RU218773U1 - MINIATURE STRIP-BAND FILTER - Google Patents

Abstract

The utility model relates to microwave technology and is intended for frequency selection of signals. A miniature strip band pass filter contains a dielectric substrate suspended between the screens, on both surfaces of which there are strip metal conductors of the resonators. Each resonator in the inventive filter is formed by two U-shaped metal strip conductors located on different sides of the dielectric substrate, in which one end is closed to the screen, and the other is free. The stripline resonators in the filter are connected in pairs by sections of overlapping stripline conductors, i.e. resonators have a total area occupied by them on a dielectric substrate. The technical result of the utility model is to reduce the size of the bandpass filter and increase its selectivity. 3 ill.

Description

The utility model relates to microwave technology and is intended for frequency selection of signals.

A known design of the bandpass filter [RF Patent No. 2237320, IPC 7 H01R 1/203, publ. 27.09.2004, Bull. No. 27]. The filter contains a suspended dielectric substrate, on one side of which strip conductors short-circuited to the screen from one end of the substrate are applied, and on the second side of the substrate, instead of a grounded base, strip conductors short-circuited to the screen from the other end of the substrate are also applied. A filter of this design has a significantly shorter length of strip conductors compared to microstrip ones, and, hence, smaller substrate sizes. This makes it possible to design bandpass filters for lower frequencies. The disadvantage of the filter design is the large size at frequencies of the meter wavelength range (<300 MHz), as well as the fact that on its amplitude-frequency characteristic (AFC) attenuation poles are either absent or are far relative to the passband, so the steepness of the slopes of the passband of the device (selectivity) is relatively low.

The closest analogue in terms of the set of essential features is the design of a band pass filter [Leksikov A.A., Serzhantov A.M., Govorun I.V., Afonin A.O., Ugryumov A.V., Leksikov An.A. Miniaturized Suspended-Substrate Two-Conductors Resonator and a Filter on Its Base // Progress In Electromagnetics Research M, 2019, Vol. 84, P. 127-135. (Prototype)]. The filter consists of two-wire resonators made on a dielectric substrate suspended in a metal case at equal distances between the upper and lower screens. Each resonator in the filter is formed by two U-shaped metal strip conductors located on different sides of the dielectric substrate, in which one end is closed to the screen, and the other is free. The filter has a smaller size compared to the first analogue due to the folding of the strip conductors into a U-shape. However, despite the high miniaturization of the resonator design used in the filter, the problem of reducing the size of multi-section filters consisting of a large number of such resonators remains unresolved, especially in the meter wavelength range (<300 MHz). In addition, on the frequency response of such filters there are no attenuation poles close to the passband, which leads to low selective properties.

The technical result of the proposed device is to reduce the size of the band pass filter and increase its selectivity.

This technical result is achieved by the fact that in a strip band pass filter containing a dielectric substrate suspended in a metal case with strip resonators formed by two U-shaped metal strip conductors located on different sides of the dielectric substrate, in which one end is closed to the screen, and the other is free, what is new is that the stripline resonators are connected in pairs by sections of overlapping stripline conductors.

The essence of the device is explained using the following graphic materials.

In FIG. 1a shows the topology of the strip conductors of the proposed filter design, and Fig. 1b the topology of the strip conductors of the prototype filter;

in fig. 2 shows the calculated frequency dependences of the transmission coefficient S ₂₁ and the reflection coefficient S ₁₁ of the second-order filters of the claimed design and the prototype filter design;

in fig. 3a shows the topology of the conductors of the band pass filter of the proposed design of four resonators;

in fig. 3b, its calculated frequency dependences of the transmission coefficient S ₂₁ and the reflection coefficient S ₁₁ .

The inventive device (Fig. 1a) contains a dielectric substrate suspended between the screens, on both surfaces of which there are strip metal conductors of the resonators. Each resonator in the inventive filter is formed by two U-shaped metal strip conductors located on different sides of the dielectric substrate, in which one end is closed to the screen, and the other is free. In FIG. 1a shows two such resonators located next to each other, while the metal walls of the housing and the substrate are not shown so as not to clutter up the figure. In this design of the resonator, U-shaped strip conductors located on different surfaces of the substrate are rotated 180° relative to each other so that their ends closed to the screen are at opposite ends of the substrate. External transmission lines with wave impedance Z=50 Ohm are connected to the outer strip conductors. The fundamental difference between the proposed filter design (Fig. 1a) and the prototype filter design (Fig. 1b) is that the resonators have regions with mutual overlap of the strip conductors, i.e. adjacent resonators have a common area occupied by them on the dielectric substrate.

The filter works as follows.

The input and output transmission lines are connected to the conductors of the resonators as shown in Fig. 1a. The distance from the grounded ends of the strip conductors of the resonators to the connection points of the external transmission lines is determined by the given level of reflections in the filter passband. Signals whose frequencies fall within the passband pass to the filter output with minimal loss, while signals outside the passband are reflected from the input of the device.

The claimed technical result is achieved as follows.

Due to the fact that the resonators of the proposed design created areas with mutual overlap of the strip conductors, i.e. adjacent resonators have a total area occupied by them on the n dielectric substrate, then, accordingly, the size of the entire device decreases. In addition, due to the mutual overlap of the strip conductors of the two resonators in the inventive filter design, additional cross-links are created, and hence additional passage channels. As a result of the interference of electromagnetic waves passing through different channels, their antiphase addition occurs at certain frequencies, leading to the formation of several zeros of the transmission coefficients (attenuation poles) on the amplitude-frequency characteristic (AFC) of the filter. The presence of these poles significantly increases the steepness of the slopes of the frequency response and increases the level of suppression in the stop band of the filter, i.e. improves device selectivity.

In confirmation of the claimed technical result in Fig. 2 shows the corresponding frequency dependences of the transmission coefficient S ₂₁ (f) and the reflection coefficient S ₁₁ (f) of two variants of the second-order bandpass filter, obtained by electrodynamic analysis of 3D models. In the first case, the resonators are located as in the claimed filter (Fig. 1a), and in the second case, as in the prototype filter (Fig. 1b). The filters have identical design parameters and differ only in the mutual arrangement of the resonators. The center frequency of the passband of both filters f ₀ =150 MHz, its relative width Δf/f ₀ =10%. The maximum level of reflections in the passband of both filters was the same S ₁₁ =-20 dB. The dependencies are calculated for the following design parameters of the filters. The relative permittivity of the substrate ε _r =80, its thickness is 0.25 mm; the size of the air gaps between the surfaces of the dielectric substrate and the planes of the metal housing is 4 mm; the internal dimensions of the U-shaped conductors W=16.0 mm and w=4.2 mm, and the copper segments of the strip lines 18 μm thick forming them had a width of 1 mm. The distance between the extreme strip conductors of the resonators in the filters (see Fig. 1) was S=0.1 mm. The topology area of the conductors of the inventive filter is 9.9×20 mm ² , and the prototype filter is 12.1×20 mm ² , i.e. the claimed design is 1.2 times smaller in size.

Of those presented in Fig. 2b dependencies it can be seen that, other things being equal, the selectivity of the filter of the proposed design is greater, since several zeros of the transmission coefficient are located near the passband. These zeros increase the steepness of the frequency response slopes and increase the attenuation in the high-frequency stopband, which confirms the claimed technical result.

It is known that one of the most effective ways to increase selectivity is to increase the number of resonators in the filters. In FIG. 3a shows the topology of the conductors of the four-resonator bandpass filter of the proposed design, and Fig. 3b, its calculated frequency dependences of the transmission coefficient S ₂₁ (f) and the reflection coefficient S ₁₁ (f), obtained by electrodynamic analysis of the 3D model. The dielectric substrate is made of TBNS material 0.25 mm thick (ε _r =80, tgδ≈0.0005). The size of the air gaps between the surfaces of the dielectric substrate and the planes of the metal housing is 4 mm. The internal dimensions of the U-shaped conductors (see Fig. 1) were W=16 mm and w=4.2 mm, and the copper segments of the strip lines 18 µm thick forming them had a width of 1 mm. The distance between the pairs of resonators in the filter was: S ₁₂ =S ₃₄ =1.1 mm, S ₂₃ =3.2 mm (subscripts show the serial numbers of the resonators). External transmission lines with a characteristic impedance Z=50 Ω were connected to the U-shaped strip conductors of the external resonators, and the distance from the connection point to the connection point of the conductors with the screen determines the level of reflections in the passband of the device. The relative bandwidth of the filter, measured at the level of -3 dB from the level of minimum loss, is Δf/f ₀ =25%, and its center frequency f ₀ =150 MHz. The measured value of the minimum insertion loss in the passband is L _min ≈1 dB.

From the presented dependences it can be seen that the proposed filter design has a high slope steepness and a symmetrical shape of the frequency response relative to the center of the passband. The dimensions of the stripe structure of the proposed filter design are 25.8×20 mm ² , while for the prototype filter the dimensions are 32.2×20 mm ² , i.e. the length of the prototype filter is 25% longer, other things being equal.

Thus, the proposed design of the strip band pass filter makes it possible to implement on its basis miniature and highly selective devices for frequency selection of signals.

Claims (1)

Strip band pass filter containing a dielectric substrate suspended in a metal case with strip resonators formed by two U-shaped metal strip conductors located on different sides of the dielectric substrate, one end of which is closed to the screen, and the other is free, characterized in that stripline resonators are connected in pairs by sections of overlapping stripline conductors.

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