KR101051584B1 - Microstrip Bandpass Filter Using Inductive Coupling and Apparatus Containing It - Google Patents

Abstract

Disclosed are a microstrip bandpass filter having a low insertion loss and excellent attenuation characteristics, and an apparatus including the same. The bandpass filter of the present invention and an apparatus including the same include: first and second capacitors connected in series between an input terminal and a ground terminal; Third and fourth capacitors connected in series between the output terminal and the ground terminal; First and second microstrip lines connected in series between the contacts of the first and second capacitors and the contacts of the third and fourth capacitors; And a third microstrip line formed between the contacts of the first and second microstrip lines and the ground terminal, and adjusting the pass band by varying the inductive coupling strength according to at least one of a width and a length.

Microstrip Lines, Bandpass Filters, Via Holes, Inductively Coupled, Capacitors

Description

MICROSTRIP BANDPASS FILTER USING INDUCTIVE COUPLING AND APPARATUS HAVING THE SAME}

The present invention relates to a microstrip bandpass filter used for wireless transmission and reception, and more particularly, to a desired frequency band (eg, DECT frequency band 1.89GHz, DCP frequency band 1.79GHz, etc.) using inductive coupling. The present invention relates to a microstrip bandpass filter having a low insertion loss and excellent attenuation characteristics, and a device including the same.

The wireless transmit / receive module is a device for selecting and transmitting a radio signal of only a set frequency band without loss. A band pass filter that passes only a frequency of a set channel, an amplifier to amplify a selected frequency, and converts a frequency by mixing an input radio signal. It consists of elements, such as a frequency converter. In particular, the band pass filter may be a device that affects the performance of the wireless transceiver module. The band pass filter should have a low insertion loss in the frequency band to be used and an excellent blocking characteristic outside the pass band.

Referring to FIG. 1, a band pass filter using a microstrip line is as follows.

The bandpass filter using a microstrip line (ML) includes first and second capacitors C1 and C2 and an output terminal OUT connected in series between an input terminal IN and a ground terminal GND. The third and fourth capacitors C3 and C4 connected in series between the ground terminal GND and the contact point N1 of the first and second capacitors C1 and C2 and the ground terminal GND are formed. The first microstrip line N1 and the second microstrip line L2 are formed between the contact point N2 of the third and fourth capacitors C3 and C4 and the ground terminal GND.

The band pass filter having such a configuration implements the inductance components required by the filter circuit into the first and second microstrip lines L1 and L2, and the first and second microstrip lines L1 and L2 at predetermined intervals. They are formed parallel to each other at distant locations, and the signal is transmitted through the coupling effect exhibited by the interaction to act as a bandpass filter.

It is important for the bandpass filter to position the first and second microstrip lines L1 and L2 in parallel and adjust the gap therebetween (in particular, to increase the bandwidth, the first and second microstrip lines L1). It is necessary to narrow the gap between L2) and the filter characteristics are greatly affected by the errors generated during PCB manufacturing. In addition, it is difficult to implement blocking characteristics outside the high passband.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microstrip bandpass filter having low insertion loss and excellent attenuation characteristics in a desired frequency band (for example, DECT frequency band 1.89GHz, DCP frequency band 1.79GHz, etc.) using inductive coupling, and including the same. It is to provide a device.

According to one aspect of the present invention, a microstrip bandpass filter having a low insertion loss and excellent attenuation characteristics and an apparatus including the same are disclosed. The bandpass filter of the present invention and an apparatus including the same include: first and second capacitors connected in series between an input terminal and a ground terminal; Third and fourth capacitors connected in series between the output terminal and the ground terminal; First and second microstrip lines connected in series between the contacts of the first and second capacitors and the contacts of the third and fourth capacitors; And a third microstrip line formed between the contacts of the first and second microstrip lines and the ground terminal, and adjusting the pass band by varying the inductive coupling strength according to the width or / and the length.

According to the present invention, a bandpass filter having a desired bandwidth can be realized by adjusting the coupling intensity (inductive coupling strength) by adjusting the length or / and width of the microstrip line. In addition, there is an advantage that a band pass filter having a desired bandwidth can be additionally implemented by adjusting the coupling strength (inductive coupling strength) through the via hole. The bandpass filter of the present invention has low insertion loss in the passband and has excellent attenuation characteristics of the passband.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

2 is a diagram illustrating a circuit configuration of a microstrip bandpass filter according to a first embodiment of the present invention.

As shown in FIG. 2, the microstrip bandpass filter according to the first embodiment of the present invention includes first and second capacitors C1 and C2 connected in series between an input terminal IN and a ground terminal GND. (21, 22), the third and fourth capacitors (C3, C4) (23, 24) connected in series between the output terminal (OUT) and the ground terminal (GND), and the first and second capacitors (21) First and second microstrip lines ML1 and ML2 (25 and 26) connected in series between the contact point N3 of the first and second capacitors 23 and 24, and the contact point N5 of the third and fourth capacitors 23 and 24, respectively. And a third formed between the contact point N4 of the first and second microstrip lines 25 and 26 and the ground terminal GND, and adjusting the pass band by varying the inductive coupling strength according to the width or / and length. Microstrip line ML3 (27).

In the microstrip bandpass filter according to the first embodiment, the first strip between the contact point N3 of the first and second capacitors 21 and 22 and the contact point N5 of the third and fourth capacitors 23 and 24. And arranging the second microstrip lines 25 and 26, one end of which is connected to a contact point N4 located at the center of the first and second microstrip lines 25 and 26, and the other end of which is connected to a ground end ( The third microstrip line 27 is arranged to be connected to GND). Contact N4 is a T contact.

As shown in FIG. 3, the microstrip bandpass filter according to the second embodiment of the present invention is a microstrip bandpass filter according to the first embodiment, and includes a third microstrip line 27 and a ground end ( And a via hole 28 formed between the GNDs.

In the first microstrip bandpass filter, the microstrip bandpass filter according to the second embodiment includes a third between the contact point N4 of the first and second microstrip lines 25 and 26 and the ground terminal GND. The microstrip line 27 and the via hole 28 are connected in series. More specifically, the third microstrip line 27 has one end connected to the contact point N4 of the first and second microstrip lines 25 and 26 and the other end connected to the via hole 28. The hole 28 has one end connected to the third microstrip line 27 and the other end connected to the ground terminal GND.

Hereinafter, the operation of the microstrip bandpass filter according to the first and second embodiments of the present invention will be described in detail.

The first to fourth capacitors C1 to C4 (21 to 24) are applied as chip capacitors of a type directly mounted on the PCB, and the first to third microstrip lines ML1 to ML3 (25 to 27). It is directly formed of copper foil on the PCB and transmits a signal through inductive coupling.

Inductive coupling is also referred to as magnetic coupling (Magnetic Coupling), the third microstrip line 27 of the present invention can be equivalently expressed in inductance, the electric field in the open end of the third microstrip line 27 The signal appears strong, which is called capacitive coupling or electric coupling. The degree of coupling can be adjusted depending on the strength of the inductance. In one embodiment, the intensity (inductive coupling strength) of the coupling can be adjusted by adjusting the value of the inductance according to the width or / and length of the third microstrip line 27, the third microstrip line 27. The longer or narrower the width of the coupling, the higher the coupling strength (inductive coupling strength) (i.e., the inductance component is stronger) and the higher the bandwidth, the shorter or wider the third microstrip line 27 The strength of the ring (inductive coupling strength) is small (ie, the inductance component is weak), reducing the bandwidth. Specifically, as the length of the third microstrip line 27 increases, the bandwidth increases, and as the length decreases, the bandwidth decreases. As the width decreases, the bandwidth increases and the width decreases. For example, in designing a bandpass filter requiring bandwidths of the DECT frequency band 1.89 GHz and the DCP frequency band 1.79 GHz, the third microstrip line 27 may have a high impedance characteristic. 27) set the width to 0.2mm, which is much larger than the typical 50 ohms, and the length to 3.5mm. When designing a wider bandwidth, the coupling strength (inductive coupling strength) is adjusted to have a desired bandwidth by increasing or narrowing the length of the third microstrip line 27.

As such, the strength (inductive coupling strength) of the coupling may be adjusted to have a desired bandwidth by adjusting either or both of the length or width of the third microstrip line 27. For example, the longer the length of the third microstrip line 27 is, the stronger the inductance component is. As shown in FIG. 6, the longer the length of the third microstrip line 27 is, the greater the coupling of the bandpass filter is. Therefore, it can be seen that the bandwidth is increased. Similar results can be obtained with the third microstrip line 27 using a chip inductor generally in use.

Meanwhile, as shown in FIG. 3, the via hole 28 may be added between the third microstrip line 27 and the ground terminal GND to adjust the coupling strength (inductive coupling strength). Since the via hole 28 also exhibits an inductance component, in the present embodiment, a band pass filter having a desired bandwidth is implemented by adjusting the coupling strength (inductive coupling strength) through the via hole 28.

FIG. 4 is a photograph in which the band pass filter of FIG. 3 is implemented on a PCB to mount a capacitor having a size of 1005 (1 mm x 0.5 mm), and the same reference numerals as in FIG. 3 are used. The PCB actually implemented based on the equivalent circuit of FIG. 3 uses a double-sided PCB having a thickness of 1 mm, a dielectric constant of 4.6, and a copper foil thickness, that is, a conductor thickness of 0.035 mm.

The widths of the first to third microstrip lines ML1 to ML3 25 to 27 are 0.2 mm and have a high impedance value, and also include the positions (bonding pads) of the chip capacitors 21 to 24.

Specifically, FIG. 5 illustrates the pattern shape including the first to third microstrip lines ML1 to ML3 25 to 27 in the bandpass filter of FIG. 4, and the length unit used is mm.

Referring to FIG. 5, the first microstrip line ML1 25 has a predetermined length connected at one end thereof to a contact N4 of the first and second microstrip lines ML1 and ML2 25 and 26. It is formed at predetermined intervals on the first conductive line 31 and the extension line of the other end of the first conductive line 31, and is bonded to the first and second capacitors (C1, C2) (21, 22) First and second bonding pads 34 and 35 are included. In one embodiment, the first microstrip lines ML1 25 form a first conductive line 31 of a length designed as a line having a high impedance of 0.2 mm in width, and the first conductive line 31. The first and second bonding pads 34 and 35 are formed to be bonded to the first and second capacitors C1 and C2 21 and 22 at predetermined intervals on an extension line of the left side of the substrate.

The second microstrip line ML2 26 has a second conductive line 32 having a predetermined length connected at one end thereof to a contact N4 of the first and second microstrip lines ML1 and ML2 25 and 26. ) And third and fourth bondings formed on the extension lines of the other ends of the second conductive lines 32 at predetermined intervals and bonded to the third and fourth capacitors C3 and C4 23 and 24. Pads 36, 37. In one embodiment, the second microstrip line ML2 26 forms a second conductive line 32 of length designed as a 0.2 mm wide line with high impedance, and the first microstrip line ML1. Is connected in series with the right extension line of the (25), bonding with the third and fourth capacitors (C3, C4) (23, 24) at predetermined intervals on the right extension of the second conductive line (32) Third and fourth bonding pads 36 and 37 are formed.

The third microstrip line ML3 27 has one end connected to the contact point N4 of the first and second microstrip lines ML1 and ML2 25 and 26 and the other end thereof to the via hole 28. It is connected to the ground terminal (GND) through the first microstrip line (ML1) 25 and the second microstrip line (ML2) 26 and a third conductive line 33 of a predetermined length located in the center of the (26) . In one embodiment, the third microstrip line (ML3) 27 is connected to the ground terminal (3) via a via hole 28 of a third conductive line 33 of a length designed as a line having a high impedance of 0.2 mm in width. GND) is formed in the middle of the first microstrip line (ML1) 25 and the second microstrip line (ML2) (26).

The length and spacing of the first to third conductive lines 31 to 33 and the spacing of the first to fourth bonding pads 34 to 37 are designed as shown in FIG. 5. That is, the PCB on which the first to third microstrip lines (ML1 to ML3) 25 to 27 are formed is a double-sided PCB having a thickness of 1 mm ± 10%, a dielectric constant of 4.6, and a thickness of copper foil of 35 µm. Line widths of the first to third conductive lines 31 to 33 of the third microstrip lines ML1 to ML3 25 to 27 are 200 μm ± 20 μm, and the first and second bonding pads 34 and 35 are respectively. The distance of each of the third and fourth bonding pads 36 and 37 is 450 μm. The above specifications are standardized to exhibit optimal pass characteristics in the 1.79 GHz and 1.89 GHz bands through a number of experiments and designs.

FIG. 6 shows the results of the S21 (insertion loss) parameter when the length of the third microstrip line (ML3) 27 is 0.3 mm when the length of the third microstrip line (ML3) 27 is 0 mm, and when the length is 0.35 mm. to be. The bandpass filter may be designed by adjusting the third microstrip line ML3 27 to have a desired bandwidth.

Figure 7 is the result of the S (scattering) parameter of the microstrip bandpass filter using inductive coupling implemented in the present invention. The microstrip bandpass filter of the present invention has an insertion loss of about -1 dB due to conductor loss and dielectric loss in the pass band, and has an insertion loss of -20 dB at 1.5 GHz and -20 dB at 2.5 GHz outside the pass band ( Excellent damping properties). Here, "S11" is return loss and "S21" is insertion loss.

The present invention as described above is a bandpass filter that can be used in the DECT frequency band 1.89GHz band and DCP frequency band 1.79GHZ band, applicable to the RF circuit in the RF module, easy to implement on the PCB, 2.4 It is applicable to wireless LAN, Bluetooth and mobile communication system and mobile communication device of GHz band.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

1 is a diagram illustrating a circuit configuration of a bandpass filter using a microstrip line according to the related art.

2 is a circuit diagram illustrating a microstrip bandpass filter according to a first embodiment of the present invention;

3 is a circuit diagram of a microstrip bandpass filter according to a second embodiment of the present invention;

4 shows a practical embodiment of a microstrip bandpass filter according to the invention.

FIG. 5 illustrates in detail the size of a printed circuit pattern in the microstrip bandpass filter of FIG. 4; FIG.

6 is a diagram illustrating S parameter characteristics according to a length of a third microstrip line of the microstrip bandpass filter according to the present invention.

7 illustrates S parameter characteristics of the microstrip bandpass filter according to the present invention.

* Explanation of symbols for the main parts of the drawings

21 ~ 24: Capacitor (C) 25 ~ 27: Microstrip line (ML)

28: via hole

Claims (13)

delete A microstrip bandpass filter, First and second capacitors connected in series between an input terminal and a ground terminal; Third and fourth capacitors connected in series between the output terminal and the ground terminal; First and second microstrip lines connected in series between the contacts of the first and second capacitors and the contacts of the third and fourth capacitors; A third microstrip line formed between a contact point of the first and second microstrip lines and a ground terminal, and adjusting a pass band by varying inductive coupling strength according to at least one of a width and a length; And And a via hole formed between the third microstrip line and a ground end. The method of claim 2, The third microstrip line, the longer the length of the bandwidth is increased, the smaller the length, the bandwidth is reduced microstrip bandpass filter. The method of claim 2, The third microstrip line, the narrower the bandwidth is increased, the wider the width, the bandwidth is reduced microstrip bandpass filter. The method of claim 2, And a chip inductor in place of said third microstrip line. The method according to any one of claims 2 to 5, The first to third microstrip lines are directly formed of copper foil on a PCB, and transmit signals through inductive coupling. The method of claim 6, And the first to fourth capacitors are chip capacitors. The method according to any one of claims 2 to 5, The first microstrip line, A first conductive line having a predetermined length at one end connected to a contact point of the first and second microstrip lines; And And a first and second bonding pads formed at predetermined intervals on an extension line of the other end of the first conductive line and bonded to the first and second capacitors. The method of claim 8, The second microstrip line, A second conductive line having a predetermined length at one end connected to a contact point of the first and second microstrip lines; And And a third and fourth bonding pads formed on the extension lines of the other ends of the second conductive lines at predetermined intervals and bonded to the third and fourth capacitors. 10. The method of claim 9, The third microstrip line, A length of a first end connected to a contact point of the first and second microstrip lines, the other end connected to a ground end through a via hole, and positioned at a center of the first microstrip line and the second microstrip line; Microstrip bandpass filter including 3 conductive lines. delete A device comprising a microstrip bandpass filter, First and second capacitors connected in series between an input terminal and a ground terminal; Third and fourth capacitors connected in series between the output terminal and the ground terminal; First and second microstrip lines connected in series between the contacts of the first and second capacitors and the contacts of the third and fourth capacitors; A third microstrip line formed between a contact point of the first and second microstrip lines and a ground terminal, and adjusting a pass band by varying inductive coupling strength according to at least one of a width and a length; And And a microstrip bandpass filter including a via hole formed between the third microstrip line and a ground end. The method of claim 12, The third microstrip line is a device having a microstrip bandpass filter, in which the length increases, the bandwidth increases, and the length decreases, the bandwidth decreases, and the width narrows, the bandwidth increases, and the width widens, the bandwidth decreases. .

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