Abstract:
Provided is an antenna system for terrestrial broadcasting. The antenna system has a dipole antenna probe receiving a broadcast signal, a signal amplifier amplifying the received broadcast signal, an antenna matching unit matching impedances between the antenna probe and the signal amplifier, an output matching unit matching impedances between an output signal of the signal amplifier and an input terminal of a broadcast receiver to which the output signal is fed, and a bias extractor converting power received from the broadcast receiver into power needed for driving the signal amplifier and supplying the converted power to the signal amplifier.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority from Korean Patent Application No. 10-2004-0024145 filed on Apr. 8, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an antenna system, and more particularly, to an antenna system for terrestrial broadcasting designed to receive a television (TV) broadcast signal and deliver the television (TV) broadcast signal.  
         [0004]     2. Description of the Related Art  
         [0005]     While a National Television Systems Committee (NTSC) standard is an analog TV broadcast standard used today in North America, an Advanced Television Systems Committee (ATSC) standard is a digital TV broadcast standard. Broadcasts adopting a new technology called data in NTSC video (dNTSC) to embed a digital signal into the existing NTSC TV frequency range are being made over a Very High Frequency-High (VHF-H) band. An indoor or outdoor antenna is needed to receive the VHF-H broadcasts. An indoor antenna is more advantageous than an outdoor antenna in many aspects since the antenna must be connected to a digital set-top box to receive digital broadcasts  
         [0006]      FIG. 1  is an exemplary diagram showing the spectrum of frequencies within a VHF-H band, over which a dNTSC technique is applied.  
         [0007]     Here, double sideband (DSB) modulation is used to mix an analog broadcast signal  100  and a digital broadcast signal  110  into a carrier. While a NTSC format allows a carrier having a frequency f visc  to carry the analog broadcast signal  100  having a frequency range of f cl  to f ch , a dNTSC format is used to additionally carry the digital broadcast signal  110 , that is, to transmit a dNTSC data signal outside the frequency range of the analog broadcast signal  100 .  
         [0008]      FIG. 2  is a table listing frequencies of the respective signals shown in  FIG. 1  for VHF channels  7  through  13 . The frequency of the carrier ranges from about 170 to about 220 megahertz (MHz) on the channels  7  through  13 . Regardless of the channel, the analog broadcast signal  100  has a bandwidth of 0.1 MHz while the dNTSC  110  has a bandwidth of 0.76 MHz.  
         [0009]     However, an indoor antenna for receiving a VHF-H signal including a digital broadcast signal is subject to space restrictions. Due to the space restrictions, it is difficult to determine the size of an antenna that varies according to a frequency band and realizes a dipole antenna. Thus, it is highly desirable to have an indoor antenna having a desired electrical length while occupying a small space to enable users to watch television broadcasts on Ultra High Frequency (UHF) band as well as VHF-H band.  
         [0010]     Furthermore, a broadcast signal needs to be amplified in an antenna to improve its signal to noise ratio (SNR), since a higher SNR is achieved when the signal is amplified in the antenna before being sent to the next stage. In the case of a dipole antenna, the antenna must be designed to solve problems arising between a balance circuit and an unbalance circuit for signal amplification.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides an antenna system designed to maximize signal propagation by compensating for an electrical length of an antenna probe by adding an inductor to the antenna probe and achieving wideband impedance matching between the antenna probe and a signal amplifier.  
         [0012]     The above stated object as well as other objects of the present invention will become clear to one skilled in the art upon review of the following description, the attached drawings and appended claims.  
         [0013]     According to an aspect of the present invention, there is provided an antenna system for terrestrial broadcasting comprising a dipole antenna probe receiving a broadcast signal, a signal amplifier amplifying the received broadcast signal, an antenna matching unit matching impedances between the antenna probe and the signal amplifier, an output matching unit matching impedances between an output signal of the signal amplifier and an input terminal of a broadcast receiver to which the output signal is fed, and a bias extractor converting power received from the broadcast receiver into power required for driving the signal amplifier and supplying the converted power to the signal amplifier.  
         [0014]     The broadcast signal may comprise data in a National Television Systems Committee (NTSC) video (dNTSC) broadcast signal transmitted over a Very High Frequency-High (VHF-H) band.  
         [0015]     In addition, the dipole antenna probe may comprise a probe with a variable length.  
         [0016]     Further, the signal amplifier may comprise a monolithic microwave integrated circuit (MMIC) reducing noise contained in the received broadcast signal and amplifying the received broadcast signal.  
         [0017]     Also, the antenna matching unit may comprise a coil structure connected in series with a negative-probe of the antenna probe.  
         [0018]     Further, the antenna matching unit may comprise a balun circuit. In this case, the balun circuit preferably comprises a ferrite core.  
         [0019]     In addition, the output matching unit may comprise a capacitor element.  
         [0020]     The bias extractor may comprise a plurality of passive circuit elements.  
         [0021]     In another preferred embodiment of the present invention, the antenna system may further comprise a circuit protector for maintaining the power supplied from the broadcast receiver substantially constant and preventing electrostatic discharge. In this case, the circuit protector may comprise an arrestor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The above and other features and advantages of the present invention will become more apparent from the following description of exemplary embodiments thereof with reference to the attached drawings in which:  
         [0023]      FIG. 1  is an exemplary diagram showing the spectrum of frequencies within a VHF-H band over which a dNTSC technique is applied;  
         [0024]      FIG. 2  is a table listing frequencies of the respective signals shown in  FIG. 1 ;  
         [0025]      FIG. 3  is a block diagram of an antenna system according to an embodiment of the present invention;  
         [0026]      FIG. 4  is a circuit diagram of an antenna system according to an embodiment of the present invention; and  
         [0027]      FIG. 5  illustrates an antenna system constructed according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Advantages and features of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of preferred embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Like reference numerals refer to like elements throughout the specification.  
         [0029]      FIG. 3  is a block diagram of an antenna system according to an embodiment of the present invention. Referring to  FIG. 3 , the antenna system  300  according to an embodiment of the present invention comprises an antenna probe  310  that receives a broadcast signal, an antenna matching unit  320  that performs impedance matching between the antenna probe  310  and a low noise amplifier  330 , the low noise amplifier  330  that amplifies the broadcast signal in such a manner as to minimize noise contained in the broadcast signal and maximize gain over frequency band of the broadcast signal, an output matching unit  340  that performs impedance matching between the low noise amplifier  330  and an input terminal of a broadcast receiver (e.g., set-top box)  370  before a signal outputted at the low noise amplifier  330  is sent to the input terminal of the broadcast receiver  370 , and a bias extractor  350  that receives power from the input terminal of the broadcast receiver  370  and then supplies a predetermined level of power to the low noise amplifier  330 .  
         [0030]     In this case, the antenna system  300  may further comprise a circuit protector  360  that protects circuit elements making up the antenna system  300 .  
         [0031]     The frequency band of the broadcast signal may include a Very High Frequency (VHF) band ranging from 30 to 300 megahertz (MHz) or an Ultra High Frequency (UHF) band ranging from 300 MHz to 3 gigahertz (GHz). Furthermore, the antenna probe  310  may be a dipole antenna. To aid in the understanding of the present invention, in the dipole antenna, a probe connected to ground and a probe not connected to ground are referred to as a ‘negative-probe’ and a ‘positive-probe’, respectively.  
         [0032]     Now, functions and operations of the above-stated elements will be described in detail.  
         [0033]     To properly deliver a broadcast signal received through the antenna probe  310  to the low noise amplifier  330 , impedance matching is performed by the antenna matching unit  320  located between the antenna probe  310  and the low noise amplifier  330 . To facilitate impedance matching, a reactance component on the antenna probe  310  can be removed by modifying the structure of the antenna probe  310 . For a typical dipole antenna, a reactance component on the antenna probe  310  varies with a dipole length. Thus, when the length of the antenna probe  310  in the dipole antenna is reduced due to space restrictions, it is desirable to change the structure of the antenna probe in a manner that institutes a desired change in the amount of reactance component, as well. To change the structure of the antenna probe  310 , one side of either the positive-probe or the negative-probe may be in the form of a coil (hereinafter referred to as a “loading coil”), which reduces capacitance of the antenna probe  310  and a voltage standing wave ratio (VSWR) of the dipole antenna.  
         [0034]     The antenna matching unit  320  uses the loading coil to match the impedance of the antenna probe  310  to the input impedance of the low noise amplifier  330  over the VHF or UHF band, thereby transmitting potential difference applied to the antenna probe  310  to the low noise amplifier  330  as much as possible while providing wideband impedance matching for reception over a wide range of frequencies.  
         [0035]     Furthermore, the antenna matching unit  320  includes a circuit used to couple a balance circuit of the dipole antenna to an unbalance circuit of a coaxial line, thereby preventing changes in radiation pattern and reception characteristics of the antenna due to unwanted surface current flowing in a coaxial line when coupling the balance circuit to the unbalance circuit.  
         [0036]     Upon receipt of the broadcast signal from the antenna matching unit  320 , the low noise amplifier  330  amplifies the same signal in such a manner as to maximize gain and minimize the noise temperature over a frequency band of the broadcast signal. In this way, the broadcast signal is amplified within the antenna system  300  before being sent to the broadcast receiver  370 , thus minimizing distortion of the broadcast signal.  
         [0037]     The output matching unit  340  matches output impedance of the low noise amplifier  330  to tuner impedance of the broadcast receiver  370 .  
         [0038]     After the broadcast signal received from the antenna probe  310  passes through the antenna matching unit  320  and is amplified by the low noise amplifier  330 , the amplified signal then passes through the output matching unit  340  to a tuner of the broadcast receiver  370 . The bias extractor  350  converts power from the broadcast receiver  370  into a level of power required for driving the low noise amplifier  330 .  
         [0039]     The antenna system  300  may further comprise the circuit protector  360  that protects the circuit elements forming the antenna system  300  against spike noise resulting from static electricity or ground potential difference. While  FIG. 3  shows that the circuit protector  360  is located at a position that enables the reception of power from the broadcast receiver  370 , the circuit protector  360  may be located at another position. For example, a separate circuit protector may also be positioned between the antenna matching unit  320  and the low noise amplifier  330  so as to protect the low noise amplifier  330 .  
         [0040]     Furthermore, the broadcast signal or power may be transmitted between the antenna system  300  and the broadcast receiver  370  via a single cable.  
         [0041]      FIG. 4  is a circuit diagram of an antenna system according to an embodiment of the present invention.  
         [0042]     An antenna probe  310  is a dipole antenna probe consisting of a positive-probe  312  and a negative-probe  314 . In this case, a loading coil  316  described as above may be connected to either an input terminal  332  or a ground terminal  334  of a low noise amplifier  330 . In the illustrative embodiment, the loading coil  316  may be connected to the ground terminal  334 . Furthermore, the lengths of the positive-probe  312  and the negative-probe  314  may be adjusted to improve the reception sensitivity of a broadcast signal. Meanwhile, for example, when an input impedance Z in  of the dipole antenna is expressed as 20-j314, the final input impedance Z in  of 20 is obtained by creating +j314 component, which can be achieved by connecting the loading coil  316  in series to the negative-probe  314 . In this case, reactance X=jwL=j(2πfL) where j is an imaginary operator, w is the angular frequency, and L is the inductance of the loading coil  316 . To provide impedance-matching characteristics over a VHF-H band ranging from 174 to 216 MHz,  314 =2*3.14*200*10 6 *L when frequency f is 200 MHz. Solving the equation results in the inductance L of 250 nH. In this case, the loading coil  316  has the number of turns of 10, a thickness of 1.1 mm, and an inside diameter of 5.2 mm.  
         [0043]     By doing so, an input impedance of the dipole antenna eventually becomes 20. Meanwhile, when the input impedance of the low noise amplifier  330  is 50 Ω, an impedance-matching transformer with a 1:2.5 turns ratio is used to match the 50 Ω for the mutual impedance matching. Furthermore, a separate circuit is preferably used to solve problems caused by coupling a balance circuit of a dipole antenna with an unbalance circuit of a coax line. In the illustrative embodiment, a balun circuit in the antenna matching unit  320  is used to enable the balance circuit to be coupled to the unbalance circuit or vice versa. When the balun circuit is realized using transmission lines, the circuit is usually bulky in size and has a narrow bandwidth. Thus, to reduce the size and widen the bandwidth, the balun circuit may be realized using a ferrite core as shown in  FIG. 5 . Meanwhile, the balun circuit may be connected to either input or output terminal of the low noise amplifier  330 , preferably, to the input terminal of the low noise amplifier  330 , so as to solve an imbalance between the balance circuit of the antenna probe  310  and the unbalance circuit of the coax line.  
         [0044]     A predetermined quality of power must be supplied to the low noise amplifier  330  to amplify the broadcast signal fed through the antenna probe  310 . In the illustrative embodiment, Gali-52LNA Monolithic Microwave IC (MMIC) is used as the low noise amplifier  330  (hereinafter called ‘&#39;Gali-52LNA’) available from Mini-Circuits.  
         [0045]     When the Gali-52LNA requires operating voltage of 4.4 V and current of 50 mA, the bias extractor  350  makes the magnitudes of power and current supplied by the broadcast receiver  370  to be equal to 4.4 V and 50 mA. In this case, the broadcast receiver  370  is a set-top box and a voltage supplied from the set-top box is 12 V direct current (DC).  
         [0046]     Here, the bias extractor  350  is comprised of a resistor, a capacitor, and an inductor.  
         [0047]     Since the Gali-52LNA requires operating voltage of 4.4 V and current of 50 mA, (12−4.4)=0.05*x where x is resistance. Solving the equation results in resistance x of 152 Ω. Thus, since power is 38 mW (0.05*0.05*152), two 75 Ω. ¼ watt resistors R 1  and R 2  are connected in series.  
         [0048]     Inductor L 1  used for bias extraction must have an impedance greater than 50 Ω, and preferably greater than 500 Ω. When a frequency is 200 MHz and jx=jwL, 2*3.14*2x10 8 *L&gt;500. A solution to this inequality is L&gt;398 nH. Actually, the inductor L 1  exhibits the same characteristics when the range of inductance is from 350 nH to 3 uH. For a chip inductor, it is preferably designed to provide for inductance of less than 3 uH and resist current of 100 mA. In the illustrative embodiment, a 2.7 uH chip inductor that is easy to mount is used.  
         [0049]     Shunt chip capacitors C 3 , C 4  and C 5  act to block radio waves that travel through a bias circuit and is reflected toward the low noise amplifier  330 . In the present embodiment, the capacitors C 3 , C 4 , and C 5  have capacitances of 1,000 pF, 100 pF, and 10 nF, respectively. The capacitor C 2  is used to remove an instantaneous pulse occurring when a coaxial cable  380  shown in  FIG. 4  is connected to the broadcast receiver  370 . Since it is desirable to use a capacitor having a large capacitance, a 10-uF tantal capacitor is used in the illustrative embodiment. Referring to  FIG. 4 , an output matching unit  340  used to properly transfer the broadcast signal amplified by the low noise amplifier  330  is realized using the DC blocking capacitor C 1  that prevents the transfer of DC signals. The capacitance of the capacitor C 1  is set such that its impedance X is much less than 50 Ω, preferably, less than 5 Ω over an available frequency range. When X=1/jwC 1 ) and frequency in hertz is 200 MHz, 5&gt;|1/(2*pi*2×10 8 *C 1 ). The solution of this inequality is C 1 &gt;169 pF. However, since with increasing frequency, the capacitor C 1  becomes self-resonant and cannot maintain its own characteristics, it is desirable to use a very small capacitor having a high self-resonant point or a capacitor having a slightly lower capacitance. In the illustrative embodiment, the capacitor C 1  has capacitance of 100 pF since its insertion loss is less than 0.3 dB over the available frequency range.  
         [0050]     Meanwhile, a circuit protector  360  protects the low noise amplifier  330  by eliminating electrostatic discharge originating from the inner wire of the coaxial cable  380  or the positive-probe  312 . In the illustrative embodiment, the circuit protector  360  is constructed using an arrestor. There are three types of arrestors available, that is, variable resistor type, capacitor type, and discharge type. Since variable resistor type and capacitor type arrestors attached to a circuit change electrical characteristics, it is desirable to use a discharge type arrestor as shown in the illustrative embodiment.  
         [0051]      FIG. 5  shows an antenna system in which the circuits shown in  FIG. 4  are placed on a printed circuit board (PCB) according to an embodiment of the present invention. The coaxial cable  380  receives power from the broadcast receiver  370  through its end (not shown) connected to the broadcast receiver  370  for supply to the low noise amplifier  330  and transmits a broadcast signal amplified by the low noise amplifier  330  to the broadcast receiver  370 .  
         [0052]     An antenna system of the present invention is designed with a reduced length of a dipole antenna suitable for indoor use and to amplify a broadcast signal fed through an antenna probe before sending it to a broadcast receiver such as a set-top box, thereby minimizing distortion in the broadcast signal. In concluding the detailed description, those skilled in the art will appreciate that many variations and modifications can be made to the preferred embodiments without substantially departing from the principles of the present invention. Therefore, the disclosed preferred embodiments of the invention are used for illustrative purposes and not for purposes of limitation.