KR0171247B1 - Small ceramic frequency filter - Google Patents

Abstract

The present invention relates to a small resonator for ultra-high frequency filters used in telegraph telephone stations, wireless base stations, and mobile stations, and a small filter using the same. The short waveguide chips are connected in series or in parallel using resonators, and the distance between them is appropriately adjusted. Filling the dielectric between them, and forming additional coupling bridges using conductors and dielectrics to control the size and ratio of the electrical and magnetic couplings during the resonance period to make the appropriate coupling inverter to obtain the desired filter characteristics. It is to be done.

Description

Mini ceramic filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultra-high frequency filters used in telegraph telephone stations, wireless base stations and mobile stations, and more particularly, to miniaturized ceramic filters miniaturized using waveguide resonators.

Originally proposed by Richtmyer in 1938, the dielectric resonator had the disadvantage of large characteristic change with temperature and high dielectric loss. However, these problems are greatly improved by the rapid development of material science today, and the miniaturized resonator is realized not only with excellent electrical and physical characteristics.

In addition, with the development of cellular mobile communication systems and PCS in various countries, including AMPS in the United States, the consumption of mobile communication devices such as base stations, vehicles, and portable devices is rapidly increasing, resulting in a relatively large volume compared to other components. Attention to miniaturization of the ultra-high frequency filter which occupies is attracting attention.

Recently, efforts have been made to miniaturize waveguide filters using ceramics having a high dielectric constant and to use them in mobile communication devices. Such waveguide type filter has great features such as large power capacity and low insertion loss, but has a large size disadvantage.

In other words, in order to reduce the size of a waveguide type filter based on a half-wave or quarter-wave resonator, a method of increasing the relative dielectric constant (ε _r ) and an image-type method using a magnetic field wall are provided. Although it is being used, the insertion loss due to the large dielectric constant and the tube wavelength (λ _g ) do not overcome the existing theoretical limitations.

In order to overcome the shortcomings of waveguide type filters, one of them is the design of L Band small ceramic filter, which was published in 1994 as the master's thesis of Sogang University. The results of this study are summarized in (1) to (3) below.

(1) Analysis of the characteristics of a short waveguide section from the resonator side reveals 'hidden-resonantmodes' directly above the cut-off frequency, which is external to the waveguide when the waveguide is a spherical waveguide. If the load impedance of Z ₀ is HTEmn mode occurs at, and the resonant frequency (ω ₀ ) is

Becomes Also, HTMmn mode occurs at, and the resonance frequency (ω ₀ ) is

Becomes

Where a, b, and l represent the width, height, and length of the waveguide, respectively, and ε represents the dielectric constant in the waveguide. On the other hand, d _r represents a constant according to the definition of the waveguide characteristic impedance, which is 2.0 when a power-voltage relationship is used. And m and n are indices representing resonance modes as zero or positive integers. Here, the lowest difference mode of the hTEmn mode is hTE ₁₀ .

(2) The resonant frequency of the resonator using the waveguide as described above is almost independent of the internal wavelength λ _g and shows a high Q value.

For example, the no-load Q _u value of an hTE ₁₀ resonator with ε _r = 90, a = 10.0 mm, b = 1.5 mm, l = 2.0 mm is measured at about 200 at 1.8 GHz. Herein, the wavelength in the tube (λ _g ) is generally defined as 2π / β, and β = K ² -Kc ² and K = ω με.

(3) A leaking electromagnetic field may also be used for coupling of such resonators.

The filter using the above research results has smaller size, larger Q value and excellent spurious response than conventional monoblock or coaxial filters.

Therefore, if the waveguide with the cutoff frequency is matched with a specific external impedance, the waveguide can be resonated at a frequency lower than the half-wave resonant point according to the above research results. responds very insensitively to l).

Because of this, the width (a) of only about 1/2 wavelength or about 1/4 wavelength (in case of using an image type resonator) is required, and the height (b) and length (l) can be adjusted almost arbitrarily. It is possible to construct a resonator having a large no load Q _u which is a characteristic of the waveguide type resonator, while being extremely small.

Therefore, the present invention was conceived based on the above-mentioned research results. A small-sized, ultra-high frequency ceramic ceramic filter having a small size and excellent insertion loss and pseudo-transfer characteristics by using a resonator using a cross section of a waveguide and a coupled inverter using a leaky electromagnetic field has been developed. For that purpose.

In order to achieve the above object, the present invention provides a magnetic field wall by removing a part of the conductor surface, and a length (l) shorter than 1/2 of the intra-wavelength wavelength (λ _g ) in which the electrode is formed on the open surface without the conductor. A waveguide resonator having a is arranged in series or in parallel in the longitudinal direction and by adjusting the distance of the resonance period or by forming an additional coupling bridge in the resonance period, characterized in that it is formed by electromagnetic coupling.

1 is an exemplary diagram of a series four stage band pass filter constructed in accordance with the present invention.

Figure 2 is an illustration of a parallel three stage band pass filter constructed in accordance with the present invention.

3 is a view showing the shape of the substrate shown in FIG.

4 is an exemplary view of a resonator constructed in accordance with the present invention.

5 is an exemplary view of a resonator constructed in accordance with the present invention.

6 is an exemplary view of an electrode formed on the open surface of the resonator.

7 is a diagram illustrating a coupling of resonance periods using leakage electromagnetic fields of a resonator.

8 is an illustration of the coupling of the resonant period using the leakage electromagnetic field of the resonator with the electrode.

9 is an illustration of a method for reducing the coupling of the resonance period.

10 is an illustration of a method for reducing the coupling between resonance periods.

11 illustrates an additional coupling method for notching a filter.

12 illustrates an additional coupling method for notching a filter.

FIG. 13 is a diagram showing data obtained by measuring characteristics of the series four-stage bandpass filter shown in FIG. 1. FIG.

* Explanation of symbols for main parts of the drawings

1, 51: substrate 2: cover

3, 4 electrode 5: ground terminal

11, 12, 13, 14: resonators 53, 54: input and output terminals

55, 56, 57: dielectric plates 58, 59, 64, 65: coupling legs

66, 67, 68: Ground terminal 1101, 1102: Open surface

1103, 1104, 1105, 1106: conductor plane 1113: magnetic field wall

2111, 2502, 2503: electrode

2301, 2411, 2413, 2511, 2513: dielectric

2312, 2412, 2512: conductor plate 2504: conductor bridge

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 shows an example of a resonator using a spherical waveguide, in which conductor surfaces 1103, 1104, 1105, and 1106 are formed on four surfaces of a hexahedral ceramic having a dielectric constant of ε, and the other two open surfaces 1101, 1102). Here, the width in the x direction of the resonator is regarded as the height in the a, y direction as the length in the b and z directions as l.

FIG. 5 is a view showing a modification of the resonator shown in FIG. 4, and the magnetic field wall 1113 is formed by removing the conductor of the conductor surface 1103 of the resonator shown in FIG. As such, when the magnetic field walls 1113 are formed and high dielectric constant ceramics are used, the size of the resonator required to generate the same resonance frequency can be reduced to about 1/2.

If the electrodes are required to connect the resonator configured as described above to an external circuit, to couple the resonators to each other, or to adjust the resonant frequency, the shapes shown in FIGS. 6 to 12 may be applied. In the figure, hatching lines of the conductor surface of the resonator are omitted.

6 shows that an electrode 2111 having an appropriate size and shape can be formed at any position on the open surface of the resonator. The shape, size and position of the electrode 2111 determine the combined value of the resonator and the external circuit or resonator and the resonance period, and also affects the resonance frequency.

7 and 8 show that the resonator and the resonator can be coupled to each other by using a leakage electromagnetic field. At this time, the distance of the resonance period is inversely inversely proportional to the coupling value. In addition, when the dielectric material 2301 having a small dielectric constant is filled in the space between the resonators, it is possible to facilitate manufacturing.

9 and 10 are structures useful for reducing the size of the filter by reducing the physical distance of the resonance period when the coupling degree of the resonance period is too high, and the dielectrics 2411, 2413, 2511, 2513 and the space between the resonators. It is shown that the conductor plates 2412 and 2512 can be properly positioned to control the electromagnetic and magnetic coupling. That is, the strength of the coupling is adjusted by moving or replacing the conductor plates 2412 and 2512 on the x-axis.

11 and 12 illustrate the ratio of the magnitudes of the electric field coupling and the magnetic field coupling using the electrode 2503-the conductor bridge 2504-the electrode 2502 or the dielectric 2313-the conductor plate 2312-the dielectric 2313. It is shown that not only can the notch be formed at the desired position, but also the characteristics of the asymmetric filter can be reduced and the coupling distance (space) can be reduced.

The filter formed using the resonator, the electrode and the coupling method described above is shown in FIGS. 1 and 2, where FIG. 1 is a diagram showing a series four-stage bandpass filter, and FIG. 2 is a parallel three-stage bandpass filter. The figure which shows.

Remove the conductors of the 103 and 104 portions of the PCB substrate, both sides of which are shown in FIG. 3, so that the electrodes 3, 4 can be formed like the filter 1 of the filter shown in FIG. 1, and the ground of the filter is removed. Terminals (not shown) were formed on the PCB substrate to be used as the terminals 5. In addition, the resonators 11, 12, 13, and 14 are arranged to have appropriate coupling values by adjusting the intervals 23, 24, and 25 in the z direction, and soldered to the substrate 1 to cover the cover 2 to be completed. If trimming is necessary, the resonant frequency and inverter value are adjusted by trimming the electrodes 3 and 4.

The substrate 51 of the filter shown in FIG. 2 is a substrate with all the top conductors removed so that the dielectric is exposed. In addition, a part (60, 61, 62, 63) of the conductor wall of the resonator is removed to prevent the short circuit when the input and output terminals (53, 54) and the coupling legs (64, 65) of the resonance period are formed. The coupling between the resonator and the resonator used the method shown in FIG. 11, which gives a notch, to form a conductor bridge electrode. Coupling legs 58 and 59 are used to adjust the coupling of the resonator to the resonator. Unexplained 55, 56 and 57 represent dielectric plates, and 66, 67 and 68 represent ground terminals.

FIG. 13 shows data obtained by measuring characteristics of a series four-stage bandpass filter implemented as shown in FIG.

As described above, the present invention constitutes a high frequency filter using a hTEmn resonator using a cross section of a waveguide and a coupling inverter using a leaky electromagnetic field. It is small and has excellent characteristics in terms of insertion loss and communication.

Claims (2)

A part of the conductor surface is removed to form a magnetic field wall, and on an open surface without a conductor, a waveguide resonator having a length (l) shorter than one-half of the internal wavelength (λ _g ) in which the electrode is formed, in series or in parallel in the longitudinal direction Small ceramic filter, characterized in that the arrangement, by adjusting the distance of the resonance period or by forming an additional coupling bridge in the resonance period, combined with each other magnetically. The small ceramic filter according to claim 1, wherein the coupling leg has a form of an electrode-conductor bridge-electrode or a dielectric plate-conductor plate-dielectric plate.