Patent Publication Number: US-2022224016-A1

Title: Electromagnetic wave radiator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/805,091, filed Feb. 28, 2020, which is a continuation of U.S. patent application Ser. No. 15/875,526, filed on Jan. 19, 2018, now U.S. Patent No., issued Mar. 24, 2020, which claims priority from U.S. Provisional Patent Application No. 62/447,963, filed on Jan. 19, 2017, in the U.S. Patent and Trademark Office, and Korean Patent Application No. 10-2017-0033205, filed on Mar. 16, 2017, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to an electromagnetic wave radiator, and more particularly, to an electromagnetic wave radiator radiating a circularly-polarized millimeter-wave/terahertz (THz)-wave. 
     2. Description of the Related Art 
     A millimeter-wave is an electromagnetic wave having a wavelength of about 1 to about 10 millimeters and has a frequency of about 30 to about 300 GHz. The millimeter-wave is used in various fields such as the military and automobile radars, satellite communication, and radio navigation, and is expected to be used for large-capacity voice, image, and data transmission in the next generation 5G ultra-wideband mobile communication network. A terahertz (THz)-wave is an electromagnetic wave having a frequency of about 0.3 to about 3 THz, which is used for security and medical purposes, and is expected to be widely used in the future. 
     Accordingly, various devices for efficiently transmitting and receiving millimeter-waves and THz-waves are being developed. For example, a millimeter-wave/THz-wave microstrip patch antenna has a large area and a low quality factor (Q-factor). In order to improve this issue, devices such as a multi-port driven antenna, a slot-ring traveling-wave radiator, and a multi-port driven antenna having a radiator core are proposed for the millimeter-wave/THz-wave. However, these devices still do not provide high-enough Q-factors. 
     SUMMARY 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented example embodiments. 
     According to an aspect of an example embodiment, an electromagnetic wave radiator may include: a first metal layer; a plurality of metal side walls vertically protruding along an edge of the first metal layer; and a second metal layer suspended over the first metal layer. The second metal layer may include a plurality of ports extending radially from edges of the second metal layer and a plurality of slots penetrating the second metal layer in a radial direction. 
     Every pair of adjacent metal side walls of the plurality of metal side walls may be spaced apart from each other, and each port of the plurality of ports may be disposed to pass through a gap between a corresponding pair of adjacent metal side walls. 
     The first metal layer and the second metal layer may have an identical regular polygonal shape. Each metal side wall of the plurality of metal side walls may be disposed perpendicular to an upper surface of the first metal layer at the edge of one side of the identical regular polygonal shape of the first metal layer. A first length of the each metal side wall of the plurality of metal side walls may be less than a second length of the one side of the first metal layer. A gap between two adjacent metal side walls may be disposed at a vertex of the identical regular polygonal shape of the first metal layer. 
     The plurality of ports may radially protrude from respective vertices of the identical regular polygonal shape of the second metal layer, and the plurality of slots may be disposed between a center of the second metal layer and the respective vertices of the identical regular polygonal shape of the second metal layer. 
     The first metal layer and the second metal layer may have an identical circular shape. Each metal side wall of the plurality of metal side walls may be disposed perpendicular to an upper surface of the first metal layer at the edge of the first metal layer. The edge of the first metal layer may correspond to a perimeter of the identical circular shape of the first metal layer. A combined length of the plurality of metal side walls may be less than a diameter of the identical circular shape of the first metal layer. The plurality of gaps between the plurality of metal side walls may be disposed at regular intervals along the perimeter of the identical circular shape of the first metal layer. 
     Each of the plurality of ports may protrude in the radial direction of the second metal layer between the plurality of gaps between the plurality of metal side walls. 
     The second metal layer may be in a space surrounded by the plurality of metal side walls. 
     The second metal layer may further include an opening penetrating through a central region of the second metal layer. 
     The electromagnetic wave radiator may further include at least one oscillator configured to provide a signal to each of the plurality of ports. The at least one oscillator may be configured so that signals provided to the plurality of ports have an identical amplitude and different phases from each other, and phase differences between signals applied to two adjacent ports are identical. 
     The second metal layer may have n ports, and a phase of the signal applied to an m-th port may be 2mπ/n, where n is a natural number and m is 0, 1, . . . , n−1. 
     The at least one oscillator may be connected to the plurality of ports in a one-to-one manner. 
     One oscillator of the at least one oscillator may be connected to the plurality of ports via a plurality of wires and each of the plurality of wires may have an electrical length providing a different phase delay from each other. 
     A space surrounded by the first metal layer, the plurality of metal side walls, and the second metal layer may define a cavity for resonance of an electromagnetic wave, and the first metal layer, the plurality of metal side walls, and the second metal layer may be configured so that the cavity functions as a resonator, a power combiner, and a radiator. 
     The electromagnetic wave radiator may further include a plurality of amplification circuits between two adjacent ports. of the plurality of ports. The plurality of amplification circuits may be disposed in a loop shape between the plurality of ports. 
     Each of the plurality of amplification circuits may include an input matching unit, an inter-stage matching unit, an output matching unit, a first common emitter transistor between the input matching unit and the inter-stage matching unit, and a second common emitter transistor between the inter-stage matching unit and the output matching unit. 
     The first common emitter transistor and the second common emitter transistor may have an identical voltage gain. 
     Each of the port impedances for the plurality of ports may be identical to each other, and port admittances for the plurality of ports may be identical to each other. 
     Each of the port admittances may have a negative resistance offsetting a cavity load impedance at a resonant frequency, and a total admittance of the electromagnetic wave radiator may have a negative real part at the resonant frequency. 
     The electromagnetic wave radiator may be configured to radiate a circularly-polarized millimeter-wave/terahertz (THz) wave. 
     According to an aspect of an example embodiment, an electromagnetic wave radiator array may include a plurality of two-dimensionally arranged electromagnetic wave radiators. Each electromagnetic wave radiator of the plurality of two-dimensionally arranged electromagnetic wave radiators may include: a first metal layer; a plurality of metal side walls vertically protruding along an edge of the first metal layer; and a second metal layer suspended over the first metal layer, wherein the second metal layer includes a plurality of ports radially extending from the edge of the second metal layer and a plurality of slots penetrating the second metal layer in a radial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an exploded perspective view of an electromagnetic wave radiator according to an example embodiment; 
         FIG. 2  is a perspective view of an electromagnetic wave radiator and illustrates a phase of a signal applied to each port of the electromagnetic wave radiator according to an example embodiment; 
         FIG. 3  illustrates an equivalent circuit of an electromagnetic wave radiator according to an example embodiment; 
         FIG. 4  illustrates an equivalent circuit of a resonance circuit at one port of the electromagnetic wave radiator; 
         FIG. 5  illustrates a configuration of an amplification circuit connected between two adjacent ports of the electromagnetic wave radiator; 
         FIG. 6  is a graph illustrating frequency response characteristics of a real part and an imaginary part of the total admittance of the electromagnetic wave radiator; 
         FIG. 7  is a graph illustrating a measurement result of a polarization pattern of an electromagnetic wave radiated from the electromagnetic wave radiator; 
         FIG. 8  is a graph illustrating a measurement result of a radiation pattern of an electromagnetic wave radiated from the electromagnetic wave radiator; 
         FIG. 9  is a graph illustrating a measurement result of spectral characteristics of an electromagnetic wave radiated from the electromagnetic wave radiator; 
         FIG. 10  is a graph illustrating a measurement result of phase noise characteristics of an electromagnetic wave radiated from the electromagnetic wave radiator; 
         FIGS. 11A through 11E  illustrate various example embodiments of the electromagnetic wave radiator; 
         FIGS. 12A and 12B  illustrate various example embodiments of a connection relationship between respective ports and oscillators of the electromagnetic wave radiator; and 
         FIG. 13  illustrates an electromagnetic wave radiator array according to another example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following drawings, like reference numerals in the drawings denote like elements, and sizes of elements may be exaggerated for clarity and convenience. In addition, embodiments to be described below are only exemplary and various modifications from such example embodiments may be possible. In the case where a position relationship between two items is described with the terms “on” or “on the top of,” one item may be not only directly on the other item while being in contact with the other item but may also be on the other item without being in contact with the other item. 
       FIG. 1  is an exploded perspective view of an electromagnetic wave radiator according to an example embodiment. Referring to  FIG. 1 , an electromagnetic wave radiator  100  according to an example embodiment may include a first metal layer  110  on a semiconductor substrate  101 , a plurality of side walls  120  vertically protruding along edges of the first metal layer  110 , and a second metal layer  130  suspended over the first metal layer  110 . The semiconductor substrate  101  may include a material for a general semiconductor device such as silicon or a compound semiconductor. Although not shown, a circuit for transmitting and receiving signals to and from the electromagnetic wave radiator  100  may be formed on the semiconductor substrate  101 . A supporting member for supporting the second metal layer  130  so as to be suspended with respect to the first metal layer  110  may be arranged on the semiconductor substrate  101 . 
     The first metal layer  110  may be a thin and flat metal plate and be disposed on the semiconductor substrate  101 . For example, a thickness of the first metal layer  110  may be in a range of about 0.3 to about 0.6 μm and have a diameter in a range of about 1 to about 2 mm. In addition, the first metal layer  110  may have a circular or regular polygonal shape. In  FIG. 1 , the first metal layer  110  is illustrated to have a regular octagonal shape. However, the example embodiment is not limited thereto. The first metal layer  110  may have a different shape depending on the number of phases of signals to be coupled. 
     The plurality of side walls  120  may include the same conductive metal as the first metal layer  110 . When the first metal layer  110  has a regular polygonal shape, each side wall  120  may be perpendicular to an upper surface of the first metal layer  110  at an edge of one side of the first metal layer  110 . For example, a height of each side wall  120  may be in a range of about 12 to about 16 μm. A width of each side wall  120  may be less than the length of one side of the first metal layer  110  so that a gap may be formed between two adjacent side walls  120 . For example, the gap between two adjacent side walls  120  may be at each vertex of the first metal layer  110 . Alternatively, when the first metal layer  110  has a circular shape, the combined widths of the side walls  120  may be less than a diameter of the first metal layer  110 , and a plurality of gaps among a plurality of side walls  120  may be equally located along the perimeter of the first metal layer  110 . 
     The second metal layer  130  may include a thin and flat metal plate and may include the same conductive metal as the first metal layer  110 . For example, a thickness of the second metal layer  130  may be in a range of about 2 to about 4 μm. In addition, the second metal layer  130  may have the same circular or regular polygonal (e.g., equilateral) shape as the first metal layer  110 . A size or diameter of the second metal layer  130  may be less than the size or diameter of the first metal layer  110  so that the second metal layer  130  may be disposed in a space surrounded by the plurality of side walls  120 . As described above, the second metal layer  130  may be suspended on the first metal layer  110  by the supporting member on the semiconductor substrate  101 . The distance between the first metal layer  110  and the second metal layer  130  may be slightly less than a height of the side wall  120 . 
     In addition, the second metal layer  130  may include a plurality of ports  131  protruding radially from edges of the second metal layer  130 , a plurality of slots  132  between the center and each of the vertices of the second metal layer  130 , and an opening  133  at the center of the second metal layer  130 . The plurality of ports  131  may receive signals from an oscillator  150  (refer to  FIGS. 12A and 12B ) to be described below and the signals generated from the oscillator  150  may be provided to the electromagnetic wave radiator  100  via the plurality of ports  131 . Each port  131  may extend from the each vertex of the second metal layer  130  and may protrude out of the first metal layer  110  through the gap between two adjacent side walls  120 . Each slot  132  formed by partial penetration through the second metal layer  130  may be formed to extend in a radial direction between the center and each vertex of the second metal layer  130 . Electromagnetic waves radiated from the electromagnetic wave radiator  100  may be radiated through respective slots  132 . In addition, the circular opening  133  formed by partial penetration through a central region of the second metal layer  130  may suppress noise. The electromagnetic wave radiator  100  may have a radially symmetric structure, and a cavity for resonating an electromagnetic wave, particularly a millimeter-wave/terahertz (THz)-wave, may be prepared inside a space surrounded by the first metal layer  110 , the plurality of side walls  120 , and the second metal layer  130 . 
       FIG. 2  is a perspective view of an electromagnetic wave radiator according to an example embodiment of the present disclosure and illustrates a phase of a signal applied to each port of the electromagnetic wave radiator. Referring to  FIG. 2 , an amplification circuit  140 , which is two-staged, may be between two adjacent ports  131 . A plurality of amplification circuits  140  may be arranged between the ports  131  of the entire electromagnetic wave radiator  100  in a loop shape. In addition, signals having evenly spaced phases may be respectively applied to the plurality of ports  131  of the electromagnetic wave radiator  100 . In other words, phase differences between the signals applied to the two adjacent ports  131  in the electromagnetic wave radiator  100  may be all the same. For example, when the electromagnetic wave radiator  100  has eight ports  131 , a signal having a phase of about 0° may be applied to the port  131  at the 12 o&#39;clock direction and, in a counter-clockwise direction, signals having phases of about 45°, about 90°, about 135°, about 180°, about 225°, about 270°, and about 315° may be respectively applied to the ports  131 . 
     Signals having evenly spaced phases applied via the plurality of ports  131  may resonate in the cavity defined by the first metal layer  110 , the plurality of side walls  120 , and the second metal layer  130 . In other words, the electromagnetic wave radiator  100  may be excited by signals having evenly spaced phases applied via the plurality of ports  131 . Then, signals applied via the plurality of ports  131  may be combined in the cavity. The cavity may store a significant amount of electromagnetic wave energy by confining the electromagnetic wave therein. Thereafter, the electromagnetic wave corresponding to a resonance frequency may be radiated to the outside via the plurality of slots  132 . The electromagnetic wave radiator  100  according to the present example embodiment may function as a slot antenna, a resonant tank, a power combining network, as well as a radiator. Thus, since it is not necessary to use a separate coupling network or an antenna buffer, the size of the electromagnetic wave radiator  100  may be manufactured to be very small; thereby downsizing of a millimeter-wave/THz-wave transceiver may be possible. 
     Since the signals having evenly spaced phases are combined, the circularly-polarized signal may be radiated from the electromagnetic wave radiator  100  according to the present example embodiment. In addition, since signals having the evenly spaced phases are radiated after having resonated in the cavity, the circularly-polarized signal may be radiated without leakage in the substrate and consequently, elements such as such as a silicon lens may not be needed. In addition, since the electromagnetic wave is distributed in a large confined area in the cavity, a cavity resonance may improve a quality factor (Q-factor). The quality factor (Q-factor) is a parameter that describes how underdamped an oscillator or resonator is, and characterizes a resonator&#39;s bandwidth relative to its center frequency. As a result, conductive loss may be reduced by lowering the current density of the signals applied to the electromagnetic wave radiator  100 . In addition, low phase noise (or phase noise) and high efficiency oscillation may be achieved by high Q-factors. 
       FIG. 3  illustrates an equivalent circuit of an electromagnetic wave radiator  100  according to an example embodiment. Referring to  FIG. 3 , amplification circuits  140  may be arranged in a loop shape between the ports  131  of the entire electromagnetic wave radiator  100  and a resonance circuit  141  may be disposed at each port  131 . As shown in  FIG. 3 , the electromagnetic wave radiator  100  may have a rotationally symmetrical cavity structure. Signals applied to the plurality of ports  131  of the electromagnetic wave radiator  100  may have the evenly spaced phases like a steady-state oscillation and all the signals may have the same amplitude. In this configuration, port impedance at all ports  131  of the electromagnetic wave radiator  100  may be the same. 
       FIG. 4  illustrates an equivalent circuit of a resonance circuit at one port  131  of the electromagnetic wave radiator  100 . Values of a coil L, a capacitor C, and a resistor R T  in the equivalent circuit, illustrated as an RLC parallel resonance circuit, of  FIG. 4  may be determined by various factors such as sizes and thicknesses of the first metal layer  110 , the side wall  120 , and the second metal layer  130 , and a gap between the first metal layer  110  and the second metal layer  130  and a length of the slot  131 , and may be appropriately selected in accordance with an oscillation frequency of the electromagnetic wave radiator  100 . For example, when L is about 1.44 pH, C is about 1.31 pF, and R T  is about 40Ω, the oscillation frequency of the electromagnetic wave radiator  100  may be about 116 GHz. 
       FIG. 5  illustrates a configuration of the amplification circuit  140  connected between two adjacent ports  131  of the electromagnetic wave radiator  100 . Referring to  FIG. 5 , each amplification circuit  140  may include an input matching unit, an inter-stage matching unit, and an output matching unit. In addition, a first common-emitter transistor Q 1  may be disposed between the input matching unit and the inter-stage matching unit, and a second common-emitter transistor Q 2  may be disposed between the inter-stage matching unit and the output matching unit. The amplification circuits  140  of the electromagnetic wave radiator  100  may be formed, for example, on the semiconductor substrate  101  illustrated in  FIG. 1 . 
     According to an example embodiment, when gains of the first and second common emitter transistors Q 1  and Q 2  are respectively A v1  and A v2 , and the first and second common emitter transistors Q 1  and Q 2  have the same optimum voltage gain (that is, A v1 =A v2 =A OPT ), oscillation having maximum RF power may be achieved. In the case the electromagnetic wave radiator  100  has, for example, eight ports  131 , the input matching unit, the inter-stage matching unit, and the output matching unit in each amplification circuit  140  may be designed to have a phase difference of π/4. In addition, the input matching unit, the inter-stage matching unit, and the output matching unit in each two-stage amplification circuit  140  may be designed to suppress frequencies other than the resonance frequency. 
     Each of the amplification circuits  140  arranged in a loop shape in the electromagnetic wave radiator  100  having a rotationally symmetric structure may have the same port admittance. In addition, each of the port admittances may, for maintaining oscillation, have a negative resistance that can offset a cavity loading impedance at the resonant frequency. When a total admittance of the electromagnetic wave radiator  100  has a negative real part at the resonance frequency, the maximum oscillation power may be delivered to the cavity. 
     For example,  FIG. 6  is a graph showing frequency response characteristics of a real part and an imaginary part of the total admittance of the electromagnetic wave radiator  100 . In the graph of  FIG. 6 , it is assumed that the electromagnetic wave radiator  100  has eight ports  131 , there is a phase difference of π/4 between two adjacent ports  131 , and the resonant frequency is about 115 GHz. Referring to  FIG. 6 , at the resonant frequency, the real part of the total admittance may be less than or equal to about 0 and the imaginary part may be equal to about 0. In addition, the real part of the total admittance is greater than about 0 at frequencies other than the resonant frequency. 
       FIG. 7  is a graph showing a measurement result of a polarization pattern of an electromagnetic wave radiated from the electromagnetic wave radiator  100  and  FIG. 8  is a graph showing a measurement result of a radiation pattern of an electromagnetic wave radiated from the electromagnetic wave radiator. The graph of  FIG. 8  is the result measured in planes having two azimuth angles ϕ of 0° and 90°. As illustrated in the graph of  FIG. 7 , the polarization pattern of the electromagnetic wave radiated from the electromagnetic wave radiator  100  may be circularly-polarized light having an axial ratio better than about 0.8 dB. In addition, as illustrated in the graph of  FIG. 8 , the radiation pattern of the electromagnetic wave radiated from the electromagnetic wave radiator  100  may have a beam width of about 25° and be almost symmetrical with respect to a boresight. 
       FIG. 9  is a graph illustrating a measurement result of spectral characteristics of an electromagnetic wave radiated from the electromagnetic wave radiator  100 , and  FIG. 10  is a graph illustrating a measurement result of phase noise characteristics of an electromagnetic wave radiated from the electromagnetic wave radiator  100 . Referring to  FIG. 9 , the electromagnetic wave radiated from the electromagnetic wave radiator  100  may have a peak at about 114.1 GHz. At the peak, the equivalent isotropically radiated power (EIRP) may be about 14 dBm, the EIRP/PDC may be about 5%, and the DC-to-RF efficiency may be about 3.7%. In addition, referring to  FIG. 10 , the electromagnetic wave radiator  100  may show phase noise of about −99.3 dBc/Hz@1 MHz offset. This low phase noise may be due to the high Q-factor through the cavity resonance of the electromagnetic wave radiator  100  and the noise reduction due to the power coupling of the ports through the cavity. In addition, even when a DC power greatly varies, the resonance frequency may be varied to less than about 1.3 GHz (about 1%) due to the high Q-factor resonance. 
     Hereto, the case has been described when the electromagnetic wave radiator  100  includes eight ports  131 . However, example embodiments are not limited thereto.  FIGS. 11A through 11E  illustrate various example embodiments of the electromagnetic wave radiator  100 . Referring to  FIG. 11A , the electromagnetic wave radiator  100  may have three ports  131 . In this case, the first metal layer  110  and the second metal layer  130  may have a circular or regular triangle shape. In addition, the phase difference between adjacent ports  131  may be 2π/3. For example, a signal having a phase of about 0° may be applied to a port  131  at the 12 o&#39;clock direction and signals having phases of 120° and 240° may be respectively applied to ports  131  in a counter-clockwise direction. In addition, as illustrated in  FIG. 11B , the electromagnetic wave radiator  100  may have four ports  131 . In this case, the first metal layer  110  and the second metal layer  130  may have a circular or square shape, and the phase difference between the adjacent ports  131  may be π/2. For example, a signal having a phase of about 0° may be applied to the port  131  at the 12 o&#39;clock direction and signals having phases of 90°, 180°, 270° may be applied to respective ports  131 . In addition, as illustrated in  FIGS. 11C to 11E , the electromagnetic wave radiator  100  may have five, six, or eight ports  131 . In addition, other numbers of ports  131  (e.g., seven, nine, ten, etc.) of the electromagnetic wave radiator  100  may be selected as necessary. 
       FIGS. 12A and 12B  illustrate various example embodiments of a connection relationship between respective ports  131  and oscillators  150  of the electromagnetic wave radiator  100 . As illustrated in  FIG. 12A , the electromagnetic wave radiator  100  may include a plurality of oscillators  150   a ,  150   b , and  150   c , which are respectively connected to a plurality of ports  131   a ,  131   b , and  131   c . For example, when the electromagnetic wave radiator  100  has three ports  131   a ,  131   b , and  131   c , the electromagnetic wave radiator  100  may include three oscillators  150   a ,  150   b , and  150   c . In this case, the first oscillator  150   a  connected to the first port  131   a  may provide a signal having a phase of about 0°, and the second oscillator  150   b  connected to the second port  131   b  may provide a phase of about 120°, and a third oscillator  150   c  connected to the third port  131   c  may provide a signal having a phase of about 240°. The first through third oscillators  150   a ,  150   b  and  150   c  may be formed on the semiconductor substrate  101  illustrated in  FIG. 1 . 
     In addition, referring to  FIG. 12B , the electromagnetic wave radiator  100  may include only one oscillator  150  connected to the plurality of ports  131   a ,  131   b , and  131   c . One oscillator  150  can supply signals to each of the plurality of ports  131   a ,  131   b , and  131   c  via a first wire  151   a , a second wire  151   b , and a third wire  151   c . In this case, phases of signals applied to the plurality of ports  131   a ,  131   b , and  131   c  may be adequately delayed by adjusting electrical lengths of the first through third wires  151   a  through  151   c . That is, the first through third wires  151   a  through  151   c  may have electrical lengths that provide different phase delays from each other. For example, when the electromagnetic wave radiator  100  has three ports  131   a ,  131   b , and  131   c , the electrical length of the second wire  151   b  connected to the second port  131   b  may be selected so as to have a phase delay of about 120° with respect to the first wire  151   a . Likewise, the electrical length of the third wire  151   c  connected to the third port  131   c  may be selected so as to have a phase delay of 120° with respect to the second lead  151   b  connected to the second port  131   b.    
       FIG. 13  illustrates an electromagnetic wave radiator array according to another example embodiment. Referring to  FIG. 13 , the electromagnetic wave radiator array  200  may include a plurality of two-dimensionally arranged electromagnetic wave radiators  100 . The electromagnetic wave radiator array  200  may increase the overall power of the radiated millimeter-wave/THz-wave by using multiple electromagnetic wave radiators  100 . In addition, the direction of a main lobe of the millimeter-wave/THz-wave may be adjusted via a beam steering technology. For example, when the phases of signals applied to a plurality of ports  131   a  through  131   h  are the same for all electromagnetic wave radiators  100  in the electromagnetic wave radiator array  200 , the millimeter-wave/THz-wave may travel toward the front of the electromagnetic wave radiator array  200 . For example, a signal having a phase of about 0° is applied to the first port  131   a , a signal having a phase of about 45° is applied to the second port  131   b , a signal having a phase of about 90° is applied to the port  131   c , a signal having a phase of about 135° is applied to the fourth port  131   d , a signal having a phase of about 180° is applied to the fifth port  131   e , a signal having a phase of about 225° is applied to the sixth port  131   f , a signal having a phase of about 270° is applied to the seventh port  131   g , and a phase of about 315° is applied to the eighth port  131   h , of all the electromagnetic wave radiators  100 , the millimeter-wave/THz-wave may travel toward the front of the electromagnetic wave radiator array  200 . 
     In addition, when the phase of the signal is slightly changed for each corresponding port of the plurality of electromagnetic wave radiators  100 , a traveling direction of the millimeter-wave/THz wave may be changed to the right or left side or the up or down direction. For example, in  FIG. 13 , a signal having a phase of about 0° is applied to the first port  131   a  of the electromagnetic wave radiators  100  arranged on a first column from a left side, a signal having a phase of about 10° is applied to the first port  131   a  of the electromagnetic wave radiators  100  arranged on a second column from the left side, and a signal having a phase of about 20° is applied to the first port  131   a  of the electromagnetic wave radiators  100  arranged on a third column from the left side. In this case, signals having phases of about 55°, about 100°, about 145°, about 190°, about 235°, about 280°, and about 325° may be respectively applied to the second through eighth ports  131   b  through  131   h  of the electromagnetic wave radiators  100  arranged on the second column from the left side. In addition, signals having phases of about 65°, about 110°, about 155°, about 200°, about 245°, about 290°, and about 335° may be respectively applied to the second through eighth ports  131   b  through  131   h  of the electromagnetic wave radiators  100  arranged on the third column from the left side. Then, the millimeter-wave/THz-wave may have a tilted wave front when viewed toward the drawing and then, travel in the right direction. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example embodiment should typically be considered as available for other similar features or aspects in other example embodiments. 
     While one or more example embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.