CN1747227A - Compensated microstrip resonator and microstrip open loop coupled bandpass filter for harmonic suppression - Google Patents

Abstract

The little band open loop coupling band-pass filter that the invention discloses a kind of offset-type micro-strip resonantor and have harmonic restraining function.Described filter comprises incoming feeder and output feeder, open circuit loop coupling device, it is characterized in that, also comprises the offset-type micro-strip resonantor, and described incoming feeder links to each other with open circuit loop coupling device respectively with after the series connection of offset-type micro-strip resonantor with output feeder again.The present invention is by on the basis of traditional open loop coupling band-pass filter, series compensation type micro-band resonance unit between input and output feeder line and open circuit loop coupling device relies on the forbidden band characteristic of compensated compact microstrip resonant cell to reach the function that increases the outer inhibition of filter band.That the present invention has is simple in structure, overall dimensions is little, and insert that loss is little, band is outer suppresses advantage such as big, can be with the backing material making of any suitable microwave circuit.

Description

Compensated microstrip resonator and microstrip open loop coupled bandpass filter for harmonic suppression

Technical field:

The invention belongs to the technical field of microwave microstrip circuits, in particular to the design of a bandpass filter, in particular to a compensated microstrip resonator and a microstrip open loop coupled bandpass filter including harmonic suppression of the resonator .

Background technique:

Band-pass filter is a very important device in microwave circuits. In the case of increasingly tight spectrum resources and more and more serious electromagnetic interference, higher requirements are put forward for the performance and cost of filters. An ideal filter characteristic should be no attenuation in the passband and as large an attenuation as possible in the forbidden band.

The open loop microstrip coupled bandpass filter was first proposed by Jia-Sheng Hong in 1995 and has been widely used in planar microwave circuits. This type of filter has good frequency selectivity and low insertion loss, and has a small area, which can be realized on ordinary printed circuit board technology without through-hole grounding. However, the out-of-band attenuation of the filter is small, especially at the second-order and third-order harmonics, there is only 10dB to 15dB attenuation, which is far from meeting the needs of practical applications, and an external low-pass filter is often required to suppress harmonics. Wave.

Figure 1 shows the structure diagram of the open-loop microstrip coupling bandpass filter. It can be seen from the figure that the coupling filter is symmetrically coupled by two open-circuit resonant rings, and uses an asymmetrical 50Ω input and output feeder. The open-loop microstrip coupling bandpass filter has a working center frequency of 1.8GHz, uses F4B material, the relative permittivity is 2.65, the thickness is 1mm, and the length of the open-loop coupling loop is 56mm, which is half of the working frequency. wavelength. Figure 2 shows the frequency response diagrams for simulation and testing of this filter. In the figure, S21 is the transmission characteristic of the filter, and the insertion loss in the passband is less than 2.7dB (including two SMA connectors); S11 is the standing wave characteristic of the filter, which is greater than 12.6dB in the passband range , at the second-order harmonic of the operating frequency, the minimum out-of-band attenuation is 12dB. It can be seen that the open loop microstrip coupling bandpass filter has good filtering characteristics in the passband. However, due to the parasitic passband effect of the microstrip circuit, the attenuation at the second-order harmonic is small, which cannot well meet the needs and applications in actual circuits.

Invention content:

The purpose of the present invention is to overcome the above-mentioned deficiencies existing in the prior art, and propose a microstrip open-loop coupled bandpass filter with harmonic suppression function, so that it increases the filtering frequency without affecting the characteristics in the passband. out-of-band rejection of the device.

The technical scheme that the present invention solves technical problem is as follows:

A compensated microstrip resonator, characterized in that it comprises a microstrip resonant unit and an open-circuit compensation microstrip line, and an open-circuit compensation microstrip line is connected in parallel in the middle of the microstrip resonator unit; the microstrip resonator unit includes The input end, the output end, a group of folded microstrip lines and the middle microstrip line. connected to the input and output respectively.

A kind of microstrip open loop coupling bandpass filter with harmonic suppression function, comprising input feeder and output feeder, open loop coupler, is characterized in that, also comprises the above-mentioned compensation type microstrip resonator, described input The feeder and the output feeder are respectively connected in series with the compensated microstrip resonator and then connected with the open loop coupler.

The line width of the input and output feeder is 50Ω characteristic line width, and an asymmetrical feeder is used, and a symmetrical feeder may also be used.

The input end and the output end of the microstrip resonant unit are respectively connected with the input feeder or output feeder of the filter and the open loop coupler. That is, one end of the input feed line of the filter is connected to the input end of the first microstrip resonant unit, and the output end of the microstrip resonant unit is connected to the input end of the open loop coupler; the output end of the open loop coupler is connected to the second The input end of the microstrip resonance unit is connected, and the output end of the microstrip resonance unit is connected to the output feeder.

The total length of the coupling open loop is 1/2 of the wavelength of the center frequency of the filter, and the width is 50Ω linewidth.

The terminal coupling gap of the open loop and the coupling gap between two open loops depend on the specific filter center frequency and substrate.

As can be seen from the technical solutions disclosed above, the beneficial effects of the present invention are as follows:

The compensated microstrip resonator of the present invention can achieve the purpose of matching the characteristic impedance of the low frequency band and increasing the forbidden band by connecting the microstrip capacitive load in parallel in the middle of the microstrip resonant unit. In addition, the open loop coupling bandpass filter for harmonic suppression of the present invention is based on the traditional open loop coupling bandpass filter, and the compensation type microstrip resonator of the present invention is connected in series between the input and output feeder and the open loop coupler , relying on the bandgap characteristics of the compensated microstrip resonator to achieve the function of increasing the out-of-band rejection of the filter. Compared with the original open loop coupling bandpass filter, the circuit area is not increased, and the insertion loss in the passband is not increased, and the invention can be made by any substrate material suitable for microwave circuits.

Description of drawings:

Fig. 1 is a schematic diagram of the structural layout of a traditional open loop coupled bandpass filter.

Figure 2 is a frequency response diagram of a traditional open-loop coupled bandpass filter with a center frequency of 1.8GHz.

FIG. 3 is a schematic diagram of the structural layout of the compensated microstrip resonator of the present invention.

Fig. 4 is a frequency response diagram of a compensated microstrip resonant unit with a cutoff frequency of 1.8 GHz according to the present invention.

FIG. 5 is a schematic diagram of the structural layout of the microstrip open loop coupled bandpass filter with harmonic suppression function of the present invention.

Accompanying drawing 6 is the frequency response diagram of the microstrip open-loop coupled bandpass filter with a harmonic suppression function having a center frequency of 1.8 GHz according to the present invention.

In the above frequency response graphs, S11 represents the standing wave characteristic curve of the filter drawn according to the analog value, S11' represents the standing wave characteristic curve of the filter drawn according to the measured value; S21 represents the standing wave characteristic curve of the filter drawn according to the simulated value The transmission characteristic curve of the filter, S21' represents the transmission characteristic curve of the filter drawn according to the measured value.

Detailed ways:

Embodiments and detailed descriptions of the microstrip open-loop coupled bandpass filter with harmonic suppression function designed by the present invention are as follows. All embodiments are fabricated on a F4B substrate with a dielectric constant of 2.65 and a thickness of 1 mm. The present invention can also be fabricated on other substrates, which all belong to the protection scope of the present invention.

As shown in Figure 3, the compensation type microstrip resonator of the present invention includes a microstrip resonant unit 10 and an open circuit compensation microstrip line 11, 12, and an open circuit compensation microstrip line 11, 12 is respectively connected in parallel in the middle of the microstrip resonator unit. The microstrip resonant unit includes an input terminal 13, an output terminal 14, a group of folded microstrip lines 15, 16 and an intermediate microstrip line 17, and the two ends of the folded microstrip lines 15, 16 are folded inwardly and are separated by a central microstrip line. The stripline 17 is symmetrically arranged on a symmetrical line, and the two ends of the middle microstrip line 17 are respectively connected to the input terminal 13 and the output terminal 14 . The open-circuit compensation microstrip lines 11 and 12 are used as capacitive loads to compensate the impedance of the low-frequency band and increase the bandgap characteristic of the microstrip resonant unit. Fig. 4 shows the simulated frequency response diagram of the compensated microstrip resonator, it can be seen that the compensated microstrip resonator has low-pass filtering characteristics, and the cutoff frequency is 1.8 GHz. The line width of the input and output terminals 13 and 14 is 2.7 mm, which is a characteristic line width of 50 Ω. The line width and gap of the microstrip resonance unit 10 are both 0.3 mm. The length of the open circuit compensation microstrip lines 11 and 12 is 11.7 mm, and the width is 1mm.

As shown in Figure 5, the microstrip open loop coupling bandpass filter with harmonic suppression function of the present invention includes input feeder 31 and output feeder 32, traditional open loop coupler 33 and 34, also includes as shown in Figure 3 Compensated microstrip resonators 35 and 36 . Based on the traditional open loop coupling bandpass filter, the present invention connects a compensation microstrip resonator 35 and 36 in series between the input feeder 31 and output feeder 32 and the open loop couplers 33 and 34 respectively. The two ends of the compensated microstrip resonator, ie the input end and output end of the middle microstrip line, are respectively connected to the open loop coupler 33 or 34, the input feeder 31 or the output feeder 32. Figure 6 shows the simulated and tested frequency response plots of the open-loop microstrip coupling filter with harmonic suppression. It can be seen that the insertion loss in the passband is less than 2.8dB, which is not significantly increased compared with the 2.7dB insertion loss of the traditional open loop microstrip coupling bandpass filter. The main reason for this loss is the substrate dielectric loss . At the second-order harmonic, the attenuation reaches 58dB, compared with the attenuation of 12dB at the second-order harmonic of the traditional open-loop microstrip coupling filter, an increase of 46dB out-of-band rejection. The line width of the input and output terminals 31 and 32 and the line width of the open coupling lines 33 and 34 are both 2.7mm, which is a characteristic line width of 50Ω. The coupling gap inside each of the open loops 33 and 34 is 0.2 mm, and the coupling gap between the open loops 33 and 34 is 0.5 mm.

Claims (5)

1. an offset-type micro-strip resonantor is characterized in that, comprises micro-band resonance unit and open circuit compensated microstrip line, and the centre of described micro-band resonance unit is each open circuit compensated microstrip line in parallel up and down; Described micro-band resonance unit comprises input, output, one group of folding microstrip line and middle microstrip line, described folding microstrip line inward at both ends is folding and be that the line of symmetry symmetry is provided with middle microstrip line, described in the middle of the two ends of microstrip line link to each other with output with input respectively.

2. little band open loop coupling band-pass filter with harmonic restraining function, comprise incoming feeder and output feeder, open circuit loop coupling device, it is characterized in that, also comprise offset-type micro-strip resonantor as claimed in claim 1, described incoming feeder links to each other with open circuit loop coupling device respectively with after the series connection of offset-type micro-strip resonantor with output feeder again.

3. little band open loop coupling band-pass filter that harmonic wave according to claim 2 suppresses is characterized in that, the input of described micro-band resonance unit, output link to each other with the incoming feeder of filter or output feeder, open circuit loop coupling device respectively.

4. little band open loop coupling band-pass filter that harmonic wave according to claim 2 suppresses is characterized in that described input and output feeder line live width is 50 Ω characteristic line breadths, adopts asymmetric feeder line, also can adopt symmetrical feeder line.

5. the little band open loop coupling band-pass filter that suppresses according to each described harmonic wave of claim 2 to 4 is characterized in that the total length of described open circuit loop coupling device is 1/2nd wavelength of operating frequency, and live width is 50 Ω characteristic line breadths.

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