Abstract:
Provided a self-biased receiver system using a multi-fed antenna, including: at least one first port connected to an electronic circuit; and a second port connected to a feeder forming a DC (direct current) voltage using an input electromagnetic wave and feeding the DC voltage to the electronic circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority from U.S. Provisional Application No. 60/729,217 filed on Oct. 24, 2005 in the United States Property Trademark Office, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a self-biased receiver system using a multi-fed antenna, and more particularly, to a self-biased receiver system using a multi-fed antenna adopted in a small-sized device so as to make the small-sized device compact and light. 
     2. Description of the Related Art 
     A rectenna is a word formed of a synthesis of a rectifier and an antenna, i.e., an element mixing a rectifier and an antenna to directly convert an electromagnetic wave into a direct current (DC) power. 
     The rectenna has a structure in which a rectifier diode is connected to a central part of a dipole antenna and an electromagnetic wave input through the dipole antenna electrically resonates in the rectifier diode as a non-linear element to form harmonic component. 
     Such a rectenna will be used in a system transmitting a power generated in the space to the earth. A huge solar battery panel is installed in a stationary satellite floating in the space to generate a power, the power is converted into an electromagnetic wave, and the electromagnetic wave is transmitted from an antenna of the stationary satellite to a rectenna array on the earth. The rectenna array converts the electromagnetic wave into a DC power. If a power is generated in the space as described above, the power is not affected by the weather and gravity unlike on the earth. Thus, a high power may be stably generated. 
     Attentions were focused on only the developments of receiving of a high power and an effective conversion of the high power using a rectenna. Also, such a system requires a large-sized rectenna array to transmit the high power. 
     However, if such rectenna technology is used in compact devices, the rectenna technology may be put to practical use and be general-purpose. For example, batteries have been removed from devices with the tendency to make devices compact. Also, rectennas may be used to supply a power so as to remove batteries from devices. Thus, the devices may be made compact and light. 
     Also, antennas having a structure in which rectennas are installed in the devices are required to adopt the rectennas. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present general inventive concept has been made to solve the above-mentioned and/or problems, and an aspect of the present general inventive concept is to provide a self-biased receiver system using a multi-fed antenna adopted to making a device compact and light. 
     According to an aspect of the present invention, there is provided a receiver system including: at least one first port connected to an electronic circuit; and a second port connected to a feeder forming a DC (direct current) voltage using an input electromagnetic wave and feeding the DC voltage to the electronic circuit. 
     The electronic circuit may be a transmitter circuit, a receiver circuit, an active circuit, or a passive circuit. 
     The feeder may be a rectenna. 
     The rectenna may include: a diode generating harmonic frequency components of the electromagnetic wave; and a filter filtering a signal generated by the diode to output a DC voltage. 
     The receiver system may further include a radiator sheet radiating the electromagnetic wave. The first port may be disposed on an identical plane to the radiator sheet, and the second port may be disposed perpendicular to the radiator sheet. 
     The radiator sheet may be formed in a disc shape and comprise a side cut in a fan shape at a predetermined angle. 
     Outputs of the harmonic frequencies generated by the diode may be intercepted. 
     A charging element charging a DC power output from the rectenna may be installed at an output node of the rectenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above aspects and features of the present invention will be more apparent by describing certain embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram of a receiver system including a multi-fed antenna according to the present invention; 
         FIG. 2  is a plan view of the multi-fed antenna shown in  FIG. 1 ; 
         FIG. 3A  is a graph illustrating an impedance characteristic of the multi-fed antenna shown in  FIG. 2 ; 
         FIG. 3B  is a graph illustrating S-parameters of the multi-fed antenna shown in  FIG. 2 ; 
         FIG. 4  is a graph illustrating a conversion gain of the LNA at receiver shown in  FIG. 1 ; 
         FIG. 5A  is a view illustrating a waveform of a signal transmitted from a transmitter; and 
         FIG. 5B  is a view illustrating a waveform of the signal of  FIG. 5A  processed by and output from the receiver system including the multi-fed antenna shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention will be described in detail with reference to the annexed drawings. In the drawings, the same elements are denoted by the same reference numerals throughout the drawings. In the following description, detailed descriptions of known functions and configurations incorporated herein have been omitted for conciseness and clarity. 
     A multi-fed antenna according to the present invention may be used in electronic circuits of various types of devices to supply a DC power. The electronic circuits may be transmitter circuits, receiver circuits, active circuits, passive circuits, or the like, and the multi-fed antenna will be installed in a receiver in an embodiment that will be described later. 
       FIG. 1  is a circuit diagram of a receiver including a multi-fed antenna according to the present invention, and  FIG. 2  is a plan view of the multi-fed antenna shown in  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the receiver includes a multi-fed antenna  10  having first and second ports  11  and  12  as a plurality of feeding ports, a receiver circuit  20  connected to the first port  11  of the multi-fed antenna  10 , and a rectenna  30  connected to the second port  12  of the multi-fed antenna  10 . 
     As shown in  FIG. 2 , the multi-fed antenna  10  includes a radiator sheet  15  connected to the first port  11  connected to the receiver circuit  20  and the second port  12  connected to the rectenna  30 . 
     The radiator sheet  15  is formed in a disc shape, and a cut part  16  cut at a predetermined angle in a fan shape with respect to a center point is formed at one side of the radiator sheet  15 . The cut part  16  must be formed at an angle of 120°. 
     The first port  11  is disposed so as to extend along the same plane as the radiator sheet  15  and form a predetermined angle with the cut part  16  of the radiator sheet  15 . The first port  11  is disposed at a distance of an angle of 30° from the cut part  16  as shown in  FIG. 2 . 
     The second port  12  is disposed perpendicular to a surface of the radiator sheet  15  at a predetermined distance from the center point of the radiator sheet  15 . Here, an end of the second port  12  contacts an end of the first port  11  advancing toward the radiator sheet  15  so that the second port  12  is perpendicular to the first port  11 . 
       FIG. 3A  is a graph illustrating an impedance characteristic of the multi-fed antenna  10  shown in  FIG. 2 , and  FIG. 3B  is a graph illustrating S-parameters of the multi-fed antenna  10  shown in  FIG. 2 . 
     The graphs shown in  FIGS. 3A and 3B  illustrate the results of an experiment performed with respect to the multi-fed antenna  10  adoptable in a local area communication system using a radio frequency identification (RFID) system and an RFID tag. 
     An impedance characteristic of the multi-fed antenna  10  will now be described. As shown in  FIG. 3A , a resonance is generated in a frequency of 2.4 GHz, but an electric field radiation is not generated in a higher harmonic frequency. 
     S-parameters shown in  FIG. 3B  will now be described. A resonance is formed in a frequency of 2.4 GHz but not formed in second and third harmonic frequencies of 4.8 GHz and 7.2 GHz. In other words, transmission and reception of a signal through the multi-fed antenna  10  is intercepted in the second and third harmonic frequencies. Here, bandwidths of reference frequencies of the first and second ports  11  and  12  are 27 MHz and 36 MHz, respectively, and return losses are 12.9 dB and 18.9 dB, respectively. 
     According to the impedance characteristic and the S-parameters, the multi-fed antenna  10  transmits and receives only a signal having a reference frequency of 2.4 GH, and a signal is not radiated through the multi-fed antenna  10  in harmonic frequencies of 4.8 GHz and 7.2 GHz of a reference frequency. Thus, the multi-fed antenna  10  may transmit and receive a signal in a specific frequency band without installing an additional filter, i.e., a band pass filter (BPF). 
     The rectenna  30  connected to the second port  12  of the multi-fed antenna  10  includes a diode  31  and a low pass filter (LPF)  33 . 
     Here, the diode  31  as a non-linear element rectifies a signal input through the multi-fed antenna  10  and generates harmonic frequency components. In other words, in a case of an RFID, a reference frequency is 2.4 GHz. Thus, the diode  31  generates frequencies of 0 GHz (direct current (DC) signal), 4.8 GHz, 7.2 GHz . . . that are harmonic frequency components of 2.4 GHz and converge the frequencies to the DC signal due to a resonance. 
     The LPF  33  of the rectenna  30  receives signals from the diode  31  and filters only a DC signal of the signals to supply a DC voltage to a low noise amplifier (LNA)  21  of the receiver circuit  20 . Since the multi-fed antenna  10  operates as a BPF, the harmonic frequency components generated by the diode  31  are not radiated to the outside through the multi-fed antenna  10 . Also, since the LPF  33  of the rectenna  30  outputs only the DC signal, the harmonic frequencies of 4.8 GHz and 7.2 GHz continuously resonate in the diode  31  and thus converge to the DC signal, and harmonic frequency components are continuously generated from signals input through the multi-fed antenna  10 . As a result, efficiency of the diode  31  may be improved, and a whole system can be realized at a low power. 
     Although not shown, a charging element may be installed between the LPF  33  of the rectenna  30  and the receiver circuit  20 . In this case, a DC voltage is charged in the charging element to supply the DC voltage to the receiver circuit  20  at a desired period. 
     The receiver circuit  20  connected to the first port  11  of the multi-fed antenna  10  includes the LNA  21 , a self-mixer  23 , and a LPF  25 . 
     The LNA  21  amplifies a signal input through the multi-fed antenna  10  and is supplied with a DC voltage from the rectenna  30  so as to operate. 
     The self-mixer  23  downs the signal amplified by the LNA  21  to a base band and does not use an existing local oscillator. An existing mixer using a local oscillator includes an input node, an output node, and an oscillator connection node, while the self-mixer  23  includes only an input node and an output node. The self-mixer  23  receives a carrier and a data signal through the multi-fed antenna  10  and downs the data signal to a base band using the carrier. 
     If a signal is received in the form of Large Carrier-Double SideBand (LC-DSB), the self-mixer  23  may be adopted. When a LC-DSB signal having a frequency band of 2.4 GHz is received and downconverted, a relative low loss of 4.5 dB occurs. Since the self-mixer  23  does not require the local oscillator, power consumption can be reduced. 
     The LPF  25  filters a downconverted data signal to extract only a signal in a desired band. 
       FIG. 4  is a graph illustrating a conversion gain of the LNA at receiver shown in  FIG. 1 . 
     A gain of the LNA  21  supplied with the DC voltage from the rectenna  30  was measured to observe a performance of the rectenna  30  installed in the multi-fed antenna  10 . Here, after a DC voltage biased by the rectenna  30  and a DC voltage supplied from a general commercial power supply are supplied to the LNA  21 , conversion gains of the LNA  21  were compared. As shown in  FIG. 4 , the performance of the LNA  21  when being supplied with the DC voltage through the rectenna  30  is almost similar to when being supplied with the DC voltage using the commercial power supply. Here, a difference occurs during the two-time measurements due to a difference between a load of the rectenna  30  and a load of the power supply and a variation in a power of a signal received from the rectenna  30 . 
     According to the results of this experiment, the rectenna  30  supplies a sufficient DC voltage to the receiver circuit  20 . Thus, the rectenna  30  may be put to practical use. 
       FIG. 5A  is a view illustrating a waveform of a signal transmitted from a transmitter, and  FIG. 5B  is a view illustrating a waveform of the signal of  FIG. 5A  processed by and output from the receiver including the multi-fed antenna shown in  FIG. 1 . 
     If the LNA  21  is supplied with the DC voltage from the rectenna  30  to operate, the carrier and the data signal are amplified, and the amplified data signal is downconverted by the self-mixer  23 . Thus, comparing a signal output from the receiver with a signal transmitted from the transmitter, the two signals hardly have a difference and are well recovered as shown in  FIGS. 5A and 5B . 
     The multi-fed antenna  10  having the above-described structure can removes a BPF to reduce a number of components. Thus, hardware size of the receiver including the multi-fed antenna  10  can be reduced. Also, the multi-fed antenna  10  allows the DC voltage consumed by the LNA  21  to be supplied to the rectenna  30  and uses the self-mixer  23  so as to reduce consumed power. 
     Harmonic frequencies continuously resonate in the diode  31  by the multi-fed antenna  10  and the LPF  33  of the rectenna  30  so as to improve efficiency of a whole system. 
     Since a power is supplied using the rectenna  30 , a battery can be removed. Thus, the whole system can be compact and light. 
     As described above, according to the present invention, a multi-fed antenna enabling an installation of a rectenna can be used to make a device compact and light, reduce consumed power, and improve efficiency of a whole system. 
     The foregoing embodiment and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.