JPS6329282Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a filter made by a linear resonator open at both ends, commonly known as a hairpin resonator or U-shaped resonator.

The size of these filters is related to the length of the resonator, which in known filters is substantially equal to half the central operating wavelength of the filter.
Furthermore, these known filters are not tunable.
In fact, it is necessary to be able to easily change the length of the hairpin resonator, and this is clearly not possible with the known ones mentioned above.

A particular object of the invention is to provide a filter comprising a linear hairpin resonator with dimensions significantly smaller than those of conventional filters of the same type.

Another object of the invention is to avoid the presence of undesired spurious passbands caused by resonator harmonics.

This is achieved by using a capacitor associated with a filter that includes a conventional hairpin resonator.

According to the present invention, where λ is the wavelength corresponding to the center frequency of the filter band, the length of each resonator is λ/
2 and a capacitor is branched between the open ends of each resonator, and the capacitance of the above capacitor is
a resonant frequency equal to said center frequency of the filter band is such as to be obtained by a resonant circuit constituted by said capacitor and associated resonator; characterized by being obtained,
A microwave filter is provided consisting of n linear hairpin resonators, where n is a positive integer.

The present invention will be better understood and other features will be appreciated from the following description and accompanying drawings.

FIG. 1 shows a bandpass filter including a conventional linear hairpin resonator. The filter in the illustrated embodiment is 2 x 2 inches, or 5.08 cm x 5.08 cm;
It is constructed on a board having a thickness of 1.27 mm, and a scale graduated from 0 to 1 cm is shown next to the board to indicate the magnification of the figure.

The filter according to FIG. 1 includes, in addition to a board 1 made of alumina, a ground plane made of gold plating having a thickness of 10 μm and covering the whole of one side (not shown) of the board. On the illustrated side of the board, two lines L ₁ and L ₂ are made by gold plating with a thickness of 10μ, and six hairpin resonators H ₁ to H ₆ are placed between these two lines. is located. Lines L ₁ and L ₂ constitute the access points of the filter; they are parallel to each other and to the U-shaped vertical bars of the resonator.

Filters of the type corresponding to FIG. 1 are clearly of the type with a fixed passband, since they do not contain tuning elements with characteristics that can be easily adjusted.

The graph of FIG. 2 shows the value of the attenuation A, expressed in decibels, produced by the filter according to FIG. 1 as a function of the frequency F, expressed in megacycles per second. According to this graph, this filter has a center frequency of 825MHz and is 3dB below its value at 825MHz.
Contains a passband with a width of 55MHz. This represents λ
This is the passband achieved when the length of the hairpin resonator in FIG. 1 is selected to be 70 mm, ie, λ/2, as the wavelength in alumina for the frequency of 825 MHz. Moreover, apart from the passband with a center frequency of 825 MHz, the filter according to FIG. It is noted that it has a passband of This spurious passband is effectively 1000MHz
and 1400 MHz, and the attenuation changes wave-like between -3 dB and -20 dB in this passband.

FIG. 3 shows an explanatory diagram of the principle of the filter according to the present invention. This filter, like the filter according to FIG. 1, is configured to have a center frequency of 825 MHz and a passband of 55 MHz. This filter is 1 inch square, or 2.54 cm x 2.54 cm, and is fabricated on an alumina board 1 with a thickness of 1.27 mm, and the 0 to 1 cm graduated scale shown on the side of the board is shown in the figure. The spread rate is shown.

Like the filter of FIG. 1, the filter according to FIG. 3 includes a ground plane consisting of a gold plating with a thickness of 10 microns which in this case covers the whole of one side, not shown, of the board. Two mutually parallel lines L ₁ ′ and L ₂ ′ are formed on the illustrated side of the board 1 by gold plating with a thickness of 10μ, and between these lines a vertical bar is connected to the line L ₁ Five U-shaped resonators from H ₁ ' to H ₅ ' are arranged parallel to ', L ₂ '. In the case of Fig. 3, five variable capacitors C ₁ are connected to resonators H ₁ ′ to H ₅ ′, respectively.
to _C5 are connected between two points located near the ends of the U-shaped resonators H1 _' to _H5 '. These variable capacitors, symbolically illustrated by two parallel bars with side arrows, are small commercial capacitors whose capacitance can be adjusted from 0.3 picofarads to 1.2 picofarads.

The length of the hairpin resonator in Figure 3 is 40 mm,
This length corresponds to a frequency of 1450 MHz for a half wavelength with this value in alumina. But the fourth
As can be seen from the figure, in the filter according to FIG. 3 the passband is no longer centered on a frequency whose corresponding half-wavelength is equal to the length of the hairpin resonator.

FIG. 4 is a graph showing the attenuation as a function of frequency produced by the filter according to FIG. 3, with the same abscissa and ordinate scale as FIG. 2; The graph of FIG. 4 shows that the filter of FIG. 3 has a passband with a center frequency of 825 MHz, which is in fact the same as the passband of the filter according to FIG. In contrast, the "spurious passband" (between 1000 MHz and 1400 MHz) of the filter of FIG. 1 is not present in the filter of FIG.
In fact, in the above embodiment, capacitors C ₁ to C ₅ are
The electrical length of the resonator is doubled and set to lower the center frequency of the filter passband by approximately one octave, but the physical length of the resonator remains unchanged. Therefore, the fourth harmonic (3300MHz) is the troublesome harmonic that appears first.

Overall, there is a reduction in the size of the filter compared to the filter of FIG. The capacitor supplements the electrical length of the coupled resonator, giving this resonator a physical length of the order of λ/4, as in the case of the filter corresponding to FIG. 3, and providing the graph of FIG. It is possible to adjust the capacitor to By appropriate selection of the variable capacitor, it is also possible to give the U-shaped resonator a length shorter than λ/4.

By continuously varying the value of the capacitor of the filter according to FIG. 3, the frequency tuning of this filter can be varied continuously.

A specific example of the tuning capacitor of the filter according to the invention is the printed wiring type. In this type, the capacitor is obtained at the same time and in the same way as the resonator, i.e. by deposition of metal on the board or by removal by chemical or mechanical action of a part of the metal capacitor of the metallized board. Figure 5 shows a resonator H to which a capacitor C obtained in the above way is connected. The capacitor C is located between the U-shaped branches of the resonator H and comprises a row of small parallel strips perpendicular to said branches. Two successive strips are respectively integral with two branches of the U. It should be noted that the filter made in this way cannot be adjusted, but has the advantage over the filter containing the variable capacitor illustrated in Figure 3 that it is thinner and can be made more quickly.

Variations of the above-described filters may be proposed without departing from the scope of the invention. It is therefore possible to make a band suppressor filter in the same way. FIG. 6 is a block diagram of this type of filter.

FIG. 6 shows a principle diagram of a band-stop filter comprising one access line L, the two ends of which constitute the input and output of the filter, respectively.

Three hairpin resonators H ₀₁ , H ₀₂ , H ₀₃ are arranged in the same plane as line L, their branches are parallel to line L, and these resonators are arranged on both sides of this line. has been done. capacitor
C ₁ ′, C ₂ ′, C ₃ ′ are similar to those in FIG. 3, but make it possible to secure the same advantages for the band cancellation function.

In another variant, the coupling between the access line or lines and the resonator is performed by an electrical connection between one resonator and the line in question. Similarly, one or both access lines may be perpendicular to the bars of the hairpin resonator and their ends may be electrically connected to the resonator. For example, it is also possible to replace the line L ₁ ' in FIG. 3 with a connection starting from the left edge of the board and ending at a single point on the left bar of the resonator H ₁ ', which point corresponds to the input coupling to be achieved. It depends on the degree.

Furthermore, instead of creating a filter in which the lines, resonators, and capacitors are formed by metal deposits on the substrate, the lines, resonators, and capacitors can be formed by removing metal from the metal plating deposited on the substrate. It is possible to produce. A filter is then obtained which includes a slot line and a resonant slot.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a filter according to the prior art, FIG. 2 is a graph related to FIG. 1, FIG. 3 is an explanatory diagram showing the principle of the filter according to the present invention, and FIG.
FIG. 5 is an explanatory diagram showing a part of one embodiment of the filter according to the present invention, and FIG. 6 is a diagram illustrating the principle of another embodiment of the filter according to the present invention. 1...Board, _L1 , _L2 ...Line, _H1 to _H6 ...
…hairpin resonator, H ₁ ′ to H ₅ ′……hairpin resonator, C ₁ to C ₅ …capacitor, H ₀₁ , H ₀₂ , H ₀₃ …
…hairpin resonator, C ₁ ′, C ₂ ′, C ₃ ′...capacitor.

Claims (1)

[Scope of utility model registration request] The length of each resonator is made smaller than λ/2, where λ is the wavelength corresponding to the center frequency of the filter band, so that there are no unwanted spurious passbands caused by harmonics of the resonator. A capacitor (C ₁ -C ₅ ) is branched between the open ends of each resonator, and the capacitance of said capacitor is such that a resonant frequency equal to said center frequency of the filter band is caused by said capacitor and associated resonator. n linear hairpins, where n is a positive integer, characterized in that the resonator and the capacitor are obtained by depositing metal on a substrate; A small microwave filter consisting of a resonator (H′ ₁ −H′ ₅ ).