Multiple-port patch antenna

The present invention relates to electronic devices, especially microwave antennas and power couplers.

One application requires that power from multiple microwave sources be combined to produce a single high power output signal, which is then radiated from a single antenna. This is typically achieved using one or more power couplers, such as microstrip power couplers, which combine power from multiple amplifiers and use one or more microstrip lines. And supply to a normal single or 2-port antenna. However, the power coupler occupies a large part of the circuit board space. If the outputs of multiple microwave sources are coupled, the area occupied by the power coupling circuit can be the majority of the total area of the circuit board. Since all power is concentrated in one or two potentially very narrow microstrip lines, problems with this power coupling method for high power applications can also arise. If so much power is supplied through the microstrip line, electrical destruction can occur.

<p num="0003"> In addition, these same applications sometimes require some degree of polarization diversity, i.e. the ability to emit different polarizations (such as right or left circular polarization or horizontal or vertical linear polarization) from a single antenna. To do.</p><p num="0004"> Choi et al., V-band Single-Chip MMIC Oscillator Array Using a 4-port Microstrip Patch Antenna, 2003 IEEE MTT-S Digest, Volume 2, June 2003, pp. 881-884, has 4 ports of output. An array of four field effect transistor (FET) oscillators coupled using patch antennas is described. Two parallel pairs of FET oscillators operating in push-pull mode drive the opposite side of a rectangular patch antenna, which combines the outputs of the four oscillators, partially providing feedback due to impedance mismatch in each port. Provides and produces a tightly coupled system. That is, the antenna is an integral part of the oscillator array and cannot be considered separately. This structure is effective as a power coupler because impedance mismatch is not harmful to system operation. However, it cannot be used if each port is driven by an independent microwave source or if circularly polarized radiation is desired.</p><p num="0005"> U.S. Pat. No. 5,880,694 by Wang et al. Discloses a phased array antenna that uses a stacked disk radiator. The two orthogonal pairs of excitation probes are coupled to the lower excitable disk. The polarization of the antenna can be a single linear polarization, a double linear polarization, or a circular polarization, depending on how a single pair or two pairs of excitation probes are excited. However, this antenna cannot be used as a power coupler for many sources.</p><p num="0006"> U.S. Pat. No. 6,549,166 by Bhattacharyya et al. Discloses a 4-port patch antenna capable of generating circularly polarized radiation. This antenna has a radiation patch, a ground plane with at least four slots located under the radiation patch, at least four feeding circuits (one for each slot), and each output is one of the feed networks. It is equipped with a hybrid network that feeds one and has a right-handed circularly polarized input port, a left-handed circularly polarized input port, and two matched termination ports. The input impedance at each port of the antenna does not have to be matched to the input impedance of the feedline, the two matched termination ports of the hybrid network absorb most of the energy reflected by the antenna and the return loss at the input port. To increase. The use of hybrid networks prevents the use of antennas to combine the outputs of more than two microwave sources. In addition, hybrid networks require a large area for configuration.</p><p num="0007"> Therefore, improvements have been made to eliminate the need for conventional power coupling circuits and to couple power from multiple microwave sources suitable for microwave energy emission with high power applications and greater polarization diversity than prior art. The system or method is required by the technology.</p>

<p num="0008"> The need for this technique is solved by the systems and methods for coupling and radiating electromagnetic energy of the present invention. The present invention includes a novel antenna, which comprises a first dielectric substrate having opposing first and second surfaces, a patch of conductive material disposed on the first surface, and a first. It has a ground plane of conductive material placed on the surface of 2 and at least 3 input ports where each input is patched at a feed point. The position of the feed point and the size of the patch are chosen to minimize the total power reflected from each input port. In the embodiments shown, the feed points are evenly distributed around a circle of radius d with the same center as the circular patch of radius a, and d and a are chosen to minimize reflections at each input. ing. According to the novel method of the present invention, the output of a multi-source is coupled by the antenna itself by coupling the source directly to the antenna. The antenna can radiate right circularly polarized waves and left circularly polarized waves or any desired linearly polarized waves when driven by the appropriate set of inputs.</p>

In order to illustrate the effective teachings of the present invention, exemplary embodiments and exemplary applications will be described with reference to the accompanying drawings.

Although the present invention is described herein with reference to exemplary embodiments for a particular application, it should be understood that the invention is not limited thereto. Those skilled in the art will recognize additional modifications, applications, and embodiments within the technical scope of the invention and additional areas in which the invention is very useful.

The present invention eliminates the need to precouple the outputs of multiple microwave sources by providing the patch antenna with multiple input ports. The power source is coupled directly to the antenna and the power is coupled by the antenna itself rather than using a separate circuit-based power coupler. Otherwise, the area occupied by the power coupler can be removed and used for other purposes. The total power radiated is distributed over a much larger volume than a single feed is used, reducing the potential for overheating or electrical destruction due to overly high fields. The present invention uses reflection elimination to increase the return loss at each input port. Properly positioned feed points eliminate direct reflections from individual ports by signals coupled from other ports, eliminating the need for additional impedance matching circuitry. In addition, a single multiport patch antenna designed according to the present invention radiates right circularly polarized light, left circularly polarized light or any desired linearly polarized light when driven by the appropriate set of inputs. Can be done.

FIGS. 1A to 1D are diagrams showing a 4-port structure of the antenna 10 designed according to an exemplary embodiment according to the teaching of the present invention. FIG. 1 (A) shows a three-dimensional view, FIG. 1 (B) shows a side view, FIG. 1 (C) shows a front view, and FIG. 1 (D) shows a rear view. .. The assembled antenna 10 includes a microstrip patch antenna and at least three input ports 22. The patch antenna 10 is arranged on a dielectric substrate 12 having first and second surfaces 14 and 16 facing each other, a conductive material patch 18 arranged on the first surface 14, and a second surface 16. It consists of a ground plane 20 made of a conductive material. It should be noted that in FIG. 1 (B), the thickness of patch 18 and ground plane 20 is exaggerated for illustration purposes. The patch itself can be manufactured using conventional printing circuit board etching techniques.

In the exemplary embodiments of FIGS. 1A to 1D, patch 18 is circular. The dimensions of patch 18 are largely determined by the desired operating frequency. It is well known that the resonance frequency of a circular patch with radius a is approximated by the following equation.<maths num="1"><img id="000002" he="27" wi="115" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

Here x'_mnIs the first type, [ie J'_mn(x'_mn) = 0] represents the nth zero of the derivative of the Bessel function Jm (x) of order m. The frequencies involved are m = 1, n = 1, x'₁₁The lowest resonance frequency of = 1.841. For example μ_r= 1, ε_rIf = 2.2, f = 1.03GHz, then the patch radius should be a = 2.264 inches.

Multiple input ports 22 are coupled to patch 18. In the exemplary embodiments of FIGS. 1A-D, each antenna 10 is mounted directly at its feed point 26, i.e., where the central conductor 24 of the coaxial port 22 is attached to patch 18. It is provided by four coaxial ports 22.

FIG. 2 is a diagram showing the position of the feed point 26 of the circular patch 18 having the radius a. In this embodiment, each input port 22 is located directly opposite its feed point 26, where the feed point 26 is the patch side 14 of the board 12 and the input port 22 is on the other side 16 of the board 12. .. According to the teachings of the present invention, the feed points 26 are evenly distributed around a circle with a radius d having the same center as patch 18. In Figure 2, the four feed points are labeled 1, 2, 3, and 4, with port 1 facing port 3 and port 2 facing port 4.

Proper selection of patch dimensions and proper position of feed points are the most critical factors in the design and construction of the present invention. With a single-port patch antenna, return loss is maximized by locating the port at an appropriate distance from the center of the patch. With a 4-port patch antenna, it is not possible to simply position a port in the same position it occupies in a 1-port design, because there is cross-coupling between the ports that does not exist in a single-port design. That is, if all four ports are excited at the same time, the reflected wave at port 1 will be, for example, the effect from all four ports, i.e. the wave directly reflected from port 1, and ports 2, 3, Consists of cross-coupled waves from 4.

According to the teachings of the present invention, the sum of the directly reflected and cross-coupled waves is so small that the direct reflection from port 1 is approximately due to the cross-coupled waves from ports 2, 3 and 4. The feed point is positioned so that it is erased. With this reflection elimination technique, each port is matched without the need for an additional impedance matching element.

The amplitude of the incident wave at the four ports is A₁, A₂, A₃, A₄If indicated by, the amplitude of the reflected wave at each of the four ports B₁, B₂, B₃, B₄Is given by the following equation. <maths num="2"><img id="000003" he="46" wi="157" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

Here element S_ijIs the S-parameter of a 4-port patch antenna. If it is desired to radiate circularly polarized waves, the inputs at each port should have approximately equal amplitude and be 90 degrees out of phase with the inputs of the immediately adjacent port. For example<maths num="3"><img id="000004" he="39" wi="116" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

This set of inputs produces a right (right-handed) circularly polarized (RHCP) output. To obtain the left circularly polarized (LHCP) output, simply A in equation (3)₂= j, A₄Let = j. The amplitude of the reflected wave at port 1 for the input given in Eq. (3) is given by Eq. B₁= S₁₁A₁+ S₁₂A₂+ S₁₃A₃+ S₁₄A₄ = S₁₁+ jS₁₂-S₁₃-jS₁₄ = S₁₁-S₁₃+ j (S₁₂-S₁₄) [Four] Obviously, the amplitude of the reflected wave is exactly equal to zero if the following conditions are met:

S₁₁= S₁₃, S₁₂= S₁₄ [Five] Since both the antenna and port positions are symmetrical, as shown in Figure 2, the same conditions are maintained for the three remaining ports. In addition, the symmetry of patch and port position is that the port 2 to port 1 bond is approximately the same as the port 4 to port 1 bond, and therefore S.₁₂Is S₁₄It is guaranteed that the relationship is almost equal to. Therefore, the reflection is | S₁₁-S₁₃It can be minimized by choosing an appropriate distance d from the center of the patch to position each of the four ports so that | is minimal.

The prototype 4-port patch antenna was designed to operate at a frequency of f = 1.03GHz. Equation 1 is the patch radius a₀= 2. Used to calculate a starting value of 64 inches. The distances d and a were determined iteratively. For the 4-port patches shown in Figures 1 (A) to (D), the best parameters were found to be a = 2.198 inches and d = 0.380 inches. This design was manufactured and its S-parameters were measured using a network analyzer. Figure 3 is a graph of effective return loss vs. frequency measured in a prototype 4-port antenna, where the amplitude of the reflected wave at each port uses Equation 2 with the set of inputs given in Equation 3. Is calculated. Effective return loss is the magnitude of the ratio of reflected power to incident power measured on a logarithmic scale.<maths num="4"><img id="000005" he="20" wi="150" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

It should be noted that the center frequency is too high at about 2MHz and in the worst case the return loss is slightly less than 15dB at the center frequency. Further design improvements can be made to correct the center frequency and increase the return loss at that center frequency.

The same design can be made to radiate linearly polarized waves by selecting different sets of input phases. Suppose the input is given by A₁= e^j0= 1, A₂= e^j0= 1, A₃= e^jπ= -1, A₄= e^jπ= -1 [7] In this case, the amplitude of the reflected wave at port 1 is S₁₂Is S₁₄Almost equal to (S₁₂And S₁₄Is almost equal in the actual antenna), so it becomes as follows.<maths num="5"><img id="000006" he="35" wi="135" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

This is the same matching condition for circularly polarized waves, and therefore the same antenna emits polarized waves with the appropriate change in input phase.

In fact, the antenna can radiate one of two orthogonal linearly polarized waves, depending on the phase of the input. Figures 4 (A) and (B) show two orthogonal, linearly polarized outputs and corresponding inputs when viewed from the back of the antenna. In FIG. 4 (A), the input is given by Equation 6 and the output polarization is in the direction from port 1 to port 4. In (B) of Fig. 4, A₁= 1, A₂= -1, A₃= -1, A₄= 1 and the output polarization is in the direction from port 1 to port 2.

The present invention is not limited to circularly shaped patches with four ports. Patches of other shapes can be used without departing from the technical scope of the invention. In addition, the invention can have any number of input ports, more than two. FIG. 5A is a diagram illustrating an exemplary embodiment of the invention for an equilateral triangular patch 18 having three input ports 22. Ports 22 can be located at intervals of 120 ° on a circle centered on the center of the patch, as shown in FIG. 5 (A). It should be noted that the triangle with three ports 22 vertices is rotated with respect to patch 18. The port must be located along the bisector of each side or along the bisector of each angle.

In this shape, each port 22 observes exactly the same environment as the other two ports, so if one port is matched, then all ports are matched. The same is true for the antenna shown in Figure 5 (B), where the triangular patch is replaced by a circular patch.

In general, use a proper shape diagram with N-fold rotational symmetry, that is, an invariant diagram when the N-port patch antenna is rotated about its axis of symmetry by any integer multiple of 360 / N degrees. Can be composed of. A special case is a circle, which is invariant at any rotation around its center. The design of such an N-port patch antenna is very simple when each port has the same "observed" shape, because if one port is matched, then all ports are matched. Is. This condition is satisfied by distributing the ports at equal intervals around a circle centered on the axis of symmetry of the patch. For circular patches, the ports are evenly distributed around a circle with the same center as the patch.

As an example, consider an 8-port patch antenna composed of 16-sided polygons with ports arranged as shown in FIG. Ports 22 are located every 45 degrees on a circle with radius d centered on the axis of rotational symmetry of the polygon. Port 22 has port 1 and port 5 facing each other, port 2 and port 6 facing each other, port 3 and port 7 facing each other, and port 4 and port 8 facing each other, labeled 1-8. There is. The patch shape and radius d are chosen to minimize the total power reflected from each port. With proper phase selection at the input port, the antenna can be made to radiate either left circularly polarized waves (LHCP) or right circularly polarized waves (RHCP). The following is an example of a set of RHCP inputs. <maths num="6"><img id="000007" he="71" wi="132" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

The following inputs can be used in LHCP. <maths num="7"><img id="000008" he="78" wi="131" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

For example, in a set of inputs that produce an RHCP output, the entire reflected wave at port 1 is given by: <maths num="8"><img id="000009" he="36" wi="158" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

To minimize the amplitude of the reflected wave, the antenna must be designed to minimize the following equation. <maths num="9"><img id="000010" he="40" wi="159" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

The procedure for achieving this is similar to the 4-port circular patch procedure described above.

Generally, for an antenna with N ports, the phase at the input to each port is clockwise or right circularly polarized reflections to generate a left circularly polarized reflected wave. Must be incremented by 360 / N degrees in either of the counterclockwise directions to generate the wave.

Therefore, the 8-port patch antenna can radiate both right and left circularly polarized waves. Since a linearly polarized wave is just a superposition of two equally amplitude circularly polarized waves of opposite helicities, the vertically polarized output has the corresponding circular bias as given by It can be obtained by driving the antenna with the same superposition of the inputs that produce the waved waves.<maths num="10"><img id="000011" he="67" wi="157" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths>

FIG. 7A is a diagram showing an 8-port patch antenna having an input given by Equation 13. The output is linearly polarized in the direction from port 1 to port 5 (vertically in (A) of Figure 7).

The horizontal linear polarization is obtained from the same set of inputs by simply rotating the inputs 90 ° clockwise or counterclockwise with respect to ports 1 through 8 by the following equation.<maths num="11"><img id="000012" he="71" wi="133" file="JP5259184B2_D0001.tif" img-format="tif" img-content="drawing" /></maths> FIG. 7B is a diagram showing an 8-port patch antenna having an input given by Equation 14. The output is linearly polarized in the direction from port 7 to port 2.

The condition that all ports observe the same shape simplifies the design of a multi-port patch antenna, but it is not essential. Other antenna structures in which different ports observe different shapes can be used without departing from the technical scope of the invention.

In the exemplary embodiments of FIGS. 1A-D, the antenna is provided by four coaxial ports, each directly attached to its feed point. This structure is inconvenient if the feed points are close to each other and any connectors interfere with each other. Other structures for feeding the antenna can be used without departing from the technical scope of the invention.

8 (A) and 8 (B) are diagrams illustrating exemplary embodiments of the antenna 10A of the invention by an alternative method for decoupling feed points from the position of the input port to feed the antenna. .. FIG. 8 (A) shows a normal state diagram, and FIG. 8 (B) shows an exploded view. In this structure, patch 18 is located on one outer surface of the two-layer circuit and microstrip feed network 30 is located on the other surface. The patch 18 is on the first surface of the first dielectric substrate 12, and the ground plane 20 is located on the second surface of the first dielectric substrate 12. The first surface of the second dielectric substrate 32 is located on the ground plane 20, and the microstrip feed network 30 is located on the second surface of the second dielectric substrate 32. Therefore, the patch antenna 18 and the microstrip feed network 30 share a common ground plane. Each port 22 (ie, coaxial connector) forms a transition to the microstrip. The microstrip transmission line 30 then transmits the energy provided by port 22 to a point directly below the corresponding feed point 26 on the antenna 18. At this point, the metal probe 34 transfers energy from the microstrip transmission line 30 through a hole in the common ground plane 20 to the feed point 26 on the lower surface of patch 18.

This antenna feeding method has several advantages. First, this scales a multi-port patch antenna for all frequencies, as there is no need to notice mechanical interference between adjacent connectors at high frequencies (when the distance between the feed points is less than the size of the connector). Allows you to. It also allows the area on the microstrip feed side of the circuit board to be used. For example, if the microwave source feeding the antenna needs to be protected from large reflections, a surface mounted isolator can be mounted at the rear of the antenna and circuited somewhere else in the large system. The need to provide a board can be eliminated.

9A and 9B are diagrams showing current best mode embodiments of the present invention. Figure 9A shows the normal condition, and Figure 9B shows an exploded view of the 4-port version of the multi-port patch antenna. Antenna 10B contains two dielectric substrates 12 and 32. Patch 18 (circular in this example) is located on the first surface of the first dielectric substrate 12. The second surface of the first substrate 12 faces the first surface of the second substrate 32. The ground plane 20 is arranged on the second surface of the second substrate 32. The coaxial connector 22 supplies microwave energy to the microstrip feedline 30 sandwiched between the two dielectric substrates 12 and 32. The four coaxial connectors 22 are arranged in a circle surrounding the circular patch 18 and attached to the ground plane 20. The central conductors of the coaxial ports 22 are each connected to the microstrip feedline 30. For each coaxial port 22, the distance of the connection point from the end of the corresponding microstrip feedline 30 is chosen to minimize the reflected power from the coaxial port and the transition of the microstrip. .. The microstrip feedline 30 transmits a microwave signal to the end 40 of the feedline, where the signal is radiated for the volume between patch 18 and ground plane 20. The position of the end 40 of the feed line is determined in a manner similar to that described above for feed points 26 in other embodiments. In this example, the end 40 of the feedline is evenly distributed in a circle with the same center as patch 18.

A prototype 4-port patch antenna was constructed using the best mode embodiment. The design procedure is the same as the design procedure for the 4-port circular patch described above. In the 4-port patch shown in Figures 9A and 9B, the circular patch 18 has a radius a of 2.073 inches and the ends of each of the four microstrip feedlines 30 are located on a circle with a radius of 1.72 inches. .. Both the first substrate 12 and the second substrate 32 are 0.125 inches thick and have a dielectric constant of 2.2. Figure 10 is a graph of effective return loss vs. frequency measured in a prototype 4-port antenna. It should be noted that the center frequency is very high at about 5MHz and in the worst case the return loss is about 27dB at the center frequency. Further design improvements can be made to correct the center frequency and reduce the dispersion at the center frequency of the individual ports.

(A) and (B) of FIG. 11 show a 16-port version of the antenna designed according to an exemplary embodiment according to the teachings of the present invention. FIG. 11 (A) shows a normal state, and FIG. 11 (B) shows an exploded view. Antenna 10C is similar to the antennas in Figures 9A and 9B, except that it has 16 ports 22 and a microstrip feedline 30. This antenna is designed to emit circularly polarized waves. To achieve this, the phase of the input for each port is incremented by 22.5 degrees, i.e. if port 1 is 0 degrees (if any port can be selected as port 1), then the input for port 2 The phase of the must be 22.5 degrees, the phase of the input to port 3 must be 45 degrees, and clockwise or right circularly polarized to generate left-circularly polarized radiation waves from port to port. It travels counterclockwise to generate the radiated waves.

The prototype 16-port patch antenna was constructed using the designs shown in Figures 11 (A) and (B). In the 16-port patches shown in Figures 11 (A) and (B), the circular patch 18 has a radius a of 2.023 inches and the ends of each of the 16 microstrip feedlines 30 are circles with a radius of 1.908 inches. It is placed on top. Both the first substrate 12 and the second substrate 32 are 0.125 inches thick and have a dielectric constant of 2.2. FIG. 12 is a graph of effective return loss vs. frequency measured at each port of the prototype 16-port antenna. It should be noted that the center frequency is very high at about 7MHz and in the worst case the return loss is about 21dB at the center frequency. Further design improvements can be made to correct the center frequency and reduce the dispersion at the center frequency of the individual ports.

The present invention requires a means to control the phase and amplitude at the input to each port of the antenna. Amplitude and phase control can be achieved by several means. FIG. 13 shows an exemplary module 50 for radiating high power microwave energy designed according to the teachings of the present invention. In many cases, each port 22 of the antenna 10 is driven by a separate microwave power amplifier 54. The amplitude controller 56 is used to control the amplitude of the input to each amplifier 54, and the phase controller 58 is used to control the phase of the input to each amplifier 54. The master signal amplified by each amplifier 54 can be obtained from the master oscillator 52 so that the inputs to each amplitude controller 56 are in phase. A plurality of different means, including a digitally controlled variable attenuator, are available in the configuration of the amplitude controller 56. The phase controller 58 can take the form of a ferrite phase shifter or digital delay line at the input or output of each amplifier 54. Simply connecting the antenna 10 to the output of each amplifier 54 using a transmission line (eg, coaxial cable) cut to the length required to produce the desired phase at the input to each port 22 of the antenna 10. It is also possible to make the phase shift a "hard wire".

The present invention has been described above with reference to specific embodiments for specific applications. Those skilled in the art will recognize additional modifications, application embodiments within the technical scope of the invention.

Therefore, the claims are intended to cover any or all such applications, modifications, and embodiments within the technical scope of the invention.

<figref num="1">A three-dimensional view, a side view, a front view, and a rear view showing a four-port structure of an antenna designed according to an exemplary embodiment according to the teaching of the present invention.</figref><figref num="2">The figure which shows the position of the feed point in a circular patch by an exemplary embodiment by teaching of this invention.</figref><figref num="3">Graph of measured effective return loss vs. frequency in a prototype 4-port antenna designed according to an exemplary embodiment according to the teachings of the present invention.</figref><figref num="4">The figure which shows the two orthogonal linearly polarized wave outputs of the 4-port antenna designed by the exemplary embodiment by the teaching of this invention, and the corresponding input.</figref><figref num="5">FIG. 6 illustrates an exemplary embodiment of the invention having an equilateral triangular patch and three input ports, and an exemplary embodiment of the invention having a circular patch and three input ports.</figref><figref num="6">The figure which shows the exemplary embodiment of this invention which has a patch of 16 sides and 8 input ports.</figref><figref num="7">The figure which shows the two orthogonal linearly polarized outputs of the 8-port antenna by the teaching of this invention.</figref><figref num="8">A normal view and an exploded view of an exemplary embodiment of the antenna of the present invention by another method for feeding the antenna.</figref><figref num="9A">A normal diagram in the current best mode embodiment of the present invention.</figref><figref num="9B">Exploded view of the present best mode embodiment of the present invention.</figref><figref num="10">Graph of measured effective return loss vs. frequency in a prototype 4-port antenna designed according to an exemplary embodiment according to the teachings of the present invention.</figref><figref num="11">The figure which shows the 16-port version of the antenna designed by the exemplary embodiment by teaching of this invention.</figref><figref num="12">Graph of measured effective return loss vs. frequency in a prototype 16-port antenna designed according to an exemplary embodiment according to the teachings of the present invention.</figref><figref num="13">The figure which shows the exemplary system for radiating the high power microwave energy designed by the teaching of this invention.</figref>