JP2011205543A - Helical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a helical filter capable of suppressing a third harmonic wave without affecting a fundamental wave.SOLUTION: A helical filter 1 has a resonator-coupled structure in which two helical coils 2, 3, one end of which is an open end and the other end of which is a ground end are accommodated in a metal case 4 and electromagnetically coupled to each other. A conductor wire 9 constituting the respective helical coils 2, 3 is not wound at a fixed pitch. Specifically, the pitch at a part having a length of 1/3 of the total length from the open end of the part in the helical form of the conductor wire 9 wound around a bobbin 7 is selected so as to be shorter than the pitch of the rest. By this, it is possible to suppress the third harmonic wave without increasing the number of parts or affecting the fundamental wave.

Description

  The present invention relates to a bandpass filter used in a frequency band such as VHF to UHF, and more particularly to a helical filter having a characteristic of suppressing harmonic components.

  One of the bandpass filters is a helical filter. The helical filter has a resonator coupling structure in which a plurality of helical coils having one end as an open end and the other end as a ground end are electromagnetically coupled. A conventional helical filter 21 illustrated in FIG. 7 accommodates two helical coils 22 and 23 in a metal case 24. The metal case 24 is provided with an input terminal 25 and an output terminal 26 adjusted to a desired impedance. Each helical coil 22, 23 is formed by winding a conductor wire 29 around the bobbin 27 at a constant pitch. In the metal case 24, a wall 30 that partitions the accommodation space of the helical coils 22 and 23 is provided. An inter-coil coupling adjustment hole 31 is provided in the wall 30. Each of the helical coils 22 and 23 has a frequency characteristic that resonates at the frequency of the fundamental wave to be passed. Then, by resonating with a signal component having a resonance frequency included in the input signal, the helica filter 21 exhibits desired attenuation characteristics and pass characteristics.

  However, the helical filter has a configuration in which a plurality of helical coils that resonate at the same frequency are connected to each other, and resonates even in a frequency band that is an integral multiple of the fundamental frequency. For this reason, even in a frequency band that is not desired to pass through, it may have a pass characteristic close to that of the fundamental frequency band. In particular, the third harmonic whose frequency is three times that of the fundamental wave passes at almost the same level as the fundamental wave.

  For this reason, for example, in a helical filter designed to pass a fundamental wave having a frequency of 191 Hz in the VHF band, a sufficient amount of attenuation is obtained for the third harmonic wave having a frequency of about 570 MHz in the UHF band, which is about three times the frequency. There was a problem that (passage loss) could not be secured.

  FIG. 8 is a diagram illustrating an example of frequency characteristics of a helical filter having a resonance frequency of 570 MHz. The horizontal axis represents frequency (Hz) and the vertical axis represents passage loss (dB). The closer the passage loss is to 0, the easier the signal passes. In this example, it can be seen that the signal passes with a low loss at about 1.6 GHz, which is about three times the frequency of the fundamental wave frequency of 570 Mz.

  As a technique for suppressing the third harmonic, a method of connecting a low-pass filter having a cutoff frequency between the fundamental wave and the third harmonic to the helical filter is often used. This method is an effective method using the fact that the frequency difference between the fundamental wave and the third harmonic is sufficiently large. However, this method increases the number of components and the area required for mounting the components due to the addition of the low-pass filter, which hinders the reduction in size and weight of the communication device.

  As another conventional technique for suppressing the third harmonic, there is a technique in which a third harmonic generated from a filter is absorbed by a radio wave absorber and suppressed (Patent Document 1). This technology is easy to design because the wave absorber can be placed in a relatively free position of the filter, but the manufacturing cost increases due to the increase in the number of parts and the number of processing steps by adding the wave absorber. Have a problem. Since the radio wave absorber slightly absorbs not only the third harmonic but also the fundamental wave, the pass characteristic of the fundamental wave is sacrificed.

  As another technique, there is a technique in which an attenuation characteristic with respect to a high long wave is improved by adopting a structure in which inductance coupling is incorporated between resonators constituting a filter (Patent Document 2). This technique is effective in principle, but the increase in the number of parts and the increase in the number of processing steps are remarkable, and it is not suitable for mass production.

JP-A-8-46406 No. 7-31604

  As described above, each of the conventional techniques has both merits and demerits, and has a common problem that the number of parts is increased in exchange for suppressing the third harmonic.

  The problem to be solved by the present invention is to provide a helical filter capable of suppressing the third harmonic without affecting the fundamental wave.

  In order to solve the above-described problems, the present invention provides a helical filter having a resonator coupling structure in which a plurality of helical coils having one end as an open end and the other end as a ground end are electromagnetically coupled. The conductor wire constituting the helical coil is not wound at a constant pitch so that the amount of suppression in the band increases.

In the helical coil of the present invention, it is desirable that the pitch of the portion having a length of about 1/3 from the open end is narrower (smaller) than the pitch of the remaining portion of the total length of the helical portion of the conductor wire.
Moreover, it is desirable to have a pitch adjusting mechanism for partially adjusting the pitch of the conductor wire.
The pitch adjustment mechanism includes a pitch holding unit that holds a part of the conductor wire at a constant pitch, and an operation unit that moves the pitch holding unit in the pitch direction to adjust the pitch of other parts. It is desirable to have
In addition, the pitch adjusting mechanism includes a pitch holding portion that holds a portion having a length of approximately 1/3 from the open end and a remaining portion at a constant pitch, and the pitch holding portion. It is desirable to have an operation part for moving in the pitch direction and adjusting the pitch of the other part.

  According to the present invention, it is possible to realize a helical filter that can suppress the third harmonic without increasing the number of components and without affecting the fundamental wave.

The conceptual diagram which illustrates embodiment of the helical filter which concerns on this invention The conceptual diagram which illustrates another embodiment of the helical filter which concerns on this invention The conceptual diagram which illustrates another embodiment of the helical filter which concerns on this invention. A characteristic diagram illustrating the relationship between the position in a helical coil of a conventional helical filter and the current intensity and voltage intensity The characteristic view which illustrates the relationship between the position in the helical coil of the helical filter of this invention, current intensity, and voltage intensity A characteristic diagram showing the frequency characteristics of the conventional helical filter and the frequency characteristics of the helical filter of the embodiment of the present invention superimposed. Conceptual diagram illustrating the configuration of a conventional helical filter Characteristic diagram showing an example of frequency characteristics of a conventional filter

Hereinafter, embodiments of the present invention will be described.
[Configuration of actual form]
The helical filter 1 according to the embodiment of FIG. 1 is a resonator coupling in which two helical coils 2 and 3 having one end as an open end and the other end as a ground end are housed in a metal case 4 and are electromagnetically coupled to each other. It has a structure. The metal case 4 is provided with an input terminal 5 and an output terminal 6 adjusted to a desired impedance. In the metal case 4, a wall 7 that partitions the accommodation space for the helical coils 2 and 3 is provided. An inter-coil coupling adjustment hole 8 is formed in the wall 7.
Each helical coil 2, 3 is formed by winding a conductor wire 9 such as an enamel wire around a cylindrical bobbin 7 having the same size. Each of the helical coils 2 and 3 has a frequency characteristic that resonates at the frequency of the fundamental wave to be passed. The helical filter 1 exhibits desired attenuation characteristics and pass characteristics by resonating with a signal component having a resonance frequency included in the input signal.

  The conductor wires 9 constituting the helical coils 2 and 3 are not wound at a constant pitch. Specifically, of the total length of the helical portion wound around the bobbin 7 of the conductor wire 9, the pitch of the portion 1/3 length from the open end is selected to be smaller than the pitch of the remaining portion. .

[Operations and effects of the embodiment]
By selecting the pitch of the conductor wire 9 as described above, the action and effect of suppressing the third harmonic can be obtained without affecting the pass characteristic with respect to the fundamental wave. This action / effect will be described with reference to FIGS.

  FIG. 4 shows the relationship between the position in the helical coil with a constant winding pitch and the current intensity and voltage intensity. FIG. 5 shows the relationship between the position in the helical coil, the current intensity, and the voltage intensity in which the pitch of the length of 1/3 from the open end is smaller than the pitch of the remaining portion of the total length of the helical portion of the conductor wire. Is shown. 4 and 5, the position in the helical coil is defined as 1 in which the total length of the helical portion of the helical coil is 1, one end (open end) of the helical portion is 1, that is, the maximum value of the position, and the other end (grounding end). The side end) is shown as normalized to 0, that is, the minimum position. The current intensity and voltage intensity are also standardized with a minimum value of 0 and a maximum value of 1.

  In FIG. 4, point A, point B and point C are helical from the point corresponding to the position of the end on the grounding end side of the helical shape portion of the conductor wire and the point corresponding to the position of the end on the grounding end side, respectively. This is a point corresponding to a position having a length of about 2/3 of the total length, and a point corresponding to the position of the open end. Points A and B are points where the voltage is 0 and the current is maximum in the case of the third harmonic. However, at point A and point B, the voltage and current are opposite to each other. If the strength of the magnetic field at point A is Ha and the strength of the magnetic field at point B is Hb, the contribution of Hb is larger than that of Ha when viewed from the entire helical coil, and the magnetic field strength H1 is (the absolute value of Hb). Value)-(absolute value of Ha).

  Therefore, in order to increase the suppression amount of the third harmonic, attention is paid to the unloaded Q value of the helical coil. In general, an inversely proportional relationship is established between the unloaded Q value of the helical coil and the insertion loss, and the insertion loss increases as the unloaded Q value decreases. From this, it is considered that the insertion loss for the third harmonic, that is, the amount of suppression can be increased by configuring the helical coil so that the unloaded Q value for the third harmonic becomes small. In order to realize this, in the present invention, the winding pitch is set so that the pitch of the 1/3 length from the open end of the length of the helical portion of the conductor wire is smaller than the pitch of the remaining portion. To change.

In FIG. 5, a point corresponding to about 2/3 of the entire length of the helical portion is a point B ′. The magnetic field strength H2 when viewed from the whole helical coil is (absolute value of Hb ′) − (absolute value of Ha ′). By changing the pitch as described above, the point B ′ is moved to the open end side of the helical coil from the point B (FIG. 4). For this reason, H2 becomes smaller than the magnetic field strength H1 when the pitch is constant.
This phenomenon is equivalent to the fact that when the third harmonic is viewed, it is difficult for current to flow through the helical coil and the resistance is increased. This means that the helical coil is configured so that the no-load Q value becomes small.

  FIG. 6 shows the frequency characteristics of the conventional helical filter and the frequency characteristics of the helical filter according to the embodiment of the present invention. Both helical filters are filters having a resonance frequency of 570 MHz, in which a helical coil is formed by a conductor wire having a total length of about 120 mm, and the helical coil is accommodated in a 7 mm square metal case. In the conventional (comparative example) helical filter, the pitch of the helical coil is constant and is selected to be about 0.6 mm. On the other hand, the pitch of the helical coil in the helical filter of the embodiment of the present invention is 0.75 mm for the 2/3 portion (length of 80 mm) of the total length of the helical portion, and 1/3 portion (length 40 mm). Min) was selected to be 0.3 mm.

  In the conventional helical filter, the frequency of the third harmonic is about 1.6 GHz. The third harmonic passage loss is about 8 dB.

In the helical filter of the embodiment, the frequency of the third harmonic is about 1.3 GHz. This is presumably because the amount of electric field coupling in the metal case changed as the pitch of the helical coil was changed. The insertion loss of the third harmonic is about 18 dB. By reducing the no-load Q value for the third harmonic, the suppression amount of the third harmonic is improved by about 10 dB. The characteristics in the 570 MHz band, which is the fundamental frequency band, have not changed much. From this, it can be seen that by adopting the configuration of the present invention, the third harmonic can be suppressed without affecting the fundamental wave.
In addition, in the band of about 1.6 GHz, it can be said that one of the effects is that the suppression amount, which was 10 dB in the past, can be improved to about 50 dB by adopting the configuration of the present invention.

  As described above, according to the present invention, the third harmonic can be suppressed by a single helical filter without adding a low-pass filter or the like. Therefore, problems such as an increase in the number of components and an increase in the area required for mounting components due to the addition of a low-pass filter or the like can be solved.

[Other Embodiments]
The helical filter of the present invention is not limited to the one shown in the above embodiment.
For example, in the above embodiment, the conductor coil 9 is wound around the bobbin 7 to form the helical coil 2. However, as with the helical filter 11 shown in FIG. 2, vapor deposition and etching are performed on the peripheral surface of the ceramic bobbin 12. The helical coils 13 and 14 may be formed using a pattern forming method such as a method.

  Further, as shown in FIG. 3, a helical filter 15 having a pitch adjusting mechanism 16 for partially adjusting the pitch of the conductor wire 9 is also effective. The pitch adjusting mechanism 16 includes a pitch holding portion 17 that holds a portion P1 having a length of 1/3 from the open end of the entire length of the helical portion of the conductor wire 9 at a constant pitch, and the helical coils 2, 3. And a cylindrical guide member 18 provided in the metal case 4 and an operation portion (not shown) for adjusting the pitch of the remaining portion P2 by moving the pitch holding portion 17 in the pitch direction. ing. The operation unit (not shown) may be operated from the outside of the metal case 4. For example, a driver or the like is inserted from the upper side of the metal case 4 and the operation unit is rotated to move the pitch holding unit 17 in the pitch direction. The structure can be considered. The pitch holding portion 17 is guided by the guide member 18 while being supported by the guide member 18 and can move in the pitch direction (vertical direction in the illustrated example), and can be adjusted in a stepless manner. According to this configuration, even after the helical filter 15 is mounted, the pitch holding unit 17 is moved in the pitch direction to change the pitch of the portion P2 that is not held by the pitch holding unit 17, thereby causing the helical filter 15 to move. Can be adjusted to desired characteristics.

In the above embodiment, the pitch of the length of 1/3 from the open end of the total length of the helical portion of the conductor wire 9 is selected to be smaller than the pitch of the remaining portion. The pitch of the predetermined length of / 3 or more or less may be selected smaller than the pitch of the remaining portion.
Moreover, although the said embodiment demonstrated the structure which suppresses a 3rd harmonic, if the structure of this invention that the pitch of the conductor wire which comprises a helical coil is not constant, it will not affect a fundamental wave. It is also possible to suppress higher-order harmonics.

DESCRIPTION OF SYMBOLS 1 Helical filter 2, 3 Helical coil 4 Metal case 5 Input terminal 6 Output terminal 7 Bobbin 8 Coil coupling adjustment hole 9 Conductor wire 11 Bobbin 12 Helical coil 13 Helical filter 14 Pitch adjustment mechanism

Claims (5)

  In a helical filter having a resonator coupling structure in which a plurality of helical coils having one end as an open end and the other end as a ground end are electromagnetically coupled, the amount of suppression in the harmonic frequency band is increased. A helical filter, characterized in that a conductor wire constituting a helical coil is not wound at a constant pitch.   2. The helical filter according to claim 1, wherein a pitch of a portion having a length of about 1/3 from the open end of a total length of the helical portion of the conductor wire is narrower than a pitch of the remaining portion.   The helical filter according to claim 2, further comprising a pitch adjusting mechanism for partially adjusting the pitch of the conductor wire.   The pitch adjusting mechanism includes a pitch holding unit that holds a part of the conductor wire at a constant pitch, and an operation unit that moves the pitch holding unit in the pitch direction to adjust the pitch of other parts. The helical filter according to claim 3.   The pitch adjusting mechanism includes a pitch holding portion that holds a portion having a length of approximately 1/3 from the open end and a remaining portion at a constant pitch, and the pitch holding portion in the pitch direction. The helical filter according to claim 4, further comprising: an operation unit that is moved to the position and adjusts the pitch of the other part.

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