CN106099268A - A kind of broadband merit filter-divider - Google Patents

Abstract

The invention discloses a broadband power division filter, which comprises a dielectric substrate (101) whose lower surface is covered with a metal grounding plate (102), and an input terminal feeder (1), The first output feeder (2), the second output feeder (3), the first three-mode resonator (4), the second three-mode resonator (5), the first grounded ladder impedance resonator (6), the second A second grounded ladder impedance resonator (7), a third grounded ladder impedance resonator (8), and an isolation resistor (9). The broadband power dividing filter of the invention has good selectivity, high isolation and good harmonic suppression characteristics, and is suitable for modern wireless communication systems.

Description

A Broadband Power Divider Filter

technical field

The invention relates to the technical field of microwave passive devices, in particular to a broadband power division filter based on a discrete element isolation network and a three-mode resonator.

Background technique

The power divider filter is an independent microwave passive device, which functionally realizes the effective combination of the power divider and filter in the radio frequency circuit, that is to say, the power divider filter has both signal power distribution and filtering functions. Therefore, a high-performance power division filter can not only effectively reduce the size of the system, but also simplify the complexity of system design, thereby further realizing the low-cost, high-performance, and miniaturized design of the wireless communication system.

In recent years, with the development of Modular Building Block (MBB) and Monolithic Microwave Integrated Circuit (MMIC), low-cost, high-integration, and miniaturized high-performance power divider filters have become Research hotspots.

In 2005, Chi-Feng Chen, Ting-Yi Huang and Ruey-Beei Wu published "Design of Microstrip Bandpass Filters With Multiorder Spurious-ModeSuppression", proposes a design method based on the theory of parallel coupling combined with the resonance characteristics of the capacitive terminal loading stub to achieve high-order harmonic suppression. Although the design theory of this design method is relatively simple, because the structure introduces a ladder impedance resonator, the bandwidth of the designed power dividing filter is relatively narrow. In addition, since the circuit is realized by pure parallel coupling theory, the filter has no out-of-band zero and the signal selectivity is poor.

In 2015, Kaijun Song published "Compact filtering power divider with high frequency selectivity and wide stopband using embedded dual-mode resonator" in IEEE Electronics Letters (vol.51, no.6, pp.495–497, 2015), proposing to adopt Embed a dual-mode resonator to achieve power division and filtering functions, and at the same time use source-carrier coupling to introduce an out-of-band zero point to improve out-of-band rejection, and the signal selectivity is better. However, because this structure simply uses isolation resistors to achieve isolation between the two output ports, the isolation in the passband is poor.

In 2015, Bo Zhang and Yuanan Liu published "Wideband Filtering Power Divider with High Selectivity" in the IEEE Electronics Letters journal (vol.51, no.23, pp.1950-1952, 2015), proposing to open the branch through parallel coupling lines and terminals The method of designing the power division filter with the combination of the two components achieves a wider working bandwidth and better signal selectivity. Although the power division filter designed by this design method has the advantage of small size in the low frequency band, it has the disadvantage of low out-of-band rejection due to its simple structure.

In a word, the existing problems in the prior art are: the wideband power division filter has poor selectivity, low isolation, and poor out-of-band rejection.

Contents of the invention

The purpose of the present invention is to provide a broadband power division filter with good selectivity, high isolation and good out-of-band suppression.

The technical solution that realizes the object of the present invention is:

A broadband power division filter, comprising a dielectric substrate covered with a metal ground plate on the lower surface,

An input feeder, a first output feeder, a second output feeder, a first three-mode resonator, a second three-mode resonator, a first grounded ladder impedance resonator, a second A grounded ladder impedance resonator, a third grounded ladder impedance resonator, and an isolation resistor, the input terminals of the first three-mode resonator and the second three-mode resonator are respectively coupled to the input feeder, and the output terminals are respectively connected to the first output The end feeder and the second output end feeder are coupled, the third grounded ladder impedance resonator is connected to the input end of the first output end feeder and the second output end feeder, and the first grounded ladder impedance resonator is connected to the first output end The output end of the feeder is connected, the second grounded ladder impedance resonator is connected to the output end of the second output end feeder, the other end of the first grounded ladder impedance resonator, the second grounded ladder impedance resonator, and the third grounded ladder impedance resonator Connect to the metal ground plate through the dielectric substrate.

Compared with the prior art, the present invention has the remarkable advantages of:

1. Good selectivity: the existing power division filters are generally simple in structure and cannot generate out-of-band zeros, resulting in poor passband out-of-band selectivity although the filtering function can be realized. In the present invention, the coupling line with one end connected to the open stub will generate a zero point on both sides of the pass band, and the zero point generated by the even mode of the three-mode resonator used in the circuit will also generate a zero point on the pass band side. The two factors mentioned above realize the high selectivity of the passband of the circuit.

2. High isolation: The isolation network of the existing power dividing filter generally only uses isolation resistors to achieve isolation in the passband, but because the simple introduction of isolation resistors cannot meet the isolation design indicators of all circuits, the isolation of these circuits Isolation is sometimes not able to achieve 15dB over the entire passband. The circuit of the present invention adopts a discrete ladder impedance resonator isolation network, and the network includes a middle-end loading ladder impedance resonator, two side-end loading ladder impedance resonators and an isolation resistor. By adopting the isolation network, the difference of odd and even mode input impedance of the output port can be reduced, so as to achieve better isolation in the entire passband.

3. Good out-of-band suppression: The existing power divider filters are generally simple in structure, and cannot generate zero points outside the band, so that the out-of-band harmonics cannot be suppressed. The reason why the present invention can produce wider up-conversion stop band is that the coupled line with one end connected to the open-circuit stub can produce several zero points in the upper sideband, and the stepped impedance resonator loaded at the middle end and the stepped impedance resonator loaded at the side end can also Several nulls are created on the upper sideband of the circuit at the point of self-resonance. Combining the above two methods, the present invention realizes a wider out-of-band suppression degree.

Description of drawings

FIG. 1 is a schematic diagram of a three-dimensional structure of a broadband power division filter of the present invention.

FIG. 2 is a top view of FIG. 1 .

Fig. 3 is a schematic diagram of the structural dimensions of the embodiment.

Fig. 4 is a simulation diagram of parameters S11, S21 and S31 of the embodiment.

Fig. 5 is a simulation diagram of S23 parameters of the embodiment.

Fig. 6 is a simulation diagram of amplitude difference of two output ports of the embodiment.

Fig. 7 is a simulation diagram of the phase difference of two output ports of the embodiment.

In the figure, a dielectric substrate 101, a metal ground plate 102,

Input feeder 1, first output feeder 2, second output feeder 3, first three-mode resonator 4, second three-mode resonator 5, first grounded ladder impedance resonator 6, second grounded ladder impedance resonance device 7, the third grounded ladder impedance resonator 8, isolation resistor 9,

The first 50 ohm microstrip conduction band 11, the first half-wavelength main transmission line 12, the second half-wavelength main transmission line 13,

The second 50 ohm microstrip conduction band 21, the first microstrip transmission line 22, the first quarter-wave coupling line 23,

The third 50-ohm microstrip conduction band 31, the second microstrip transmission line 32, the second quarter-wave coupling line 33,

A first quarter-wavelength resonator 41, a second quarter-wavelength resonator 42, a low-impedance resonator 43 loaded on a branch of the first symmetry plane, and a high-impedance resonator 44 loaded on a branch of the first symmetry plane,

A third quarter-wavelength resonator 51, a fourth quarter-wavelength resonator 52, a low-impedance resonator 53 loaded with a branch of the second symmetry plane, and a high-impedance resonator 54 loaded with a branch of the second symmetry plane,

The first high-impedance resonator 61, the first low-impedance resonator 62,

The second high impedance resonator 71, the second low impedance resonator 72,

A third high-impedance resonator 81 and a third low-impedance resonator 82 .

detailed description

As shown in Figure 1, the broadband power division filter of the present invention includes a dielectric substrate 101 covered with a metal ground plate 102 on the lower surface,

On the upper surface of the dielectric substrate 101, there are input feeder 1, first output feeder 2, second output feeder 3, first three-mode resonator 4, second three-mode resonator 5, first grounding ladder Impedance resonator 6, second grounded ladder impedance resonator 7, third grounded ladder impedance resonator 8, isolation resistor 9,

The input ends of the first three-mode resonator 4 and the second three-mode resonator 5 are respectively coupled to the input feeder 1, and the output ends thereof are respectively coupled to the first output feeder 2 and the second output feeder 3, and the The third grounded ladder impedance resonator 8 is connected to the input ends of the first output end feeder 2 and the second output end feeder 3, and the first grounded ladder impedance resonator 6 is connected to the output end of the first output end feeder 2. Two grounding ladder impedance resonators 7 are connected to the output end of the second output end feeder 3, and the other end of the first grounding ladder impedance resonator 6, the second grounding ladder impedance resonator 7, and the third grounding ladder impedance resonator 8 pass through The dielectric substrate 101 is connected to the metal ground plate 102 .

As shown in Figure 1, the dielectric substrate 101 is rectangular, the input end feeder 1 is close to one wide side, the input end is arranged on the wide side, and the first output end feeder 2 and the second output end feeder 3 are close to the other wide side. side, the first output end and the second output end are respectively arranged on two opposite narrow sides.

As shown in FIG. 2, the input feeder 1 includes a first 50-ohm microstrip conduction strip 11 perpendicular to the broadside of a rectangular dielectric substrate 101, a first half-wavelength main transmission line 12 and a second half-wavelength parallel to the broadside. The main wavelength transmission line 13, the input end of the first 50 ohm microstrip line conduction band 11 is located at the midpoint of a wide side of the rectangular dielectric substrate 101, and its input end is connected to the first half-wavelength main transmission line 12 and the second half-wavelength main transmission line simultaneously. The beginning ends of the transmission lines 13 are connected, and the ends of the first half-wavelength main transmission line 12 and the second half-wavelength main transmission line 13 are connected to the metal ground plate 102 through connecting posts.

As shown in FIG. 2 , the first output feeder 2 includes a second 50-ohm microstrip line conduction strip 21 parallel to the broadside of the rectangular dielectric substrate 101 and a first microstrip transmission line 22 and perpendicular to the broadside of the rectangular dielectric substrate 101. The first quarter wavelength coupling line 23;

The input end of the first microstrip transmission line 22 is connected to the output end of the first quarter-wavelength coupled line 23, and its output end is connected to the input end of the second 50 ohm microstrip line conduction band 21, and the second The output end of the 50-ohm microstrip conduction tape 21 is located on a narrow side of the rectangular dielectric substrate 101;

The first grounded ladder impedance resonator 6 includes a first high-impedance resonator 61 and a first low-impedance resonator 62, and one end of the first low-impedance resonator 62 is vertically connected to the first microstrip transmission line 22;

The second output feeder 3 includes a third 50 ohm microstrip line conduction strip 31 parallel to the wide side of the rectangular dielectric substrate 101 and a second microstrip transmission line 32, and a second quarter of the line perpendicular to the wide side of the rectangular dielectric substrate 101 A wavelength coupling line 33;

The input end of the second microstrip transmission line 32 is connected to the output end of the second quarter wavelength coupling line 33, and its output end is connected to the input end of the third 50 ohm microstrip line conduction band 31, and the third The output end of the 50-ohm microstrip conduction tape 31 is located on the other narrow side of the rectangular dielectric substrate 101;

The second grounded ladder impedance resonator 7 includes a second high-impedance resonator 71 and a second low-impedance resonator 72, and one end of the second low-impedance resonator 72 is vertically connected to the second microstrip transmission line 32;

The third grounded ladder impedance resonator 8 includes a third high-impedance resonator 81 and a third low-impedance resonator 82, one end of the third low-impedance resonator 82 is connected to the first quarter wavelength coupling line 23 and the second The quarter wavelength coupling line 33 is connected to the input end.

As shown in FIG. 2, the first three-mode resonator 4 includes a first quarter-wavelength resonator 41, a second quarter-wavelength resonator 42, a first symmetrical plane stub-loaded low-impedance resonator 43, The first symmetrical plane stub loads the high impedance resonator 44,

The first quarter-wavelength resonator 41 is parallel to the broadside of the rectangular dielectric substrate 101, the second quarter-wavelength resonator 42 is perpendicular to the broadside of the rectangular dielectric substrate 101, and the first symmetrical plane branch loads the low-impedance resonator The axis of 43 and the axis of the high-impedance resonator 44 loaded with stubs on the first symmetry plane both form an angle of 45 degrees with the wide side of the rectangular dielectric substrate 101,

One end of the first symmetry plane stub loaded low-impedance resonator 43 is connected with the output end of the first quarter wavelength resonator 41 and the input end of the second quarter wavelength resonator 42 simultaneously, and its other end is connected with the first The central axis of the high-impedance resonator 44 loaded on the branches of the symmetrical plane is connected,

The first quarter-wavelength resonator 41 is coupled in parallel with the first half-wavelength main transmission line 12, and the second quarter-wavelength resonator 42 is coupled in parallel with the first quarter-wavelength coupling line 23;

The second three-mode resonator 5 includes a third quarter-wavelength resonator 51, a fourth quarter-wavelength resonator 52, a second symmetrical plane stub-loaded low-impedance resonator 53, a second symmetrical plane stub-loaded high impedance resonator 54,

The third quarter-wavelength resonator 51 is parallel to the broadside of the rectangular dielectric substrate 101, the fourth quarter-wavelength resonator 52 is perpendicular to the broadside of the rectangular dielectric substrate 101, and the second symmetrical plane branch loads the low-impedance resonator The axis of 53 and the axis of the second symmetry plane stub-loaded high-impedance resonator 54 form an angle of 135 degrees with the wide side of the rectangular dielectric substrate 101,

One end of the second symmetry plane stub loaded low-impedance resonator 53 is connected with the output end of the third quarter-wavelength resonator 51 and the input end of the fourth quarter-wavelength resonator 52 simultaneously, and its other end is connected with the second The central axis of the high-impedance resonator 54 loaded on the branches of the symmetrical plane is connected,

The third quarter-wavelength resonator 51 is coupled in parallel with the second half-wavelength main transmission line 13 , and the fourth quarter-wavelength resonator 52 is coupled in parallel with the second quarter-wavelength coupling line 33 .

The present invention is based on the broadband power division filter of the discrete component isolation network and the three-mode resonator, wherein the first quarter-wavelength resonator 41 of the first three-mode resonator 4 and the second three-mode resonator 5, the second four The length and width of the quarter-wavelength resonator 42, the third quarter-wavelength resonator 51, and the fourth quarter-wavelength resonator 52 determine the position of the passband, and adjust the low-impedance resonant load of the first symmetrical plane stub The device 43, the first symmetry plane stub loading high impedance resonator 44, the second symmetry plane stub loading low impedance resonator 53, and the second symmetry plane stub loading high impedance resonator 54 can change the positions of the two modes, so that the passband More flat; the first half-wavelength main transmission line 12 and the second half-wavelength main transmission line 13 are respectively coupled with the first quarter-wavelength resonator 41 and the third quarter-wavelength resonator 51 in parallel with the distance between them The strength of the influence is greater, the smaller the spacing, the greater the coupling strength, the higher the amplitude and phase coincidence of the two output ports; adjust the first grounding ladder impedance resonator 6, the second grounding ladder impedance resonator 7 and the third grounding ladder The first high-impedance resonator 61 and the first low-impedance resonator 62 of the impedance resonator 8, the second high-impedance resonator 71 and the second low-impedance resonator 72, and the third high-impedance resonator 81 and the third low-impedance resonator The impedance ratio and length of the circuit breaker 82 can change the odd and even mode input impedance of the circuit and reduce the amplitude difference between them, thereby simultaneously producing better in-band isolation and out-of-band harmonic suppression.

The present invention is based on the broadband power dividing filter of the discrete element isolation network and the three-mode resonator. In manufacturing, the metal surface of the front and back of the circuit substrate is processed and corroded by the printed circuit board manufacturing process to form the required metal pattern.

The present invention will be further described in detail below in conjunction with specific embodiments.

Example

The structure of the broadband power divider filter based on discrete component isolation network and three-mode resonator is shown in Figure 1, the top view is shown in Figure 2, and the relevant dimensions are shown in Figure 3. The dielectric substrate 10 used has a relative permittivity of 3.55, a thickness of 0.508 mm, and a loss tangent of 0.0027. The characteristic impedance of the 50-ohm microstrip line conduction tape 11 at the input end, the 50-ohm microstrip line conduction tape 21 at the two-port output end, and the 50-ohm microstrip line conduction tape 31 at the three-port output end are all 50 ohms, and their widths are all W ₁ = 1.08 mm. With reference to Figure 3, the size parameters of the power division filter are as follows: W ₁ =1.08mm, L ₁ =24.3mm, W ₂ =0.26mm, L ₂ =1.74mm, W ₃ =0.26mm, L ₃ =14.5mm, W ₄ =5mm, L ₄ =22mm, W ₅ =0.2mm, L ₅ =3.8mm, W ₆ =0.1mm, L ₆ =12.4mm, W ₇ =0.26mm, L ₇ =23mm, W ₈ =0.9mm , L ₈ =2 mm, W ₉ =0.2 mm, L ₉ =10.2 mm, W ₁₀ =0.1 mm, L ₁₀ =10.2 mm, W ₁₁ =1.8 mm, L ₁₁ =7.3 mm, L ₁₂ =7.3 mm, L ₁₃ =0.92 mm, L ₁₄ =0.97 mm, g ₁ =0.13 mm, g ₂ =0.11 mm. The overall area of the power dividing filter is 32×60mm, and the corresponding guide wavelength size is 0.47λ _g ×0.88λ _g , where λ _g is the guide wavelength corresponding to the center frequency of the passband.

The power dividing filter of this example is modeled and simulated in the electromagnetic simulation software HFSS.13. Figure 4 is the S-parameter simulation diagram of the power division filter in this example. It can be seen from the figure that the passband center frequency of the power division filter is 2.4GHz, the relative bandwidth is 33%, and the return loss in the passband is low at 15dB. There are four transmission zeros outside the passband respectively, which make the power division filter of this example have good selectivity.

Figure 5 shows the amplitude difference between the two output ports of the power division filter in this example. It can be seen from the figure that the amplitude difference between the two balanced output ports within the passband of the power division filter in this example is within 0.012dB.

Figure 6 shows the phase difference between the two output ports of the power division filter in this example. It can be seen from the figure that the phase difference between the two balanced output ports within the passband of the power division filter in this example is within 0±1.2 degrees.

In summary, the present invention is based on a discrete component isolation network and a broadband power dividing filter of a three-mode resonator, combined with the three-mode resonator and the stepped impedance resonator characteristics of the terminal short circuit to achieve a good selectivity, high isolation, A three-mode broadband power divider filter with good harmonic suppression, which is very suitable for modern wireless communication systems.

Claims (5)

1. a broadband power division filter, is characterized in that: comprise the dielectric substrate (101) that lower surface is covered with metal ground plate (102), On the upper surface of the dielectric substrate (101) are provided an input end feeder (1), a first output end feeder (2), a second output end feeder (3), a first three-mode resonator (4), a second A three-mode resonator (5), a first grounded ladder impedance resonator (6), a second grounded ladder impedance resonator (7), a third grounded ladder impedance resonator (8), and an isolation resistor (9). The input ends of the first three-mode resonator (4) and the second three-mode resonator (5) are respectively coupled with the input feeder (1), and the output ends are respectively connected with the first output feeder (2), the second The output feeder (3) is coupled, the third grounded ladder impedance resonator (8) is connected to the first output feeder (2) and the second output feeder (3), and the first grounded ladder impedance resonator ( 6) Connected to the output end of the first output end feeder (2), the second grounding ladder impedance resonator (7) is connected to the output end of the second output end feeder line (3), the first grounding ladder impedance resonator (6) The other ends of the second grounded ladder impedance resonator (7) and the third grounded ladder impedance resonator (8) are connected to the metal ground plate (102) through the dielectric substrate (101). 2. broadband power dividing filter according to claim 1, is characterized in that: described dielectric substrate (101) is rectangular, and input end feeder (1) is close to one broadside thereof, and input end is located on this broadside, The first output end feeder (2) and the second output end feeder (3) are close to the other broad side, and the first output end and the second output end are respectively arranged on two opposite narrow sides. 3. broadband power division filter according to claim 2, is characterized in that: The input feeder (1) includes a first 50-ohm microstrip conduction strip (11) perpendicular to the broadside of the rectangular dielectric substrate (101), a first half-wavelength main transmission line (12) parallel to the broadside, and a second Two half-wavelength main transmission lines (13), the input end of the first 50 ohm microstrip line conduction band (11) is located at a broadside midpoint of the rectangular dielectric substrate (101), and its input end is connected to the first half-wavelength main transmission line simultaneously. The transmission line (12) is connected to the beginning of the second half-wavelength main transmission line (13). 4. broadband power division filter according to claim 3, is characterized in that: The first output feeder (2) includes a second 50 ohm microstrip line conduction strip (21) parallel to the wide side of the rectangular dielectric substrate (101) and a first microstrip transmission line (22) and a rectangular dielectric substrate (101) ) a first quarter-wavelength coupling line (23) perpendicular to the broadside; The input end of the first microstrip transmission line (22) is connected with the output end of the first quarter wavelength coupling line (23), and its output end is connected with the input end of the second 50 ohm microstrip line conduction band (21) connected, the output end of the second 50 ohm microstrip line conduction tape (21) is located on a narrow side of the rectangular dielectric substrate (101); The first grounding ladder impedance resonator (6) includes a first high impedance resonator (61) and a first low impedance resonator (62), and one end of the first low impedance resonator (62) is connected to the first microstrip transmission line (22) vertically connected; The second output feeder (3) includes a third 50-ohm microstrip line conduction strip (31) parallel to the wide side of the rectangular dielectric substrate (101) and a second microstrip transmission line (32) and a rectangular dielectric substrate (101) ) a second quarter-wavelength coupling line (33) perpendicular to the broadside; The input end of the second microstrip transmission line (32) is connected with the output end of the second quarter wavelength coupling line (33), and its output end is connected with the input end of the third 50 ohm microstrip line conduction band (31) connected, the output end of the third 50 ohm microstrip line conduction tape (31) is located on the other narrow side of the rectangular dielectric substrate (101); The second grounding ladder impedance resonator (7) includes a second high impedance resonator (71) and a second low impedance resonator (72), and one end of the second low impedance resonator (72) is connected to the second microstrip transmission line (32) Vertical connection; Described the 3rd grounding ladder impedance resonator (8) comprises the 3rd high impedance resonator (81) and the 3rd low impedance resonator (82), one end of the 3rd low impedance resonator (8) is connected with the first quarter respectively The one-wavelength coupled line (23) is connected to the input end of the second quarter-wavelength coupled line (33). 5. broadband power division filter according to claim 4, is characterized in that: The first three-mode resonator (4) includes a first quarter-wavelength resonator (41), a second quarter-wavelength resonator (42), a first symmetrical plane stub-loaded low-impedance resonator (43 ), the first symmetry plane stub loaded high impedance resonator (44), The first quarter-wavelength resonator (41) is parallel to the broadside of the rectangular dielectric substrate (101), the second quarter-wavelength resonator (42) is perpendicular to the broadside of the rectangular dielectric substrate (101), and the first The axis of the low-impedance resonator (43) loaded with branches on the symmetry plane and the axis of the high-impedance resonator (44) loaded with branches on the first symmetry plane form an angle of 45 degrees with the wide side of the rectangular dielectric substrate (101), One end of the first symmetry plane stub loaded low-impedance resonator (43) is simultaneously connected with the output end of the first quarter-wavelength resonator (41) and the input end of the second quarter-wavelength resonator (42), Its other end is connected with the central axis of the first symmetry plane branch-loaded high-impedance resonator (44), The first quarter-wavelength resonator (41) is coupled in parallel with the first half-wavelength main transmission line (12), and the second quarter-wavelength resonator (42) is coupled with the first quarter-wavelength coupling line ( 23) Parallel coupling; The second three-mode resonator (5) includes a third quarter-wavelength resonator (51), a fourth quarter-wavelength resonator (52), a second symmetrical plane stub-loaded low-impedance resonator (53 ), the second symmetry plane stub loaded high impedance resonator (54), The third quarter-wavelength resonator (51) is parallel to the broadside of the rectangular dielectric substrate (101), the fourth quarter-wavelength resonator (52) is perpendicular to the broadside of the rectangular dielectric substrate (101), and the second The axis of the low-impedance resonator (53) loaded with branches on the symmetry plane and the axis of the high-impedance resonator (54) loaded with the branches on the second symmetry plane form an angle of 135 degrees with the wide side of the rectangular dielectric substrate (101), One end of the second symmetry plane stub loaded low-impedance resonator (53) is simultaneously connected with the output end of the third quarter-wavelength resonator (51) and the input end of the fourth quarter-wavelength resonator (52), Its other end is connected with the central axis of the second symmetry plane branch-loaded high-impedance resonator (54), The third quarter-wavelength resonator (51) is coupled in parallel with the second half-wavelength main transmission line (13), and the fourth quarter-wavelength resonator (52) is coupled with the second quarter-wavelength coupling line ( 33) Parallel coupling.