JP6866454B2 - PCB-structured wideband filter to minimize signal phase balance - Google Patents

Description

The present invention relates to a wideband filter for mobile communication, and more particularly to a wideband filter having a PCB structure that can cover all 4G and 5G frequency bands and minimizes the phase balance of signals.

Generally, a filter is a frequency selection element that appears by a combination of L (industance) and C (capacity), and depends on band-pass characteristics, LPF (Low Pass Filter), HPF (High Pass Filter), BPF (Band Pass Filter). , BSF (Band Stop Filter).

The characteristics of the filter can be evaluated by insertion loss, skirt, group delay characteristics, and the like. Insertion loss means the power loss generated when a signal passes through a filter, and the skirt is the angle of inclination (sharpness) that separates the pass band and the blocking band, and is the order (Order) in the structure of the filter. Involved. Generally, as the order increases, the skirt characteristics improve, but the insertion loss and group delay increase. Here, the group delay (GD) means "GD = δθ / δω", that is, the amount of change in the phase (θ) due to the angular frequency (ω), and the relative time during which the signal is delayed for each frequency. Represents.

In addition, the filter has good Chebyshev and Group delay characteristics with a flat passband and constant ripple due to the pass characteristics and skirt characteristics (this is called the filter response). It can be classified into bessel / Butterworth, Elliptic type with good skirt characteristics, and the like.

Then, the filter can be classified into a Lumped Element, Microstrip / Stripline, Ceramic / Dielectric, Waveguide, and Saw (Surface Acoustic Wave) method depending on the form to be embodied.

On the other hand, in 5G mobile communication, a Massive MIMO (Multi Input Multi Output) system using a large number of antennas is adopted in order to maximize the capacity of the channel and ensure the reliability of the signal. The phase delay of a filter is a very important index in a Massive MIMO system in which a large number of filters are built in one antenna. When the phase delays of the filters built into the Massive MIMO system are different from each other, it is necessary to minimize the phase delays in order to induce signal distortion. That is, in the case of a filter used by being directly connected to an antenna, the phase characteristic of the filter is an important index. This is because the shape and direction of the beam generated by the antenna can change depending on the phase characteristics of the filter, but when multiple filters are used in combination with the antenna at the same time, the phase error between the filters should be minimized. is important.

FIG. 15 is a schematic diagram for explaining the cavity structure of the conventional wideband filter.

As shown in FIG. 15, the filter (filter; 50) having a cavity structure conventionally used in a mobile communication base station includes a housing (Housing; 51), a resonator (Resonator; 52), and a tuning screw (Tuning). It is composed of components such as a filter; 53), a wire loop (Wire Loop; 54) of the input / output stage 50a, and a disk loop (Disc Loop; 55) of the input / output stage 50b.

Referring to FIG. 15, in the case of the cavity filter 50, the tuning screw 53 for adjusting the resonance frequency of each cavity and the tuning screw 53'for adjusting the coupling amount between the cavities are applied to all filters in the process of tuning the characteristics of the filter. Similarly, it is difficult to apply, so a phase error between filters occurs.

Further, also in the case of the short-circuit type Wire Loop 54 or the open type Disc Loop 55 used in the input stage or the output stage 50a or 50b of the filter, the assembly result is not uniform due to the manual work, which may cause a phase error.

Therefore, in the case of a cavity filter, it is necessary to proceed with tuning with tuning screws 53 and 53'in order to adjust the electrical characteristics due to manufacturing tolerances and to form the resonance and passband of the required frequency.

However, even if the tuning work for adjusting the tuning screw is performed by a skilled worker, a lot of time and effort are required to have the same phase delay characteristic, and each filter (Filter) is required by such a tuning process. The deviation of the phase delay characteristic of is generated.

An object of the present invention is to provide a wideband filter having a PCB structure capable of eliminating the deviation of the phase delay of a conventional filter having a cavity structure and ensuring a uniform phase delay characteristic. Is.

Another object of the present invention is to provide a wideband filter with a PCB structure for minimizing the phase balance of signals.

Examples of the present invention disclose a wideband filter having a PCB structure.

The disclosed broadband filter includes a PCB board and a housing for mounting the PCB board. The PCB board includes a 4G input / output port, a 5G input / output port, an antenna input / output port, a 4G filter unit that functions as a low-pass filter (LPF) between the 4G input / output port and the antenna input / output port, and the above. It includes a 5G filter unit that functions as a high-pass filter (HPF) between the 5G input / output port and the antenna input / output port.

The housing is arranged between the 4G filter unit and the 5G filter unit, and has an isolation unit for blocking an electrical signal coupled between lines and an unnecessary signal generated by resonance of the signal by the housing. Anomalous resonance suppression rods can be included to eliminate.

The 4G filter unit has a first stub that embodies a resonator having a first transmission zero point, a second stub that embodies a resonator having a second transmission zero point, and a second stub that embodies a resonator having a third transmission zero point. The 3 stub, the 1st strip line connecting the 4G input / output port and the 1st stub, the 2nd strip line connecting the 1st stub and the 2nd stub, the 2nd stub and the 1st stub. It includes a third strip line connecting the three stubs and a fourth strip line connecting the third stub and the antenna input / output port.

The 5G filter unit connects a fourth stub that embodies a resonator having a fourth transmission zero point, a fifth stub that embodies a resonator having a fifth transmission zero point, the 5G input / output port, and the fourth stub. A first open coupling portion, a second open coupling portion connecting between the fourth stub and the fifth stub, and a third open coupling connecting between the fifth stub and the antenna input / output port. Includes part.

The broadband filter can be mounted on a base station antenna.

According to the embodiment of the present invention, the shape of the coupling line forming the LC resonator and the band of the filter (Filter) is fixedly formed on the PCB substrate to eliminate the tuning step that affects the phase delay characteristic. As a result, productivity can be improved and costs can be reduced.

Further, the PCB-structured filter according to the embodiment of the present invention can realize a uniform phase delay characteristic in a non-tuning method, and therefore has a phase when applied to a Massive MIMO system of next-generation (5G) mobile communication. The delay characteristics can be greatly improved.

A drawing illustrating a wideband filter having a PCB structure for minimizing the phase balance of signals according to an embodiment of the present invention. The pattern diagram of the upper surface of the PCB substrate illustrated in FIG. The pattern diagram of the lower surface of the PCB substrate illustrated in FIG. An example of embodying the stub shown in FIG. An embodiment of the open coupling portion shown in FIG. The S-parameter characteristic graph of the wideband filter illustrated in FIG. The S parameter characteristic graph of the 4G filter part illustrated in FIG. The phase characteristic graph of the 4G filter part illustrated in FIG. The S parameter characteristic graph of the 5G filter part illustrated in FIG. The phase characteristic graph of the 5G filter part illustrated in FIG. The equivalent circuit diagram of the 4G filter part which concerns on embodiment of this invention. The characteristic graph of the 4G filter part which concerns on embodiment of this invention. The equivalent circuit diagram of the 5G filter part which concerns on embodiment of this invention. The characteristic graph of the 5G filter part which concerns on embodiment of this invention. The schematic diagram for demonstrating the cavity structure of the conventional wide band filter.

The technical challenges achieved by the present invention and the practice of the present invention will be clarified by the preferred embodiments of the present invention described below. The examples below are merely exemplary to illustrate the invention and are not intended to limit the scope of the invention.

FIG. 1 is a drawing illustrating a wideband filter having a PCB structure (hereinafter, simply referred to as “broadband filter”) for minimizing the phase balance of signals according to an embodiment of the present invention.

First, the wideband filter 100 having a PCB structure embodies a filter in a high frequency band of several GHz by using a transmission line. Typically, a filter is embodied on both sides of a PCB substrate 10 by utilizing the principles of coupling between lines, resonance on a line, and multiple impedance connection by using a microstrip or stripline.

Such a broadband filter can be used to realize multi-band in mobile communication technology, but in the embodiment of the present invention, as shown in Table 1 below, multi-band in 4G mobile communication network band and 5G mobile communication network band. Will be described by taking as an example the one that embodies.

As shown in FIG. 1, the wideband filter 100 having a PCB structure according to an embodiment of the present invention includes a PCB substrate 10 and a housing 20 for mounting the PCB substrate 10.

Referring to FIG. 1, the PCB board 10 is a low pass filter (LPF) between the 4G I / O port 110, the 5G I / O port 120, the antenna I / O port 130, the 4G I / O port 110 and the antenna I / O port 130. It is composed of a 4G filter unit 140 that functions as above, and a 5G filter unit 150 that functions as a high-pass filter (HPF) between the 5G input / output port 120 and the antenna input / output port 130.

Further, the 4G filter unit 140 has three stubs ST1 to ST3 that act as first to third resonators, and four inductors for connecting input / output ports 110 and 130 between the stubs ST1 to ST3. It consists of component striplines 141-144.

Each stub ST1 to ST3 is embodied in an open stub structure in the form of three square patches having transmission zeros (Transmission zero; TZ1 to TZ3) in order to form a blocking band in a desired frequency band. The transmission zero point is a point on the complex frequency plane where the transmission amount becomes 0, and at this time, the attenuation amount becomes infinite, so that it is also called an attenuation pole.

Impedance matching and adjustment of the amount of signal coupling to reduce signal reflection can be obtained by adjusting the length and width of the stub and the line (strip line) connecting the stub.

The first strip line 141 connects between the 4G input / output port 110 and the first stub ST1, and the second strip line 142 connects between the first stub ST1 and the second stub ST2. The third strip line 143 connects between the second stub ST2 and the third stub ST3 in the form of a bent pattern, and the fourth strip line 144 connects the third stub ST3 and the antenna input / output port 130.

The line length of each stripline 141-144 is a factor that determines series L, the length must be less than λ / 8, and the width of the line is a factor that determines impedance. Therefore, the width and length of the lines can be adjusted so that the lines are matched.

The 5G filter unit 150 is composed of two stubs ST4 and ST5 that act as resonators, and three open coupling units 151 to 153 that are capacitive components that connect the input / output ports 120 and 130 and the resonator. It is composed.

Each stub ST4, ST5 is embodied in an open stub structure in the form of two square patches having a transmission zero (Transmission zero; TZ4, TZ5) in order to form a blocking band in a desired frequency band.

The open coupling portions 151 to 153 have a MIM (Metal-Insulate-Metal) structure, and form a kind of capacitor to suppress low frequency signals and allow high frequency signals to pass through. For this purpose, the line spacing and width are adjusted so that impedance matching is performed in the high frequency region.

The first open coupling portion 151 connects between the 5G input / output port 120 and the fourth stub ST4, and the second open coupling portion 152 connects between the fourth stub ST4 and the fifth stub ST5, and the third open The coupling portion 153 connects between the fifth stub ST5 and the antenna input / output port 130.

The housing 20 is arranged between the 4G filter unit 140 and the 5G filter unit 150 adjacent to each other, and has a isolation unit 210 for blocking electrical signals coupled between lines and a signal depending on the internal size of the housing. Is composed of anomalous resonance suppression rods 220-1 to 220-3 that remove unnecessary signals generated by resonance.

The isolation unit 210 plays a role of blocking the electrical signal coupled between the lines by the 4G filter unit 140 and the 5G filter unit 150 to improve the isolation characteristics between the input / output ports, and the abnormal resonance suppression rods 220-1 to 1 to 2. The 220-3 serves to separate the internal space of the housing and suppress the signal from being resonated by the housing 20.

FIG. 2 is a pattern diagram of the upper surface of the PCB substrate shown in FIG. 1, FIG. 3 is a pattern diagram of the lower surface of the PCB substrate shown in FIG. 1, and FIG. 4 is a stub circuit shown in FIG. It is a characteristic diagram, and FIG. 5 is a realization example of an open coupling portion for high frequency transmission between the lines shown in FIG.

As shown in FIGS. 2 and 3, the PCB substrate 10 according to the embodiment of the present invention is arranged so that the conductive patterns (strip lines) of the top surface 10a and the bottom surface 10b are symmetrical with each other in a predetermined shape. The conductive patterns on both sides can be connected through a large number of via holes 12.

Each input / output port 110, 120, 130 is composed of an impedance line of 50Ω, and the width and length of the line can be adjusted for impedance matching.

Further, five stubs ST1 to ST5 are arranged on the top surface 10a and the bottom surface 10b of the 4G filter unit 140 and the 5G filter unit 150, respectively. In the embodiment of the present invention, as shown in FIG. 4, each stub ST1 to ST5 is a short-circuit circuit stub ST-L acting as an inductor (L) and an open stub ST-C acting as a capacitor (C). It is configured to embody a series LC circuit. Here, the L value and C value of the series LC circuit can be adjusted by changing the length and width of the square patch type stub, whereby the transmission zero point is determined.

Further, as shown in FIG. 5, the open coupling portions 151 to 153 of the 5G filter unit 150 sandwich the substrate main body 10c in which the top surface pattern 10a and the bottom surface pattern 10b of the substrate are dielectrics in the cutting region of the transmission line. The capacitors are embodied so as to overlap each other. The coupling amount of the open coupling portions 151 to 153 increases as the area where the lines overlap is larger, becomes smaller as the area overlaps, becomes larger as the interval becomes smaller, and becomes smaller as the distance becomes smaller.

FIG. 6 is an S-parameter characteristic graph of the wideband filter shown in FIG. In the embodiment of the present invention, the port number 1 in the S parameter graph represents the antenna input / output port 130, the port number 2 represents the 4G input / output port 110, and the port number 3 represents the 5G input / output port 120.

As shown in the graph illustrated in FIG. 6, the broadband filter 100 according to the embodiment of the present invention receives the power returned to the port 1 when a signal is applied to the port 1 (Port 1) which is the antenna input / output port 130. The ratio and reflection coefficient S (1, 1), the ratio of the power transmitted from port 1 to port 2 and the transmission coefficient S (2, 1), and the transmission coefficient S (2, 1) are transmitted from port 1 to port 3. The characteristics of S (3, 1) which is a transmission coefficient are shown.

Referring to FIG. 6, the horizontal axis of the illustrated graph indicates the frequency (freq, unit GHz), and the vertical axis indicates the value of the signal magnitude (dB).

The S (2, 1) graph of FIG. 6 shows the characteristics of a low-pass filter (LPF) that passes through the 728 to 2150 MHz band, which is a relatively low frequency, and the S (3, 1) graph is a relatively high frequency. It shows the characteristics of a high-pass filter (HPF) that allows high frequencies in the 3440 to 3520 MHz (4G), 3600 to 4200 MHz (5G), and 4400 to 4900 MHz (5G) bands to pass through and blocks low frequencies. The S (1, 1) graph shows the characteristic of separating the low frequency band and the high frequency band from each other.

FIG. 7 is a S (2, 1), S (2, 2) parameter characteristic graph of the 4G filter unit shown in FIG. 1, and FIG. 8 shows S (2, 1) of the 4G filter unit shown in FIG. ) It is a phase characteristic graph.

Referring to FIG. 7, according to the S (2, 1) graph, the transmission of the signal from the 4G input / output port to the antenna input / output port shows the characteristics of the low frequency passing filter that passes a low frequency of about 2.4 GHz or less. According to the S (2, 2) graph, it can be seen that the reflected wave at the 4G input / output port exhibits a characteristic of blocking high frequencies.

Further, referring to FIG. 8, the phase graph of S (2, 1) shows the phase angle of the signal seen when the signal applied to the port 1 reaches the port 2, according to the frequency, and the PCB. In the case of the type, the same phase result will be obtained because the line is constant, that is, the distance traveled by the signal is constant.

Normally, the wavelength of a phase characteristic graph becomes shorter as the frequency increases, so when traveling the same distance along a line with a single-character structure, the phase graph shows a linear graph that decreases as the frequency increases, and is 180 °. Since the graph is inverted to −180 ° to 180 ° in order to represent the entire graph in the range of ~ -180 °, it shows a sawtooth-like graph characteristic that no signal distortion occurs in the line.

According to the illustrated graph, the S (2,1) phase characteristic is found to be 169.550 at m1 (728 MHz) and 124.769 at m2 (2.15 GHz), which is the band between m1 and m2. The linear representation of the phase graph indicates that the signal in the corresponding band travels constantly without distortion of the signal.

FIG. 9 is a graph of S (3, 1) and S (3, 3) parameter characteristics of the 5G filter unit shown in FIG. 1, and FIG. 10 shows S (3, 1) of the 5G filter unit shown in FIG. ) It is a phase characteristic graph.

Referring to FIG. 9, according to the S (3, 1) graph, the transmission of the signal from the 5G input / output port to the antenna input / output port shows the characteristics of the high frequency passing filter that passes a high frequency of about 3.2 GHz or more. (3, 3) According to the graph, it can be seen that the reflected wave at the 5G input / output port exhibits a characteristic of blocking low frequencies.

Further, referring to FIG. 10, the S (3, 1) phase characteristic shows the phase angle of the signal seen when the signal applied to the port 1 reaches the port 3, according to the frequency, and the PCB. In the case of the type, the same phase result will be obtained because the line is constant, that is, the distance traveled by the signal is constant.

According to the illustrated graph, it can be seen that it is 119.545 at m1 (3.44 GHz), 165.057 at m2 (4.9 GHz), and shows a linear phase characteristic at 728-2150 MHz. ..

FIG. 11 is an equivalent circuit diagram of the 4G filter unit according to the embodiment of the present invention, and FIG. 12 is an S-parameter characteristic graph of the 4G filter unit according to the embodiment of the present invention.

Filters are generally designed by the insertion loss method. The insertion loss method allows a high degree of adjustment over the amplitude and phase characteristics of the passband and stopband, but is designed by selecting filter responses such as Butterworth, Chebyshev, Equal ripple, and Elliptic according to the desired specifications. To do. The structure of the filter is based on the low-pass structure, and when the design is started, the structure is changed according to the type of filter (LPF, HPF, BPF, BRF) to embody the filter. The value of each element configured inside is determined by the filter response, and the wideband filter having a PCB structure according to the embodiment of the present invention uses an Elliptic filter response.

The Elliptic filter response is obtained by the following mathematical formula 1, the ripple factor (Ripple factor) determines the ripple in the pass band, and the combination of the ripple factor and the selectivity (Selective factor) determines the ripple in the blocking band.

In mathematical formula 1, R _n indicates an Nth-order Elliptic rational function, ω ₀ indicates Cutoff Frequency, ε indicates a Ripple frequency, and ξ indicates a Selective factor.

The LP region is embodied in a band blocking filter to obtain an attenuation value in the desired band using a relatively low order. The band blocking response can be obtained from the basic form by substituting the frequency as shown in the following mathematical formula 2.

In the low-pass basic circuit, the parallel capacitor is converted into a series LC circuit having the element values of the following mathematical formula 3 for band blocking.

In the embodiment of the present invention, the Richard conversion is used to convert the inductor (L' _k ) into a short-circuit circuit stub and the capacitor ( _C'k ) into an open circuit stub, as shown in FIG. Embody an equivalent circuit.

Referring to FIG. 11, the 4G filter unit 140 is _{represented by four inductors L k} ′ in which the first to fourth strip lines 141 to 144 are connected in series, and the first to third stubs ST1 to ST3 are three. It is displayed by the series LC resonator of. L of the series LC resonator has a 1 / ω ₀ ΔC _k value, and C has a ΔC _k / ω ₀ value. The three LC resonators are shown by the three transmission zeros TZ1 to TZ3 in FIG.

FIG. 13 is an equivalent circuit diagram of the 5G filter unit according to the embodiment of the present invention, and FIG. 14 is a characteristic graph of the 5G filter unit according to the embodiment of the present invention.

Referring to FIG. 13, 5G filter unit 150 is displayed in the three capacitors _{C k} 'of the first to third open coupling portion 151 to 153 are connected in series, the fourth and fifth stubs ST4, ST5 is Displayed with two series LC resonators. L of the series LC resonator has a 1 / ω ₀ ΔC _k value, and C has a ΔC _k / ω ₀ value. The two LC resonators are shown by two transmission zeros TZ4 and TZ5 in FIG.

As in the embodiment of the present invention, a wideband filter using a combination of filters can be used for a duplexer, a duplexer, and the like. The duplexer is to share one antenna between the transmission and reception stages, and after embodying it with a BPF that passes only the frequency of the transmission stage and a BPF that passes only the frequency of the reception stage, the middle is intermediate. It matches the antenna properly. Unlike the duplexer, the duplexer uses the LPF and the HPF instead of the BPF, and can be used for the realization of Massive MIMO in mobile communication.

The present invention has been described above with reference to one embodiment illustrated in the drawings, but any person having ordinary knowledge in the art can now make various modifications and uniform other embodiments. You can understand that.

10: PCB board 20: Housing 100: Wideband filter 110: 4G input / output port 120: 5G input / output port 130: Antenna input / output port 140: 4G filter unit 141-144: Strip line 150: 5G filter unit 151-153: Open Coupling part ST1 to ST5: Stub TZ1 to TZ5: Transmission zero point

Claims (3)

In a broadband filter including a PCB board and a housing that forms a space for mounting the PCB board.
The PCB board is
1st I / O port,
2nd I / O port,
Antenna input / output port,
A square patch-shaped first stub forming a resonator having a first transmission zero point, a square patch-shaped second stub forming a resonator having a second transmission zero point, and a resonator having a third transmission zero point are formed. A square patch-shaped third stub, a first strip line connecting the first input / output port and the first stub to form an inductor, and connecting the first stub and the second stub to form an inductor. A fourth strip line to be formed, a third strip line connecting the second stub and the third stub to form an inductor, and a fourth strip line connecting the third stub and the antenna input / output port to form an inductor. A first filter unit, which is composed of a strip line and functions as a low frequency pass filter (LPF) between the first input / output port and the antenna input / output port, and
A square patch-shaped fourth stub that realizes a resonator having a fourth transmission zero point, a square patch-shaped fifth stub that realizes a resonator having a fifth transmission zero point, the second input / output port and the fourth stub. The first open coupling portion that capacitively couples the stub, the second open coupling portion that capacitively couples the fourth stub and the fifth stub, and the fifth stub and the antenna input / output port are capacitively connected. A broadband filter having a PCB structure, which is composed of a third open coupling unit and includes a second filter unit that functions as a high frequency pass filter (HPF) between the second input / output port and the antenna input / output port. .. The housing is
An isolation unit formed between the space in which the first filter unit is mounted and the space in which the second filter unit is mounted, and for separating the first filter unit and the second filter unit,
Separating the inner space of the housing, the including abnormal resonance suppression rods to suppress the resonance of the signal by the housing, a broadband filter P CB structure according to claim 1. The wideband filter is characterized in that it is implemented in a base station antenna, a broadband filter P CB structure according to claim 1 or 2.

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