CN104037477A - Multi-band tunable microstrip band-pass filter - Google Patents

Abstract

The invention discloses a multi-band tunable microstrip band-pass filter which comprises a three-layer structure: a front metal microstrip line, a middle dielectric plate layer, input and output ports and an earthing metal through hole, and a metal coating at the back of a dielectric plate, wherein the metal microstrip line is a symmetric resonator consisting of a half-wavelength uniform impedance line resonator and an open-loop dual-mode resonator; the two resonators share input and output coupling lines; and a variable capacitance diode is loaded between the tail end of the open-loop dual-mode resonator and the earthing metal through hole to form a tunable structure. The filter is compact in structure, low in passband insertion loss, steep in passband edge and high in selectivity, and meets a development trend of filter miniaturization.

Description

Multiband Tunable Microstrip Bandpass Filter

technical field

The invention relates to a multi-band tunable microstrip bandpass filter, which belongs to the field of wireless communication systems. While realizing three adjustable passbands, it has high out-of-band suppression and satisfies the characteristics of miniaturization.

Background technique

At present, the application frequency bands of communication systems are all concentrated in the low-frequency bands of radio frequency and microwave bands, which makes spectrum resources particularly crowded. In order to improve system capacity and avoid interference between the system and adjacent channels, it is necessary to set up multiple communication frequency bands that can work simultaneously in the communication system. However, to realize dual-band or multi-band communication, each frequency band requires an independent RF front-end component, which makes the overall system larger in size and power consumption, and higher in cost. If the RF front-end components can be designed in a dual-band or multi-band form, the volume, cost, and power consumption of the system can be greatly reduced, its reliability can be enhanced, and the communication system can be miniaturized and highly integrated.

In modern wireless communication systems, the electric tuner filter is located between the antenna and the mixer in the receiver. Receiver signal-to-noise ratio. Multi-band tunable filters can enable a single device to cover different frequency bands and support different communication standards, thus meeting the requirements of future mobile communication broadband coverage. Based on the electric tuning filter technology, the present invention designs a three-band tunable bandpass filter, which has high out-of-band rejection, compact structure, and is convenient for system integration, meeting the requirements of modern wireless communication miniaturization and high performance . By introducing the coupling between the source and the load, an additional finite frequency transmission zero point is added when the loading voltage is low, and the attenuation characteristics of the filter are improved.

Contents of the invention

The purpose of the filter of the present invention is to provide a multi-band tunable filter for the traditional multi-band system with large volume and high system cost, and the filter bank composed of multiple single-band filters and a single signal processing frequency band. bandpass filter. The introduction of input-output coupling increases the out-of-band transmission zero point when the applied voltage is low, and the center frequencies of the first and third passbands are adjustable at 760MHz and 800MHz, and the filter has a compact structure, which realizes the miniaturization of the filter.

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

(1) On the basis of the traditional microstrip open-loop resonator, a Ψ-shaped section is added inside it to achieve dual-mode resonance, and the passband frequency can be adjusted by changing the frequency of the two modes to achieve an adjustable effect.

(2) A varactor diode is added at the end of the microstrip line of the open-loop dual-mode resonator to change the reverse bias voltage of the DC bias circuit to change its capacitance and change the electrical length of the resonator to achieve the purpose of adjustment.

(3) Utilize the folded structure of the traditional uniform impedance resonator (UIR), share the input and output coupling lines with the open-loop dual-mode resonator, independently adjust the resonant frequency of the open-loop dual-mode resonator, and achieve the purpose of asynchronous adjustment .

(4) The present invention adopts the following dielectric plate materials: the dielectric constant of the dielectric substrate is =2.2, thickness h =0.508mm.

(5) The 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 plate is a layer of metal plating, and two SMA connectors are welded at the input and output ports. in actual measurement. The front metal microstrip line structure is composed of a uniform impedance impedance line, an open-loop dual-mode resonator, and an input-output coupling line. A varactor diode is added at the end of the open-loop dual-mode resonator, and the frequency can be adjusted by changing the bias voltage. .

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

A multi-band tunable microstrip bandpass filter includes a three-layer structure: a metal microstrip line on the front, a middle dielectric plate layer, input and output ports and ground metal through holes, and a metal plating layer on the reverse side of the dielectric plate. The metal microstrip line is a resonator with a symmetrical structure composed of a half-wavelength uniform impedance line resonator and an open-loop dual-mode resonator. The two resonators share an input and output coupling line, and the end of the open-loop dual-mode resonator is connected to the ground. Varactor diodes are loaded between the metal vias to form a tunable structure.

The open-loop dual-mode resonator is composed of a Ψ-shaped open-circuit stub loaded in the middle of an open-loop square-ring resonator, has a symmetrical structure, and produces resonance frequencies of two modes, so it can be analyzed by odd and even mode theory. The half-wavelength uniform impedance line resonator adopts a bent structure to meet the requirement of miniaturization. The input-output coupling is that the open-loop dual-mode resonator shares an input-output coupling line with the half-wavelength uniform impedance line, and feeds through the gap coupling. When the loading voltage is low, an additional finite frequency transmission zero point is added to improve the filter attenuation characteristics.

The bias circuit uses a varactor diode to load a 1000pF capacitor and a resistance value of 10k on the open-loop dual-mode resonator Resistors, and a varactor diode, such as a varactor diode BB857, is loaded at the end of the branch, and the voltage changes at 7.5-15V. Where two identical varactor diodes are added at the end of the split ring, the capacitance variation is 0.7-1.5pF, and a varactor diode is added at the end of the Ψ-shaped section, the capacitance variation is 0.4-0.9pF.

The dielectric plate layer is a dielectric constant The dielectric board, the thickness of the dielectric board h=0.508mm.

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.

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

1. The filter of the present invention adopts an open-loop dual-mode resonator structure. By adding a Ψ-shaped joint in the middle of the split ring, the structure of the resonator is more compact, which simplifies the complexity of the design and meets the requirements of modern filter design miniaturization .

2. By adding a bias circuit, adjusting the voltage to change the capacitance value of the varactor diode to achieve adjustable passband, it has the advantages of fast tuning speed, wide tuning frequency range, convenient debugging, and low cost.

3. By introducing input-output coupling, an additional finite frequency transmission zero point is added when the loading voltage is low, which improves the frequency selectivity of the filter.

4. A varactor diode is added at the end of the open-loop dual-mode resonator to realize the adjustment of the two passband frequencies, while the passband frequency caused by the uniform impedance line resonance can remain unchanged.

Description of drawings

Figure 1 is a schematic diagram of the structure of a multi-passband tunable microstrip bandpass filter.

Figure 2 is a schematic diagram of the structure of the metal microstrip line on the upper layer of the multi-passband tunable microstrip bandpass filter.

Figure 3 is a schematic diagram of a varactor diode.

Figure 4 is a schematic diagram of the overall structure of the multi-passband tunable microstrip bandpass filter of the present invention

Figure 5 is a schematic diagram of the frequency response of the microstrip filter when the voltage is 15V.

Fig. 6 is a schematic diagram of S11 of the microstrip filter when the voltage is adjustable between 7.5-15V.

Fig. 7 is a schematic diagram of S21 of the microstrip filter when the voltage is adjustable between 7.5V and 15V.

Detailed ways

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

Embodiment one:

Referring to Figure 1, the multi-band tunable microstrip bandpass filter includes a three-layer structure: the front metal microstrip line (1), the middle dielectric layer (2), and the input and output ports (3, 4) and the grounding metal Through holes (5), and metal plating on the reverse side of the dielectric sheet. The metal microstrip line is a resonator with a symmetrical structure composed of a half-wavelength uniform impedance line resonator (1-1) and an open-loop dual-mode resonator (1-2), so it can be analyzed by odd and even mode theory, The two resonators share the input and output coupling lines, and a varactor diode is loaded between the end of the open-loop dual-mode resonator and the ground metal through hole (5), forming a tuneable structure.

Embodiment two:

This embodiment is basically the same as Embodiment 1. The metal microstrip line on the front is shown in Figure 2. The special feature is that the open-loop dual-mode resonator is composed of a split square ring resonator (1) loaded in the middle with a Ψ-shaped open circuit short The stub (2) consists of a symmetrical structure that produces two modes of resonant frequencies. The half-wavelength uniform impedance line (3) resonator adopts a bent structure, which reduces the area of the filter and meets the requirement of miniaturization. The input-output coupling line (4) is fed through the gap coupling, and an additional limited-frequency transmission zero point is added when the applied voltage is low, thereby improving the attenuation characteristics of the filter. The dielectric plate layer is a dielectric constant The medium plate, the thickness of the medium plate h = 0.508mm.

Embodiment three:

This embodiment is basically the same as Embodiment 2, in particular, a varactor diode is loaded between the open-loop dual-mode resonator and the grounded metal via (Figure 3), and a reverse bias is applied to the varactor diode through a DC bias circuit. Change the resonant frequency of the odd and even modes to achieve the purpose of adjusting the center frequency and bandwidth of the band-pass filter.

Fig. 4 is the structural representation of present embodiment, through design, emulation and optimization, finally determine the specific size of this multi-pass band adjustable band-pass filter as follows:

L1=8.0mm, L2=7.75mm, L3=7.6mm, L4=6.1mm, L5=1.6mm, L6=0.8mm,

W1=3.3mm, W2=4.32mm, W3=3.75mm, W4=2.75mm, W5=4.0mm, W6=2.8mm,

D1=0.3mm, D2=0.25mm, D3=0.6mm, D4=0.3mm, D5=0.4mm, d=0.508mm,

r=0.4mm

Based on the above method, a three-band microstrip filter with a center frequency of 2.68GHz/4.66GHz/5.88GHz is designed, which is simulated and debugged by the electromagnetic simulation software Sonnet.

Figure 5 shows the simulation results of the microstrip filter when the voltage is 15V.

Figure 6 and Figure 7 respectively show the simulation results of S11 and S21 of the microstrip filter when the voltage is adjustable between 7.5-15V. Simulation results show

(1) The filter realizes the response characteristic of three frequency bands, and both the first frequency band and the third frequency band are adjustable, and the center frequency and bandwidth of the second frequency band remain unchanged.

(2) When the loading voltage is low, there is a transmission zero point between the first frequency band and the second frequency band, the cut-off edge of the passband is steep, the insertion loss in the passband is low, and the selectivity is good.

(3) The adjustable range of the center frequency of the first frequency band is adjustable from 2.1GHz to 2.86GHz, and the center frequency of the third frequency band is adjustable within the range of 5.3GHz to 6.1GHz. As the frequency increases, the absolute bandwidth of each frequency band gradually widens.

(4) The structure of the microstrip is simple, the size is also miniaturized, the printing is simple, and the material loss is relatively small.

Claims (4)

1. a multi-band tunable microstrip bandpass filter, comprise three-decker: positive metal micro-strip line (1), middle medium flaggy (2) and input/output port (3, 4) and grounded metal through hole (5), and the coat of metal of medium sheet material reverse side, it is characterized in that: described metal micro-strip line (1) consists of the resonator of symmetrical structure a half-wavelength uniform impedance line resonator (1-1) and open loop dual-mode resonator (1-2), two resonator (1-1, 1-2) share input and output coupling line (1-3), between open loop dual-mode resonator (1-2) end and grounded metal through hole (5), load variable capacitance diode, form tunable structure.

2. multi-band tunable microstrip bandpass filter according to claim 1, it is characterized in that: described open loop dual-mode resonator (1-2) forms by loading Ψ shape open stub in the middle of an opening quadratic loop resonator, its symmetrical configuration, the resonance frequency of two kinds of patterns of generation; Described half-wavelength uniform impedance line resonator (1-1) adopts bending type structure, has reduced the area of filter, meets the demand of miniaturization; Described input and output coupling line (1-3), by aperture-coupled, produces extra finite frequency transmission zero when on-load voltage is lower, has improved the attenuation characteristic of filter.

3. multi-band tunable microstrip bandpass filter according to claim 1, it is characterized in that: between described open loop dual-mode resonator (1-2) and grounded metal through hole (5), load variable capacitance diode, by DC bias circuit, to variable capacitance diode, load reverse biased, the resonance frequency that changes parity mode reaches band pass filter centre frequency and the adjustable object of bandwidth.

4. multi-band tunable microstrip bandpass filter according to claim 1, is characterized in that: described medium flaggy (2) is dielectric constant dielectric-slab, this dielectric-slab thickness h=0.508mm.