The present disclosure generally relates to antenna, and more particularly relates to dipole antennas.
Dipole antennas typically include a feed and two dipole arms or branches. The length of the dipole arms affect the frequency range in which the dipole antenna can radiate within. In some instances, the dipole antenna may include a balun to balance the current on both dipole arms.
In one embodiment, for example, a dipole antenna is provided. The dipole antenna may include, but is not limited to, a first transmission line configured to receive a radio frequency signal from a first feed, a first balun galvanically coupled to the first transmission line, a first conductive strip galvanically coupled to the first transmission line and the first balun, a second conductive strip galvanically coupled to the first transmission line and the first balun, a first dipole arm, and a second dipole arm, wherein the first balun and the first transmission line are only capacitively coupled to the first and second dipole arms via the first and second conductive strips.
In accordance with another embodiment, a dual polarized antenna is provided. The dual polarized antenna may include, but is not limited to, a first dipole antenna which includes, but is not limited to, a first transmission line configured to receive a radio frequency signal from a first feed, a first balun galvanically coupled to the first transmission line, a first conductive strip galvanically coupled to the first transmission line and the first balun, a second conductive strip galvanically coupled to the first transmission line and the first balun, a first dipole arm, and a second dipole arm, wherein the first balun and the first transmission line are only capacitively coupled to the first and second dipole arms via the first and second conductive strips, and a second dipole antenna which may include, but is not limited to, a second transmission line configured to receive a radio frequency signal from a second feed, a second balun galvanically coupled to the second transmission line, a third conductive strip galvanically coupled to the second transmission line and the second balun, a fourth conductive strip galvanically coupled to the second transmission line and the second balun, a third dipole arm, and a fourth dipole arm, wherein the second balun and the second transmission line are only capacitively coupled to the third and fourth dipole arms via the third and fourth conductive strips, and wherein the first dipole arm and the second dipole arm have a first polarization and the third dipole arm and fourth dipole arm have a second polarization different than the first polarization.
The detailed description will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or detail of the following detailed description.
A dipole antenna is disclosed herein. In a typical dipole antenna having two radiating dipole arms, the radiating dipole arms are directly electrically connected (i.e., galvanically connected) to a balun and a feed. However, as discussed in further detail below, the radiating arms of the dipole disclosed herein are only capacitively coupled, and not galvanically coupled, to a balun. This arrangement allows the height of the dipole to be reduced, resulting in the dipole arms of the antenna being closer to a reflector, which has numerous advantages as discussed in further detail below.
The dipole antenna 100 includes a dipole arm 125 and a dipole arm 130 formed on the side 110 of the substrate 105. The length of the dipole arms 125 and 130 affect the frequency range at which the dipole antenna 100 radiates. In other words, by adjusting the length of the dipole arms 125 and 130, the dipole antenna 100 can radiate at different frequency ranges depending upon the application of the dipole antenna 100.
The dipole antenna 100 further includes a balun 135 formed on the side 110 of the substrate 105. In this embodiment the balun 135 is formed from a slotted line. In other words, the balun is formed from an electrically conductive strip 140 in parallel with an electrically conductive strip 145 separated by a non-conductive material (e.g., a dielectric on a PCB). In the embodiment illustrated in
A feed 155, such as a coaxial cable or the like, provides a radio frequency signal to a transmission line 160 formed on the side 110 of the substrate 105. The transmission line 160 may be, for example, a conductive strip on the substrate 105. The transmission line 160 couples to the electrically conductive strip 145 of the balun 135 through a via 165 which connects the sides of the substrate 105.
The electrically conductive strip 140 is galvanically coupled to a conductive strip 170 arranged on an opposite side of the substrate 105 as dipole arm 125. In other words, the conductive strip 170 is positioned on a portion of the side 115 of substrate 105 which overlaps at least a portion of the dipole arm 125 on the side 110 of the substrate 105, but is galvanically isolated from the dipole arm 125 via the substrate 105 between the them. Likewise, electrically conductive strip 145 is galvanically coupled to a conductive strip 175 arranged on an opposite side of the substrate 105 as dipole arm 130. When fed a radio frequency signal from the feed 155, the conductive strips 170 and 175 capacitively couple to the dipole arms 125 and 130, respectfully, causing the dipole arms 125 and 130 to radiate. By adjusting the area (i.e., the length and width) of the conductive strips 170 and 175, the amount of capacitive coupling between the dipole arms 125 and 130 and the conductive strips 170 and 175 can be adjusted. This allows the reactance of the dipole arms 125 and 130 to be controlled. The length of the conductive strips 170 and 175 is smaller than a resonant length for the dipole antenna 100, and, thus, the conductive strips 170 and 175 do not radiate themselves.
Using dipoles of this design allows for dipole antennas which are smaller in size while having a wider bandwidth. For example, the height of the antenna 100 can be reduced by utilizing a shorter balun 135. In one embodiment, for example, the height of the balun 135, as indicated by arrow 180, may be around twenty to thirty percent less than a dipole antenna which directly connects the dipole arms to a balun. However, the exact height reduction can vary as other parameters may contribute to a final desired height. Furthermore, in some embodiments, the length of the dipole arms 125 and 130 may need to be lengthened to compensate for the shorter balun 135. By having a shorter balun 135, the dipole arms 125 and 130 may be located closer to a reflector. In a traditional dipole design, when a dipole is located closer to a reflector, the antenna reactance increases in the lower part of the radiating band, reducing the performance of the antenna. By utilizing the capacitive coupling between the balun 135 and the dipole arms 125 and 130, and by controlling the capacitance value by adjusting the size of the conductive strips 165 and 170, the reactance of the antenna 100 is reduced in lower part of the band to compensate for the dipole arms 125 and 130 being closer to a reflector. Accordingly, the capacitive connection allows the antenna impedance to be matched to the feed 155 (for example, a fifty ohm coaxial cable) when the dipole arms 125 and 130 are close to reflector without sacrificing the performance of the antenna.
Furthermore, having the dipole arms 125 and 130 closer to a reflector has several other advantages. The shorter balun 135, and not being galvanically connected to dipole arm 125 and 130, reduces the parasitic impact of the reflector on the antenna 100 in lower bands. In traditional dipole designs, the whole dipole and the balun radiate in the lower band as monopole and degrades the desired radiation pattern of the dipole arms. The height of the balun plus the length of dipole define the undesired resonant wavelength. When the dipole arms 125 and 130 and balun 135 are not galvanically connected as discussed herein, their undesired radiation is less destructive. Furthermore, by having the dipole arms 125 and 130 closer to the reflector, antenna gain increases due to higher current in the reflector caused by the arms being closer to the reflector. Further still, having a balun 135 which is shorter, reduces PCB use and cost when PCBs are used to implement the antenna 100.
Another advantage of the antenna design is that the capacitive coupling enables multi-band operation which allows for the interleaving of multiple dipoles to form an array of dipoles. For example, if dipole antennas using this design and operating in, for example, a mid-band band (e.g., 1695-2690 MHz) are used in an array with other dipole antennas of this deign operating in, for example, a low band (e.g., 698-896 MHZ), the dipole antennas operating in the mid band may resonate and act as parasitic mono-poles in the low band when two arrays co-exist. In a typical dipole antenna not using the capacitive coupling concept discussed herein, a dominant length (i.e., a length of the dipole antenna at which the dipole antenna radiates as a monopole) of exemplary mid-band dipoles is the length of the balun (e.g., a slotted line) plus the length of the dipole arm, which may be a length that would resonate in the low-band, thereby negatively affecting the radiation pattern of the low band antennas in the array. However, by applying the capacitive coupling concept as discussed herein, the dominant length is the balun (e.g., slotted line) length which may have a resonance frequency out of the low band, thereby not affecting the operation of the low-band antennas in the array.
Yet another benefit of the antenna design is that the capacitive coupling enables each dipole antenna 100 to have a smaller volume. The smaller volume allows arrays of these dipole antenna elements to be smaller, thereby reducing the size of the antenna array.
Multiple dipole antennas 100 can be used to make an antenna array. The dipole antennas 100 can be distributed in a line or over a planar surface. In addition, the dipole antennas 100 can be distributed over a conformal or multi-sector surface to create multi-sector or omnidirectional patterns.
The dipole 205 includes dipole arms 215 and 220. The dipole 210 includes dipole arms 225 and 230. The dipole arms 215-230 form the main part of the antenna 200 that radiates. In one embodiment, for example, the length of the dipole arms 215-230 may be around a quarter wavelength of radiating frequency. However, the dipole arms could be designed at other resonant lengths. The antenna 200 may operate over, for example, a 617-896 MHz band. However, the frequency range of the antenna 200 can vary by adjusting the length of the dipole arms 215-230. The dipole arms 215 and 220 form one dipole radiating element having a first polarization. The dipole arms 225 and 230 form a second dipole radiating element having a second polarization normal to the polarization of the dipole formed by arms 215 and 220. Accordingly, antenna 200 is a dual-polarized antenna. The antenna 200 may have, for example, zero/ninety degree polarization, +/−forty-five degree polarization or the like.
The dipoles 205 and 210 are similar to the dipole antenna 100 illustrated in
In the embodiment illustrated in
The substrates 245 and 250 each include a portion 260 which extends above the substrate 240. The length of the portion 260 of the substrates 245 and 250 defines a distance that the parasitic element 255 is above the dipole arms 215-230. When the substrates 240-250 are formed from PCBs, the length of the portion 260, and thus the distance that the parasitic element 255 is above the dipole arms 215-230, can be controlled with a high degree of accuracy. As a result, the amount of capacitive coupling between the parasitic element 255 and the dipole arms 215-230 can be controlled with a high degree of accuracy, improving the consistency of the performance of the antenna 200.
The substrates 245 and 250 may further include features which lock the parasitic element 255 in place.
Returning to
Returning to
The dipole antenna 600 includes a dipole arm 625 formed on the side 610 of the substrate 605 and a dipole arm 630 formed on the side 615 of the substrate 605. The length of the dipole arms 625 and 630 affect the frequency range at which the dipole antenna 600 radiates. In other words, by adjusting the length of the dipole arms 625 and 630, the dipole antenna 600 cam radiate at different frequency ranges depending upon the application of the dipole antenna 600.
The dipole antenna 600 further includes a balun 635 partially formed on both sides 610 and 615 of the substrate 605. In this embodiment the balun 635 is formed from a slotted line. In other words, the balun 635 is formed from an electrically conductive strip 640 in parallel with an electrically conductive strip 645 separated by anon-conductive material (e.g., a dielectric on a PCB). In this embodiment, the electrically conductive strip 640 is formed on the side 615 of the substrate 605 and the electrically conductive strip 645 is formed on the side 610 of the substrate 605. In the embodiment illustrated in
A feed 655, such as a coaxial cable or the like, provides a radio frequency signal to a transmission line 660 formed on the side 610 of the substrate. The transmission line 660 couples to the electrically conductive strip 645 of the balun 635.
The electrically conductive strip 640 is galvanically coupled to a conductive strip 665 arranged on an opposite side of the substrate 105 as dipole arm 125. In other words, the conductive strip 665 is positioned on a portion of the side 615 of substrate 605 which overlaps at least a portion of the dipole arm 625 on the side 610 of the substrate 105, but is galvanically isolated from the dipole arm 625 via the substrate 605 between the them. Likewise, electrically conductive strip 645 is galvanically coupled to a conductive strip 670 arranged on an opposite side of the substrate 105 as dipole arm 130. When fed a radio frequency signal from the feed 655, the conductive strips 665 and 670 capacitively couple to the dipole arms 625 and 630, respectfully, causing the dipole arms 625 and 630 to radiate. By adjusting the area of the conductive strips 665 and 670, the amount of capacitive coupling between the dipole arms 625 and 630 and the conductive strips 665 and 670 can be adjusted. This allows the reactance of the dipole arms 625 and 630 to be controlled.
The dipole antenna 600 includes all the advantages of the dipole antenna 100 illustrated in
Furthermore, the dipole arms 715 are arranged in a vertical orientation, unlike the dipole arms 225 and 230 illustrated in
By optimizing the dimensions of the parasitic element 810 and its location, the bandwidth of the antenna 800 can be increased. The parasitic element 810 has no galvanic connection to the dipole arms 850. In the embodiment illustrated in
In the embodiment illustrated in
While numerous embodiments are illustrated herein, any of the features from any of the antennas discussed herein may be used in any combination. In other words, any combination of the dipole configurations, the parasitic elements, and the mounting mechanisms may be used.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
This application claims the benefit of U.S. provisional patent application Ser. No. 62/595,274, filed Dec. 6, 2017, the entire content of which is incorporated by reference herein.
Number | Date | Country | |
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62595274 | Dec 2017 | US |