Strip-line filter with wide stop band

FIELD: electricity.

SUBSTANCE: strip-line filter with wide stop band containing a dielectric plate suspended between screens with strip resonator conductors applied at the edge of one of its surfaces with short-circuited neighbouring ends is distinguished by the fact that inside the dielectric plate there are additional strip conductors short-circuited by one end at the opposite edge of the dielectric plate.

EFFECT: increasing length of filter stop band and level of attenuation in it.

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The invention relates to techniques for ultra-high frequencies, and is intended for frequency selection signals, for example, transceiver systems.

Known stripline band pass filter for suspended between screens dielectric substrate [A.R. Brown, G.M. Rebeiz. A varactor-tuned RF filter // IEEE Trans on MTT. - 2000. - Vol.48, No. 7. - p.1157-1160]. The filter is formed by resonators, each of which represents a short-circuited on the screen from one end of the strip conductor. All conductors of the resonators are placed on one surface of the substrate. The disadvantages of this design of the filter are relatively large dimensions in the meter wavelength range and a narrow band boom.

Also known for the design of band pass filter [RF Patent №2237320, MPK7 H01P 1/203, publ. 27.09.2004, bull. No. 27], which contains suspended dielectric substrate (dielectric plate)on one side which caused short-circuited on the screen at one end of the substrate strip conductors, and on the second side of the substrate instead of the grounded base also caused short-circuited to the screen, but from the other side of the substrate, the strip conductors. A filter of this design is significantly smaller compared with the first analogue. The length of the stopband this filter significantly more, but she okazyvaetsya some cases insufficient.

The closest to the essential features analog is strip band-pass filter [RF Patent №2390889, MPK7 H01P 1/203, publ. 27.05.2010, bull. No. 15 (prototype)]. The device contains suspended between the dielectric plate, both surfaces of which caused short-circuited with one end of the strip conductors, the conductors are short-circuited on the screen at one edge of the substrate. Such a filter has smaller dimensions compared with the first and second analog, but the length of the stopband it significantly less compared to them.

The technical result of the invention is to increase the length of the stopband and the level of damping in it.

This technical result is achieved in that in the filter strip containing suspended between the dielectric plate, both surfaces of which are deposited cage adjacent ends of one edge of the strip conductors of the resonators, the new is what's on the inside of the dielectric plate are additional strip conductors short-circuited at one end with the opposite edges of the dielectric plate.

The differences between the claimed device from the closest analogue is that each resonator filter is formed of three metal is a mini-use strip conductors, separated by a dielectric material plate. While the outer conductors of each resonator adjacent ends short-circuited with one edge of the plate, and the inner conductor with the opposite edge of the plate. These differences allow to draw a conclusion on the conformity of the proposed technical solution the criterion of "novelty". The features distinguishing the claimed technical solution to the prototype, not identified in other technical solutions in the study of this and related areas of technology and, therefore, provide the claimed solution according to the criterion of "inventive step".

The invention is illustrated by drawings: Figa, b - specic design of the proposed filter strip on a suspended dielectric plate, Figure 2 - calculation of the amplitude-frequency characteristics (AFC) of the proposed filter (solid line) and second analog (dashed), 3 - the signs of the potentials and direction of the currents in the conductors of the resonator filter at the frequencies of the first, second and third vibration modes; Figure 4 - calculated response chetyrehetapnogo filter of the claimed design on the plate thickness of 1 mm with connection Figb; Figure 5 - measured amplitude-frequency response losses on passage made layout four-stage band-pass filter time savsevieria; 6 is a calculated frequency response of the filter of the claimed design for the case of thin (10 µm) dielectric layers separating the conductors of the resonators.

The inventive device (Figa) contains a dielectric plate 7, is suspended between the two screens (not shown)on both surfaces of which inside of it is made metal strip conductors of the resonators. Each resonator consists of three use strip conductors 2, 3 and 4, separated from each other by a dielectric material plate, and the outer conductors of the resonators adjacent ends connected to the screen from one edge of the plate, and the inner conductors with opposite edges of the plate. The input and output transmission line connected to the strip conductors extreme resonators of the filter. Figure 3 shows a section of the structure along the strip conductors of the resonator filter of the claimed design.

As you know, the filters based on stripline and microstrip resonators on population characteristics such as small size, manufacturability and cost are some of the best. At the same time one of the major drawbacks of such filters is a relatively narrow band boom, which at best can be up to two octaves. However, for modern wireless communication often requires more protagen the I band boom at a high level of attenuation in it.

The inventive design of the band pass filter allows you to implement a device with a larger width of the stopband (over two octaves) and a significant level of attenuation (over 100 dB) only four resonators. This filters the claimed design are significantly smaller compared to the prototype when other conditions are equal.

Figure 2 shows the calculated frequency response chetyrehetapnogo filter (Figa) of the claimed design (solid line) and chetyrehetapnogo filter (dashed line) of the second equivalent (having the longest streak of boom from all the analogues used). Both filters have a center frequency bandwidth f₀=900 MHz and a relative bandwidth -3 dB ∆ F/f₀=5%. With all the design parameters, with the exception of the length of the wires were the same for both filters. The dielectric constant of the substrate (dielectric plate) ε=9.8, the thickness of the substrate (wafer) 1 mm, the distance from the surface of the substrate (wafer) to screens 4 mm and the width of the strip conductors 3 mm Distance between a pair of internal cavities in the filters was S₁=8 mm, and between the inner and outer S₂=7.25 mm, the Length of each of the conductors in the pair of internal cavities in the proposed filter would be the and 7.8 mm, and the external - 8.1 mm For filter prototype, the lengths were equal to 14.25 14.75 mm and mm, respectively. The total area of the substrate of the filter prototype was 18.5×42.5 mm²and the area of the dielectric plate of the inventive filter 10×42.5 mm²that is almost two times less.

An important advantage of the proposed design is the presence of extended stopband extending to frequencies ~6f₀when the level of damping in it no worse than 60 dB, which provides improved selective properties compared with the traditional use strip and microstrip filters.

The filter works in the following way. The input and output transmission lines are connected to the outer conductors of the external resonators (Figa). The distance from the grounded ends of the conductors to the connection point of the external transmission lines is determined by the level of reflections in the filter bandwidth. Signals of frequencies which fall within the bandwidth are part of the output filter with minimal losses, while at frequencies outside the pass band is reflected signals from the input device.

The claimed technical result is achieved in the following way. As is known, the parasitic bandwidth in traditional designs stripline and microstrip filters are formed resonances of higher modes of oscillation. Figure 3 of brainy signs of the potentials at the open ends of the conductors of the resonator in the present filter, as well as the direction of high-frequency currents to the first (working, Figa), and the second and third (parasitic, Figb,) oscillation modes. It is seen that the frequencies of the first oscillation modes of the high-frequency currents have the same direction in the conductors. This leads to an increase of the equivalent inductance of the resonator, the lower its resonant frequency and increase the quality factor at the frequencies of the working bandwidth of the filter. At the frequencies of the second and third modes of oscillation of high frequency currents are directed oppositely, so the equivalent inductance of the resonator and, therefore, its quality become significantly less. This leads to an increase of the attenuation at the frequencies of higher modes of oscillation and expansion of the stopband.

Significantly improve the parameters of the stopband can, if you connect the input and the output transmission line to the inner conductors of extreme resonators in the filter (Figb). As the frequency of the second (spurious) modes of vibration the potential of the inner conductor is equal to zero, then the connection of the resonators of the filter with an external transmission lines will be practically absent on its frequency, and the corresponding parasitic resonances will not appear on the frequency response of the filter. 4 shows the calculated frequency response chetyrehetapnogo filter of the claimed design connected Figb the same to instructiuni parameters that were described above for Fig.la. It shows that the connection of the external transmission lines to the inner conductors of extreme resonators in the filter allows you to form a band boom that extends up to frequencies of ~6f₀when the level of attenuation of not less than 100 dB, which provided a significant improvement in its selective properties. Figure 5 presents the measured frequency response is made chetyrehetapnogo filter design parameters specified above, by connecting the external lines to internal conductors extreme resonators. It is seen that the frequency response is made layout has a length stopband ~7f₀when the level of attenuation of not less than 100 dB, which confirms the claimed technical result.

Much better performance of the proposed filter can be achieved by using to create integrated technology. It becomes possible to realize a thin dielectric layer thickness of tens of microns (for example, of silicon monoxide SiO)separating the metal strip conductors of the resonators of the filter. With all the strip structure of the filter to ensure the mechanical strength can be on fairly thick (mm fraction) of the carrier dielectric substrate. In this case, in addition to even greater stopband also reduces the dimensions of the filter, which increases the quality of its resonators. Figure 6 shows the calculated frequency response of such chetyrehetapnogo filter center frequency bandwidth f₀=350 MHz with a relative bandwidth -3 dB ∆ F/f₀=5%. The design parameters of the filter were the following. The thickness of the dielectric substrate on which is located the strip structure of the filter, 0.5 mm, dielectric constant of the material of the carrier layer and substrate between the conductors of the resonator ε=3.7, the thickness of the layers is 10 μm, the distance from the surface of the structure to 2 mm and the width of the strip conductors 1 mm Distance between a pair of internal cavities in the filters was S₁=3.5 mm, and between the inner and outer S₂=3.25 mm, the length of the inner conductors of the resonators in the filter was 8 mm, the outer 8.2 mm. Internal dimensions of the filter housing was 10×19×4 mm³. It is seen that, despite the lower operating frequency, the filter size is significantly decreased, and the length of the stopband level -100 dB increased to ~40f₀.

Also, such a filter can be made in the amount of solid dielectric in thick-film technology of manufacturing integrated circuits (Low temperature cofired ceramic (LTCC) technology.

Thus, the proposed design of the stripline band pass filter allows you to implement on the basis of the miniature is trojstva with extended high-frequency band boom and a high level of damping in it.

Strip filter with a broad band boom containing suspended between the dielectric plate, both surfaces of which are deposited cage adjacent ends of one edge of the strip conductors of the resonators, characterized in that the inside of the dielectric plate are additional strip conductors short-circuited at one end with the opposite edges of the dielectric plate.