RU2644976C1 - Microstrip broadband filter - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: microstrip broadband filter contains a dielectric substrate with a grounded base on one side and strip conductors electrically connected to each other on the second side. Narrow and wide rectangular strip conductors are connected to each other in the form of irregular meander, its extreme narrow conductors at the loose ends are base-grounded, with input and output ports are connected conductively to the extreme wide meander conductors through the lengths of microstrip lines with a wave impedance jump.

EFFECT: expansion of the stop band, increase in the steepness of the low-frequency slope of the frequency characteristic, expansion of the working bandwidth.

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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 band-pass filter (RF Patent No. 2480867, H01P 1/203), containing a dielectric substrate, on one side of which is grounded metalized base, and on the second side is a strip conductor, partially split by a longitudinal gap at one end. The relative length of the unsplit section of the two-mode resonator is from 16% to 65% of its length. The band-pass filter, consisting of one two-mode hairpin microstrip resonator, operates as follows. It has two low-frequency oscillation modes, one of which is even and the other is odd. For an even mode of oscillation, the currents in the split section of the conductor on both sides of the gap flow in the same direction and continue to flow in the un split section. For the odd mode, the currents in the split region flow in opposite directions and are absent in the und split region.

The disadvantage of the described band-pass filter is the use of a small number of (two) vibration modes of the resonator, which is a partially split strip conductor on a dielectric substrate, which limits the possibility of improving its frequency-selective properties, as well as their deterioration when implementing a wide relative passband.

The closest in the set of essential features is a microstrip broadband bandpass filter (RF Patent No. 2504870, Н01Р 1/203) containing a dielectric substrate, on which one side is grounded the base, and on the other side, straight-line strip conductors of resonators are applied, and additional strip conductors, the sides of which are connected to adjacent resonators, and the conductors of the external resonators are short-circuited at one end, and additional e strip conductors are open. The filter works as follows. The input and output transmission lines are connected to the conductors, and the distance from the grounded ends of the conductors to the connection points of the external transmission lines is determined by the specified level of reflections in the filter passband. Signals whose frequencies fall into the passband pass to the filter output with minimal losses, while at frequencies outside the passband, signals from the input of the device are reflected.

The disadvantages of the prototype include a not too wide operating bandwidth and low frequency-selective filter properties due to the low slope of the low-frequency slope of the pass-band and a relatively narrow high-frequency obstacle.

The objective of the invention is to expand the working bandwidth and improve the frequency-selective properties of the microstrip broadband bandpass filter.

This problem is solved due to the fact that in a microstrip wide-band filter containing a dielectric substrate, on one side of which a grounded base is applied, and on the second side are strip conductors electromagnetically connected to each other, according to the invention, narrow and wide rectangular strip conductors are connected to each other in in the form of an irregular meander, its extreme narrow conductors from the side of the free ends are grounded to the base, the input and output ports of the filter are connected conductively to ynim wide conductors meander through the segments of microstrip line with a jump in the wave resistance.

The technical result of the invention is the expansion of the operating frequency band and the improvement of the frequency-selective properties of the filter due to the claimed arrangement of strip conductors on a dielectric substrate.

The invention is illustrated by drawings: FIG. 1 - device of the inventive microstrip broadband filter; FIG. 2 - measured amplitude-frequency characteristics (S ₂₁ , S ₁₁ ) of the manufactured filter.

The inventive microstrip broadband filter (Fig. 1) contains a dielectric substrate 7, on one side of which a grounded base is applied, and on the second side are strip conductors 2-12 having axial symmetry, connected to each other, and also interconnected electromagnetically. Strip conductors are segments of microstrip lines. Rectangular narrow 2, 4, 6, 8 and wide 3, 5, 7 strip conductors have the form of an "irregular meander", its extreme narrow conductors 2 from the free ends are grounded to the base. The input and output ports of the filter are conductively connected to the extreme wide conductors of the 3 meanders through four consecutive rectangular conductors 9-12, the conductors 9, 11, 12 being narrow and the conductors 10 being wide, due to this a jump in the wave resistance of the microstrip line segments occurs.

The principle of operation of a microstrip broadband filter is as follows. An irregular meander is a connected alternating narrow and wide strip conductors of various lengths and widths located on a dielectric substrate, which allows for a large jump in wave impedances of segments of transmission lines. Since the extreme narrow conductors of the 2 meander are grounded to the base, it is a quarter-wave resonator, which, due to the folding of the conductor and its topology, has the five lowest vibration modes, the resonant frequencies of which participate in the formation of the working passband. Moreover, a significant expansion of the passband is achieved due to the “repulsion” of the resonances of these vibration modes due to the strong interaction. If necessary, the number of such resonances is easy to increase or decrease, increasing or decreasing the number of meander periods, respectively. For example, when using a meander consisting of strip conductors 2-5, only three resonances are transmitted from it to the passband frequencies.

Additionally, the resonance bandwidth of the device is formed by two resonances from rectangular conductors 9-12, which also facilitate matching of a broadband filter, conductively connected to the 50 Ω input and output ports. When implementing a filter on substrates with a low dielectric constant, the extreme wide conductor 3 of the meander is conductively connected to the ports.

As a result of the design features of the used strip conductors, the filter’s working bandwidth is significantly expanded, which is formed by seven resonances (Fig. 2), also on the amplitude-frequency characteristic there is an increase in the steepness of the low-frequency slope of the passband and the expansion of the high-frequency obstacle band.

Significant amplification of power suppression at the frequencies of the high-frequency obstacle band is facilitated by several attenuation poles of microwave power located adjacent to each other on the amplitude-frequency characteristic (Fig. 2), a pair of which arises due to the strong coupling between the line segments 10 and 7. The origin of the power attenuation poles is connected so that at these frequencies the capacitive and inductive coupling of line segments mutually cancel each other out. The expansion of the high-frequency obstacle band is due to the large jump in wave impedances of the transmission line segments.

Execution example

The filter was made on a substrate of traditional microwave technology material (TBNS ceramics) with a thickness of 1 mm with a dielectric constant of ε = 80. The length and width of the strip conductors of the filter in mm: (2) - 5.8 × 0.6; (3) - 15.7 × 2.6; (4) - 1.9 × 0.1; (5) - 8.8 × 3.8; (6) - 14.1 × 0.1; (7) - 2.5 × 2.0; (8) - 2.5 × 0.1; (9) - 6.8 × 0.1; (10) - 4.3 × 1.6; (11) - 9.5 × 0.2; (12) - 5.6 × 0.1. The gap between 3 and 11 conductors is 1.2 mm. The substrate area, taking into account the indentation of 1 mm from its three edges to the conductors, was 31.3 × 23.9 mm ² .

The amplitude-frequency characteristics of the forward and reverse losses (transmission losses S ₂₁ and reflection S ₁₁ ) of the inventive microstrip broadband filter, taken in a wide frequency band, are shown in FIG. 2. The filter has a relative passband width Δƒ / ƒ ₀ ≈95%, measured at a level of -3 dB of the level of minimum losses, which amounted to L _min ≈0.8 dB at the center frequency of the passband ƒ ₀ ≈0.45 GHz. The advantages of such a broadband filter are the four poles of power attenuation observed on the amplitude-frequency characteristic, one of which is located next to the high-frequency slope of the working passband and contributes to the growth of the slope of this slope. In addition, all attenuation poles significantly enhance the suppression of microwave power at the frequencies of the high-frequency filter obstacle, and thereby improve its frequency-selective properties.

Thus, the inventive device with improved frequency-selective properties has a wider working bandwidth with a steep low-frequency slope, as well as an expanded high-frequency barrier band.

Claims (1)

A microstrip wide-band filter containing a dielectric substrate, on one side of which a grounded base is applied, and on the other side are strip conductors electromagnetically coupled to each other, characterized in that the narrow and wide rectangular strip conductors are connected to each other in the form of an irregular meander, its extreme narrow conductors from the side of the free ends are grounded to the base, and the input and output ports of the filter are conductively connected to the extreme wide conductors of the meander through cutt ing microstrip lines with a shock wave resistance.

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