RU2657311C1 - Bandpass microwave filter - Google Patents

Abstract

FIELD: electronics.

SUBSTANCE: bandpass microwave filter belongs to the technique of ultrahigh frequencies and can be used in selective ducts of receiving and transmitting systems. Filter comprises dielectric substrate (1), on one side of which there is grounded base (2), and on the second one there are strip conductors (2-19) of three electromagnetically interconnected resonators applied. Novelty is in fact, that the narrow and the wide rectangular strip conductors interconnected in series and grounded to the base from the free end of the input (output) of the strip conductor are three times folded in the form of an irregular meander. Also, the filter is characterized in that the strip conductors are folded p times in the form of an irregular meander, where p = 5, 7, 9, …, and it contains n electromagnetically interconnected resonators, where n = 4, 5, 6, … .

EFFECT: technical result of the claimed solution is to improve frequency-selective properties of the band-pass microwave filter.

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Description

The invention relates to techniques for microwave frequencies and can be used in the selective paths of receiving and transmitting systems.

Known microstrip bandpass filter (RF Patent No. 2227350, Н01Р 1/203), containing a dielectric substrate, on one side of which is grounded metallized base, and on the second side are strip conductors of two U-shaped resonators, one side of each of U-shaped resonators are placed between the sides of another U-shaped resonator and are additionally connected to its other side, while the conductor of each of these resonators in its middle part is connected to a grounded base trezkom stripline. In the passband of the filter, coupled vibrations are excited at the resonant frequencies of the two vibration modes of each resonator, the energy of which is transmitted to the “output” due to electromagnetic interaction. As a result, the filter passband is formed by four resonances. Due to the closure of the resonator conductor to ground, the attenuation in both obstacle bands increases, and the second spurious passband shifts upward in frequency by more than an octave.

A disadvantage of the described microstrip bandpass filter, consisting of a pair of resonators, is the weak suppression of power at the frequencies of the obstacle bands, as well as the relatively narrow high-frequency obstacle band.

The closest in combination of essential features is a three-resonator band-pass filter (RF Patent No. 2480867, Н01Р 1/203, Fig. 6), containing a dielectric substrate, on one side of which a grounded metallized base is applied, and a strip conductor is partially applied on the second side, partially split by a longitudinal slit at one end, two-mode microstrip resonators are used in the filter, electromagnetically coupled to each other. This filter is distinguished by the mutual orientation of neighboring resonators. The spurious filter passband is located at approximately twice the frequency of the main passband.

The disadvantages of the prototype include weak suppression of power at the frequencies of the barriers, as well as a relatively narrow high-frequency bar.

The technical result of the invention is to improve the frequency-selective properties of a band-pass microwave filter.

The technical result is achieved due to the fact that in a band-pass microwave filter containing a dielectric substrate, on one side of which a grounded metallized base is applied, and on the second side are strip conductors of three electromagnetically coupled microstrip resonators, according to the technical solution, connected in series narrow and wide rectangular strip conductors, grounded to the base from the side of the free end of the input (output) strip conductor, three times Uta in the form of an irregular square wave.

And also because the strip conductors are folded p times in the form of an irregular meander, where p = 5, 7, 9, ....

And also the fact that the band-pass microwave filter contains n electromagnetically coupled resonators, where n = 4, 5, 6, ....

The invention is illustrated by drawings: Figure 1 - an example of a three-resonator band-pass microwave filter with triple-rolled in the form of an irregular meander strip conductors. FIG. 2 - measured amplitude-frequency characteristics (S ₂₁ , S ₁₁ ) manufactured three-resonator microwave filter.

The microwave pass-band filter (FIG. 1) contains a dielectric substrate 1, on one side of which a grounded metallized base is applied, and on the second - strip conductors 2-19 are applied, all together they form microstrip lines, which are one of the types of transmission lines. The segments of microstrip lines have their own vibration frequencies and are microstrip resonators. So connected to each other strip conductors 2-10, located on a dielectric substrate with a grounded metallized base, are a multimode resonator (first and third) of the claimed filter. Similarly, strip conductors 11-19 connected to each other, located on the same dielectric substrate with a grounded metallized base, are the second multimode resonator in the filter.

In the first (third) resonator, narrow rectangular strip conductors 2, 4, 5, 7, 8, 10 and wide rectangular strip conductors 3, 6, 9 are connected in series with each other in the following order: 2, 3, 4, 5, 6, 7, 8, 9, 10 in the form of three times (p = 3) folded irregular meander. While the strip conductors 2-7 are connected to each other in the form of twice (p = 2) folded irregular meander. And the strip conductors 2-4 in the form of a single (p = 1) rolled meander, i.e. in the form of a hairpin.

In the second resonator, similarly, narrow rectangular strip conductors 11, 13, 14, 16, 17, 19 and wide rectangular strip conductors 12, 15, 18 are connected in series with each other in the following order: 11, 12, 13, 14, 15, 16, 17, 18, 19 in the form of a triple-folded irregular meander. Similarly, the strip conductors 11-16 are connected to each other in the form of a double-folded irregular meander. And the strip conductors 11-13 in the form of a single folded meander.

The number of windings of strip conductors p in the form of an irregular meander is easy to increase by adding three series-connected strip conductors to each of the existing conductors of the filter. Moreover, the filters with even number of windings of strip conductors p = 2, 4, 6 ... are significantly inferior in frequency-selective properties, in particular, to the filters using an odd number of windings p = 3, 5, 7, ..., in terms of the width of the high-frequency obstacle strip. The number of resonators n in the filter is increased by duplication of the central resonator.

The strip conductors 2, 6, 10, 11, 15, 19 of the filter are grounded to the metallized base on the side of the free end of the input (output) strip conductor 2. In this case, all the strip conductors of the three-cavity filter have axial symmetry, and located in a row, aligned with each other, either counter-directionally, the resonators are electromagnetically coupled to each other.

The principle of operation of a band-pass microwave filter is as follows. The signal is fed to the input strip conductor 2 (Fig. 1, input). In the first (third) resonator, strip conductors 2-6 connected to each other and grounded to a metallized base, as well as conductors 6-10 located on a dielectric substrate with a grounded metallized base, can be represented as a pair of half-wave resonators, with the lowest oscillation mode of both the first and the second is involved in the formation of the passband of the filter, therefore, in fact, such a resonator is multimode, or rather two-mode. The second resonator is similarly two-mode, there are three resonators in the microwave filter; therefore, six resonances form its passband (Fig. 2, inset). The signal is removed from the output strip conductor 2 (Fig. 1, output).

The improvement of such frequency-selective filter properties as the steepness of the passband slopes and suppression of power at the frequencies of low-frequency and high-frequency obstacle bands is achieved both by increasing the number of n resonators (n = 4, 5, 6, ...), and by increasing the number p folding (p = 5, 7, 9, ...) of strip conductors in the form of an irregular meander, which proportionally increases the number of resonances from each resonator involved in the formation of the working passband.

The expansion of the high-frequency barricades of the band-pass microwave filter (Fig. 2) is due to the large jump in wave impedances of the segments of microstrip lines. Numerous microwave attenuation poles located on the amplitude-frequency characteristic (Fig. 2) contribute to the amplification of power suppression at the frequencies of the low-frequency and high-frequency obstacle bands. The origin of the attenuation poles is due to the fact that at these frequencies the capacitive and inductive interactions of the resonators mutually cancel each other out.

An example of implementation: the filter was made on a substrate of traditional microwave technology material (polycor material) 1 mm thick with a dielectric constant of ε≈9.8. The length and width of the filter strip conductors in mm: (2) - 13.40 × 0.70, (3) - 9.60 × 7.70, (4, 5) - 3.25 × 1.00, (6) - 6.90 × 5.90, (7, 8) - 3.30 × 0.90, (9) - 9.50 × 7.60, (10) - 13.50 × 0.90, (11, 19) - 13.70 × 1.00, (12, 18) - 9.20 × 7.10, (13, 14, 16, 17) - 3.40 × 0.50, (15) - 6.90 × 6.00. The gaps between the resonators are 0.60 mm. The substrate area, taking into account a spacing of 0.50 mm from its three edges to the conductors, was 60.00 × 23.50 mm ² .

The amplitude-frequency characteristics of the forward and reverse losses (transmission losses S ₂₁ and reflection S ₁₁ ) of the inventive band-pass microwave filter, taken in a wide and narrow (on the inset) frequency band, are shown in FIG. 2. The filter has a relative bandwidth of Δƒ / ƒ ₀ ≈17%, measured at a level of -3 dB from the level of minimum losses, which amounted to L _min ≈1.4 dB at the center frequency of the passband ƒ ₀ ≈0.94 GHz. The width of the extended high-frequency stop band ₀ ~ 3ƒ suppression power at its frequencies not less than 50 dB.

The advantages of such a microwave filter are the numerous power attenuation poles that are observed both at the low-frequency and high-frequency frequencies of the obstacle, which greatly enhance the suppression of microwave power, and thereby improve the frequency-selective properties of the filter.

Thus, the inventive band-pass microwave filter with improved frequency-selective properties has a stronger suppression of power at the frequencies of low-frequency and extended high-frequency obstacle bands.

Claims (3)

1. A band-pass microwave filter containing a dielectric substrate, on one side of which is grounded a metallized base, and on the second side are strip conductors of three electromagnetically coupled microstrip resonators, characterized in that the series-connected narrow and wide rectangular strip conductors, grounded to the base from the free end of the input or output strip conductor, three times folded in the form of an irregular meander. 2. The filter according to claim 1, characterized in that the strip conductors are folded p times in the form of an irregular meander, where p = 5, 7, 9, .... 3. The filter according to claim 1, characterized in that it contains n electromagnetically coupled resonators, where n = 4, 5, 6, ....

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