CN102255125B - A dual-frequency narrowband bandpass filter - Google Patents

Abstract

The invention relates to a novel double-frequency narrow-band bandpass filter. The novel double-frequency narrow-band bandpass filter comprises a metal microstrip line on the front surface, a medium plate layer, an input port and an output port on the middle part, and a metal plating layer on the rear side of a medium plate, wherein in the metal microstrip line, a resonator consisting of a section of low impedance line and a stepped impedance line connected with the low impedance line, and a novel resonator formed by connecting a quarter wavelength uniform impedance line and a feeder with a rectangular short microstrip line. The resonator structure is symmetrical, so that an odd-even mode theory can be used for analyzing the resonator structure; and the input port and the output port of the feeder are in the same level line. A transmission zero is inserted into a stop band between two pass bands, a zero position in a transmission characteristic curve can be flexibly adjusted, the stop band characteristics are improved, and a transmission zero is inserted outside two center frequencies respectively to improve out-of-band rejection characteristics. The novel double-frequency narrow-band bandpass filter has a simple structure and extremely high frequency selectivity and meets the requirements on miniaturization.

Description

A dual-frequency narrowband bandpass filter

technical field

The invention relates to a dual-frequency narrow-band band-pass filter, which belongs to the category of dual-frequency band-pass filters with transmission zero points in the technical field of wireless communication.

Background technique

With the rapid development of communication technology, especially the development of wireless communication technology, the requirements for filters in wireless communication systems are getting higher and higher. In 1997, the Institute of Electrical and Electronics Engineers (IEEE) formulated the 802.11 Wireless Local Area Network (WLAN) protocol, which opened a new milestone for the development of wireless communication.

Traditional filters can no longer meet the needs of wireless communication systems, and now that spectrum resources are scarce, people's demand for large-capacity transmission of information is becoming more and more urgent, so dual-frequency or multi-frequency filters can well meet wireless communication requirements. Communication system needs. The traditional design is to add multiple filters in the communication system, which not only increases the cost, but also takes up more system space. Therefore, it is the development trend of filters to realize dual-frequency or multi-frequency in one device and realize miniaturization design.

Contents of the invention

The purpose of the present invention is to provide a novel dual-frequency narrow-band band-pass filter based on low-impedance lines and parallel coupled lines for the defects in the prior art, so that the in-band loss is low, and the transmission zero point is added outside the band, and has a large Good harmonic suppression characteristics, and at the same time realize the simplification of the structure, and then realize the miniaturization of the filter.

To achieve the above object, design of the present invention is:

1. On the basis of the traditional parallel coupling lines, by adding a short impedance line between the two parallel coupling lines to form a step impedance resonator, a new coupling is realized, and the transmission zero point can be changed by changing the length of the short impedance line Location.

2. On the basis of the traditional Uniform Impedance Resonator (UIR) structure, by adding a short microstrip line at the corner where the resonator is connected to the feeder, it achieves good harmonic suppression characteristics and reduces the insertion loss of spurious frequencies .

3. The present invention adopts the following dielectric plate material: the dielectric constant of the dielectric substrate is =10.2, thickness h =0.635mm. Adopt low impedance line and parallel coupled line structure.

4. The processed circuit board is divided into three layers, that is, the front is a metal microstrip line structure, the middle is a dielectric layer and the input and output ports, and the back of the dielectric board is a layer of metal plating, and two SMA connectors are welded at the input and output ports. , for actual measurement. The front metal microstrip line structure is composed of a low-impedance line, a new parallel coupling line, and a new resonator. By changing the distance between the two parallel coupling lines, the position of the zero point and the broadband of the frequency band can be adjusted.

According to above-mentioned inventive concept, the present invention adopts following technical scheme:

A dual-frequency narrow-band bandpass filter, including a three-layer structure: a metal microstrip line on the front, a dielectric plate layer in the middle and an input and output port, and a metal coating on the reverse side of the dielectric plate. The metal microstrip line structure is: A first resonator composed of a section of low impedance line and a step impedance line connected to it, and a second resonator composed of a quarter-wavelength uniform impedance line and a feeder connected to a rectangular short microstrip line; due to the first resonance The structure of the transformer is symmetrical, so it can be analyzed by the theory of odd and even modes; the input and output ports of the feeder are on the same horizontal line. the

The step impedance line is formed by connecting the ends of two parallel coupling lines with a short impedance line, which realizes new coupling.

The rectangular microstrip line is located at the corner where the quarter-wavelength uniform impedance line is connected to the feeder line, thereby realizing good harmonic suppression characteristics.

The dielectric plate layer is a dielectric constant =10.2 medium plate, the thickness of the medium plate h =0.635mm.

The metal plating layer of the metal microstrip line and the back part can be a metal material with good electrical conductivity, such as gold, or silver, or copper.

The dielectric constant of the dielectric plate in the middle layer can be various values, because the dielectric constant is inversely proportional to the square of the length of the resonator, so a higher dielectric constant corresponds to a smaller size of the filter.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

The filter structure of the present invention can be regarded as composed of two traditional step impedance resonators (SIR), but the improvement from the traditional one is that a short impedance line is added in the middle of the parallel coupling lines to form a step impedance resonator, And it is formed by adding a short microstrip line at the corner of the quarter-wavelength uniform impedance resonator (UIR) and the feeder. Compared with the structural characteristics of the traditional dual-band filter based on UIR and SIR, this structural unit has low in-band loss. , good out-of-band suppression characteristics.

There are many methods to improve the out-of-band suppression characteristics, and two methods are usually used, one is to increase the number of filter stages, and the other is to introduce transmission zeros outside the band, and the method adopted in the present invention is the latter. There are three methods for introducing transmission zeros, one is to introduce cross-coupling structures, the other is to add open-circuit stubs, and the third is to use parallel coupling lines. The method for introducing transmission zeros in the present invention adopts the third method. The position of the transmission zero can be adjusted by changing the distance of the parallel coupled lines.

The feeder mode of the resonator structure adopts direct access, and the direct access method uses a microstrip line with a characteristic impedance of 50 ohms to directly connect to the resonator.

Description of drawings

Figure 1 is a traditional step impedance resonator (SIR) unit structure diagram.

Figure 2 is a schematic diagram of the unit structure composed of improved low-impedance lines and parallel coupled lines.

Figure 3 is a schematic diagram of the traditional feeder and resonator structure.

Fig. 4 is a structural schematic diagram of the improved feeder and resonator.

Figure 5 is a schematic diagram of the microstrip line structure of a dual-band bandpass filter with a traditional structure.

Fig. 6 is a schematic diagram of the overall structure of the novel dual-frequency narrowband bandpass filter of the present invention.

Figure 7 is a schematic diagram of the frequency response of a dual-band filter implemented with a traditional structure.

Figure 8 is a schematic diagram of the frequency response of the simulation of the novel dual-frequency narrowband bandpass filter of the present invention.

Detailed ways

A preferred embodiment of the present invention is described in detail below in conjunction with accompanying drawing:

The schematic diagram of the unit structure composed of the improved low-impedance line and parallel coupling line proposed by the present invention is shown in Figure 2, which divides the high-impedance line into Two parallel coupled lines, changing the coupling characteristics. The position of the transmission zero between the two passbands can be changed by changing the distance of the parallel coupled lines.

As shown in Figure 3, it is a schematic diagram of the structure of the traditional feeder and resonator, which adopts the direct feeding method. Figure 4 is a schematic diagram of the structure of the improved feeder and resonator, and a short microstrip line is added at the corner of the feeder and the resonator , enhanced harmonic suppression characteristics.

Embodiment 1: Referring to Fig. 6, this dual-band narrow-band bandpass filter includes a three-layer structure: a metal microstrip line on the front, a dielectric plate layer in the middle and an input and output port, a metal coating on the reverse side of the dielectric plate, and the metal The microstrip line structure is: a first resonator composed of a low impedance line and a step impedance line connected to it, and a second resonator composed of a quarter-wavelength uniform impedance line and a feeder connected to a rectangular short microstrip line. Resonator; Since the structure of the first resonator is symmetrical, it can be analyzed by odd and even mode theory; the input and output ports of its feeder are on the same horizontal line. the

Embodiment 2: This embodiment is basically the same as Embodiment 1, and the special feature is: the step impedance line is formed by connecting a short impedance line (11) at the end of two parallel coupling lines (7), realizing a new coupling. The rectangular short microstrip line (9) is located at the corner where the quarter-wavelength uniform impedance line (8) connects to the feeder line (12), thereby achieving excellent harmonic suppression characteristics. The dielectric plate layer (5) is a dielectric constant =10.2 medium plate, the thickness of the medium plate h =0.635mm.

Embodiment three: this embodiment is basically the same as embodiment two, and the special feature is: Fig. 6 is the structural representation of this embodiment, through design, emulation and optimization, finally determine the specific size of this microstrip ultra-narrowband bandpass filter as follows:

L1=7.3mm, L2=10.0mm, L3=8.4mm, L4=0.8mm

W1=6.0mm, W2=0.6mm, W3=0.6mm, W4=1.1mm

G=0.2mm, D=0.2mm,

Based on the above method, a microstrip filter with a center frequency of 2.62GHz/5.98GHz and a relative bandwidth of about 6% was designed, and was simulated and debugged by the electromagnetic simulation software Sonnet.

Figure 7 shows the frequency response simulation results of a dual-band filter implemented with a traditional structure.

Fig. 8 shows the simulation structure of the microstrip filter, and the simulation results show that the present invention has great advantages in both in-band characteristics and out-of-band suppression. At the same time, compared with Figure 7, the center frequency is reduced, and the out-of-band steepness is obvious. Moreover, the structure of the filter is simple, the size is small, and miniaturization is realized.

The above simulation results show that:

(1) The passband bandwidth is about 120MHz, and the in-band insertion loss is less than 0.1dB;

(2) The passband cut-off edge is steep, dropped to -80dB at 1.06GHz, and transmission zeros are inserted at 4.66GHz and 6.8GHz;

The in-band and out-of-band properties are good, and the structure of the microstrip is simple, the size is also miniaturized, the printing is simple, and the material loss is relatively small.

Claims (2)

1. a double-frequency narrow-band bandpass filter, comprise three-decker: positive metal micro-strip line (1), middle medium flaggy (5), the coat of metal (2) of medium flaggy reverse side, is characterized in that described metal micro-strip line (1) is made up of first resonator and two the second resonators; The structure of the first described resonator is: one end of two parallel coupled lines (7,13) connects one section of low-impedance line (6), and the end of two parallel coupled lines (7,13) connects a short impedance line (11), realize coupling, axially symmetric structure centered by this first resonator; The second described resonator is to be connected the short microstrip line of rectangle (9) to form by quarter-wave uniform impedance line (8) with feeder line (12), and feeder line (12) is to be vertically connected at uniform impedance line (8) in one end of uniform impedance line (8), the short microstrip line of described rectangle (9) is positioned at described quarter-wave uniform impedance line (8) corner that is connected with feeder line (12), and the input/output port (4,10) of described feeder line (12) in the same horizontal line; Two described the second resonators are positioned at the end of described the first resonator, and about the symmetrical distribution of the first resonator, the uniform impedance line (8) in these two second resonators respectively with described the first resonator in parallel coupled line (7,13) coupling; Because the first resonator structure is symmetrical, so available even odd mode theory is analyzed.

2. a kind of double-frequency narrow-band bandpass filter according to claim 1, is characterized in that described medium flaggy (5) is dielectric constant =10.2 dielectric-slab, this dielectric-slab layer thickness h=0.635mm.