Broadband wide-beam circularly polarized antenna

Abstract

The invention discloses a broadband wide-beam circularly polarized antenna with a compact structure. The broadband wide-beam circularly polarized antenna is characterized by comprising a first square dielectric substrate, a second square dielectric substrate, a double-cylindrical dielectric substrate, a floor I, a floor II, an FPC dielectric substrate, a radiation patch, a metal column I, a metal column II, a feed metal column, a nylon column, a metal bonding pad I, a metal bonding pad column II and an orthogonal four-feed network, the double-cylindrical dielectric substrate, the first square dielectric substrate and the second square dielectric substrate are sequentially arranged in parallel from top to bottom, the feed metal column is inserted into the three substrates, and the metal column I and the nylon column are inserted into the first square dielectric substrate and the second square dielectric substrate.

Description

Technical Field

[0001] The invention relates to the field of microwave antennas, and in particular to a wide-bandwidth beam circularly polarized antenna with a compact structure. Background Art

[0002] Circularly polarized antennas are widely used in satellite communications and other fields because they can effectively overcome multipath interference, the influence of Faraday rotation effect, and polarization mismatch problems. In order to meet the needs of high-power scenarios, the performance of a single antenna is difficult to meet, so high gain is obtained through antenna array technology. With the growth of people's demand for practical applications, the requirements for the scanning angle range of phased array beams are further improved, and a wider impedance bandwidth is also required to expand channel capacity and improve anti-interference capabilities. For circularly polarized large-angle scanning phased arrays, antenna units with wide impedance bandwidth, wide half-power beam and wide axial ratio beam are crucial.

[0003] In recent years, many researchers have devoted themselves to improving the beam width of circularly polarized antennas. In the literature, the half-power beam performance and 3-dB axial ratio beam performance of circularly polarized antennas have been studied separately and many effective methods have been proposed. Most antennas cannot always maintain good circular polarization performance in all directions. Some antennas use technologies such as loading special structures and introducing parasitic units to widen the 3-dB axial ratio beam width, but their half-power beam width is narrow; some antennas use technologies such as loading metal cavities and loading parasitic structures to widen the half-power beam width, but they only achieve performance at a single frequency point and do not cover a wide frequency band; in addition, although some antennas have a wide half-power beam, their impedance matching bandwidth is narrow. Most of the wide-beam circularly polarized antenna units reported so far are relatively large in size and are not suitable for antenna array applications. To this end, the present invention proposes a compact wide-bandwidth beam circularly polarized antenna with the advantages of wide axial ratio beam, wide half-power beam, wide impedance bandwidth and small size. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention discloses a compact wide-bandwidth beam circularly polarized antenna, comprising: a first square dielectric substrate, a second square dielectric substrate, a double cylindrical dielectric substrate, a floor I, a floor II, an FPC dielectric substrate, a radiation patch, a metal column I, a metal column II, a feeding metal column, a nylon column, a metal pad I, a metal pad column II and an orthogonal four-feed network;

[0005] The double cylindrical dielectric substrate, the first square dielectric substrate and the second square dielectric substrate are arranged in parallel from top to bottom, the feeding metal column is plugged into the three substrates, and the metal column I and the nylon column are plugged into the first square dielectric substrate and the second square dielectric substrate;

[0006] The floor I is arranged on the lower surface of the first square dielectric substrate and is provided with a feeding protection hole; the floor II is arranged on the upper surface of the second square dielectric substrate and is provided with a feeding protection hole and a rectangular groove, wherein the metal column II is arranged on the floor II;

[0007] The FPC dielectric substrate is arranged on the upper surface of the double cylindrical dielectric substrate;

[0008] The radiation patches include 4 groups, and every two groups are placed on the upper surface of the FPC dielectric substrate at an interval of 90°, wherein each group of radiation patches includes a feed metal patch, an arc metal patch, a vertical metal patch and a horizontal metal patch;

[0009] The metal pillars I include 16 in number, wherein the spacing angle is 22.5°, and the bottom of the metal pillars I is connected to the metal pad I; the metal pillars II include 4 in number, wherein the spacing angle is 90°, and the metal pillars II include 4 in number, wherein the top of the metal pillars II is connected to the floor I, and the bottom thereof passes through the second square dielectric substrate and the floor II and is connected to the floor II;

[0010] The feeding metal column is connected to the radiation patch through the first square dielectric substrate, the second square dielectric substrate, the double cylindrical dielectric substrate and the FPC dielectric substrate;

[0011] The nylon columns include four, wherein the top ends of the nylon columns pass through the upper surface of the first square dielectric substrate, and the bottom ends of the nylon columns pass through the lower surface of the second square dielectric substrate;

[0012] The metal pad I is arranged on the upper surface of the first square dielectric substrate and connected to the bottom of the metal column I; the metal pad column II is arranged on the lower surface of the second square dielectric substrate and connected to the bottom of the metal column II;

[0013] The orthogonal four-feed network is placed on the lower surface of the second square dielectric substrate, and includes a broadband anti-phase equal-radiation power divider, a first coupler and a second coupler;

[0014] The broadband anti-phase equal-radiation power divider comprises a first transmission line, a second transmission line, a third transmission line, a fourth transmission line, a fifth transmission line, a first output port and a second output port;

[0015] The first transmission line is connected to the second transmission line, and the upper end of the first transmission line is connected to the fourth transmission line and the second output port; the right end of the second transmission line is connected to the first transmission line, and the left end thereof is connected to the third transmission line, and the middle part of the second transmission line is connected in parallel with an open branch I; the right end of the third transmission line is connected to the first transmission line, and the left end thereof is connected to the fifth transmission line, and the middle part of the third transmission line is connected in parallel with an open branch II; the right end of the fourth transmission line is connected to the first transmission line and the second output port, and the left end thereof is connected to the fifth transmission line and the first output port, and the middle part of the fourth transmission line is connected in parallel with an open branch III and a first matching load; the lower end of the fifth transmission line is connected to the third transmission line, and the upper end thereof is connected to the fourth transmission line and the first output port; the first output port is connected to a first coupler; and the second output port is connected to a second coupler;

[0016] The first coupler includes a first input transmission line, a first double-layer coupled line, a first output transmission line, a second output transmission line, and a second matching load;

[0017] The first output port is connected to the right end of the first input transmission line; the left end of the first input transmission line is connected to the upper right end of the first double-layer coupling line; wherein the first double-layer coupling line is composed of two parallel coupling lines, one is placed on the upper surface of the second square dielectric substrate, and the other is placed on the lower surface of the second square dielectric substrate, and the two parallel coupling lines are connected through a short-circuit pin; the upper left end of the first double-layer coupling line is connected to the first output transmission line, the lower right end is connected to the second output transmission line, and the lower left end is connected to the second matching load;

[0018] The second coupler includes a second input transmission line, a second double-layer coupled line, a third output transmission line, a fourth output transmission line and a third matching load; the structure of the second coupler is the same as that of the first coupler.

[0019] The broadband characteristic is obtained by setting the feeding metal patch to realize coupled feeding.

[0020] The half-power beam of the antenna is effectively widened by setting a vertical metal patch and adjusting the height.

[0021] The axial ratio beamwidth is improved by adjusting the height of the metal pillar I and the distance between the metal pillar I and the double cylindrical dielectric substrate.

[0022] The second transmission line, the third transmission line and the fourth transmission line are loaded with an open-circuit branch I, an open-circuit branch II and an open-circuit branch III respectively, so as to reduce the size of the feeding network.

[0023] Due to the adoption of the above technical solution, the present invention provides a compact wide-bandwidth circularly polarized antenna, which has the following advantages: (1) The antenna has broadband performance, the impedance bandwidth is 4.58GHz to 7.06GHz (42.6%), and the axial ratio within the bandwidth is less than 3-dB. (2) The antenna has a wide 3-dB axial ratio beamwidth within the impedance bandwidth, specifically, the 3-dB axial ratio beamwidth at 4.7GHz frequency reaches 153°; the 3-dB axial ratio beamwidth at 5.8GHz frequency reaches 237°; and the 3-dB axial ratio beamwidth at 6.5GHz frequency reaches 240°. (3) The antenna has a wide half-power beamwidth within the impedance bandwidth, specifically, the half-power beamwidth at 4.7GHz frequency reaches 135°; the half-power beamwidth at 5.8GHz frequency reaches 192°; and the half-power beamwidth at 6.5GHz frequency reaches 122°. (4) The antenna size is small (0.41λ×0.41λ×0.19λ). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a 3D structural diagram of a compact wide bandwidth beam circularly polarized antenna of the present invention;

[0026] Figure 2 It is a horizontal structural decomposition diagram of a compact wide bandwidth beam circularly polarized antenna of the present invention;

[0027] Figure 3 It is a 3D structural exploded diagram of a compact wide bandwidth beam circularly polarized antenna of the present invention;

[0028] Figure 4 It is a structural diagram of an orthogonal four-feed network of a compact wide-bandwidth beam circularly polarized antenna of the present invention;

[0029] Figure 5 The invention discloses an S parameter curve of a circularly polarized antenna with a wide bandwidth beam and a compact structure.

[0030] Figure 6 The present invention provides a curve diagram showing the variation of the axial ratio and gain of a compact wide bandwidth circular polarization antenna with respect to frequency.

[0031] Figure 7These are the half-power beamwidth curves of the antenna at 4.7 GHz, 5.8 GHz, and 6.5 GHz when phi is 0°.

[0032] Figure 8 These are the axial ratio beam curves of the antenna at 4.7 GHz, 5.8 GHz, and 6.5 GHz when phi is 0°.

[0033] In the figure: 1. first square dielectric substrate, 2. second square dielectric substrate, 3. double cylindrical dielectric substrate, 4. floor I, 41, feeding protection hole, 5. floor II, 51, feeding protection hole, 52, rectangular groove, 53, metal column II, 6. FPC dielectric substrate, 7. radiation patch, 71, feeding metal patch, 72, arc metal patch, 73, vertical metal patch, 74, horizontal metal patch, 8. metal column I, 9. metal column II, 10. feeding metal column, 11. nylon column, 12. metal pad I, 13. metal pad column II, 14. orthogonal four-feed network, 141, broadband anti-phase equal-radiation power divider, 1411 A transmission line, 1412, a second transmission line, 1413, a third transmission line, 1414, a fourth transmission line, 1415, a fifth transmission line, 1416, a first output port, 1417, a second output port, 142, a first coupler, 1421, a first input transmission line, 1422, a first double-layer coupled line, 1423, a first output transmission line, 1424, a second output transmission line, 1425, a second matching load, 143, a second coupler, 1431, a second input transmission line, 1432, a second double-layer coupled line, 1433, a third output transmission line, 1434, a fourth output transmission line, 1435, a third matching load. DETAILED DESCRIPTION

[0034] In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0035] like Figure 1 , 2A compact wide bandwidth beam circularly polarized antenna shown in Figures 3 and 4 includes: a first square dielectric substrate 1, a second square dielectric substrate 2, a double cylindrical dielectric substrate 3, a floor I 4, a floor II 5, an FPC dielectric substrate 6, a radiation patch 7, a metal column I 8, a metal column II 9, a feeding metal column I0, a nylon column 11, a metal pad I12, a metal pad column II 13 and an orthogonal four-feed network 14. The first square dielectric substrate 1 is provided with a nylon column 11 and a feeding metal column I0; the second square dielectric substrate 2 is provided with a nylon column 11, a metal column II 9 and a feeding metal column I0; the double cylindrical dielectric substrate 3 is provided with a feeding metal column I0; the floor I 4 is provided on the lower surface of the first square dielectric substrate 1, and is provided with a feeding protection hole 41; the floor II 5 is provided on the upper surface of the second square dielectric substrate 2, and is provided with a feeding protection hole 51, a rectangular groove 52 and a metal column II 953; the FPC dielectric substrate 6 is provided on the upper surface of the double cylindrical dielectric substrate 3; the radiation patch 7 has 4 groups, and each two groups are placed on the upper surface of the FPC dielectric substrate 6 at an interval of 90°, and each group of the radiation patch 7 includes a feeding metal patch 71, an arc-shaped metal patch 72, a vertical metal patch 73, and a horizontal metal patch 74, wherein the height of the vertical metal patch 73 is set to 6.5 mm; the metal column I There are 16 metal pillars 8, with an interval angle of 22.5° and a height of 10mm, and a center distance of 10.5mm from the double cylindrical dielectric substrate 3. The bottom of the metal pillar I 8 is connected to the metal pad I12; there are 4 metal pillars II 9, with an interval angle of 90°, and there are 4 metal pillars II 9. The top of the metal pillar II 9 is connected to the floor I 4, and the bottom passes through the second square dielectric substrate 2 and the floor II 5 and is connected to the floor II 5; the feeding metal pillar I0 passes through the first square dielectric substrate 1, the second square dielectric substrate 2, the double cylindrical dielectric substrate 3 and the FPC dielectric substrate 6 to be connected to the radiation patch 7; there are 4 nylon pillars 11, the top of the nylon pillar 11 passes through the upper surface of the first square dielectric substrate 1, and the bottom passes through the lower surface of the second square dielectric substrate 2; the metal pad I12 is arranged on the upper surface of the first square dielectric substrate 1 and is connected to the bottom of the metal pillar I 8; the metal pad pillar II 13 is arranged on the lower surface of the second square dielectric substrate 2 and is connected to the metal pillar II 9 are connected at the bottom;

[0036] The orthogonal four-feed network 14 is placed on the lower surface of the second square dielectric substrate 2, and includes a broadband anti-phase equal-radiation power divider 141, a first coupler 142 and a second coupler 143; the broadband anti-phase equal-radiation power divider 141 includes a first transmission line 1411, a second transmission line 1412, a third transmission line 1413, a fourth transmission line 1414, a fifth transmission line 1415, a first output port 1416 and a second output port 1417; the first transmission line 1411 is connected to the second transmission line 1412, and the upper end is connected to the fourth transmission line 1414 and the second output port 1417; the right end of the second transmission line 1412 is connected to the first transmission line 1411, the left end is connected to the third transmission line 1413, and the middle part of the second transmission line 1412 is connected with an open-circuit branch I in parallel. 14121; the right end of the third transmission line 1413 is connected to the first transmission line 1412, the left end is connected to the fifth transmission line 1415, and the middle of the third transmission line 1413 is connected in parallel with an open-circuit branch II 14131; the right end of the fourth transmission line 1414 is connected to the first transmission line 1411 and the second output port 1417, the left end is connected to the fifth transmission line 1415 and the first output port 1416, the middle of the fourth transmission line 1414 is connected in parallel with an open branch III14141 and a first matching load 14142; the lower end of the fifth transmission line 1415 is connected to the third transmission line 1413, and the upper end is connected to the fourth transmission line 1414 and the first output port 1416; the first output port 1416 is connected to the first coupler 142; the second output port 1417 is connected to the second coupler 143; the first coupler 142 includes a first input transmission line 1421, a first double-layer coupled line 1422, a first output transmission line 1423, a second output transmission line 1424 and a second matching load 1425; the first output port 1416 is connected to the first input transmission line 1421; the left end of the first input transmission line 1421 is connected to the upper right end of the first double-layer coupling line 1422; the first double-layer coupling line 1422 is respectively placed on the upper surface and the lower surface of the second square dielectric substrate 2, and the two layers are connected by a short-circuit pin; the upper left end of the first double-layer coupling line 1422 is connected to the first output transmission line 1423, the lower right end is connected to the second output transmission line 1424, and the lower left end is connected to the second matching load 1425; the first output transmission line 1423 and the second output transmission line 1424 have the same width and are respectively connected to one of the feeding metal pillars I0; the second coupler 143 includes a second input transmission line 1431, a second double-layer coupling line 1432, a third output transmission line 1433, a fourth output transmission line 1434 and a third matching load 1435; the structure of the second coupler 143 is the same as that of the first coupler 142.

[0037] The compact wide bandwidth circular polarization antenna adopts a three-dimensional structure to achieve good radiation characteristics. The feeding metal patch 71 is provided to achieve coupled feeding to obtain broadband characteristics. The half-power beam of the antenna can be effectively widened by providing a vertical metal patch 73 and adjusting the height. The axial ratio beam width can be effectively improved by providing a metal column I 8 and adjusting the height of the metal column I 8 and the distance between the metal column I 8 and the double cylindrical dielectric substrate 3. The second transmission line 1412, the third transmission line 1413, and the fourth transmission line 1414 are respectively loaded with open branch I 14121, open branch II 14131, and open branch III 14141 to reduce the size of the feeding network.

[0038] The technical indicators adopted by the present invention are as follows:

[0039] Center frequency: 5.8GHz

[0040] Polarization: RHCP

[0041] 10-dB impedance bandwidth: >40%

[0042] 3-dB axial ratio bandwidth: >40%

[0043] 3-dB axial ratio beamwidth: >120°

[0044] Half power beam width: >120°

[0045] Figure 5 The S parameter curve of a compact wide bandwidth circular polarization antenna of the present invention shows that the return loss of the antenna is greater than 10dB within the frequency range of 4.58GHz to 7.06GHz (42.6%). Figure 6 This is a graph showing the axial ratio and gain of a compact wide bandwidth circular polarization antenna according to the present invention. The results show that the axial ratio of the antenna is less than 3dB in the frequency range of 4.58GHz to 7.06GHz (42.6%). The above results indicate that the antenna has a wide operating frequency band.

[0046] Figure 7 The half-power beamwidth curves of the antenna at 4.7 GHz, 5.8 GHz, and 6.5 GHz when phi is 0°. The half-power beamwidth measured at 4.7 GHz is 135°, the half-power beamwidth measured at 5.8 GHz is 192°, and the half-power beamwidth measured at 6.5 GHz is 122°. This shows that the antenna has a wide half-power beamwidth.

[0047] Figure 8The axial ratio beamwidth of the antenna at 4.7 GHz, 5.8 GHz, and 6.5 GHz when phi is 0° is shown in Figure 2. The axial ratio beamwidth measured at 4.7 GHz is 153°, the axial ratio beamwidth measured at 5.8 GHz is 237°, and the axial ratio beamwidth measured at 6.5 GHz is 240°. This shows that the antenna has a wide axial ratio beamwidth.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A compact wide bandwidth circularly polarized antenna, characterized in that include: A first square dielectric substrate (1), a second square dielectric substrate (2), a double cylindrical dielectric substrate (3), a floor I (4), a floor II (5), an FPC dielectric substrate (6), a radiation patch (7), a metal column I (8), a metal column II (9), a feeding metal column (10), a nylon column (11), a metal pad I (12), a metal pad column II (13) and an orthogonal four-feed network (14); The double cylindrical dielectric substrate (3), the first square dielectric substrate (1) and the second square dielectric substrate (2) are arranged in parallel from top to bottom, the feeding metal column (10) is plugged into the three substrates, and the metal column I (8) and the nylon column (11) are plugged into the first square dielectric substrate (1) and the second square dielectric substrate (2); The floor I (4) is arranged on the lower surface of the first square dielectric substrate (1) and is provided with a feeding protection hole (41); the floor II (5) is arranged on the upper surface of the second square dielectric substrate (2) and is provided with a feeding protection hole (51) and a rectangular groove (52), wherein the metal column II (9) is arranged on the floor II (5); The FPC dielectric substrate (6) is arranged on the upper surface of the double cylindrical dielectric substrate (3); The radiation patches (7) include four groups, and each two groups are placed on the upper surface of the FPC dielectric substrate (6) at an interval of 90 degrees, wherein each group of radiation patches (7) includes a feeding metal patch (71), an arc-shaped metal patch (72), a vertical metal patch (73) and a horizontal metal patch (74); The metal pillars I (8) include 16 in number, wherein the spacing angle is 22.5°, and the bottom of the metal pillars I (8) is connected to the metal pad I (12); the metal pillars II (9) include 4 in number, wherein the spacing angle is 90°, and the metal pillars II (9) include 4 in number, wherein the top of the metal pillars II (9) is connected to the floor I (4), and the bottom thereof passes through the second square dielectric substrate (2) and the floor II (5) and is connected to the floor II (5); The feeding metal column (10) passes through the first square dielectric substrate (1), the second square dielectric substrate (2), the double cylindrical dielectric substrate (3) and the FPC dielectric substrate (6) to be connected to the radiation patch (7); The nylon columns (11) include four nylon columns (11), wherein the top end of the nylon column (11) passes through the upper surface of the first square dielectric substrate (1), and the bottom end of the nylon column (11) passes through the lower surface of the second square dielectric substrate (2); The metal pad I (12) is arranged on the upper surface of the first square dielectric substrate (1) and connected to the bottom of the metal column I (8); the metal pad column II (13) is arranged on the lower surface of the second square dielectric substrate (2) and connected to the bottom of the metal column II (9); The orthogonal four-feed network (14) is placed on the lower surface of the second square dielectric substrate (2), and comprises a broadband anti-phase equal-radial power divider (141), a first coupler (142) and a second coupler (143); The broadband anti-phase equal-radiation power divider (141) comprises a first transmission line (1411), a second transmission line (1412), a third transmission line (1413), a fourth transmission line (1414), a fifth transmission line (1415), a first output port (1416) and a second output port (1417); The first transmission line (1411) is connected to the second transmission line (1412); the upper end of the first transmission line (1411) is connected to the fourth transmission line (1414) and the second output port (1417); the right end of the second transmission line (1412) is connected to the first transmission line (1411), the left end of the second transmission line (1412) is connected to the third transmission line (1413), and the middle part of the second transmission line (1412) is connected in parallel with an open-circuit branch I (14121); the right end of the third transmission line (1413) is connected to the fifth transmission line (1415), and the left end of the third transmission line (1415) is connected to the fifth transmission line (1415); the middle part of the third transmission line (1413) is connected in parallel with an open-circuit branch II (14131); The right end of the four transmission lines (1414) is connected to the first transmission line (1411) and the second output port (1417), and the left end is connected to the fifth transmission line (1415) and the first output port (1416); the middle of the fourth transmission line (1414) is connected in parallel with an open-circuit branch III (14141) and a first matching load (14142); the lower end of the fifth transmission line (1415) is connected to the third transmission line (1413), and the upper end of the fifth transmission line (1415) is connected to the fourth transmission line (1414) and the first output port (1416); the first output port (1416) is connected to a first coupler (142); and the second output port (1417) is connected to a second coupler (143); The first coupler (142) comprises a first input transmission line (1421), a first double-layer coupled line (1422), a first output transmission line (1423), a second output transmission line (1424) and a second matching load (1425); The first output port (1416) is connected to the right end of the first input transmission line (1421); the left end of the first input transmission line (1421) is connected to the upper right end of the first double-layer coupling line (1422); wherein the first double-layer coupling line (1422) is composed of two parallel coupling lines, one of which is placed on the upper surface of the second square dielectric substrate (2) and the other is placed on the lower surface of the second square dielectric substrate (2), and the two parallel coupling lines are connected via a short-circuit pin; the upper left end of the first double-layer coupling line (1422) is connected to the first output transmission line (1423), the lower right end is connected to the second output transmission line (1424), and the lower left end is connected to the second matching load (1425); The second coupler (143) comprises a second input transmission line (1431), a second double-layer coupling line (1432), a third output transmission line (1433), a fourth output transmission line (1434) and a third matching load (1435); the structure of the second coupler (143) is the same as that of the first coupler (142).

2. A compact wide bandwidth circular polarization antenna according to claim 1, characterized in that: A feeding metal patch (71) is provided to realize coupled feeding and obtain broadband characteristics.

3. The compact wide bandwidth circular polarization antenna according to claim 1, characterized in that: The half-power beam of the antenna is effectively widened by arranging a vertical metal patch (73) and adjusting the height.

4. The compact wide bandwidth circular polarization antenna according to claim 1, characterized in that: The axial ratio beam width is improved by adjusting the height of the metal column I (8) and the distance between the metal column I (8) and the double cylindrical dielectric substrate (3).

5. The compact wide bandwidth circular polarization antenna according to claim 1, characterized in that: The second transmission line (1412), the third transmission line (1413), and the fourth transmission line (1414) are respectively loaded with an open branch I (14121), an open branch II (14131), and an open branch III (14141), thereby reducing the size of the feeding network.

Images