Thin film filter

Abstract

The utility model discloses a thin film filter, which adopts a substrate with a larger dielectric constant so as to reduce the length of a resonator in the filter. A thinner substrate is adopted, so that the diameter of the metalized through hole is reduced; a stepped impedance resonator is adopted to replace a traditional resonator, and a wider stop band is achieved by adjusting the impedance ratio and the electrical length of the stepped impedance resonator; a microstrip line is arranged between the two stepped impedance resonators, so that the bandwidth and in-band fluctuation of the filter are reduced, and the stop-band attenuation is increased; the input tap and the output tap are fixed in the middle of the substrate, so that the layout of other components is facilitated, further miniaturization of the filter is realized, the coupling strength of the filter can be obviously reduced, and a narrow-band filter under high frequency is realized.

Description

TECHNICAL FIELD

[0001] The utility model relates to filter technical field especially relates to a film filter. BACKGROUND

[0002] With the development of phased array radar, multi-channel receiving technology is widely used, and in each receiving channel, the film filter before down conversion has the advantages of compact structure, unique frequency selection characteristics, etc. The structure of the film filter includes parallel coupling structure, interdigital structure, etc. The interdigital structure film filter is more compact and solid, and the roll-off range is relatively narrow, there is no parasitic response between the first and second passbands, and is widely used in the fields of electronics and communication.

[0003] At present, the filter uses a medium substrate with a small dielectric constant, which causes the length of the microstrip resonator to be relatively long. In the radio frequency channel, the width of the commonly used soft substrate is 1.9mm, and the metal film on the soft substrate is 0.37mm. The long length of the interdigital filter resonator causes the width of the filter substrate to be relatively wide, which is not conducive to the space utilization in the channel and the placement of other devices. Due to the influence of bandwidth and in-band fluctuation, the existing interdigital filter often uses a thickness of 0.508mm. However, the thickness of the microstrip line in the radio frequency channel is usually 0.127mm, and the height difference between the two is 0.381mm, which causes the input and output matching of the filter to decrease during the gold wire bonding process, thereby causing the performance of the filter to decrease. In addition, one end of the interdigital filter needs to be made into a metalized via. Due to the influence of the processing technology, the diameter of the metalized via is usually 0.8 times the diameter of the medium substrate. The edge distance of the interdigital filter resonator from the metalized via is relatively short, which causes the width of the interdigital filter resonator to be relatively wide, making it difficult to realize the miniaturization of the filter. In addition, the tap position of the filter with different bandwidths, different frequencies and different orders is affected by the group delay, and sometimes it is not in the middle of the substrate. During the filter echo optimization process, the tap needs to be shifted up and down. If the tap is not in the middle of the substrate, it will cause the layout of the microstrip line to need to be shifted, which will cause the layout space to be insufficient and make it difficult to place other components. It is difficult to realize the further miniaturization of the filter. UTILITY MODEL CONTENTS

[0004] The utility model discloses a film filter which is designed to solve the above problems.

[0005] The utility model discloses a film filter which is designed to solve the above problems.

[0006] The film filter comprises:

[0007] The dielectric constant of the substrate is greater than 2.2, and the thickness of the substrate is less than 0.508mm.

[0008] Two step impedance resonators, a microstrip line is arranged between the two step impedance resonators;

[0009] A tap structure includes an input tap and an output tap, and the input tap and the output tap are fixed in the middle of the substrate.

[0010] The thin film filter has the advantages that:

[0011] The thin film filter adopts a substrate with a larger dielectric constant to reduce the length of the resonator in the filter, adopts a substrate with a smaller thickness to reduce the diameter of the metallized via, and adopts a step impedance resonator to replace the traditional resonator, so that a wider stop band is realized by adjusting the impedance ratio and the electrical length of the step impedance resonator; a microstrip line is arranged between the two step impedance resonators, so that the bandwidth and the in-band fluctuation of the filter are reduced, and the stop band attenuation is increased; the input tap and the output tap are fixed in the middle of the substrate, so that the layout of other components is facilitated, the filter is further miniaturized, the coupling strength is obviously reduced, and a narrow-band filter at a high frequency is realized. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 It is an overall structural diagram of the thin film filter of the utility model;

[0013] Figure 2 It is a structural schematic diagram of the thin film filter of the utility model;

[0014] Figure 3 It is a high-frequency filter response curve simulation diagram of the thin film filter of the utility model;

[0015] Figure 4 It is another high-frequency filter response curve simulation diagram of the thin film filter of the utility model. DETAILED DESCRIPTION

[0016] To make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the technical scheme in the embodiments of the utility model will be described clearly and completely in combination with the drawings in the embodiments of the utility model below. Obviously, the described embodiments are part of the embodiments of the utility model, rather than all the embodiments. The components of the embodiments of the utility model described and shown in the drawings can be arranged and designed in various different configurations.

[0017] Therefore, the following detailed description of the embodiments of the utility model provided in the drawings is not intended to limit the scope of the claimed utility model, but only represents selected embodiments of the utility model. Based on the embodiments in the utility model, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the utility model.

[0018] It should be noted that like numerals and letters refer to like items throughout the several views, and once an item is defined in one view, it should not require further defining and explaining in subsequent views.

[0019] In the description of the utility model, it needs to be understood that the orientation or position relationship indicated by the terms "upper", "lower", "inner", "outer", "left", "right" and the like is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship commonly placed when the utility model product is used, or is the orientation or position relationship commonly understood by the person skilled in the art, and is only for the convenience of describing the utility model and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the utility model.

[0020] In addition, the terms "first", "second" and the like are only used for distinguishing description, and cannot be understood as indicating or implying relative importance.

[0021] In the description of the utility model, it also needs to be explained that, unless otherwise explicitly specified and limited, the terms "arrange", "connect" and the like should be understood in a broad sense, for example, "connect" can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, or can be electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or can be the communication inside two elements. For the person skilled in the art, the specific meaning of the above terms in the utility model can be understood according to the specific circumstances.

[0022] The specific embodiments of the utility model will be described in detail below with reference to the drawings.

[0023] As shown in the drawings, the thin film filter comprises: Figures 1-4 The substrate has a dielectric constant greater than 2.2 and a thickness less than 0.508 mm;

[0024] Two stepped impedance resonators, a microstrip line is arranged between the two stepped impedance resonators;

[0025]

[0026] A tap structure comprising an input tap and an output tap, the input tap and the output tap are fixed in the substrate.

[0027] In an embodiment, the microstrip line is an L-shaped microstrip line.

[0028] In an embodiment, the thin film filter further comprises a wire extension.

[0029] In an embodiment, the substrate further comprises a defective ground structure.​

[0030] In the embodiment, in order to solve the problem of long resonator length in the filter, the dielectric substrate is implemented by a substrate with a larger dielectric constant, so as to reduce the resonator length of the filter; the substrate is implemented by a substrate with a smaller thickness, so as to reduce the diameter of the metalized via, and the reduction of the substrate thickness is conducive to reducing the height difference between the microstrip line in the radio frequency channel and the filter, facilitating the matching of the filter input and output in the process of gold wire bonding; thus, the thickness and the dielectric constant of the filter and the substrate are related to each other, that is, the thin substrate thickness can reduce the volume of the filter, and the large dielectric constant can reduce the size of the filter circuit. The change of the microstrip line dielectric substrate can significantly reduce the length and width of the resonator in the filter, and facilitate the miniaturization of the filter, but can cause the spacing between the resonators in the filter to be too small or too large in the case of a relatively wide or narrow relative bandwidth, and cannot meet the minimum precision requirement in processing. In addition, the increase of the dielectric constant of the substrate and the reduction of the thickness of the substrate can cause the deterioration of the in-band flatness of the filter, thus, the structure and position of the interdigital filter resonator need to be adjusted to meet the processing requirements, so as to optimize the in-band flatness.

[0031] The conventional thin film filter can cause the deterioration of the high end insertion loss in the passband at high frequency, so that the in-band flatness cannot meet the index requirement, and the embodiment can effectively improve this defect by a specific tap structure and an external matching structure, that is, the coupling strength can be obviously reduced by expanding and optimizing the structure of the center resonant unit, so that the narrowband filter at high frequency can be realized. In the embodiment, the tap structure is fixed at the center of the substrate by fixing the input tap and the output tap, and cooperates with the L-shaped microstrip line structure to optimize the time delay of the filter, although the length of the filter is increased a little, but it is more conducive to the optimization of the return loss of the filter, and can ensure that the input tap and the output tap of the filter are in the middle of the substrate, so as to facilitate the layout of the microstrip line and the remaining components in the micro-assembly, and further realize the miniaturization of the filter.

[0032] In the embodiment, the stepped impedance resonator is used to replace the conventional resonator, a wider stopband design is realized by adjusting the impedance ratio and the electrical length ratio of the stepped impedance resonator; in addition, a microstrip line is added between the two resonators in the middle of the filter, so that the bandwidth and the in-band fluctuation of the filter are smaller, and the stopband attenuation is increased; a delay line and a defect ground structure using the stepped impedance resonator are added to optimize the structure of the filter; the resonant unit structure is adjusted to weaken the coupling, so as to realize the narrowband filter at high frequency; the coupling strength of the center resonant unit structure can be obviously reduced by expanding and optimizing the structure, so as to realize the narrowband filter at high frequency, the improved filter has the characteristics of wide stopband, and the passband bandwidth is increased; the resonators of the filter are displaced, and the resonator coupling interval is optimized to optimize the bandwidth and the in-band fluctuation of the filter.

[0033] In the embodiment, the thin film filter adopts a substrate with a larger dielectric constant to reduce the length of resonators in the filter, adopts a substrate with a smaller thickness to reduce the diameter of the metalized via, and adopts a stepped impedance resonator to replace a conventional resonator to achieve a wider stop band by adjusting the impedance ratio and electrical length of the stepped impedance resonator, and a microstrip line is arranged between two stepped impedance resonators to reduce the bandwidth and in-band fluctuation of the filter and increase the stop band attenuation, the input and output taps are fixed in the middle of the substrate to facilitate the layout of other components, thereby achieving further miniaturization of the filter and significantly reducing the coupling strength, thereby achieving a narrow-band filter at a high frequency.

[0034] The thin film filter in the utility model is miniaturized while ensuring that the performance of the filter meets the use requirements, such as flatness, bandwidth, insertion loss, and out-of-band suppression, and in addition, the tap position of the filter is ensured to be in the middle of the substrate, the utility model is mainly optimized from four aspects of substrate material, substrate thickness, filter structure, and tap structure, and finally the purpose of miniaturization of the interdigital filter is achieved.

[0035] The above is only the preferred embodiment of the utility model, and it should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the technical principles of the utility model, and these improvements and refinements should also be considered as the protection range of the utility model.

Claims

1. A thin film filter, characterized by, The thin film filter comprises: a substrate, a dielectric constant of the substrate being greater than 2.2, a thickness of the substrate being less than 0.508 mm; two stepped impedance resonators, a microstrip line being arranged between the two stepped impedance resonators; a tap structure, the tap structure comprising an input tap and an output tap, the input tap and the output tap being fixed in the substrate.

2. The thin film filter according to claim 1, wherein The microstrip line is an L-shaped microstrip line.

3. The thin film filter of claim 1, wherein The thin film filter further comprises an extension line.

4. The thin film filter of claim 1, wherein The substrate further comprises a defective ground structure.

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