TW595141B - Open-short end coupled filter - Google Patents

Abstract

An open-short end coupled filter at least includes a input port for receiving input signal, a bent first resonator, a short second resonator, a bent third resonator and a output port for outputting the filtered input signal. Wherein, the bent first resonator and the bent third resonator are cross-coupled to each other. Therefore, the open-short end coupled filter can get better frequency response and avoid being interfered by image signal.

Description

595141

FIELD OF THE INVENTION The present invention relates to a cross-link filter, and more particularly to an open-short terminal cross-link filter. With the advancement of communication technology, wireless communication devices have become more and more widely used. In various wireless communication devices, the transmission frequency band used has also increased from radio frequency (RF) to microwave frequency. However, no matter what frequency band it is used in, the interference of electromagnetic noise will become more serious because of the widespread use of wireless products. Therefore, the performance of the filter becomes an important factor for the overall performance of the communication device. The filters used in the microwave frequency band are usually made by transmission lines, that is, the characteristics of the microstrip line (micr 0 strip 1 ine) open or short are used to make the resonant cavity (R es ο nator). ), And the microwave signal is transmitted in the resonant cavity, and the electromagnetic field is coupled to a plurality of resonant cavities to cause a filter effect. Please refer to FIG. 1, which is a diagram of a conventional third-order microstrip transmission line cross-connected wave filter (Microstrip Coupled Line F i 11 e r) applicable to the microwave frequency band. As shown in the figure, this transmission line cross-link filter includes an input port 110, a first resonant cavity 120, a second chirped cavity 130, a third resonant cavity 140, and an output end 150. The input terminal 110 is used to receive an input signal. The first resonant cavity 120 is coupled to the input terminal 110, which is an open-circuit resonant cavity, and the second resonant cavity 130 is coupled to the first resonant cavity 120, which is also An open-circuit resonant cavity, the third resonant cavity is coupled to the second

595141 V. Description of the invention (2) The resonant cavity 1 3 0 is also an open-circuit resonant cavity, and the output terminal 15 0 is coupled to the third resonant cavity 1 4 0 to output a signal. This type of transmission line cross-link filter has the following disadvantages when applied to today's communication systems: 1. The cut-off frequency band (st oopband) has insufficient attenuation amplitude to effectively eliminate the image signal (imagesigna 1), which can be referred to in Figure 2 The frequency response diagram of the microstrip transmission line cross-link filter is shown. 2. If you want to obtain a transmission line cross-linked filter with a faster cutoff frequency band, you must increase the number of resonant cavities. When the number of resonant cavities increases, the length of the entire filter will be stretched so long that it takes up too much space. It is not in line with the current development trend of electronic circuits toward light, thin and short. SUMMARY OF THE INVENTION In view of this, the present invention provides an open-short-circuit terminal cross-linking filter, which can achieve the frequency response curve of fast attenuation of the stop band and adjust and eliminate the interference of the image signal without occupying too much space. To achieve the above and other objectives, the present invention provides an open-short-terminated cross-link filter. The open-short-circuit termination cross-linking filter includes: an input end, a first resonant cavity, a second resonant cavity, a third resonant cavity, and an output end. The input terminal is used to receive input signals. The first resonant cavity is a discounted resonant cavity and is coupled to the input terminal. The second resonant cavity is a vibrating cavity with short-circuited ends and is coupled to the first vibrating cavity. The resonant cavity is a discounted resonant cavity and is coupled to the second resonant cavity and the staggered vehicle is coupled to the first resonant cavity, and the output end is coupled to the third resonant cavity to output a signal.

10785twf. Ptd Page 7 595141 V. Description of the invention (3) In one embodiment, the input and output terminals of the open-short-term cross-link filter are in the same direction, and there is a weak electromagnetic field coupling. This is also staggered coupling. One form is to form a phenomenon similar to the transmission zero in the high-frequency cut-off frequency band, thereby improving noise interference in adjacent frequency bands. In one embodiment, the input terminal, the first resonant cavity, the second resonant cavity, the third resonant cavity, and the output terminal of the open-short-terminated cross-linked filter are fabricated on a substrate. Among them, the substrate has a dielectric constant of 3.38 and a thickness of 20 m i 1. The two ends of the second resonant cavity are grounded by through-hole metal plating, or grounded by punching. In an embodiment, the lengths of the first and third resonant cavities are 6 1 2 mi 1, the length of the second resonant cavity is 6 3 6 mi 1, and the coupling distance is 4ni i 1 〇 Of course, also This open-short-term terminal cross-linked filter with a discounted resonant cavity, a short-circuited resonant cavity, and a staggered coupled resonant cavity can be applied to a third-order or higher-order cross-linked filter, such as In the case of multiple spaces, it has the frequency response curve for rapid attenuation of the cut-off frequency band and the function of eliminating the interference of the image signal. In order to make the above and other objects, features, and advantages of the present invention more comprehensible, a detailed description is given below with preferred embodiments and the accompanying drawings as follows: Implementation: Please refer to FIG. 3 , Which is a diagram of an open-short-term termination cross-link filter according to a preferred embodiment of the present invention. In Figure 3, except for the input terminal 3 1 0 which also receives the input signal and the input signal after the output filtering

10785twf. Ptd Page 8 595141 V. Description of the invention (4) In addition to the output terminal 3 5 0, one of the first resonant cavity 3 2 0, the second resonant cavity 3 3 0 and the third resonant cavity 3 4 0 have been separated, respectively. Change to a resonant cavity with a discount or a short circuit at both ends, and introduce the concept of cross coupling. In the figure, the first resonant cavity 3 2 0 and the third resonant cavity 3 4 0 are discounted resonant cavities, and the second resonant cavity 3 3 0 are resonant cavities with short-circuited ends. The first resonant cavity 3 2 0 is coupled to the input terminal 3 1 0, the second resonant cavity 3 3 0 is coupled to the first resonant cavity 3 2 0, and the third resonant cavity 3 4 0 is coupled to the second resonant cavity 3 3 0 There is a staggered coupling structure between the first resonant cavity 3 2 0 and the third resonant cavity 3 40. This structure arrangement, in addition to making the entire filter length not too long, is also due to the staggered coupling effect between the first resonant cavity 3 2 0 and the third resonant cavity 3 4 0, and the second resonance The cavity 350 is short-circuited at both ends as an arrangement of the terminal short-circuit resonant cavity, so that a transmission zero is generated in the lower-side stop band, and a very steep frequency response curve is achieved. For a system with an RF frequency greater than the L0 frequency (Upside Band), using the characteristics of the frequency response curve of the transmission zero point, we can design the transmission zero point in the frequency band where the image signal will appear, and greatly attenuate the image signal to improve The interference of the mirror signal on the main signal after frequency reduction. For example, when the center frequency of the open-short-terminated cross-link filter is designed at fRF = 5.8 GHz, and the local seismic frequency of the mixer using this open-short-terminated cross-link filter is f = 5. 1 G Η z, Since the frequency of the IF signal after mixing is f IF = 0.7 G Ηζ, the transmission zero point can be designed as a mirror signal of 2 * 5. 1 G Η ζ-5. 8 GH z = 4.4 G Η ζ Frequency band to eliminate the image signal

10785twf. Ptd Page 9 595141 V. Description of the invention (5) Interference after frequency reduction of the main signal. The design adjustment method is to advance or extend the distance of the staggered coupling between the first resonant cavity 3 2 0 and the third resonant cavity 3 4 0 in FIG. 3 to change the zero point for eliminating the transmission zero point of the image signal. position. In addition, the open-to-short-term terminal cross-linked filter in FIG. 3 has the first resonant cavity 3 2 0 and the third resonant cavity 3 4 0 discounted at a right angle. Therefore, the input terminal 310 and the output terminal 350 can be arranged. Toward the same direction, there is a weak electromagnetic field coupling, which makes the high-frequency cut-off frequency band form a similar effect of the transmission zero point, thereby improving the noise interference of adjacent frequency bands. In order to verify the frequency response curve of the open-short-terminal cross-linked filter, the input terminals 3 1 0, the first resonant cavity 320, the second resonant cavity 330, the third resonant cavity 340, and The output terminal 350 is fabricated on a substrate having a dielectric constant of 3.38 and a thickness of 20 mils. Its production method uses the general circuit board production method, that is, graphics, photography, chemical processes (including: photoresist, exposure, etching), etc. have been applied to microwave communication production technology, and the second resonant cavity 3 3 0 Grounding at both ends can be made by through-hole metal plating or by hitting the grounding post. Among them, because the center frequency of the selected open-short-terminated cross-link filter is 5.8 GHz, the length of the first chirped cavity 320 and the third resonant cavity 34 0 is 612 mil, and the length of the second resonant cavity 3 3 0 The length is 6 3 6 in i 1 and the coupling distance between the resonators is 4 mi 1 to match the required center frequency. Please refer to Figure 4, which is a measurement of the frequency response curve of the open-short-terminated cross-link filter. The figure shows that this is made based on Figure 3.

10785twf.ptd Page 10 595141 V. Description of the invention (6) The frequency response curve of the open-to-short-term terminal cross-link filter, whose center frequency is 5.8 61 ^, and the filter band width (? 833 乜 311 (1) is about 5.5 ~ 6.2 } ^, The insertion loss (Insertion Loss) is about 1.5 ~ 2 dB, the return loss (Return Loss) is greater than 10 dB, and the image signal rejection (Image Rejection) capability of the transmission zero point C is greater than 40 dB. In addition, because the first The resonant cavity 3 2 0 and the third resonant cavity 3 4 0 are discounted at right angles, and the input end 310 and the output end 350 are arranged in the same direction, and there is a weak electromagnetic field coupling, so that point D in the figure , Forming a high-frequency wear-resistance band similar to the effect of zero transmission. Of course, as the person skilled in the art knows, if this has both a discounted resonant cavity, a short-circuited resonant cavity at both ends, and an open-short-term terminal cross-linked filtering of the staggered coupled cavity Device, which can be flexibly applied to a third-order or higher cross-link filter, and choose to arrange the input end and the output end in the same direction, and there is a weak electromagnetic field coupling, which can also reach the cost of the invention. The advantages are as follows: 1. The method of adjusting the resonant cavity can make the length of the entire filter not too long. 2. The interleaved coupling method such as the first resonant cavity and the third resonant cavity, and the second resonant The way of shorting the two ends of the cavity makes the transmission zero point in the low-frequency cut-off frequency band. In addition to obtaining a steep frequency response, the transmission zero point can be designed in the frequency band where the image signal will appear to improve the image signal to reduce the main signal. After the high-frequency interference. 3. The input and output terminals can be designed to be oriented in the same direction, and there is a weak electromagnetic field coupling, which makes the high-frequency load band similar.

10785twf. Ptd Page 11 595141 V. Description of the invention (7) The effect of the transmission zero point, thereby improving the interference of noise in adjacent frequency bands. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and retouches without departing from the spirit and scope of the present invention. The scope of protection shall be determined by the scope of the attached patent application.

10785twf.ptd Page 12 595141 Brief description of the diagram Figure 1 shows a conventional third-order transmission line cross-link filter and wave filter suitable for microwave frequency bands; Figure 2 shows the frequency response of the transmission line cross-link filter in Figure 1 FIG. 3 is a diagram showing an open-short-term terminal cross-link filter according to a preferred embodiment of the present invention; and FIG. 4 is a diagram showing a frequency response diagram of the open-short-term terminal cross-link filter measured in FIG. 3. Description of the diagrams: 1 1 0, 31 0 Input 1 2 0, 3 2 0 First resonant cavity 1 3 0, 3 3 0 Second resonant cavity 1 4 0, 3 4 0 Third resonant cavity 1 50, 3 5 0 output

10785twf. Ptd Page 13

Claims (1)

595141 VI. Scope of patent application 1. An open-circuit and short-circuit termination cross-linking filter, comprising: an input terminal for inputting a signal; a first resonant cavity, which is a discounted resonant cavity and is coupled to the input A second resonant cavity, the second resonant cavity being a short-circuited resonant cavity and coupled to the first resonant cavity; a third resonant cavity, the third resonant cavity being a discounted resonant cavity and coupled to The second resonant cavity and the staggered coupling are coupled to the first resonant cavity; and an output terminal is coupled to the third resonant cavity to output the filtered signal. 2. The open / short-circuited terminal cross-connect filter according to item 1 of the scope of the patent application, wherein the input terminal and the output terminal are directed in the same direction and there is a weak electromagnetic field coupling. 3 · The open-short-term terminal cross-linked filter according to item 1 of the scope of patent application, wherein the input end, the first resonant cavity, the second resonant cavity, the third resonant cavity, and the output end are made in one On the substrate. 4 · The open / short-circuited terminal cross-linked filter as described in item 3 of the scope of patent application, wherein the substrate has a dielectric constant of 3.38 and a thickness of 20 mil. 5. The open / short-circuited terminal cross-linked filter according to item 3 of the scope of patent application, wherein both ends of the second resonant cavity are grounded by through-hole metal plating. 6. The open / short-circuited terminal cross-linked filter according to item 3 of the scope of patent application, wherein both ends of the second resonant cavity are grounded by making a grounding post. 10785twf. Ptd Page 14 595141 6. Scope of patent application 7. The open and short-circuited terminal cross-linked filter described in item 3 of the scope of patent application, wherein the length of the first resonant cavity and the third resonant cavity is 6 1 2 mi 1. The length of the second resonant cavity is 6 3 6 mi 1, and the coupling distance between the resonant cavities is 4 mi 1. 8. A cross-link filter with open and short terminals, at least comprising: an input terminal for inputting a signal; a first resonant cavity, the first resonant cavity is a discounted resonant cavity; a second resonant cavity, the second The resonant cavity is a resonant cavity with a short circuit at both ends; a third resonant cavity, which is a discounted resonant cavity and is staggered coupled to the first resonant cavity; and an output terminal for outputting the filtered signal . 9. The open / short-circuit terminal cross-connect filter according to item 8 of the scope of the patent application, wherein the input terminal and the output terminal are oriented in the same direction and a weak electromagnetic field is engaged. 10. The open-short-circuit termination cross-linking filter according to item 8 of the scope of patent application, wherein the input end, the first resonant cavity, the second resonant cavity, the third resonant cavity, and the output end are manufactured at On a substrate. 11. The open-short-terminated cross-linked filter as described in item 10 of the scope of patent application, wherein both ends of the second resonant cavity are grounded by through-hole metal plating. 1 2. The open-short-circuit terminal cross-linked filter according to item 10 of the scope of patent application, wherein the two ends of the second resonant cavity are grounded by making a grounding post. 10785twf.ptd Page 15