JPS5826842B2 - interdigital filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink digital filter, and particularly to an interdigital bandpass filter in which, for example, a plurality of resonators are coupled by even and odd modes of a TEM.

BACKGROUND ART Conventionally, ink digital bandpass filters have been put into practical use, for example, in transmitters and the like because of their high Q.

In such an ink digital filter, a plurality of resonators are coupled in an even-odd mode rather than in a higher-order mode of TEM.

FIG. 1 is an illustrative diagram showing an ink digital bandpass filter which is the background of the present invention.

FIG. 1a shows a sectional view taken along line IA-IA in FIG.

In that configuration, the upper conductor 1 and the lower conductor 2 are held parallel, separated by a height H.

The upper conductor 1 and the lower conductor 2 are each made of metal, such as aluminum, and act as ground conductors.

A metal spacer 1a is provided on the lower surface of the upper conductor 1, and a metal spacer 1a is provided on the lower surface of the upper conductor 1.
A metal spacer 2a is attached to the upper surface of each.

And between these two metal spacers 1a and 2a,
Resonant rods 3, 3.・
... are provided in an arrangement as shown in Figure 1.

In this first figure, an input coupler 41 is arranged in the same row close to the resonance rod 3 at the left end, and an output coupler 42 is arranged close to the resonance rod 3 at the right end.

Furthermore, the input coupler 41 is coupled to an input coaxial connector 51 via a matching terminal, and the output coupler 42 is coupled to an output coaxial connector 52 via a similar matching terminal.

Such an array is packaged and configured as an interdigital filter 10.

Such an ink digital filter 10 includes a resonance rod 3,
3. ...is the even-odd mode of TEM (eVen
, odd).

As a result, such an interdigital filter 10 exhibits a particular resonance characteristic as shown in FIG. 2, for example.

In the above-described particular interdigital filter 10, its package size, that is, the effective height H2 length 2 width W cannot be made very small due to restrictions on their respective characteristics.

That is, such a filter is generally required to have a high Q, and its effective height H cannot be lower than a predetermined value.

Furthermore, if the distance d between the resonators or the resonant rods 3, 3 is too small, the coupling will be strong and the bandwidth will be too wide.

Furthermore, said length L is constrained by the inherent length l of the resonant rod 3 and the cut-off space at its open end.

Furthermore, it is possible to make a narrow band filter by weakening the degree of coupling between the resonant rods 3, but in such a case, it is necessary to increase the width W, and although the Q is high, there is a drawback that temperature characteristics are poor.

In other words, if the band is made narrow, its center frequency f will change depending on the temperature change.

may change drastically.

As mentioned above, it is still difficult to miniaturize conventional interdigital filters despite the demand for system miniaturization.

Therefore, such difficulty in miniaturization is one of the reasons that prevents miniaturization of the entire system.

Therefore, the main object of the present invention is to provide an interdigital "filter" which can be made extremely compact, eliminating the above-mentioned difficulty in miniaturization.

In summary, this invention consists of an interdigital filter composed of a plurality of dielectric resonators, coupling apertures formed on both sides of each resonator to form electrodes, and each resonator being connected to an even-odd mode by the coupling aperture. This is an interdigital filter in which the filters are coupled to each other.

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 3 is a schematic cross-sectional view showing an embodiment of the present invention.

This FIG. 3 is a sectional view corresponding to FIG. 1a.

In the configuration, between the upper conductor 1 and the lower conductor 2,
A plurality of dielectric (coaxial) resonators 6°6.6... are arranged.

Each of the dielectric resonators 6 is made of a dielectric material such as titanium oxide ceramic or forsterite and has a rectangular cross section, as shown in FIG. 4, for example.

This dielectric resonator 6 includes an inner conductor 6c formed in a hollow portion of the dielectric, and an upper surface electrode 6a and a lower surface electrode 6b formed on an upper end surface and a lower end surface.

The length l is 1/4 or 1/4 of the wavelength used.
It has been selected as number 2.

The upper surface electrode 6a and the lower surface electrode 6b are in electrical contact with the upper conductor 1 and lower conductor 2, respectively.

Side electrodes 6d and 6e are formed on the side surfaces of such a dielectric resonator 6 so as to have an opening T having a certain width W.

One side electrode 6d is electrically connected to the upper electrode 6a, and the other side electrode 6e is electrically connected to the lower electrode 6b.

The open lower portion between the side electrodes 6d and 6e acts as a coupling opening for coupling the respective dielectric resonators to each other in an even-odd mode.

In this embodiment, dielectric resonators 6 as shown in FIG. 4 are arranged between an upper conductor 1 and a lower conductor 2 in close contact with each other.

Mutual coupling between the dielectric resonators 6, 6 is distantly related by the coupling aperture T, and the degree of coupling is determined by the width W of the lower coupling amount.

Further, when the length l of the dielectric resonator 6 is 1/4 wavelength, a short-circuit electrode 6f is formed at the short-circuit end.

In this way, since each resonator of the ink digital filter is a dielectric (coaxial) resonator, and the coupling is made through the coupling opening provided on the side surface of the outer conductor, the distance or space between each dielectric resonator is reduced. is completely unnecessary, and therefore the lateral length or width of the ink digital filter can be made extremely small.

More specifically, the degree of coupling between each resonator is generally determined by the ratio of the characteristic impedance Zoo of the TEM odd mode to the characteristic impedance Zoe of the TEM even mode.

Therefore, if the particular configuration of this actual case is used, the odd mode characteristic impedance Zoo will not change much.
The even mode characteristic impedance Zoe decreases, and the ratio increases as a whole.

Therefore, the degree of coupling that depends on the ratio of characteristic impedances becomes weaker, and the bandwidth becomes narrower.

In other words, if the characteristics (bandwidth) are the same, it can be made smaller than the conventional interdigital filter shown in Figure 1, and if the size is the same, the band can be made even narrower. .

In addition, since the resonator is made of a dielectric material, by appropriately selecting the temperature coefficient of the dielectric resonator 6, the influence of the linear expansion coefficient of each conductor can be canceled out, and the filter itself can have extremely excellent temperature characteristics. Become.

Therefore, even if it is a narrow-band device, there is no fluctuation in the resonance frequency and it can operate stably.

FIG. 5 is a perspective view showing another example of the dielectric resonator 6 that can be used in the present invention.

In structure, this actual case is the fourth example, with the following exceptions:
It is similar to the one shown in the figure.

That is, in the embodiment shown in FIG. 4, the side electrodes 6d and 6e are divided vertically to form a lower coupling amount in the height direction of the resonator 6, but in this embodiment, the two side electrodes 6d and 6e are 6g and 6h are separated in the length direction to form a lower coupling amount in the length direction of the resonator 6.

Of course, similar effects can be obtained by using such a dielectric resonator.

In the above-described embodiment, the degree of coupling is made arbitrary by adjusting the width W of the lower coupling amount for coupling between the dielectric resonators 6. However, assuming that this width W is constant, , it goes without saying that the same effect can be achieved even if the width d' of the resonator is adjusted.

It is also possible to use the embodiment shown in FIG. 4 and the embodiment shown in FIG. 5 together.

In addition, such side electrodes, top electrodes, bottom electrodes, etc. may be made by baking silver paste into a certain ceramic mold, or by coating the entire side surface and then chemically (etching) the desired width W. ) or may be removed mechanically.

As described above, according to the present invention, each resonator of an interdigital filter is a dielectric resonator, and these resonators are closely arranged so as to be mutually coupled through the coupling opening of the side conductor. As a result, compared to conventional ink digital filters, it is possible to make the filter even more compact with the same characteristics, and to obtain a narrowband filter without wasting space.

Furthermore, the upper and lower conductors of the dielectric resonators are both electrically connected to the case and mechanically fixed, making assembly easier and making each dielectric resonator more solid. It can be firmly fixed, has excellent impact resistance, and is extremely stable from the electrical and mechanical aspects even when there are temperature changes.

[Brief explanation of the drawing]

FIG. 1 is an illustrative diagram showing a conventional ink digital band pass filter which is the background of this invention. FIG. 2 is a graph showing the resonance characteristics of FIG. 1. FIG. 3 is a schematic cross-sectional view showing an embodiment of the present invention. FIGS. 4 and 5 are schematic perspective views showing an example of a dielectric resonator that can be used in the present invention. In the figures, the same reference numerals indicate the same or corresponding parts, 1 is the upper conductor, 2 is the lower conductor, 6 is the dielectric resonator, 6a is the upper surface electrode, 6b is the lower surface electrode, 6c is the inner conductor, 6
d, 6e, 6g, and 6h are side electrodes, and 7 is a coupling opening.

Claims (1)

[Scope of Claims] 1. A case including an upper conductor and a lower conductor facing the upper conductor, an inner conductor having a rectangular cross section, an upper groove body, and a lower groove body facing the upper groove body; a dielectric interposed between the inner conductor, the upper groove body, and the lower groove body, each including a dielectric resonator coupled in an even-odd mode of a TEM, and an upper groove body of each of the dielectric resonators; and a lower groove body are electrically connected and mechanically fixed to the upper conductor and lower conductor of the case, respectively, and each of the dielectric resonators has a coupling opening on each opposing side surface. An ink digital filter, characterized in that: a side conductor is formed, and the dielectric resonators are closely arranged so as to be mutually coupled by the coupling openings.