CN203826525U - Low-pass filter - Google Patents

Abstract

The utility model provides a low-pass filter, comprising: adopting a ladder impedance hairpin structure, including a coupled microstrip line, a high impedance line, a microstrip line end and an open branch; wherein, the high impedance line has two ends Connect the coupled microstrip line, and have at least two bends between the two ends; the microstrip line end, formed on the end face of the high-impedance line connected to the coupled microstrip line; open-circuit branch, two open-circuit branches with different transmission zero points , formed on the end face of the high-impedance line connecting the coupled microstrip line. The miniaturization and compactness of the device are further improved, and the two open-circuit branches increase the width of the stop band suppression, and it is easy to integrate with other microwave circuits, and the structure is simple and easy to process.

Description

a low pass filter

technical field

The utility model relates to the field of semiconductor devices and filters, in particular to a low-pass filter.

Background technique

In the field of wireless communication, filter is a key passive device. With the continuous development of wireless technology, higher requirements are put forward for filter devices in terms of performance and size.

The ladder impedance hairpin low-pass filter was first proposed by Dong Hwan Lee et al. in 1999. As shown in Figure 1, it consists of a coupled microstrip line 102 and a high impedance line 106 connected to the coupled microstrip line. The coupled microstrip line With microstrip line terminals 104 for input and output signals, the low-pass filter has the characteristics of simple structure, small size and low insertion loss, but has the problem of narrow stopband width. Then, the structure of applying the open-circuit branch to the hairpin filter is proposed to widen the stopband bandwidth of the hairpin low-pass filter. However, this will increase the area of the filter and increase the The size of the device is increased. For this reason, it is necessary to propose a design of a high-performance low-pass filter with a small size and a wide stop band.

Utility model content

The utility model aims to solve one of the above-mentioned problems, and provides a low-pass filter, which realizes the design of a high-performance low-pass filter with a small size and a wide stop band.

In order to achieve the above object, the embodiment of the utility model provides the following technical solutions:

A low pass filter comprising:

A ladder impedance hairpin structure is adopted, including coupled microstrip lines, high impedance lines, microstrip line ends and open-circuit branches; among them,

A high-impedance line, the two ends of which are connected to the coupled microstrip line, and there are at least two bends between the two ends;

A microstrip line terminal formed on an end face of a high-impedance line connected to a coupled microstrip line;

Open-circuit stubs, two open-circuit stubs with different transmission zeros, are formed on the end face of the high-impedance line connecting the coupled microstrip line.

Preferably, the bending is a right angle bending.

Preferably, there are two open-circuit branches, and the characteristic impedances of the two open-circuit branches are the same.

Preferably, the transmission zeros of the two open-circuit stubs are different.

Preferably, the length of the open branch is a quarter of the wavelength corresponding to its transmission zero.

Preferably, the open branch nodes are respectively located between the microstrip line end and the high impedance line.

Preferably, at least one open branch is a bent structure.

Preferably, the bending of the open branch is a right-angle bending.

The low-pass filter provided by the embodiment of the utility model adopts a plurality of bent high-impedance lines, and forms an open-circuit branch on the end face of the high-impedance line connected to the coupled microstrip line, and the miniaturization and compactness are further improved. The improvement of the two open-circuit branches increases the width of the stop band suppression, and the insertion loss of the pass band is small. The single-sided structure is easy to integrate with other microwave circuits. The structure is simple and easy to process.

Description of drawings

Fig. 1 is the structural representation of traditional ladder impedance hairpin type low-pass filter;

Fig. 2 is a schematic structural diagram of a low-pass filter according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of the frequency-echo/insertion loss curve of the low-pass filter of the embodiment of the present invention.

Detailed ways

In order to make the above purpose, features and advantages of the present utility model more obvious and understandable, the specific implementation of the present utility model will be described in detail below in conjunction with the accompanying drawings.

In the following description, a lot of specific details have been set forth in order to fully understand the utility model, but the utility model can also be implemented in other ways different from those described here. Technical Essence of the Utility Model Any simple modifications, equivalent changes and modifications made to the following embodiments still belong to the protection scope of the technical solution of the utility model, so the utility model is not limited by the specific examples disclosed below.

As shown in FIG. 2, in this embodiment, the low-pass filter adopts a ladder impedance hairpin structure, including a coupled microstrip line 5, a high impedance line 6, a microstrip line terminal 4 and an open branch 7, wherein, A high-impedance line 6, whose two ends are connected to the coupled microstrip line 5, and has at least two bends between the two connection terminals; the microstrip line end 4 is formed on the end face of the high-impedance line connected to the coupled microstrip line; the open branch Section 7, two open-circuit branches with different transmission zero points are formed on the end face of the high-impedance line connecting the coupled microstrip line.

In this embodiment, the low-pass filter can be formed on the dielectric substrate. As shown in FIG. A ground metal layer 2 is formed on the lower surface of the dielectric substrate 1 for the stripline 5 , the high impedance line 6 , the microstrip line terminal 4 and the open branch 7 .

In this embodiment, the high-impedance line 6 has two bends between two connection terminals, each bend is a right-angle bend similar to a hump shape, and the connection terminal is located at the end surface 5 directly above the coupled microstrip line 5 -1 on. It can be understood that, in other embodiments, the number of bends here is only an example, and the number and shape of bends can be selected according to specific design requirements. The right-angle bends in this embodiment are easier to route and implement. A high-impedance line is a circuit line that can be equivalent to an inductor.

The open-circuit branch is located on the end face 5-1 of the coupled microstrip line 5 where the connection terminal of the high-impedance line 6 is located. In this embodiment, two open-circuit branches are used, which are respectively located between the microstrip line end 4 and the high-impedance line 6 , each open-circuit branch can have the same characteristic impedance but have different lengths, so that the two have different transmission zeros to suppress high-frequency harmonics of different frequencies, and the length of the open-circuit branch can be the wavelength corresponding to the transmission zero 1/4 for better high-frequency filtering performance. When the length of the open-circuit branch exceeds the height of the bent high-impedance line, the open-circuit branch can be bent, for example, at a right angle, so as to reduce the overall size of the filter.

Similarly, the microstrip line terminal 4 is also located on the end face 5-1 of the coupled microstrip line 5 where the high-impedance line 6 is connected. The microstrip line terminal 4 can be a 50-ohm matching line for signal input and output port. The miniaturization and compactness of the device are further improved, and the two open-circuit branches increase the width of the stop band suppression, and it is easy to integrate with other microwave circuits, and the structure is simple and easy to process.

When designing the low-pass filter of the present invention, firstly determine the cut-off frequency f _c of the low-pass filter, select the PCB board material, and specify the relative permittivity and thickness of the board material. According to the design theory of the ladder impedance hairpin low-pass filter, the width W1, spacing g, length L2 of the coupled microstrip line and the width W1 and total length L of the high-impedance line are selected to make the filter cut-off frequency f _c . The high-impedance line is bent, and its total length is still L. Then add two branches between the high-impedance line and the matching line, and adjust their length so that the introduced transmission zero point is at the high-frequency harmonic of the filter. If the length of the branch is longer than the bent high-impedance line, the branch can be bent. The designed filter can optimize the overall performance of the filter by adjusting the width W3 and the position of the branch.

The filter provided by the utility model can be directly printed on the high-frequency PCB board. The line width and line length of the actual filter vary with the cut-off frequency and PCB board material.

The low-pass filter provided by the embodiment of the present invention has good filtering performance. As shown in FIG. 3 , it is a schematic diagram of a frequency-echo/insertion loss curve of a specific embodiment, wherein S ₂₁ is an insertion loss parameter, and S ₁₁ is Return loss parameters, in this embodiment, the -3dB cutoff frequency is 1.2GHz, and the -15dB stopband suppression ranges from 1.9GHz to 10.3GHz.

The utility model has been disclosed above with preferred embodiments, but it is not intended to limit the utility model. Any person familiar with the art, without departing from the scope of the technical solution of the utility model, can use the methods and technical content disclosed above to make many possible changes and modifications to the technical solution of the utility model, or modify it to an equivalent change Equivalent embodiment. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are still within the protection scope of the technical proposal of the present invention.

Claims (8)

1. A low-pass filter, characterized in that, adopts a ladder impedance hairpin structure, including a coupled microstrip line, a high impedance line, a microstrip line end and an open branch; wherein, A high-impedance line, the two ends of which are connected to the coupled microstrip line, and there are at least two bends between the two ends; A microstrip line terminal formed on an end face of a high-impedance line connected to a coupled microstrip line; The open stub is formed on the end face of the high-impedance line connecting the coupled microstrip line. 2. The low-pass filter according to claim 1, wherein the bend is a right-angle bend. 3. The low-pass filter according to claim 1, characterized in that it has two open-circuit branches, and the characteristic impedances of the two open-circuit branches are the same. 4. The low-pass filter according to claim 3, wherein the transmission zeros of the two open-circuit branches are different. 5. The low-pass filter according to claim 4, characterized in that, the length of the open-circuit branch is a quarter of the wavelength corresponding to its transmission zero point. 6 . The low-pass filter according to claim 3 , wherein the open-circuit branches are respectively located between the microstrip line end and the high-impedance line. 7. The low-pass filter according to claim 1, wherein at least one open branch is a bent structure. 8. The low-pass filter according to claim 7, wherein the bending of the open-circuit branch is a right-angle bending.