Balanced band-pass filter

Abstract

To provide a balanced band-pass filter capable of suppressing common mode passage in a wide band by using a coupling resonator and a ring resonator in combination.SOLUTION: A balanced band-pass filter having a balanced circuit configuration for differentially transmitting a transmission signal, the balanced band-pass filter having a balanced circuit configuration for differentially transmitting seven pairs of transmission signals in which coupled lines are symmetrically arranged, each of the coupled lines being formed by electromagnetically coupling two λ / 4 lines having a line length of 1 / 4 of a wave length λ at a f0 frequency center of the transmission signal, the filter structure is loaded with a both-end-open-type resonator and ring resonators 2 and 4 and a coupled-line resonator 3, the both-end-open-type resonator and ring resonators 2 and 4 being composed of a plurality of pairs (here, seven pairs) of coupled lines f0 and 1B, 2A and 2B,., 7A and 7B obtained by electromagnetically coupling two λ / 4 lines each having a line length of 1 / 4 of a wave length λ of a center frequency 1A of a transmission signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a balanced band-pass filter having a balanced circuit configuration for differentially transmitting a transmission signal, and more particularly to a balanced band-pass filter using coupled-line resonators and ring resonators. [Background technology]

[0002] In recent years, discussions have been underway regarding the sixth generation mobile communication system (6G), which is the next generation mobile communication system.

[0003] In order to achieve communication speeds 10 times faster than those of the fifth-generation mobile communication system (5G), the sixth-generation mobile communication system is expected to utilize terahertz waves, which have a higher frequency than millimeter waves. Generally, the terahertz band is defined as the range from 100 GHz to 10 THz, and at the World Radiocommunication Conference (WRC-19) held in 2019, a total of 137 GHz was identified for communication use out of the previously unallocated frequencies above 275 GHz. By utilizing this vast range of frequencies in mobile communications, it is hoped that even higher speeds and larger capacity communications will be realized.

[0004] FIG. 17 is a schematic diagram showing signal bands used in both 5G and 6G.

[0005] The addition of sub-THz bands above 100 GHz has been attracting attention, but the use of sub-THz bands has significant attenuation and makes it difficult to expand communication areas at high cost. Therefore, the current challenge is to consider using the 7 GHz to 24 GHz band in combination with both 5G and 6G, as shown in Figure 17, which will promote their use. In particular, it is expected that the use of the 7.125 GHz to 15.35 GHz band will make next-generation communication infrastructure more powerful and multifunctional.

[0006] The International Telecommunication Union (ITU) held its quadrennial meeting, WRC-23, in November and December 2023 to discuss frequency bands for mobile communications. The report, which spans 623 pages and covers a wide range of topics, also included new frequency allocations for mobile communications. It decided that the 6G-7GHz band would be used worldwide (excluding North and South America) in the 6.245G-7.124GHz band, while the 10G-10.5GHz band would be used in North and South America, where it overlaps with unlicensed frequency bands. Additionally, the 2.7GHz band would be allocated for high-altitude / stratospheric mobile communications using balloons and aircraft, which are considered NTNs.

[0007] Furthermore, in signal transmission, differential transmission using a balanced circuit that transmits signals over two lines of equal length and equal spacing is widely used.

[0008] Figures 18(A) and (B) are diagrams used to explain signal transmission through two lines, where (A) is a schematic diagram showing differential mode signal transmission, and (B) is a schematic diagram showing common mode signal transmission.

[0009] In differential mode, where a differential signal is transmitted over two lines, as shown in Figure 18(A), opposite positive and negative voltages are applied to the forward and return lines, with GND 0V as the reference potential, and the sum of the two becomes 0, canceling out the noise.In common mode, where an in-phase signal is transmitted over two lines, as shown in Figure 18(B), ideally no noise would be generated, but unbalanced common-mode noise would be generated due to distortion of the signal waveform and phase shift.

[0010] Differential transmission is excellent for high-speed transmission, such as having high noise resistance, but common mode noise is generated due to various factors, so there is a need to suppress the transmission of common mode, which transmits noise (for example, see Non-Patent Documents 1 and 2).

[0011] FIG. 19 is a schematic diagram illustrating a low temperature co-fired ceramics (LTCC) substrate.

[0012] There is a demand for smaller and thinner high-frequency circuits, and as shown in Figure 19, many laminate structures using LTCC substrates are being used, such as high-frequency modules in which high-frequency electronic components are arranged on a co-fired LTCC substrate made by laminating dielectric ceramics on which silver conductor patterns are formed using silver (Ag: melting point = 960°C), a low-resistance conductor, as a wiring conductor. However, there have been few studies on filters with wideband characteristics for differential transmission assuming an LTCC substrate (see, for example, Non-Patent Document 3). [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] Y. Shimizu, T. Murata, S. Oshima, Y. Shimakata, and K. Wada, "Analytical Study on a Wideband Microstrip Line BPF with Attenuation Poles Using a Coupled-Line BPF and a λ / 4 Resonator-Coupled Open-Ended Stub," Transactions of the Institute of Electronics, Information and Communication Engineers, 91(12), pp. 780-781, 2008. [Non-patent document 2] Zhao-An Ouyang and Qing-Xin Chu, “An Improved Wideband Balanced Filter Using Internal Cross-Coupling and 3 / 4λ Stepped-Impedance Resonator,” in IEEE Microwaveand Wireless Components Letters, vol. 26, no. 3, pp. 156-158, March 2016, doi:10.1109 / LMWC.2016.2521176. [Non-patent document 3] Tao Yang, Ruimin Xu, Lan Xiao, and Shuyi Wang, “An improved SIR filter designed using LTCC technology,” 2008 International Conference on Microwave and Millimeter Wave Technology, Nanjing, China, 2008, pp. 587-590, doi: 10.1109 / ICMMT.2008.4540461. Summary of the Invention [Problem to be solved by the invention]

[0014] Non-Patent Document 1 discloses a wideband microstrip line bandpass filter (BPF) with attenuation poles that uses an open-ended stub in which a coupled line BPF and a λ / 4 resonator are coupled.

[0015] 20A and 20B are diagrams illustrating a coupled-line band-pass filter (BPF) 100 in which coupled-line resonators 101A and 101B realized by a planar circuit are coupled, where (A) is a schematic plan view of the coupled-line band-pass filter (BPF) 100, and (B) is a characteristic diagram showing the transmission characteristics of the coupled-line band-pass filter (BPF) 100 obtained by analysis using an electromagnetic field simulator.

[0016] In a coupled-line bandpass filter (BPF) 100 in which coupled-line resonators 101A and 101B are coupled and realized as a planar circuit as shown in FIG. 20(A), the transmission characteristics obtained by analyzing with an electromagnetic field simulator produce attenuation poles by using the coupled-line resonators 101A and 101B as shown in FIG. 20(B).

[0017] In Figure 20(B), the horizontal axis is frequency (GHz) and the vertical axis is S parameter |S 11 |,|S 21|[dB], and the transmission characteristics are shown for Case A (circuit size 58×25 mm) and Case B (circuit size 33×20 mm) of the coupled-line bandpass filter (BPF) 100.

[0018] This coupled-line bandpass filter (BPF) 100 has a planar structure, so there is a limit to how small it can be made, and only single-ended transmission in an unbalanced type has been discussed.

[0019] 21A and 21B are diagrams illustrating a coupled-line resonator 110 in which a λ / 4 one-end grounded line 111 is coupled to an open-end stub 112, where (A) is a schematic circuit diagram showing the configuration of the coupled-line resonator 110, and (B) is a characteristic diagram showing the transmission characteristics of the coupled-line resonator 110 obtained by analysis using an electromagnetic field simulator.

[0020] In a coupled-line resonator 110 in which a λ / 4 one-end grounded line 111 is coupled to an open-end stub 112 as shown in FIG. 21(A), the transmission characteristics obtained by analyzing using an electromagnetic field simulator show attenuation poles on both sides of the center frequency f0 as shown in FIG. 21(B).

[0021] 22A and 22B are diagrams for explaining an example of the structure of the coupled-line resonator 110, where (A) is a cross-sectional view schematically showing an example of broadside coupling, and (B) is a cross-sectional view schematically showing an example of broadside coupling.

[0022] The coupled line resonator 110 has a GP whose both surfaces are full conductors as shown in FIG. A , G.P. B In the dielectric substrate 113 covered with a conductor, a pair of λ / 4 lines 111 and 112 are broadside coupled. ... A , G.P. B The pair of λ / 4 lines 111 and 112 can be edge-coupled within a dielectric substrate 114 covered with a dielectric material, and the circuit size can be reduced by adopting broadside coupling and forming a layered structure.

[0023] Furthermore, (A) and (B) of Figure 23 are diagrams used to explain a balanced band-pass filter (BPF) 120 having two pairs of coupled-line resonators 110A and 110B, where (A) is a circuit diagram that schematically shows the configuration of the balanced band-pass filter (BPF) 120, and (B) is a characteristic diagram that shows the transmission characteristics of the balanced band-pass filter (BPF) 120 obtained by analysis using an electromagnetic field simulator.

[0024] As shown in Figure 23(A), a balanced bandpass filter (BPF) 120 equipped with two pairs of coupled-line resonators 110A and 110B can achieve a wide passband in differential mode, as shown in Figure 23(B), based on the transmission characteristics obtained by analyzing the characteristics using an electromagnetic field simulator. However, in common mode, the filter resonates near the passband.

[0025] Therefore, a balanced bandpass filter composed only of coupled resonators has a problem in that common mode resonance occurs at both shoulders of the passband, and common mode transmission is not sufficiently suppressed.

[0026] In view of the above-described conventional situation, an object of the present invention is to provide a balanced band-pass filter that can suppress common-mode transmission over a wide band by using a coupled resonator and a ring resonator in combination.

[0027] Another object of the present invention is to provide a balanced band-pass filter having wideband characteristics in differential transmission intended for an LTCC substrate for a wireless communication module, which has a balanced circuit configuration that differentially transmits a transmission signal by using coupled-line resonators and ring resonators.

[0028] Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the following description of the embodiments. [Means for solving the problem]

[0029] In the present invention, a balanced band-pass filter having a balanced circuit configuration that differentially transmits a transmission signal uses a coupled resonator and a ring resonator together, thereby suppressing common mode transmission in a balanced band-pass filter configured only with coupled resonators by using the ring resonator that has an attenuation pole at the center frequency of the transmission signal.

[0030] That is, the present invention provides a balanced bandpass filter having a balanced circuit configuration for differentially transmitting a transmission signal, the balanced bandpass filter comprising a plurality of coupled lines using λ / 4 lines each having a line length of ¼ of the wavelength λ of the center frequency of the transmission signal, the balanced bandpass filter comprising a first coupled line input / output section comprising a pair of coupled lines connected to a first input / output port, a second coupled line input / output section comprising a pair of coupled lines connected to a second input / output port, a first ring resonator comprising two pairs of coupled lines including the pair of coupled lines connected to the first coupled line input / output section, a second ring resonator comprising two pairs of coupled lines including the pair of coupled lines connected to the second coupled line input / output section, and and a coupled-line resonator consisting of a pair of coupled lines connected to a second ring resonator, wherein the λ / 4 lines constituting each pair of coupled lines of the first and second coupled-line input / output units and the λ / 4 lines constituting each pair of coupled lines of the first and second ring resonators have one end open and the other end connected to each other to form a λ / 2 open-ended resonator, and the filter has a structure loaded with open-ended resonators, ring resonators and coupled-line resonators, each consisting of at least seven pairs of coupled lines symmetrically arranged, each pair of coupled lines being formed by electromagnetically coupling two λ / 4 lines, each having a line length of ¼ of the wavelength λ of the center frequency of the transmission signal.

[0031] A balanced bandpass filter according to the present invention may have the balanced circuit configured in a laminated substrate made of a plurality of dielectric layers, and the first and second ring resonators may each have a ring structure made of four λ / 4 lines arranged between the same layers.

[0032] Furthermore, the balanced band-pass filter according to the present invention can improve the shoulder characteristics of the passband in the differential mode by providing a correction line for correcting the resonance characteristics at the open end portions of a pair of coupled lines constituting the coupled-line resonator so as to face the line connecting the coupled-line resonator to the first and second ring resonators.

[0033] Furthermore, in the balanced band-pass filter according to the present invention, the shapes of the coupled lines of the first and second coupled line input / output sections connected to the excitation lines of the first and second ring resonators are made to conform to a ring shape, thereby eliminating uncoupled sections and suppressing the common-mode transmission characteristics.

[0034] Furthermore, the balanced band-pass filter according to the present invention may have a filter structure in which a plurality of n (n is an integer equal to or greater than 2) coupled-line resonators and (n-1) ring resonators are loaded between the first ring resonator and the second ring resonator. [Effects of the Invention]

[0035] In the present invention, a balanced bandpass filter having a balanced circuit configuration for differentially transmitting a transmission signal can be provided, which includes a first coupled line input / output section consisting of a pair of coupled lines connected to a first input / output port, a second coupled line input / output section consisting of a pair of coupled lines connected to a second input / output port, a first ring resonator consisting of two pairs of coupled lines including the pair of coupled lines connected to the first coupled line input / output section, a second ring resonator consisting of two pairs of coupled lines including the pair of coupled lines connected to the second coupled line input / output section, and a coupled line resonator consisting of a pair of coupled lines connected to the first and second ring resonators.

[0036] The balanced bandpass filter may have the balanced circuit configured in a laminated substrate made of multiple dielectric layers, and the first and second ring resonators may each have a ring structure made of four λ / 4 lines arranged between the same layers, and may have wideband characteristics in differential transmission intended for an LTCC substrate for a wireless communication module.

[0037] Furthermore, the balanced band-pass filter can improve the shoulder characteristics of the passband in the differential mode by providing a correction line for correcting the resonance characteristics at the open end portions of a pair of coupled lines constituting the coupled-line resonator so as to face the line connecting the coupled-line resonator to the first and second ring resonators.

[0038] Furthermore, in the balanced band-pass filter, the shapes of the coupled lines of the first and second coupled line input / output sections connected to the excitation lines of the first and second ring resonators are made to conform to a ring shape, thereby eliminating uncoupled sections and suppressing the common-mode transmission characteristics.

[0039] Therefore, according to the present invention, a balanced band-pass filter having wideband characteristics in differential transmission intended for an LTCC substrate for a wireless communication module can be provided, which has a balanced circuit configuration that differentially transmits a transmission signal by using a coupled-line resonator and a ring resonator. [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 1 is a circuit diagram showing a schematic basic configuration of a balanced bandpass filter according to the present invention. [Figure 2] Figure 2 (A), (B), and (C) are diagrams used to explain signal transmission in this balanced bandpass filter. (A) is a schematic plan view showing the configuration of a ring resonator, (B) shows a differential mode signal transmission path, and (C) shows a common mode signal transmission path. [Figure 3](A), (B), and (C) in Figure 3 are diagrams used to explain a single ring resonator, where (A) is a circuit diagram showing the configuration of a single ring resonator, (B) is a characteristics diagram showing differential mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator, and (C) is a characteristics diagram showing common mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator. [Figure 4] (A), (B), and (C) in Figure 4 are diagrams used to explain a signal transmission line equipped with two ring resonators, where (A) is a circuit diagram showing the configuration of the signal transmission line, (B) is a characteristics diagram showing differential mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator, and (C) is a characteristics diagram showing common mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator. [Figure 5] FIG. 5 is a characteristic diagram showing the signal transmission characteristics obtained by analyzing, using an electromagnetic field simulator, a balanced bandpass filter having a filter structure in which the above-described ring resonator and coupled-line resonator are loaded. [Figure 6] FIG. 6 is a perspective view showing the structure of a balanced bandpass filter employing a multilayer structure. [Figure 7] 7A and 7B are diagrams showing the structure of the balanced band-pass filter, where (A) is a plan view showing the structure of the balanced band-pass filter as a perspective view, and (B) is an end view of the longitudinal cross section of the balanced band-pass filter as seen from the front side. [Figure 8] Figures 8(A) and (B) show the transmission characteristics obtained by analyzing, using an electromagnetic field simulator, a balanced bandpass filter with a balanced circuit configuration structured using an LTCC laminate substrate. (A) is a characteristic diagram showing differential mode signal transmission characteristics, and (B) is a characteristic diagram showing common mode signal transmission characteristics. [Figure 9] FIG. 9 is a perspective view showing the structure of a balanced band-pass filter with improved shoulder characteristics in the pass band in the differential mode. [Figure 10]10A and 10B are diagrams showing the structure of the balanced band-pass filter, where (A) is a plan view showing the structure of the balanced band-pass filter as a perspective view, and (B) is an end view of the balanced band-pass filter as seen from the front side in vertical cross section. [Figure 11] 11A and 11B are diagrams explaining the correction coupled line provided in the balanced band-pass filter, where (A) is an enlarged perspective view of the vicinity of the correction coupled line, and (B) is a schematic diagram showing the correction coupled line. [Figure 12] Figures 12(A) and (B) show the transmission characteristics obtained by analyzing, using an electromagnetic field simulator, a balanced bandpass filter in which a compensation coupled line is loaded at the open end of a pair of coupled lines that make up a coupled-line resonator. (A) is a characteristic diagram showing the differential mode signal transmission characteristics, and (B) is a characteristic diagram showing the common mode signal transmission characteristics. [Figure 13] FIG. 13 is a perspective view showing the structure of a balanced bandpass filter in which the common-mode transmission characteristics are suppressed. [Figure 14] 14A and 14B are diagrams showing the structure of the balanced band-pass filter, where (A) is a plan view showing the structure of the balanced band-pass filter as a perspective view, and (B) is an end view of the balanced band-pass filter in vertical section as seen from the front side. [Figure 15] FIG. 15 is an enlarged perspective view showing the vicinity of the coupled line of the first coupled line input / output section in the balanced bandpass filter. [Figure 16] FIG. 16 is a characteristic diagram showing the transmission characteristics of the balanced bandpass filter 30 obtained by analyzing it using an electromagnetic field simulator. [Figure 17] FIG. 17 is a schematic diagram showing signal bands used in both 5G and 6G. [Figure 18] Figures 18(A) and (B) are diagrams used to explain signal transmission through two lines, where (A) is a schematic diagram showing differential mode signal transmission, and (B) is a schematic diagram showing common mode signal transmission. [Figure 19]FIG. 19 is a schematic diagram illustrating a low temperature co-fired ceramics (LTCC) substrate. [Figure 20] Figures 20(A) and (B) are diagrams used to explain a coupled-line bandpass filter (BPF) in which coupled-line resonators are coupled and realized as a planar circuit. (A) is a schematic plan view of the coupled-line bandpass filter (BPF), and (B) is a characteristic diagram showing the transmission characteristics of the coupled-line bandpass filter (BPF) obtained by analysis using an electromagnetic field simulator. [Figure 21] 21A and 21B are diagrams explaining a coupled-line resonator realized by a planar circuit, where (A) is a circuit diagram that schematically shows the configuration of the coupled-line resonator, and (B) is a characteristic diagram that shows the transmission characteristics of the coupled-line resonator obtained by analysis using an electromagnetic field simulator. [Figure 22] (A) and (B) of Figure 22 are diagrams used to explain structural examples of the above-mentioned coupled-line resonator, where (A) is a cross-sectional view schematically showing an example of broadside coupling, and (B) is a cross-sectional view schematically showing an example of broadside coupling. [Figure 23] 23A and 23B are diagrams illustrating a balanced band-pass filter (BPF) having two pairs of coupled-line resonators, where (A) is a circuit diagram that schematically shows the configuration of the balanced band-pass filter (BPF), and (B) is a characteristic diagram that shows the transmission characteristics of the balanced band-pass filter (BPF) obtained by analysis using an electromagnetic field simulator. DETAILED DESCRIPTION OF THE INVENTION

[0041] A preferred embodiment of the present invention will be described in detail below. Note that the embodiment described below does not unduly limit the content of the present invention as defined in the claims, and not all of the configurations described in the embodiment are necessarily essential as means for solving the problems of the present invention.

[0042] FIG. 1 is a schematic plan view showing the basic configuration of a balanced bandpass filter 10 according to the present invention.

[0043] This balanced band-pass filter 10 is a balanced band-pass filter with a balanced circuit configuration that differentially transmits a transmission signal, and is composed of multiple pairs (here, seven pairs) of coupled lines 1A·1B, 2A·2B, ···, 7A·7B, in which two λ / 4 lines, each with a line length of ¼ of the wavelength λ of the center frequency f0 of the transmission signal, are electromagnetically coupled together, and the coupled lines are arranged symmetrically.

[0044] That is, the balanced band-pass filter 10 has a first input / output port P 1A P 1B The first coupled-line input / output section 1 is comprised of a pair of coupled lines 1A and 1B, which are formed by electromagnetically coupling λ / 4 lines 1A1 and 1B1 and λ / 4 lines 1A2 and 1B2, one end of which is connected to a first coupled-line input / output section 1, and a first ring resonator 2, which is comprised of two pairs of coupled lines 2A and 2B, 3A and 3B, is connected to the first coupled-line input / output section 1.

[0045] The first ring resonator 2 includes coupled lines 2A and 2B formed by electromagnetically coupling λ / 4 lines 2A1 and 2B1 with λ / 4 lines 2A2 and 2B2, and coupled lines 3A and 3B formed by electromagnetically coupling λ / 4 lines 3A1 and 3B1 with λ / 4 lines 3A2 and 3B2. One end of the λ / 4 lines 2A2 and 2B2 of the coupled lines 2A and 2B is connected to the other end of the λ / 4 lines 3A2 and 3B2 of the coupled lines 3A and 3B. The four λ / 4 lines 2A2, 2B2, 3B1, and 3A1 connected in a ring form a ring resonator of one wavelength λ, with the center frequency f0 of the transmission signal as the resonant frequency.

[0046] In this first ring resonator 2, the other ends of the λ / 4 lines 2A1 and 2B1 of the coupled lines 2A and 2B are connected to the other ends of the λ / 4 lines 1A2 and 1B2 of the coupled lines 1A and 1B that constitute the first coupled line input / output section 1.

[0047] The λ / 4 line 1A2 of the coupled line 1A and the λ / 4 line 2A1 of the coupled line 2A each have one open end and the other ends connected to each other to form a λ / 2 open-ended resonator, and the λ / 4 line 1B2 of the coupled line 1B and the λ / 4 line 2B1 of the coupled line 2B each have one open end and the other ends connected to each other to form a λ / 2 open-ended resonator. That is, the λ / 4 lines 1A2 and 1B2 of the coupled lines 1A and 1B that form the first coupled-line input / output section 1, together with the λ / 4 lines 2A1 and 2B1 of the coupled lines 2A and 2B that form the first ring resonator 2, form a λ / 2 open-ended resonator.

[0048] Connected to this first ring resonator 2 are a coupled line resonator 3 consisting of a pair of coupled lines 4A and 4B, and a second ring resonator 4 consisting of two pairs of coupled lines 5A and 5B, 6A and 6B.

[0049] That is, in this first ring resonator 2, the other ends of the λ / 4 lines 3A2 and 3B3 of the coupled lines 3A and 3B are connected to the other ends of the λ / 4 lines 4A2 and 2B2 of the pair of coupled lines 4A and 4B that constitute the coupled line resonator 3, and are also connected to the other ends of the λ / 4 lines 5A1 and 5B1 of the two pairs of coupled lines 5A and 5B, 6A and 6B that constitute the second first ring resonator 4.

[0050] The coupled-line resonator 3 is formed by electromagnetically coupling λ / 4 lines 4A1 and 4B1, each having one end connected to the other end as an open end, with λ / 4 lines 4A2 and 4B2, each having one end as an open end, and the other ends of the λ / 4 lines 4A2 and 4B2 are connected to the other ends of the λ / 4 lines 3A2 and 3B2 of the coupled lines 3A and 3B of the first ring resonator 2, and to the other ends of the λ / 4 lines 5A1 and 5B1 of the coupled lines 5A and 5B of the second ring resonator 4.

[0051] The second ring resonator 4 includes coupled lines 5A and 5B, which are formed by electromagnetically coupling λ / 4 lines 5A1 and 5B1 with λ / 4 lines 5A2 and 5B2, and coupled lines 6A and 6B, which are formed by electromagnetically coupling λ / 4 lines 6A1 and 6B1 with λ / 4 lines 6A2 and 6B2. One end of the λ / 4 lines 5A2 and 5B2 of the coupled lines 5A and 5B is connected to the other end of the λ / 4 lines of the coupled lines 6A and 6B. The four λ / 4 lines 5A2, 5B2, 6B1, and 6A1 connected in a ring shape form a ring resonator of one wavelength λ whose resonant frequency is the center frequency f0 of the transmission signal.

[0052] In this second ring resonator 4, the other ends of the λ / 4 lines 6A1 and 6B1 of the coupled lines 6A and 6B are connected to the other ends of the λ / 4 lines 7A1 and 7B1 of the coupled lines 7A and 7B that constitute the second coupled line input / output section 5.

[0053] The second coupled line input / output section 45, the second input / output port P 2A P 2B The λ / 4 lines 7A1 and 7B1 are electromagnetically coupled to the λ / 4 lines 7A2 and 7B2, one end of which is connected to the λ / 4 lines 7A1 and 7B1.

[0054] That is, the balanced band-pass filter 10 is a balanced band-pass filter having a balanced circuit configuration that differentially transmits a transmission signal, and has a first input / output port P 1A P 1B a first coupled line input / output section 1 consisting of a pair of coupled lines 1A and 1B connected to a second input / output port P 2A P 2Ba second coupled-line input / output section 5 consisting of a pair of coupled lines 7A and 7B connected to the first coupled-line input / output section 1; a first ring resonator 2 consisting of two pairs of coupled lines 2A-2B, 2A-2B including a pair of coupled lines 2A-2B connected to the first coupled-line input / output section 1; a second ring resonator 4 consisting of two pairs of coupled lines 5A-5B, 6A-6B including a pair of coupled lines 6A-6B connected to the second coupled-line input / output section 5; and a coupled-line resonator 3 consisting of a pair of coupled lines 4A-4B connected to the first and second ring resonators 2 and 4. The coupled-line resonator 3 comprises seven pairs of coupled lines 1A-1B, 2A-2B, . . . , 7A-7B, each of which is formed by electromagnetically coupling two λ / 4 lines, each having a line length of ¼ the wavelength λ of the center frequency f0 of the transmission signal.

[0055] The λ / 4 line 6A2 of the coupled line 6A and the λ / 4 line 7A1 of the coupled line 7A each have one open end and the other ends connected to each other to form a λ / 2 open-ended resonator, and the λ / 4 line 6B2 of the coupled line 6B and the λ / 4 line 7B1 of the coupled line 7B each have one open end and the other ends connected to each other to form a λ / 2 open-ended resonator. That is, the λ / 4 lines 7A1 and 7B1 of the coupled lines 7A and 7B that form the second coupled-line input / output section 5, together with the λ / 4 lines 6A2 and 6B2 of the coupled lines 6A and 6B that form the second ring resonator 4, form a λ / 2 open-ended resonator.

[0056] As described above, the balanced band-pass filter 10 has a filter structure loaded with open-ended resonators, ring resonators 2 and 4, and coupled-line resonator 3, each consisting of seven pairs of coupled lines 1A-1B, 2A-2B, . . . , 7A-7B, which are symmetrically arranged coupled lines formed by electromagnetically coupling two λ / 4 lines, each with a line length of ¼ of the wavelength λ of the center frequency f0 of the transmission signal.

[0057] 2A, 2B, and 2C are diagrams illustrating signal transmission in the balanced band-pass filter 10. FIG. 2A is a schematic plan view showing the configuration of the ring resonator 2(4), FIG. 2B shows a differential mode signal transmission path, and FIG. 2C shows a common mode signal transmission path.

[0058] In this balanced band-pass filter 10, as shown in FIG. 2(A), a ring resonator 2 (4) consisting of four symmetrically arranged λ / 4 lines 2A2·2B2·3B1·3A1 (5A2·5B2·6B1·6A1) functions as a transmission line for differential mode signal transmission with both ends grounded as shown in FIG. 2(B), and as a transmission line for common mode signal transmission with both ends open as shown in FIG. 2(C).

[0059] 3A, 3B, and 3C are circuit diagrams showing the configuration of a single ring resonator 2(4), where 3B is a characteristic diagram showing differential mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator, and 3C is a characteristic diagram showing common mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator.

[0060] In Figure 3(B), the horizontal axis is frequency (GHz) and the vertical axis is S-parameter |S DD11 |,|S DD21 The differential mode signal transmission characteristics are shown as |[dB]. In Fig. 3(C), the horizontal axis is frequency (GHz) and the vertical axis is S parameter |S CC11 |,|S CC21 |[dB] indicates the common mode signal transmission characteristics.

[0061] In the single ring resonator 2 (4) shown in Figure 3(A), the transmission characteristics obtained by analyzing using an electromagnetic field simulator show an attenuation pole at the center frequency, as shown in Figures 3(B) and 3(C), and the common mode is suppressed over a wide band.

[0062] 4A, 4B, and 4C are diagrams illustrating a signal transmission line having two ring resonators 2 and 4, where 4A is a circuit diagram showing the configuration of the signal transmission line, 4B is a characteristics diagram showing differential mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator, and 4C is a characteristics diagram showing common mode signal transmission characteristics obtained by analysis using an electromagnetic field simulator.

[0063] In this balanced band-pass filter 10, as shown in FIG. 4A, when the coupled-line resonator 3 is not loaded, that is, when the transmission characteristics of the two ring resonators 2 and 4 are analyzed using an electromagnetic field simulator, the transmission characteristics obtained show an attenuation pole at the center frequency, and the common mode is suppressed to 40 dB or less over a wide band, but the slope of the shoulder characteristic is gentle, as shown in FIGS. 4B and 4C.

[0064] FIG. 5 shows the signal transmission characteristics (|S DD11 |,|S DD21 ,|S CC21 |) is a characteristic diagram showing the relationship between the

[0065] The balanced band-pass filter 10 has a filter structure in which the ring resonators 2 and 4 and the coupled-line resonator 3 are loaded using the seven pairs of coupled lines 1A·1B, 2A·2B, . . . , 7A·7B. The signal transmission characteristics (|S DD11 |,|S DD21 ,|S CC21 As shown in Figure 5, the coupled-line resonator 3 generates an attenuation pole near the passband, realizing a steep shoulder characteristic, and the ring resonators 2 and 4 not only generate an attenuation pole of the common mode at the center frequency, but also suppress the common mode to 40 dB or less over a wide band.

[0066] As described above, the balanced band-pass filter 10 has a balanced circuit configuration in which a transmission signal is differentially transmitted using seven pairs of coupled lines 1A·1B, 2A·2B, ···, 7A·7B. The seven pairs of coupled lines 1A·1B, 2A·2B, ···, 7A·7B can be realized by using a planar structure such as edge-coupled microstrip lines. However, the filter can be made smaller by using a multilayer structure as a balanced band-pass filter with wideband characteristics for differential transmission.

[0067] That is, in the balanced band-pass filter 10, the balanced circuit is configured in a laminated substrate made of multiple dielectric layers, as shown in Figures 6, 7(A), and 7(B), and the first and second ring resonators 2 and 4 can have ring structures made of four λ / 4 lines 2A2·2B2·3B1·3A1 and 5A2·5B2·6B1·6A1, respectively, arranged between the same layers.

[0068] FIG. 6 is a perspective view showing the structure of a balanced band-pass filter 10 employing a multilayer structure, FIG. 7A is a plan view showing the structure of the balanced band-pass filter 10 in perspective, and FIG. 7B is an end view of the longitudinal cross section of the balanced band-pass filter 10 as seen from the front side.

[0069] The balanced bandpass filter 10 shown in Figures 6, 7(A), and 7(B) has a multilayer structure intended for an LTCC substrate for a wireless communication module. Within an LTCC layer 8 measuring 5.6 x 1.95 mm and 0.207 mm thick, seven pairs of broadside-coupled λ / 4 lines, 1A·1B, 2A·2B, . . . , 7A·7B, are arranged with a spacing of 0.18 mm. The seven pairs are then broadside-coupled to form a balanced circuit for differentially transmitting a transmission signal.

[0070] The LTCC layer 8 is made of 0.007 mm thick conductor GP on both sides. A ,GP B It is covered with

[0071] A first input / output port P is provided on one end side of the LTCC layer 8. 1A P1B The first coupled line input / output section 1 is formed by a pair of coupled lines 1A and 1B, in which λ / 4 lines 1A2 and 1B2 are arranged opposite each other with a gap of 0.02 mm between them, above λ / 4 lines 1A1 and 1B1 connected to the first coupled line.

[0072] In addition, a second input / output port P 2A P 2B The second coupled line input / output section 5 is formed by a pair of coupled lines 7A and 7B, in which λ / 4 lines 7A1 and 7A1 are arranged facing each other with a gap of 0.02 mm between them, above the λ / 4 lines 7A2 and 7B2 connected to the first coupled line 7A.

[0073] That is, the first input / output port P 1A P 1B λ / 4 line 1A1·1B1 connected to the second input / output port P 2A P 2B λ / 4 lines 7A1 and 7B1 connected to the LTCC layer 8 are provided between the same layers in the LTCC layer 8, and λ / 4 lines 1A2 and 1B2 and λ / 4 lines 7A1 and 7B1 are provided between the same layers 0.02 mm above.

[0074] Four λ / 4 lines 2A2, 2B2, 3B1, and 3A1 that form the ring structure of the first ring resonator 2 and four λ / 4 lines 5A2, 5B2, 6B1, and 6A1 that form the ring structure of the second ring resonator 4 are provided 0.02 mm below the inter-layer space within the LTCC layer 8 where the λ / 4 lines 1A1 and 1B1 and the λ / 4 lines 7A2 and 7B2 are provided.

[0075] Furthermore, between the LTCC layers 8 in which the λ / 4 lines 1A2 and 1B2 and the λ / 4 lines 7A1 and 7B1 are arranged, two λ / 4 lines 2A1 and 2B1 are provided to face two λ / 4 lines 2A2 and 2B2 of the four λ / 4 lines 2A2, 2B2, 3B1 and 3A1 that constitute the ring structure of the first ring resonator 2, and two λ / 4 lines 6B2 and 6A2 are provided to face two λ / 4 lines 6B1 and 6A1 of the four λ / 4 lines 5A2, 5B2, 6B1 and 6A1 that constitute the ring structure of the second ring resonator 4.

[0076] Furthermore, in the LTCC layer 8, two λ / 4 lines 3B2 and 3A2 are provided 0.02 mm above the inter-layer space where the λ / 4 lines 1A2 and 1B2 and the λ / 4 lines 7A1 and 7B1 are arranged, so as to face two λ / 4 lines 3B1 and 3A1 of the four λ / 4 lines 2A2, 2B2, 3B1, and 3A1 that constitute the ring structure of the first ring resonator 2, and two λ / 4 lines 5A1 and 5B1 are provided so as to face two λ / 4 lines 5A2 and 5B2 of the four λ / 4 lines 5A2, 5B2, 6B1, and 6A1 that constitute the ring structure of the second ring resonator 4.

[0077] That is, of the two pairs of coupled lines 2A-2B and 3A-3B constituting the second ring resonator 4, one pair of coupled lines 2A-2B consists of λ / 4 lines 2A1-2A2 and λ / 4 lines 2B1-2B2 arranged opposite each other with a gap of 0.04 mm, and the other pair of coupled lines 3A-3B consists of λ / 4 lines 3A1-3A2 and λ / 4 lines 3B1-3B2 arranged opposite each other with a gap of 0.06 mm.

[0078] Furthermore, the λ / 4 lines 4A1 and 4B1 of a coupled-line resonator 3 consisting of a pair of coupled lines 4A and 4B are provided between the same layers of the LTCC layer 8 where the four λ / 4 lines 2A2, 2B2, 3B1, and 3A1 that form the ring structure of the first ring resonator 2 and the four λ / 4 lines 5A2, 5B2, 6B1, and 6A1 that form the ring structure of the second ring resonator 4 are provided. Furthermore, the two λ / 4 lines 3B2 and 3A2 of the first ring resonator 2 are provided, and the λ / 4 line 4A2 of a coupled-line resonator 3 consisting of a pair of coupled lines 4A and 4B is provided between the same layers of the LTCC layer 8 where the two λ / 4 lines 5A1 and 5B1 of the second ring resonator 4 are provided.

[0079] That is, the pair of coupled lines 4A and 4B constituting the coupled line resonator 3 are each made up of the λ / 4 lines 4A1 and 4A2 and the λ / 4 lines 4B1 and 4B2, which are arranged facing each other with an interval of 0.06 mm between them.

[0080] In this way, the first input / output port P 1A P 1B a first coupled line input / output section 1 consisting of a pair of coupled lines 1A and 1B connected to a second input / output port P 2A P 2B a second coupled-line input / output section 5 consisting of a pair of coupled lines 7A and 7B connected to the first coupled-line input / output section 1; a first ring resonator 2 consisting of two pairs of coupled lines 2A and 2B, 2A and 2B including a pair of coupled lines 2A and 2B connected to the first coupled-line input / output section 1; a second ring resonator 4 consisting of two pairs of coupled lines 5A and 5B, 6A and 6B including a pair of coupled lines 6A and 6B connected to the second coupled-line input / output section 5; The balanced bandpass filter 10 having the balanced circuit configuration shown in Figure 1 can be fabricated using an LTCC laminated substrate. The balanced bandpass filter 10 comprises seven pairs of coupled lines 1A-1B, 2A-2B, ..., 7A-7B, each of which is formed by electromagnetically coupling two λ / 4 lines, each with a line length of ¼ of the wavelength λ of the center frequency f0 of the transmission signal. The seven pairs of coupled lines are symmetrically arranged.

[0081] 8A and 8B are diagrams showing the transmission characteristics of a balanced bandpass filter 10 having a balanced circuit configuration structured with an LTCC laminate substrate, which were obtained by analyzing the filter using an electromagnetic field simulator. FIG. 8A is a characteristic diagram showing the differential mode signal transmission characteristics, and FIG. 8B is a characteristic diagram showing the common mode signal transmission characteristics.

[0082] In Figure 8(A), the horizontal axis is frequency (GHz) and the vertical axis is S-parameter |S DD11 |,|S DD21 The differential mode signal transmission characteristics are shown as |[dB]. In Fig. 8(B), the horizontal axis is frequency (GHz) and the vertical axis is S parameter |S CC11 |,|S CC21 |[dB] indicates the common mode signal transmission characteristics.

[0083] That is, when the transmission characteristics of the balanced bandpass filter 10 having a balanced circuit configuration structured using this LTCC laminated substrate were analyzed using an electromagnetic field simulator, it became clear that, as shown in Figures 8(A) and 8(B), a collapse occurred in the shoulder characteristics of the passband in the differential mode, and that resonance occurred near the center frequency in the common mode.

[0084] Furthermore, in the balanced bandpass filter 10 having a balanced circuit configuration structured using the above-mentioned LTCC laminated substrate, it was confirmed by an analysis of transmission characteristics using an electromagnetic field simulator that the connection lines, i.e., the line connecting the first coupled-line input / output unit 1 and the first ring resonator 2, the line connecting the first ring resonator 2 and the coupled-line resonator 3, the line connecting the coupled-line resonator 3 and the second ring resonator 4, and the line connecting the second ring resonator 4 and the second coupled-line input / output unit 5, deteriorate outside the passband in differential mode due to changes in the line length, but resonate within the band in common mode even with slight changes.

[0085] In the balanced bandpass filter 10 having a balanced circuit configuration structured using the above-mentioned LTCC laminated substrate, the circuit can be designed to reduce these effects by loading open-ended resonators on the connection lines and adjusting their resonance characteristics.

[0086] For example, as in a balanced band-pass filter 20 shown in FIGS. 9, 10(A) and 10(B), and 11(A) and 11(B), a balanced band-pass filter 10 having a balanced circuit configuration structured using the LTCC laminate substrate has correction lines 9A1 and 9B1 that correct the resonance characteristics at the open ends of a pair of coupled lines 4A1 and 4B1 constituting a coupled-line resonator 3, and correction coupled lines 9A and 9B that are provided opposite the lines connecting the coupled-line resonator 3 to the first and second ring resonators 2 and 4, thereby improving the shoulder characteristics of the pass band in the differential mode.

[0087] FIG. 9 is a perspective view showing the structure of a balanced band-pass filter 20 in which the shoulder characteristics of the pass band in differential mode are improved, FIG. 10(A) is a plan view showing the structure of the balanced band-pass filter 20 in a perspective view, FIG. 10(B) is an end view of the longitudinal section of the balanced band-pass filter 20 as seen from the front side, FIG. 11(A) is a perspective view showing an enlarged perspective view of the vicinity of the correction coupled line 9A formed by the correction line 9A1 shown in FIG. 9, and FIG. 11(B) is a schematic diagram showing the correction coupled line 9A formed by the correction line 9A1.

[0088] Here, this balanced band-pass filter 20 is a filter in which the shoulder characteristics of the passband in the differential mode of the balanced band-pass filter 10 having a multilayer structure intended for an LTCC substrate for a wireless communication module shown in FIGS. 6 and 7(A) and 7(B) are improved by using correction coupled lines 9A and 9B. Components that are the same as those of the balanced band-pass filter 10 are given the same reference numerals in the drawings, and detailed descriptions of them will be omitted.

[0089] That is, in this balanced band-pass filter 20, correction coupled lines 9A and 9B, each composed of correction lines 9A1 and 9B1, are loaded at the open end portions of a pair of coupled lines 4A1 and 4B1 constituting the coupled-line resonator 3 so as to face the connection lines connecting the coupled-line resonator 3 to the first and second ring resonators 2 and 4.

[0090] The correction coupled line 9A is coupled to a line connecting the first ring resonator 2 and the coupled-line resonator 3 and a line connecting the coupled-line resonator 3 and the second ring resonator 4, and as a result, the coupling line 9A is connected to the connecting line between the first ring resonator 2 and the coupled-line resonator 3, as shown in the schematic diagram of FIG. 11(B). a and a coupled line 9B is connected to the connection line between the coupled line resonator 3 and the second ring resonator 4. b can be loaded.

[0091] Similarly, the correction coupled line 9B can be configured such that a coupled line is loaded on the connection line between the first ring resonator 2 and the coupled line resonator 3 and the connection line between the coupled line resonator 3 and the second ring resonator 4.

[0092] 12A and 12B are diagrams showing the transmission characteristics obtained by analyzing, using an electromagnetic field simulator, a balanced band-pass filter 20 in which correction coupled lines 9A and 9B are loaded at the open end portions of a pair of coupled lines 4A1 and 4B1 constituting a coupled-line resonator 3, where (A) is a characteristic diagram showing differential mode signal transmission characteristics, and (B) is a characteristic diagram showing common mode signal transmission characteristics.

[0093] In Fig. 12(A), the horizontal axis is frequency (GHz) and the vertical axis is S-parameter |S DD11 |,|S DD21 The differential mode signal transmission characteristics are shown as |[dB]. In Fig. 8(B), the horizontal axis is frequency (GHz) and the vertical axis is S parameter |S CC11 |,|S CC21 |[dB] indicates the common mode signal transmission characteristics.

[0094] The correction coupled lines 9A and 9B, each formed by correction lines 9A1 and 9B1 arranged opposite the connecting lines, function as open-ended resonators. In the balanced band-pass filter 20, the transmission characteristics exhibit a steep shoulder characteristic in the differential mode, as shown in Figures 12(A) and 12(B). This improves the shoulder characteristic of the passband in the differential mode of the balanced band-pass filter 10 having a multilayer structure intended for the LTCC substrate for the wireless communication module, and also suppresses the passage of common-mode signals by 16 dB.

[0095] In the balanced band-pass filter 20, the resonance characteristics of the open-ended resonators can be optimized by adjusting the line lengths of the compensation lines 9A1 and 9B1 and by circuit design. For example, as in the balanced band-pass filter 30 shown in Figures 13, 14(A) and 14(B), and 15, the shapes of the coupled lines 1A', 1B', 7A', and 7B' of the first and second coupled-line input / output sections 1 and 5 connected to the excitation lines of the first and second ring resonators 2 and 4 are aligned with the ring shapes of the first and second ring resonators 2 and 4, thereby eliminating uncoupled sections and suppressing the coupled-mode transmission characteristics.

[0096] FIG. 13 is a perspective view showing the structure of a balanced band-pass filter 30 in which the common-mode transmission characteristics are suppressed. FIG. 14A is a plan view showing the structure of the balanced band-pass filter 30 in a perspective view. FIG. 14B is an end view of the longitudinal section of the balanced band-pass filter 30 as seen from the front. FIG. 15 is a perspective view showing an enlarged view of the vicinity of a coupled line 1B' formed by λ / 4 lines 1B1' and 1B2' of the first coupled line input / output section 1 in the balanced band-pass filter 30 shown in FIG. 13.

[0097] Here, this balanced band-pass filter 30 is a filter that suppresses the common-mode transmission characteristics of the balanced band-pass filter 20 shown in Figures 9, 10(A) and 10(B), and 11(A) and 11(B) above, which has improved shoulder characteristics in the pass band in the differential mode. Components that are the same as those of the balanced band-pass filter 20 above are given the same reference numerals in the drawings, and detailed descriptions of them will be omitted.

[0098] This balanced bandpass filter 30 has a multilayer structure intended for an LTCC substrate for a wireless communication module. Within an LTCC layer 8' measuring 5.6 x 2.015 mm and 0.207 mm thick, seven pairs of broadside-coupled coupled lines 1A·1B, 2A·2B, . . . , 7A·7B, each of which has a λ / 4 line width of 0.045 mm and a line length of 2.11 mm, are arranged at a line spacing of 0.25 mm, to form a balanced circuit for differentially transmitting a transmission signal.

[0099] In this balanced bandpass filter 30, the first coupled-line input / output section 1 comprises a pair of coupled lines 1A' and 1B', each composed of λ / 4 lines 1A1' and 1B1' and λ / 4 lines 1A2' and 1B2', which are shaped to fit the ring shape of the first ring resonator 2, and the second coupled-line input / output section 5 comprises a pair of coupled lines 7A' and 7B', each composed of λ / 4 lines 7A1' and 7B1' and λ / 4 lines 7A2' and 7B2', which are shaped to fit the ring shape of the second ring resonator 4.

[0100] That is, the shapes of the λ / 4 lines 1A1' and 1B1' and the λ / 4 lines 1A2' and 1B2' constituting the pair of coupled lines 1A' and 1B' of the first coupled-line input / output section 1 are aligned with the ring shape of the first ring resonator 2 to eliminate uncoupled sections, and the shapes of the λ / 4 lines 7A1' and 7B1' and the λ / 4 lines 7A2' and 7B2' constituting the pair of coupled lines 7A' and 7B' of the second coupled-line input / output section 5 are aligned with the ring shape of the second ring resonator 4 to eliminate uncoupled sections, thereby suppressing the coupled-line transmission characteristics.

[0101] FIG. 16 is a characteristic diagram showing the transmission characteristics of the balanced bandpass filter 30 obtained by analyzing it using an electromagnetic field simulator.

[0102] In Figure 16, the horizontal axis is frequency (GHz) and the vertical axis is S parameter |S DD11 |,|S DD21 |,|S CC21 The transmission characteristics of the balanced bandpass filter 30 are indicated as |[dB].

[0103] In this way, the shapes of the coupled lines 1A', 1B', 7A', 7B' of the first and second coupled line input / output sections 1, 5 connected to the excitation lines of the first and second ring resonators 2, 4 are made to conform to the ring shapes of the first and second ring resonators 2, 4, thereby eliminating the uncoupled sections. In this balanced band-pass filter 30, as shown in the transmission characteristics in FIG. 16, a steep shoulder characteristic is realized in the differential mode, and the passage of the common mode can be suppressed to 40 dB or more in a wide band.

[0104] The balanced bandpass filter 30 described above can be made compact and ultra-thin by using a laminated structure, and can be realized as a module-type component-embedded substrate, enabling the realization of a balanced bandpass filter having multi-band pseudo-elliptic function filter characteristics.

[0105] The balanced bandpass filters 10, 20, and 30 each have a filter structure loaded with open-ended resonators each consisting of seven pairs of coupled lines 1A-1B, 2A-2B, . . . , 7A-7B, ring resonators 2 and 4, and coupled-line resonator 3. However, the filter structure loaded with open-ended resonators each consisting of seven pairs of coupled lines 1A-1B, 2A-2B, . . . , 7A-7B, each of which is formed by electromagnetically coupling two λ / 4 lines, each with a line length of ¼ of the wavelength λ of the center frequency f0 of the transmission signal, symmetrically arranged, ring resonators 2 and 4, and coupled-line resonator 3, may also have a filter structure loaded with n coupled-line resonators and (n-1) ring resonators between the ring resonator 2 and ring resonator 4, where n is an integer greater than or equal to 2. [Explanation of symbols]

[0106] 1,5 coupled line input / output section, 2,4 ring resonator, 3 coupled line resonator, 1A,1A',1B,1B',2A,2B,3A,3B,...6A,6B,7A,7A',7B,7B' Coupled line, 1A1,1A2,1A1',1A2',1B1,1B2,1B1',1B2',2A1,2A2,2B1,2B2,...,7A1,7A2,7A1',7A2',7B1,7B2,7B1,7B1',7B2,7B2' λ / 4 line, 8, 8' LTCC layer, 9A, 9B correction coupling line, 9A1, 9B1 correction line, 9A a ,9B b Coupled line, 10, 20, 30 Balanced bandpass filter, Gp A ,Gp B Full conductor, P 1A P 1B ,P 2A P 2B Input / Output Ports

Claims

1. A balanced band-pass filter having a balanced circuit configuration that differentially transmits a transmission signal, the balanced band-pass filter comprising a plurality of coupled lines using λ / 4 lines each having a line length of ¼ of the wavelength λ of the center frequency of the transmission signal, a first coupled line input / output section comprising a pair of coupled lines connected to a first input / output port; a second coupled line input / output section comprising a pair of coupled lines connected to the second input / output port; a first ring resonator including two pairs of coupled lines including one pair of coupled lines connected to the first coupled line input / output section; a second ring resonator including two pairs of coupled lines including one pair of coupled lines connected to the second coupled line input / output section; a coupled-line resonator consisting of a pair of coupled lines connected to the first and second ring resonators; Equipped with the λ / 4 lines constituting each pair of coupled lines of the first and second coupled line input / output units and the λ / 4 lines constituting each pair of coupled lines of the first and second ring resonators have one end open and the other end connected to each other to form a λ / 2 open-ended resonator; A balanced bandpass filter having a filter structure loaded with open-ended resonators, ring resonators, and coupled-line resonators, each consisting of at least seven pairs of coupled lines symmetrically arranged, each pair being formed by electromagnetically coupling two λ / 4 lines, each having a line length of ¼ of the wavelength λ of the center frequency of a transmission signal.

2. 2. The balanced bandpass filter according to claim 1, wherein the balanced circuit is configured in a laminated substrate made of a plurality of dielectric layers, and the first and second ring resonators each have a ring structure made of four λ / 4 lines arranged between the same layers.

3. 3. The balanced bandpass filter according to claim 2, wherein a correction line for correcting resonance characteristics is provided at an open end portion of a pair of coupled lines constituting the coupled-line resonator so as to connect the coupled-line resonator to the first and second ring resonators, thereby improving the shoulder characteristics of the passband in a differential mode.

4. 3. The balanced bandpass filter according to claim 2, wherein the shapes of the first and second coupled line input / output sections connected to the excitation lines of the first and second ring resonators are made to conform to a ring shape, thereby eliminating uncoupled sections and suppressing common-mode transmission characteristics.

5. 5. The balanced bandpass filter according to claim 1, further comprising a filter structure in which a plurality of n (n is an integer of 2 or more) coupled-line resonators and (n-1) ring resonators are loaded between the first ring resonator and the second ring resonator.

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