CN103490127A - Three-pass-band filter - Google Patents

Abstract

The invention discloses a three-pass-band filter which is applied to the field of communication. The three-pass-band filter comprises a medium substrate provided with grounding through holes, a main circuit located on the upper surface of the medium substrate and a metal grounding layer located on the lower surface of the medium substrate. The main circuit is formed by the concatenation of two quarter-wave stepped impedance resonators which are distributed in axial symmetry, the two quarter-wave stepped impedance resonators are connected through the grounding through holes, the two quarter-wave stepped impedance resonators are respectively connected with an input/output feeder line, each quarter-wave stepped impedance resonator comprises three transmission lines connected end to end, and an open circuit transmission line is loaded on the middle section of each transmission line located in the middle. The three-pass-band filter has the advantages that central frequency and bandwidth are easy to control, the selectivity of the frequency is high, separating strength among pass-bands is high, and the size is small.

Description

Three-pass band filter

technical field

The invention belongs to the technical field of microwave communication, and in particular relates to a compact three-pass band filter with a planar microstrip structure.

Background technique

With the rapid development of multi-band and multi-standard wireless communication systems, higher requirements are put forward for the high frequency selectivity and miniaturization of multi-band bandpass filters.

To realize the screening of three-band signals, the traditional method is to use three single-pass-band filters to screen each pass-band signal respectively. This method is simple and feasible, but the integration level is not enough to meet the needs of small-sized, light-weight wireless communications. Quantified development requirements. Therefore, designing a "highly selective, miniaturized" three-pass band filter that can be effectively integrated is an important topic at present.

There are many ways to realize the three-pass band filter. At present, the more common structures and their corresponding characteristics are as follows: (1) The three-pass band filter structure is realized by connecting two or three sets of resonators in parallel, and the common input and output ports are used. , each group of resonators produces one passband or two passbands, the disadvantage of this filter structure is its complexity and large size; (2) by introducing transmission zeros in single-passband or double-passband filters to achieve three-pass Band filter, but the filter also has the problem of complex structure and difficult design.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned problems in the prior art, and provide a planar microstrip compact three-pass filter with simple structure, easy processing, good frequency selectivity and high isolation.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A planar microstrip compact three-pass band filter, including a dielectric substrate provided with a grounding via hole, a main line located on the upper surface of the dielectric substrate and a metal formation located on the lower surface of the dielectric substrate, the main line is formed by two Axisymmetrically distributed quarter-wavelength stepped impedance resonators are cascaded. Two quarter-wavelength stepped impedance resonators are connected through ground vias, and the two quarter-wavelength stepped impedance resonators are respectively connected to the input The /output feeder is characterized in that: each stepped impedance resonator includes three transmission lines connected end to end, and the middle section of the transmission line in the middle is loaded with an open transmission line.

Further, the open-circuit transmission line is a spiral structure.

Further, the transmission line located at the end of the ladder impedance resonator and not connected to the ground via is a spiral structure.

Further, the input/output feeders are all microstrip lines with a characteristic impedance of 50 ohms.

Further, the input/output feeder is a tap structure.

Compared with the prior art, the beneficial effects of the planar microstrip compact three-pass band filter proposed by the present invention are as follows:

First of all, the planar microstrip compact three-pass band filter of the present invention is realized by loading open-circuit transmission lines respectively on two cascaded two quarter-wavelength stepped impedance resonators. After determining the quarter-wavelength stepped impedance resonator, The center frequency and bandwidth of the passband can be effectively controlled by controlling the length of the loading open line and the loading position;

Secondly, in the planar microstrip compact three-pass band filter of the present invention, electromagnetic coupling is formed between the transmission lines of the two stepped impedance resonators, and the grounding through hole is through magnetic coupling between the two stepped impedance resonators. Practice has proved that, This structure can generate six transmission zeros near both sides of the filter passband, so that the filter has high frequency selective characteristics and isolation;

Again, the planar microstrip compact three-pass band filter of the present invention is a planar structure, and the circuit structure is compact, and by designing the part of the transmission line of the open-circuit transmission line and the stepped impedance resonator as a spiral structure, the space utilization rate is further improved, and the the circuit size;

Finally, the planar microstrip compact three-pass band filter of the present invention has a simple structure and is easy to process.

Description of drawings

Fig. 1 is the structural representation of planar microstrip compact three-pass band filter of the present invention;

Fig. 2 is the frequency response curve of the planar microstrip compact three-pass band filter in the embodiment.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, the planar microstrip compact three-pass band filter in the present embodiment comprises the dielectric substrate 1 that is provided with grounding via hole 11, the main line that is positioned at the upper surface of dielectric substrate 1 and is positioned at the dielectric substrate below. Surface metal formation 3. The main line is formed by cascading two axisymmetrically distributed quarter-wavelength stepped impedance resonators 21 and 21 ′, and the two stepped impedance resonators 21 and 21 ′ are connected through the grounding hole 11 to achieve grounding. The ladder impedance resonator 21 includes three end-to-end transmission lines 211, 212 and 213; the ladder impedance resonator 21' includes three end-to-end transmission lines 211', 212' and 213', wherein the transmission lines 212 and 212' and between Electromagnetic coupling is formed between 213 and 213', and the grounding via 11 provides magnetic coupling. By adjusting the electromagnetic coupling strength between the ladder impedance resonators 21 and 21', the filter bandwidth can be effectively controlled. At the same time, by adjusting the electrical coupling and The magnetic coupling ratio can effectively control the out-of-band transmission zero of the filter. The middle sections of the transmission lines 212 and 212' located in the middle of the stepped impedance resonators 21, 21' are loaded with open transmission lines 4 and 4', by loading the open transmission lines 4 and 4, the quarter wavelength stepped impedance resonator 21 can be effectively Or the high-order resonance mode of 21' moves to the low frequency end. Two cascaded ladder impedance resonators 21 and 21' together with the open transmission lines 4, 4' constitute the three-pass band filter of this embodiment, and the three-pass band filter can realize the screening of signals in three different frequency bands, so that the same The radio frequency front end can support the work of multiple communication systems of different frequencies.

In order to further improve the space utilization rate, reduce the size of the circuit, and further reduce the size of the filter, the open transmission lines 4, 4' and the transmission lines 213, 213' here all adopt a spiral structure.

Two quarter-wavelength stepped impedance resonators 21, 21' are respectively connected to the input/output feeders 5, 5', and the input/output feeders 5, 5' in this embodiment all adopt a tap structure, and both have characteristic impedance A 50 ohm microstrip line.

Fig. 2 shows the frequency response curve of the planar microstrip compact three-pass band filter in the present embodiment, and curve S ₁₁ in the figure is the characteristic curve of signal port reflection, and curve S ₂₁ is the transmission characteristic curve of signal, by It can be seen from the figure that the center frequency of the first passband is 1.92GHz, and its 3dB bandwidth is 6.4%, which meets the requirements of the GSM system. The insertion loss is 0.9dB, and the return loss is greater than 17.5dB. The passband is at 1.66GHz and 2.65GHz. Two transmission zero points Tz ₁ and Tz ₂ are produced; the center frequency of the second passband is 3.50GHz, and its 3dB bandwidth is 4.0%, which meets the requirements of the WIMAX system. The insertion loss is 1.8dB, and the return loss is greater than 15.5dB. The band produces two transmission zeros Tz ₃ and Tz ₄ at 3.07GHz and 3.96GHz; the center frequency of the third passband is 5.75GHz, and its 3dB bandwidth is 2.4%, which meets the requirements of the WLAN (5.7GHz) system, and the insertion loss is 1.9dB, the return loss is greater than 19.5dB, and the passband produces two transmission zeros Tz ₅ and Tz ₆ at 5.40GHz and 6.17GHz. Transmission zeros Tz ₁ , Tz ₂ , Tz ₃ , Tz ₄ , Tz ₅ , and Tz ₆ greatly improve the frequency selectivity of the filter, while transmission zeros Tz ₂ and Tz ₃ improve the first passband and the second passband The isolation between the transmission zeros Tz ₄ and Tz ₅ improves the isolation between the second passband and the third passband.

Those skilled in the art will appreciate that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical revelations disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims (5)

1. A three-pass band filter, comprising a dielectric substrate provided with grounding vias, a main line positioned at the upper surface of the dielectric substrate and a metal formation positioned at the lower surface of the dielectric substrate, the main line is composed of two axisymmetrically distributed The quarter-wavelength stepped impedance resonators are cascaded, the two quarter-wavelength stepped impedance resonators are connected through the ground via, and the input/output feeders are respectively connected to the two quarter-wavelength stepped impedance resonators , which is characterized in that: each stepped impedance resonator includes three transmission lines connected end to end, and the middle section of the transmission line in the middle is loaded with an open transmission line. 2. The three-pass band filter according to claim 1, wherein the open transmission line is a spiral structure. 3 . The three-pass band filter according to claim 1 , wherein the transmission line located at the end of the stepped impedance resonator and not connected to the ground via is a spiral structure. 4 . 4. The three-pass band filter according to claim 1, wherein the input/output feeders are all microstrip lines with a characteristic impedance of 50 ohms. 5. The three-pass band filter according to claim 1 or 4, characterized in that: the input/output feeder is a tapped structure.

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