CN115863942B - Dual-passband independently adjustable band-pass filter with constant bandwidth - Google Patents

Abstract

The present invention provides a dual-passband independent adjustable filter that maintains a constant bandwidth, which is realized by using a structure in which two different resonators share input and output feed lines. The resonator includes a microstrip line loaded with a varactor diode, and the varactor diode is connected to an external bias circuit. The filter mainly includes an upper microstrip line structure, an intermediate dielectric substrate, and a lower grounding metal, and has the characteristics of simple structure, miniaturization, and excellent characteristics. The shortcomings of insufficient selectivity and bandwidth variation of the dual-passband adjustable filter can be overcome, and the dual passbands can be independently adjustable to maintain a constant bandwidth. It is easy to realize circuit integration and system packaging, and can also be widely used in industrial production.

Description

A dual-passband independently adjustable bandpass filter with constant bandwidth

Technical Field

The invention relates to the technical field of microwave communications, and in particular to a dual-passband independently adjustable bandpass filter with a constant bandwidth.

Background Art

With the rapid development of modern wireless communication technology, mobile communication, satellite communication, radar tracking and remote sensing technology increasingly need to rely on microwave and millimeter wave technology, which has led to an increasingly complex electromagnetic environment, and ultimately made spectrum resources increasingly tight. The contradiction between limited spectrum resources and application needs has become increasingly prominent. Traditional narrowband communication systems have been unable to adapt to the actual needs of these application scenarios due to their small transmission capacity and low transmission rate. Therefore, adjustable technology has received more and more attention.

In order to meet the urgent needs of multiple users for different communication modes and high transmission rates, modern communication systems need to combine multi-band technology and adjustable technology. Therefore, adjustable multi-passband filters come into being. On the other hand, with the rapid development of wireless communication technology, it is usually necessary to communicate through a series of channels with the same bandwidth. Although a large number of adjustable dual-passband filters have been reported, these filters cannot meet the requirements of constant bandwidth and independent adjustment, and the structure is complex, which increases many design uncertainties.

The tunable filter structure designed in the past has the following disadvantages:

(1) Bandwidth changes during frequency adjustment range;

(2) The passbands in a multi-passband tunable filter are not independently adjustable;

(3) During the adjustment process, the filter performance deteriorates and becomes unstable.

Summary of the invention

In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a dual-passband independently adjustable bandpass filter with a constant bandwidth, which has a compact structure and can simultaneously achieve high selectivity, independent adjustability, and maintain a constant bandwidth.

To achieve the above object, the present invention provides the following solutions:

A dual-passband independently adjustable filter maintaining a constant bandwidth, comprising: an upper microstrip structure, an intermediate dielectric substrate, a lower grounding metal, a first port, a second port, a first microstrip line connected to the first port, and a second microstrip line connected to the second port; the upper microstrip structure is attached to the upper surface of the intermediate dielectric substrate, and the lower grounding metal is attached to the lower surface of the intermediate dielectric substrate; the first port and the second port are respectively located on both sides of the intermediate dielectric substrate; the first microstrip line and the second microstrip line are connected to each other to form a common input and output feeder;

The upper microstrip structure includes a first resonator and a second resonator; the first resonator and the second resonator are both symmetrical about the vertical axis; the first resonator is located outside the common input and output feeder, and is connected to the common input and output feeder in a slot coupling manner; the first resonator includes two symmetrical impedance line structures; the impedance line structure includes a low impedance line, a first high impedance line, a second high impedance line, a third high impedance line, a fourth high impedance line and a first varactor; one end of the low impedance line is connected to the first bias voltage through a large resistor, the other end of the low impedance line is connected to the first high impedance line and the second high impedance line, the other end of the second high impedance line is connected to one end of the first varactor, the other end of the first varactor is connected to the third high impedance line and the fourth high impedance line, and the other end of the fourth high impedance line is connected to the ground; the two symmetrical low impedance lines are coupled to each other, and the two symmetrical first high impedance lines are coupled to each other;

The second resonator is located on the inner side of the common input-output feeder and is connected to the common input-output feeder in a slot coupling manner; the second resonator includes a third varactor, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line and two symmetrical microstrip line structures; the microstrip line structure includes a second varactor, a third microstrip line and a fourth microstrip line connected to the third microstrip line; the other end of the fourth microstrip line is connected to one end of the second varactor, the other end of the second varactor is connected to the fifth microstrip line, both ends of the fifth microstrip line are grounded through large resistors, and the center of the fifth microstrip line is connected to the sixth microstrip line and the seventh microstrip line by loading the third varactor; the sixth microstrip line is connected to a second bias voltage through a large resistor.

Preferably, the first resonator is used to generate two modes to form a first passband, and the frequency of the first passband is adjustable by changing the capacitance of the first varactor diode; the second resonator is used to generate two odd and even modes to form a second passband, and the frequency of the second passband is adjustable by changing the capacitance of the second varactor diode; the sixth microstrip line and the seventh microstrip line of the branch structure are loaded with a third varactor diode to generate a transmission zero point of their own.

Preferably, the intermediate layer dielectric substrate is R04003C, with a thickness of 0.508 mm, a dielectric constant of 3.55, and a loss tangent of 0.0027.

Preferably, the radius of the grounding hole at both ends of the fifth microstrip line respectively connected to the ground through a large resistor is 0.3 mm.

Preferably, the first bias voltage and/or the second bias voltage is 0-15V.

Preferably, the model of the first varactor diode is a silicon varactor diode SMV1233; the model of the second varactor diode and/or the third varactor diode is a silicon varactor diode SMV1234.

Preferably, the resistance value of the large resistor is 100K ohms.

Preferably, the common input-output feed line comprises a source-load coupling structure, and the source-load coupling structure is used to generate three additional adaptive transmission zeros.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The present invention provides the following beneficial effects

The present invention can generate four transmission zeros of the upper and lower passbands through branch loading and source-load coupling structures to achieve high selectivity; and realize independent adjustment of the upper and lower passbands through two different resonators through a common input and output feeder. In a specific embodiment, the bandwidth is constant during the frequency tuning process by controlling the coupling coefficient _K12 and the external quality factor _Qe . The present invention can make the device structure compact and realize independent adjustment of the two passbands while maintaining a constant absolute bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

FIG1 is a schematic diagram of a three-dimensional structure of an adjustable filter provided in an embodiment of the present invention;

FIG2 is a schematic diagram of a specific structure of an adjustable filter provided in an embodiment of the present invention;

FIG3 is a schematic diagram of the physical dimensions of an adjustable filter provided in an embodiment of the present invention;

FIG4 is a schematic diagram of an S-parameter simulation curve of an adjustable passband provided by an embodiment of the present invention;

FIG. 5 is a schematic diagram of an S-parameter simulation curve of an adjustable two-passband provided in an embodiment of the present invention.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

The terms "first", "second", "third" and "fourth" in the specification and claims of the present application and the drawings are used to distinguish different objects rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a series of steps, processes, methods, etc. are not limited to the listed steps, but may optionally include steps that are not listed, or may optionally include other step elements inherent to these processes, methods, products or devices.

The object of the present invention is to provide a dual-passband independently adjustable bandpass filter with a constant bandwidth, which has a compact structure and can simultaneously achieve high selectivity, independent adjustment, and maintain a constant bandwidth.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

Figure 1 is a schematic diagram of the three-dimensional structure of the tunable filter provided in an embodiment of the present invention. As shown in Figure 1, this embodiment provides a dual-passband independent tunable filter that maintains a constant bandwidth, including an upper microstrip structure, a middle dielectric substrate and a lower grounding metal.

As shown in FIG2 , the upper microstrip structure is symmetrical about the vertical axis. The microstrip structure of the filter is realized by two different resonators through a common input and output feeder, and the two different resonators are respectively the first resonator and the second resonator; the first resonator and the second resonator are both symmetrical about the vertical axis; the first port of the filter is located on one side of the dielectric substrate, and the second port is located on the other side of the dielectric substrate; two 50-ohm microstrip lines are respectively connected to the corresponding two ports, and the two 50-ohm microstrip lines are the first microstrip line 12 (12_1), and the two microstrip lines are arranged on the same horizontal line; the first microstrip line 12 is connected to the second microstrip line 11 (11_1) to form a common input and output feeder.

The first resonator is located on the outer side of the common feeder and is connected to the feeder in a slot coupling manner; the first resonator comprises a symmetrical low impedance line 1 (1_1) and a first high impedance line 2 (2_1), a second high impedance line 3, a third high impedance line 4, a fourth high impedance line 5 and a first variable capacitance diode Cv1, a section of the low impedance line 1 is connected to a first bias voltage (bias 1) through a large resistor, and the other end is connected to the first high impedance line 2 and the second high impedance line 3, the other end of the second high impedance line 3 is connected to one end of the first variable capacitance diode _Cv1 , the other end of the first variable capacitance diode _Cv1 is connected to the third high impedance line 4 and the fourth high impedance line 5, and the other end of the fourth high impedance line 5 is connected to the ground; wherein the low impedance line 1 is coupled to the low impedance line 1_1, and the first high impedance line 2 is coupled to the first high impedance line 2_1.

The second resonator is located on the inner side of the common feeder and is connected to the feeder in a slot coupling manner; the second resonator includes a symmetrical third microstrip line 6 connected to a fourth microstrip line 7, the other end of the fourth microstrip line 7 is connected to one end of a second variable capacitance diode C _v2 , the other end of the second variable capacitance diode C _v2 is connected to a fifth microstrip line 8, both ends of the fifth microstrip line 8 are grounded through large resistors respectively, the center of the fifth microstrip line 8 is connected to a seventh microstrip line 9 and a sixth microstrip line 10 by loading a third variable capacitance diode C _v3 ; the seventh microstrip line 9 is connected to a second bias voltage (bias 2) through a large resistor.

The first resonator is a pair of dual-mode resonators coupled with the feed line to generate two resonance modes, forming the first passband, and the frequency of the first passband can be adjusted by changing the external bias 1. The second resonator is a branch-loaded step impedance resonator, which can generate two resonance modes, one odd and one even, to form the second passband. The frequency of the second passband can be adjusted by changing the external bias 2. The resonator can also generate an additional zero point.

This embodiment analyzes the coupling coefficient _K12 and the external quality factor _Qe of the upper and lower passbands respectively. When the passband width remains constant, as the frequency increases during the tuning process, the coupling coefficient _K12 decreases, while the external quality factor _Qe increases.

As shown in Figure 1, the intermediate layer dielectric plate used in this embodiment is R04003C, with a thickness of 0.508 mm, a dielectric constant of 3.55, and a loss tangent of 0.0027. The feeder structure adopts a source-load coupling structure for feeding, which can introduce additional transmission zeros to improve the selectivity of the passband and the isolation between the passbands.

As shown in FIG3 , the detailed circuit dimensions of the resonator structure are: L ₁ =1.1 mm, L ₂ =2.4 mm, L ₃ =4.15 mm, L ₄ =5.65 mm, L ₅ =2.7 mm, L ₆ =12.1 mm, L ₇ =5.8 mm, L ₈ =4.3 mm, L ₉ =7.85 mm, L ₁₀ =6.95 mm, L ₁₁ =19.95 mm, w ₁ =2.3 mm, w ₂ =0.1 mm, w ₃ =0.3 mm, w ₄ =0.7 mm, w ₅ =0.3 mm, w ₆ =0.15 mm, w ₇ =0.4 mm, w ₈ =1.1 mm, g ₁ =0.3 mm, g ₂ =0.4 mm, s ₁ =0.3 mm, s ₂ =0.2mm, s ₃ =0.8mm. The radius of the grounding hole is 0.3mm.

This embodiment uses high-frequency simulation software sonnet to optimize and analyze the overall structure, and the obtained S parameter simulation curves are shown in Figures 4 and 5. It can be seen from Figures 4 and 5 that the center frequency of the first passband of the filter can vary in the range of 2.06-2.22GHz, and the absolute bandwidth can remain unchanged at 60MHz during the variation; the center frequency of the second passband can vary in the range of 3.1-3.6GHz, and the absolute bandwidth can remain unchanged at 72MHz during the variation; in the entire tuning range, the insertion loss is less than 1.4dB, and the return loss is better than 12dB; and the tuning process of the upper and lower passbands does not affect each other, and the two passbands can be independently adjustable. The two adaptive zeros on both sides of the upper and lower passbands make the filter highly selective.

In summary, the constant bandwidth dual-passband independently adjustable filter of the present invention combines a multi-mode resonator and a step impedance resonator to realize a dual-passband independently adjustable filter with a compact structure, high selectivity, low loss, and a bandwidth that can be kept constant during the adjustment process. The filter is suitable for modern wireless communication systems.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of the present invention. At the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (7)

1. A dual-passband independently adjustable filter maintaining a constant bandwidth, characterized in that it comprises: an upper microstrip structure, an intermediate dielectric substrate, a lower grounding metal, a first port, a second port, a first microstrip line connected to the first port, and a second microstrip line connected to the second port; the upper microstrip structure is attached to the upper surface of the intermediate dielectric substrate, and the lower grounding metal is attached to the lower surface of the intermediate dielectric substrate; the first port and the second port are respectively located on both sides of the intermediate dielectric substrate; the first microstrip line and the second microstrip line are connected to each other to form a common input and output feeder; The upper microstrip structure includes a first resonator and a second resonator; the first resonator and the second resonator are both symmetrical about the vertical axis; the first resonator is located outside the common input and output feeder, and is connected to the common input and output feeder in a slot coupling manner; the first resonator includes two symmetrical impedance line structures; the impedance line structure includes a low impedance line, a first high impedance line, a second high impedance line, a third high impedance line, a fourth high impedance line and a first varactor; one end of the low impedance line is connected to the first bias voltage through a large resistor, the other end of the low impedance line is connected to the first high impedance line and the second high impedance line, the other end of the second high impedance line is connected to one end of the first varactor, the other end of the first varactor is connected to the third high impedance line and the fourth high impedance line, and the other end of the fourth high impedance line is connected to the ground; the two symmetrical low impedance lines are coupled to each other, and the two symmetrical first high impedance lines are coupled to each other; The second resonator is located on the inner side of the common input-output feeder and is connected to the common input-output feeder in a slot coupling manner; the second resonator includes a third varactor, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line and two symmetrical microstrip line structures; the microstrip line structure includes a second varactor, a third microstrip line and a fourth microstrip line connected to the third microstrip line; the other end of the fourth microstrip line is connected to one end of the second varactor, the other end of the second varactor is connected to the fifth microstrip line, both ends of the fifth microstrip line are grounded through large resistors, and the center of the fifth microstrip line is connected to the sixth microstrip line and the seventh microstrip line by loading the third varactor; the seventh microstrip line is connected to a second bias voltage through a large resistor; The first resonator is used to generate two modes to form a first passband, and the frequency of the first passband is adjustable by changing the capacitance of the first varactor diode; the second resonator is used to generate two odd and even modes to form a second passband, and the frequency of the second passband is adjustable by changing the capacitance of the second varactor diode; the sixth microstrip line and the seventh microstrip line of the branch structure are loaded with a third varactor diode to generate a transmission zero point of their own. 2. According to claim 1, a dual-passband independently tunable filter maintaining a constant bandwidth is characterized in that the intermediate layer dielectric substrate is R04003C, with a thickness of 0.508 mm, a dielectric constant of 3.55, and a loss tangent of 0.0027. 3. A dual-passband independently tunable filter maintaining a constant bandwidth according to claim 1, characterized in that the radius of the grounding hole at both ends of the fifth microstrip line respectively connected to the ground through a large resistor is 0.3 mm. 4. A dual-passband independently tunable filter maintaining a constant bandwidth according to claim 1, characterized in that the first bias voltage and/or the second bias voltage is 0-15V. 5. A dual-passband independently tunable filter maintaining a constant bandwidth according to claim 1, characterized in that the model of the first varactor diode is a silicon varactor diode SMV1233; the model of the second varactor diode and/or the third varactor diode is a silicon varactor diode SMV1234. 6 . The dual-passband independently adjustable filter maintaining a constant bandwidth according to claim 1 , wherein the resistance value of the large resistor is 100K ohms. 7. A dual-passband independently tunable filter maintaining a constant bandwidth according to claim 1, characterized in that the common input and output feed lines include a source-load coupling structure, and the source-load coupling structure is used to generate three additional adaptive transmission zeros.