the present invention, the first radiating element  11  and the second radiating element  12  are simply film-shaped structures. Therefore, when the antenna  1  is applied as a USB DTV receiving antenna, an aesthetic appearance of the antenna  1  can be easily designed in an operating state. Also, in the non-operating state, the antenna  1  can be easily folded along a folding line  14  shown in  FIG. 1  and  FIG. 2 . 
     FIG. 3  illustrates a schematic diagram of measured return loss of the antenna  1 . To perform the experiment, the first radiating element  11  is formed by a rectangular metal plate, 90 mm long and 20 mm wide. In the second radiating element  12 , the wide radiating metal plate  121  is 25 mm long and 20 mm wide, while the narrow radiating metal strip  122  is 75 mm long, 1 mm wide and between the feeding point  13  and the center of the wide radiating metal plate  121 . The distance d between the feeding point  13  and the edge  111  of the first radiating element  11  is 2 mm. The flare angle between the first radiating element  11  and the second radiating element  12  is 90°. The first radiating element  11  and the second radiating element  12  are formed on a dielectric substrate (not shown in  FIG. 1  and  FIG. 2 ) with a 0.8-mm thickness by printing or etching. In  FIG. 3 , y-axis represents the values of measured return loss, and x-axis represents the operating frequencies. As shown in  FIG. 3 , the return loss values of the present invention antenna are greater than 5 dB between the operating frequencies of 520 and 630 MHz, which meets the requirements for DTV signal reception. In this case, the total length of the first radiating element  11  and the second radiating element  12  is equal to 0.36 times the wavelength of the center frequency 570 MHz. However, in the prior art, the total length of the first radiating element and the second radiating element must be equal to 0.5 times the wavelength of the center frequency 570 MHz. Therefore, the present invention can decrease by about 70 mm of the total length of the antenna. Preferably, the distance d is smaller than 5 mm, and the flare angle is greater than 45° in the operating state. 
     FIG. 4  illustrates a schematic diagram of a radiation pattern of the antenna  1  at 570 MHz. As shown in  FIG. 4 , the radiation pattern of x-y plane is approximately omni-directional, which meets the requirements for DTV signal reception. 
     FIG. 5  illustrates a schematic diagram of radiation efficiencies of the antenna  1 . In  FIG. 5 , y-axis represents the radiation efficiencies, and x-axis represents the operating frequencies of the antenna  1 . The radiation efficiencies of the antenna  1  operating at frequencies between 500 and 650 MHz are higher than 50%, which meets the requirements for DTV signal reception. 
     FIG. 6  illustrates a schematic diagram of an antenna  2  in accordance with an embodiment of the present invention. The structure of the antenna  2  is similar to that of the antenna  1 , except that the shape of a wide radiating metal plate  621  in the antenna  2  is different from that of the wide radiating metal plate  121  in the antenna  1 . A narrow radiating metal strip  622  of the antenna  2  can also increase the inductance of the antenna, so that the resonance frequency of the antenna  2  can be decreased to compact the size of the antenna  2 . In addition, similar to the antenna  1 , the wide radiating metal plate  621  in the antenna  2  can make the excited surface current more uniform, which further decreases the resonance frequency and improves the impedance bandwidth of the antenna. 
     FIG. 7  illustrates a schematic diagram of an antenna  3  in accordance with an embodiment of the present invention. The structure of the antenna  3  is similar to that of the antenna  1 , except that the shape of a wide radiating metal plate  721  in the antenna  3  is different from that of the wide radiating metal plate  121  in the antenna  1 , and a second radiating element  72  is formed by segmenting a single metal plate. A narrow radiating metal strip  722  of the antenna  3  can also increase inductance of the antenna, so that the resonance frequency of the antenna  3  can be decreased to compact the size of the antenna  3 . In addition, similar to the antenna  1 , the wide radiating metal plate  721  in the antenna  3  can make the excited surface current more uniform, which further decreases the resonance frequency and improves the impedance bandwidth of the antenna. 
     FIG. 8  illustrates a schematic diagram of the antenna  4  in accordance with an embodiment of the present invention. The antenna  4  includes a first radiating element  81  and a second radiating element  82 . The first radiating element  81  is formed by a metal plate with a rectangular shape, and is taken as a ground of a plug and play (ex. USB) device. A flare angle is formed between the second radiating element  82  and the first radiating element  11 . The second radiating element  82  includes a wide radiating metal plate  821  and a third radiating element  15 . The third radiating element  15  is composed of a first narrow radiating metal strip  151 , a second narrow radiating metal strip  152 , and an inductance element  16 . Widths of the first narrow radiating metal strip  151  and the second narrow radiating metal strip  152  are less than 3 mm. The inductance element  16  is between the first narrow radiating metal strip  151  and the second narrow radiating metal strip  152 . One end of the radiating element  15  is electrically connected to the wide radiating metal plate  821 , while the other end is a feeding point  83  of the antenna  4 . The feeding point  83  and an edge  811  of the first radiating element  81  are separated with a distance d less than 5 mm. The flare angle is in a range of 45° to 180°. The inductance element  16  is a chip inductor. In the present invention, the narrow radiating metal strip  151 , the second narrow radiating metal strip  152 , and the inductance element  16  are used for increasing the inductance of the antenna  4 , so that the resonance frequency of the antenna  4  can be decreased to compact the size of the antenna  1 , and the height of the antenna  4  after opening up can be decreased. Moreover, the wide radiating metal plate  821  is used for making the excited surface current more uniform, which further decreases the resonance frequency and improves the impedance bandwidth of the antenna. 
     FIG. 9  illustrates a schematic diagram of measured return loss of the antenna  4 . To perform the experiment, the first radiating element  81  is formed by a rectangular metal plate, 90 mm long and 20 mm wide. In the second radiating element  82 , the wide radiating metal plate  821  is 25 mm long and 20 mm wide. In the radiating element  15 , the first narrow radiating metal strip  151  is 53 mm long and 1 mm wide, the second narrow radiating metal strip  152  is 10 mm long and 1 mm wide, and the inductance element  16  is a 2 mm-long and 1.2 mm-wide chip inductor having an inductance of 15 nH. The inductance element  16  is between the first narrow radiating metal strip  151  and the second narrow radiating metal strip  152 . The distance d between the feeding point  83  and the edge  811  of the first radiating element  81  is 2 mm. The flare angle between the first radiating element  81  and the second radiating element  82  is 90°. The first radiating element  81 , the first narrow radiating metal strip  151 , and the second narrow radiating metal strip  152  are formed on a dielectric substrate with a 0.8-mm thickness by printing or etching. In  FIG. 9 , y-axis represents the values of return loss, and x-axis represents the operating frequencies. As shown in  FIG. 9 , the return-loss values of the antenna  4  are greater than 5 dB for frequencies between 530 and 620 MHz, which meets the requirements of DTV signal reception. Preferably, the distance d is smaller than 5 mm, and the flare angle is greater than 45° in the operating state. 
   Certainly, other than the antenna  1  and antenna  4 , the present invention can provide antennas with different shapes from those of wide radiating metal plates mentioned above. Such as trapezoid, polygonal, elliptic, or circular shapes also are within the scope of the present invention. In summary, the present invention can increase the inductance of the antenna by using the bar-shaped narrow radiating metal strip or using the narrow radiating metal strip and the chip inductor, so as to compact the size of the antenna, and decrease the height of the antenna after opening up. Therefore, the present invention antenna is suitable for P&amp;P DTV receiving antenna, and has a simple structure, so that production cost can be decreased. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.