CN103117438A - Terahertz waveguide cavity filter - Google Patents

Abstract

The invention relates to a terahertz waveguide cavity filter, which is composed of an upper cavity at the upper part and a lower cavity at the lower part. The upper cavity is covered on the lower cavity and has a hollow structure at the junction of the two. A waveguide cavity, the waveguide cavity is located in the lower cavity; the third resonant cavity and the waveguide output section are connected in series through the fifth inductive coupling window; the waveguide input section, the first inductive coupling window, the first resonant cavity, the second Three inductive coupling windows, the second resonant cavity, the second inductive coupling window and the waveguide output section are sequentially connected in series to form a coupling path—as the main signal path; the waveguide input section, the fourth inductive coupling window, the third resonant cavity, the fifth inductive The coupling window and the waveguide output section are sequentially connected in series to form the second coupling path, which is used to form a transmission zero point at the low end of the passband. The beneficial effect of the present invention is that: the passband of the waveguide cavity filter is located in the 380-390 GHz frequency band, and the atmospheric absorption window of this frequency band can be used to realize communication under specific conditions and the like.

Description

Terahertz waveguide cavity filter

technical field

The invention belongs to the technical field of terahertz passive devices, in particular to a WR2.2 (cross-sectional area of 0.56mm×0.28mm) rectangular waveguide cavity band-pass filter suitable for 325-500GHz frequency band based on bulk silicon etching process device.

Background technique

Terahertz frequency generally refers to the electromagnetic frequency band in the range of 300GHz to 3000GHz. It is located between the microwave frequency band (300MHz to 300GHz) and the infrared frequency band. It is limited to the technical level and has not been used in the past. It has become a Terahertz gap (Terahertz Gap). Due to the increasingly crowded electromagnetic spectrum, the spectrum resources below 300 GHz have been exhausted, and this "blank" needs to be utilized urgently. In recent years, with the advancement of technology, research on devices and systems suitable for terahertz frequency bands has been carried out, and terahertz filters, as an important component of terahertz systems, have become a hot research topic at present. However, in different frequency bands in the terahertz frequency range, the transmission of electromagnetic waves has different characteristics. Therefore, it is very difficult to research and develop waveguide filters suitable for specific frequency bands in the terahertz frequency band. In order to expand the utilization range of spectrum resources and change the increasingly crowded electromagnetic spectrum, research and development of waveguide filters applicable to specific frequency bands of terahertz frequencies is a common task faced by scientific and technological workers in the field.

A filter is a two-port network that is used to select the frequency response somewhere in the system by providing signal transmission in the passband frequency of the filter and attenuation in the stopband. Typical frequency responses include low-pass, high-pass, band-pass and band-stop characteristics. Filters are actually widely used in various types of communication, radar test or measurement systems. The implementation forms of filters are mainly divided into planar circuits (microstrip lines, coplanar waveguides, etc.) and metal cavity circuits (rectangular waveguides). The realization principle is to connect one or more resonant units through coupling to achieve a certain Frequency response. Its frequency response is directly determined by the characteristics of the resonant unit, the strength of the coupling between units, and the overall structural topology: the characteristics of the resonant unit mainly include its specific shape and Q value; the form of coupling can be divided into magnetic and magnetic based on the field distribution on the coupling surface. Coupling, electrical coupling, and hybrid coupling can be divided into capacitive coupling, inductive coupling, etc. according to the nature of the equivalent circuit at the coupling surface; while the overall structural topology determines the order of the filter and the position of the zero pole. At present, in the terahertz frequency band, the traditional planar circuit filter cannot be used due to its high dielectric loss; the pure metal waveguide circuit cannot be realized by traditional metal processing technology due to its fine structure; other photonic crystal structure filters lack versatility, so There is also a lack of mature and versatile filter forms.

Contents of the invention

The purpose of the present invention is to provide a terahertz waveguide cavity filter applicable to the 325-500 GHz frequency band in view of the shortcomings of existing filters in the terahertz frequency band, and strive to change the current situation of lack of general filters in the terahertz frequency band.

The technical solution of the present invention is: a terahertz waveguide cavity filter, which is composed of an upper cavity on the upper part and a lower cavity on the lower part, the upper cavity is covered on the lower cavity and has a A waveguide cavity formed by a hollow structure, the waveguide cavity is located in the lower cavity; it is characterized in that the waveguide cavity includes a cuboid waveguide input section and a waveguide output section, which are located between the waveguide input section and the waveguide output section and are also in the shape of a cuboid The first resonant cavity, the second resonant cavity and the third resonant cavity, the waveguide input section and the first resonant cavity are connected in series through the first inductive coupling window, and the first resonant cavity and the second resonant cavity are connected through the third resonant cavity The inductive coupling window is connected in series, the second resonant cavity is connected in series with the waveguide output section through the second inductive coupling window, the waveguide input section and the third resonant cavity are connected in series through the fourth inductive coupling window, and the third resonant cavity is connected in series with the third resonant cavity. The waveguide output sections are connected in series through the fifth inductive coupling window; the waveguide input section, the first inductive coupling window, the first resonant cavity, the third inductive coupling window, the second resonant cavity, the second inductive coupling window and the waveguide output section The first coupling path is formed in series as the main signal path; the waveguide input section, the fourth inductive coupling window, the third resonant cavity, the fifth inductive coupling window and the waveguide output section are sequentially connected in series to form a coupling path two, which is used for the low passband The ends form a transmission zero point; the middle parts of the first resonant cavity, the second resonant cavity and the third resonant cavity have bosses for separating the three resonant cavities, waveguide input section and waveguide output section.

The beneficial effects of the present invention are: the passband of the waveguide cavity filter of the present invention is located in the 380-390 GHz frequency band, and the atmospheric window of 94 GHz can be used to realize quadrupling frequency high-power output, and the atmospheric absorption window of this frequency band can be used to realize high-power output under specific conditions. Communication and other characteristics, with excellent transmission performance. At the same time, the design structure of half of the filter structure etched in the upper and lower cavities of the filter in the prior art is abandoned, which completely avoids the problem of misalignment that may occur when the upper and lower cavities are closed, and greatly improves the efficiency of the filter. Manufacturability.

Description of drawings

Fig. 1 is a schematic diagram of the front view structure of the terahertz waveguide cavity filter of the present invention.

Fig. 2 is a schematic top view structure diagram of the terahertz waveguide cavity filter of the present invention.

Fig. 3 is a front view schematic diagram of the lower cavity of the terahertz waveguide cavity filter of the present invention.

FIG. 4 is a schematic plan view of the lower cavity of the terahertz waveguide cavity filter of the present invention.

FIG. 5 is a schematic diagram of key dimensions of the top view structure of the lower cavity of the terahertz waveguide cavity filter of the present invention.

Fig. 6 is a test curve of the terahertz waveguide cavity filter of the present invention in the frequency band of 325-440 GHz.

Description of reference numerals: upper cavity 1, lower cavity 2, waveguide cavity 3, waveguide input section 4, waveguide output section 5, first resonant cavity 6, second resonant cavity 7, third resonant cavity 8, first inductive cavity Coupling window 9 , second inductive coupling window 10 , third inductive coupling window 11 , fourth inductive coupling window 12 , fifth inductive coupling window 13 , boss 14 , short-circuit end 15 , short-circuit end 16 .

Detailed ways

The inventors of the present application found that in the terahertz frequency band, the dielectric loss of various dielectric materials increases sharply, and it is difficult to apply filters with dielectric filling in this frequency band, such as planar filters based on microstrip. The inventor also discovered that in the 380-390GHz terahertz frequency band of its passband, the 94GHz atmospheric window can be used to achieve quadrupled high-power output, and the atmospheric absorption window of this frequency band can be used to realize communication under specific conditions. Based on the above findings, the inventors researched and developed a terahertz waveguide cavity filter with a passband in the range of 380-390 GHz.

As shown in Fig. 1, Fig. 2, Fig. 3 and Fig. 4, the terahertz waveguide cavity filter provided by the present application is composed of an upper cavity 1 on the upper part and a lower cavity 2 on the lower part. The cavity 1 is covered on the lower cavity 2 and has a waveguide cavity 3 formed by a hollow structure at the junction of the two. The waveguide cavity 3 is located in the lower cavity 2; it is characterized in that the waveguide cavity 3 includes a cuboid The waveguide input section 4 and the waveguide output section 5 are located between the waveguide input section 4 and the waveguide output section 5 and are also rectangular parallelepiped first resonant cavity 6, second resonant cavity 7 and third resonant cavity 8, the waveguide input section 4 is connected in series with the first resonant cavity 6 through the first inductive coupling window 9, the first resonant cavity 6 is connected in series with the second resonant cavity 7 through the third inductive coupling window 11, and the second resonant cavity 7 is connected with the waveguide output The section 5 is connected in series through the second inductive coupling window 10, the waveguide input section 4 and the third resonant cavity 8 are connected in series through the fourth inductive coupling window 12, and the third resonant cavity 8 and the waveguide output section 5 are connected in series through the first Five inductive coupling windows 13 are connected in series; the waveguide input section 4, the first inductive coupling window 9, the first resonant cavity 6, the third inductive coupling window 11, the second resonant cavity 7, the second inductive coupling window 10 and the waveguide output section 5 are sequentially connected in series to form a coupling path—as the main signal path, which is used to form a second-order bandpass filter characteristic with a center frequency at 385 GHz; the waveguide input section 4, the fourth inductive coupling window 12, the third resonant cavity 8, and the fifth inductive The coupling window 13 and the waveguide output section 5 are sequentially connected in series to form a second coupling path, which is used to form a transmission zero point at the low end of the passband, thereby optimizing the out-of-band suppression of the bandpass filter at the low end; the first resonant cavity 6, the second The middle part of the resonant cavity 7 and the third resonant cavity 8 has a boss 14 for separating the three resonant cavities, the waveguide input section 4 and the waveguide output section 5 .

The above-mentioned waveguide cavity 3 is filled with air, the upper cavity 1 and the lower cavity 2 are made of silicon-based gold-plated material, the waveguide input section 4 and the waveguide output section 5 of the waveguide cavity 3 are standard WR2.2 rectangular waveguides, and the width of the cross section is , High dimensions are 560μm±5μm, 280μm±5μm respectively.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the present invention will be further specifically described through the embodiments.

As shown in Figures 4 and 5, the waveguide cavity of the terahertz waveguide filter is mainly composed of a waveguide input section 4, a waveguide output section 5, and three rectangular resonators (6, 7) between the waveguide input section 4 and the waveguide output section 5. , 8) composition. The waveguide input section 4 and the waveguide output section 5 are standard rectangular waveguides of WR2.2 specification, and the width and height of the cross section are 0.56mm±5μm and 0.28mm±5μm respectively. The whole filtering structure is composed of waveguide input section 4, waveguide output section 5, two WR2.2 standard rectangular waveguides and three rectangular resonant cavities, each structure is separated by inductive coupling windows (9, 10, 11, 12, 13). , which is divided into two signal coupling paths in principle. The first coupling path passes through the first resonant cavity 6 and the second resonant cavity 7 with a resonant frequency of 385Ghz in series on the right side, and is the main signal path, which is used to form a center frequency at 385GHz second-order band-pass filter characteristics, the thickness and width of the three inductive coupling windows will determine the frequency response waveform; the second coupling path passes through a rectangular resonant cavity on the left (ie the third resonant cavity 8), used form a transmission zero at the low end, optimizing the out-of-band rejection of the bandpass filter at the low end.

Coupling path 1 includes waveguide input section 4 [2403μm×(560±5μm)×(280±5μm)], the first resonant cavity 6 [(506±3μm)×(506±3μm)×(280±5μm)], the first Two resonant cavity 7 [(506±3μm)×(506±3μm)×(280±5μm)], waveguide output section 5[2403um×(560±5μm)×(280±5μm)], waveguide input section 4 and the first The first inductive coupling window 9 [(306±3μm)×(44±3μm)×(280±5μm)] between the first resonant cavity 6 and the third inductive coupling window between the first resonant cavity 6 and the second resonant cavity 7 Coupling window 11 [(216±3μm)×(74±3μm)×(280±5μm)], second inductive coupling window 10 between the second resonant cavity 7 and waveguide output section 5 [(306±3μm)×( 44 ± 3 μm) × (280 ± 5 μm)]. The data in square brackets represent the three-dimensional dimensions of the length, width and height of the cuboid-shaped resonator and coupling window, respectively, and ± represents the allowable error value of the three-dimensional dimensions.

Coupling path 2 includes waveguide input section 4 [2403um×(560±5μm)×(280±5μm)], third resonant cavity 8[(506±3μm)×(806±3μm)×(280±5μm)], waveguide Output section 5 [2403um×(560±5μm)×(280±5μm)], fourth inductive coupling window 12 between waveguide input section 4 and third resonant cavity 8 [(206±3μm)×(114±3μm) ×(280±5μm)], the fifth inductive coupling window 13 between the third resonant cavity 8 and the waveguide output section 5 [(206±3μm)×(114±3μm)×(280±5μm)].

The distance between the first inductive coupling window 9 and the short-circuit end 15 of the waveguide input section 4 is 50 ± 5 μm, the distance between the second inductive coupling window 10 and the short-circuit end 16 of the waveguide output section 5 is 50 ± 5 m, and the third inductive coupling window 11 The distance from the end face of the first inductive coupling window 9 of the first resonant cavity 6 is 140±5m, the fourth inductive coupling window 12 is close to the short-circuit end 15 of the waveguide input section 4, and the fifth inductive coupling window 13 is close to the waveguide output section 5 The short-circuit terminal 16.

The above-mentioned inductive coupling window is composed of partition walls located on both sides thereof, the upper edge of the partition wall is flush with the surface of the silicon substrate of the lower cavity 2, and the lower edge of the partition wall is flush with the bottom surface of the resonant cavity of the lower cavity 2, That is, the height of the inductive coupling window is also 280 μm±5 μm.

In order to better realize the purpose of the present invention, the present invention can further adopt the following technical measures. The following technical measures can be taken individually, in combination, or even together.

The above-mentioned terahertz waveguide filter has a split structure, the joint surface of the upper cavity 1 closed to form the filter waveguide cavity 3 is a flat substrate, and the joint surface of the lower cavity 2 is a filter waveguide cavity processed by etching on the substrate In the overall structure, the upper cavity 1 is covered and bonded to the lower cavity 3 to form a terahertz waveguide filter. The terahertz waveguide filter adopts the above structure, which can completely avoid the problem of misalignment that may occur when the upper and lower cavities of the traditional filter are respectively etched with half of the filter structure when the upper and lower cavities are closed.

The planar structure of the above-mentioned waveguide cavity can be designed to be symmetrical with respect to the center line perpendicular to the signal transmission direction, for example, it is symmetrical with respect to the center line A-A in FIG. 4 .

The upper edge of the partition walls on both sides of the inductive coupling window is flush with the surface of the lower cavity substrate, and the lower end is flush with the bottom surface of the resonant cavity.

Preferably, the above-mentioned waveguide cavity adopts the overall structure of the waveguide cavity processed by etching on the silicon substrate, and then a gold-plated layer is plated on the waveguide cavity structure by sputtering gold-plating process. The thickness of the gold-plated layer is preferably 2.5-3.5 μm.

The terahertz waveguide cavity filter provided by the present invention is manufactured by bulk silicon processing technology. The bulk silicon processing technology is a representative one of the MEMS (Microelectromechanical Systems, microelectromechanical systems) technology. MEMS represents a system integrated with components with a feature size of 0.001 mm to 0.1 mm, and has a processing accuracy of the order of microns. Bulk silicon processing technology has the characteristics of relatively low processing cost, relatively simple processing conditions and relatively low technical requirements while ensuring a certain technological level.

The bulk silicon processing technology, its technological process is roughly as follows:

First, a mask layer with different chemical compositions is formed on the surface of the silicon substrate.

Then, generate a pattern on the mask layer by photolithography, the pattern is located at the corresponding position on the mask layer of the silicon substrate part that needs to be etched, and remove this part of the mask layer to expose the underlying silicon. quality substrate.

Subsequently, the silicon substrate is etched by a gas-phase etchant to obtain a rectangular groove of specified depth and shape. A mask layer can protect the underlying silicon substrate from corrosion.

Thereafter, the residual mask layer is removed by an etchant, which should have no corrosion effect on the silicon substrate, and only the etched silicon substrate remains after the process is completed.

Thereafter, a metallization operation is performed on the surface of the silicon substrate and the surface of the rectangular groove by metal sputtering.

Finally, bond the substrate with another substrate that has undergone surface metallization to form a metallized cavity on the inner surface, which is the resonant cavity of the filter (6, 7 or 8 in Figure 4) .

As shown in Fig. 6, the terahertz waveguide cavity filter provided by the present invention is a waveguide filter structure with air as the filling medium, that is, the functional component of the filter is a waveguide with air as the filling medium. The vector network analyzer system (Agilent N5245A) combined with the frequency expansion module (OML-V022VNA2) is used to measure it. The measurement result shows that the loss at the center frequency of 387GHz is 4.37dB, and the 3-dB bandwidth is 12.8GHz (380.6～393.4GHz). , the reflection is about -20dB, and the out-of-band rejection is greater than 20dB. This means that the waveguide filter of the present invention can achieve complete filtering performance and low insertion loss at the low end of terahertz (325-500 GHz), which solves the problem that other types of filters are difficult to apply in this frequency band due to excessive loss.

The passband of the waveguide cavity filter of the present invention is located in the 380-390 GHz frequency band, and the 94 GHz atmospheric window can be used to realize quadruple frequency high-power output, and the atmospheric absorption window of this frequency band can be used to realize communication under specific conditions, etc., and has excellent performance transmission performance.

The structure design of the terahertz waveguide filter provided by the present invention adopts a flat substrate as the upper cavity to close the filter waveguide cavity, and the overall structure of the filter waveguide cavity is processed by etching on the substrate as the lower cavity. The cover of the upper cavity is bonded to the lower cavity to form a terahertz waveguide filter, which abandons the design structure of the filter in the prior art to etch half of the filter structure in the upper and lower cavities respectively, and completely avoids the problem when the upper and lower cavities are closed. There may be a problem of inaccurate alignment, which greatly improves the manufacturability of the filter.

The terahertz waveguide cavity filter of the present invention adopts the WR2.2 standard rectangular waveguide interface, has the advantages of high operating frequency, low loss, easy manufacture, strong versatility, etc., and has good application prospects in terahertz systems.

It is necessary to point out that the above embodiments are only used to further illustrate the present invention, so that those skilled in the art can better understand the present invention. The present invention has disclosed its preferred embodiment by text, but can comprehend optimization and modifiability wherein by reading these technical text description, and can improve without departing from the scope and spirit of the present invention, but such improvement should Still belong to the protection scope of the claims of the present invention.

Claims (10)

1. Terahertz waveguide cavity filter, which is composed of an upper cavity at the upper part and a lower cavity at the lower part. The upper cavity is covered on the lower cavity and has a waveguide formed by a hollow structure at the junction of the two Cavity, the waveguide cavity is located in the lower cavity; it is characterized in that the waveguide cavity includes a cuboid waveguide input section and a waveguide output section, a first resonant cavity located between the waveguide input section and the waveguide output section and also in the shape of a cuboid , the second resonant cavity and the third resonant cavity, the waveguide input section and the first resonant cavity are connected in series through the first inductive coupling window, the first resonant cavity and the second resonant cavity are connected in series through the third inductive coupling window, The second resonant cavity is connected in series with the waveguide output section through the second inductive coupling window, the waveguide input section and the third resonant cavity are connected in series through the fourth inductive coupling window, and the third resonant cavity and the waveguide output section are connected in series. The fifth inductive coupling window is connected in series; the waveguide input section, the first inductive coupling window, the first resonant cavity, the third inductive coupling window, the second resonant cavity, the second inductive coupling window and the waveguide output section are sequentially connected in series to form a coupling path One is used as the main signal path; the waveguide input section, the fourth inductive coupling window, the third resonant cavity, the fifth inductive coupling window and the waveguide output section are sequentially connected in series to form the second coupling path, which is used to form a transmission zero point at the low end of the passband ; The middle parts of the first resonant cavity, the second resonant cavity and the third resonant cavity have bosses for separating the three resonant cavities, waveguide input section and waveguide output section. 2. The terahertz waveguide cavity filter according to claim 1, wherein the waveguide input section and the waveguide output section of the waveguide cavity are standard WR2.2 rectangular waveguides. 3 . The terahertz waveguide cavity filter according to claim 1 , wherein the spatial structure of the three resonant cavities of the waveguide cavity is a cuboid. 4 . 4. The terahertz waveguide cavity filter according to claim 1, wherein the spatial structure of the five inductive coupling windows of the waveguide cavity is a cuboid. 5. The terahertz waveguide cavity filter according to claim 1, wherein the inductive coupling window is composed of partition walls on both sides thereof, and the upper edge of the partition wall is connected to the silicon substrate of the lower cavity. The surface is flush, and the lower edge of the partition wall is flush with the bottom surface of the resonant cavity of the lower cavity. 6. The terahertz waveguide cavity filter according to claim 5, wherein the distance between the first inductive coupling window and the short-circuit end of the waveguide input section is 50 ± 5 μm, and the distance between the second inductive coupling window and the waveguide output section The distance between the short-circuit end of the waveguide is 50±5μm, the distance between the third inductive coupling window and the end face of the first inductive coupling window of the first resonator is 140±5μm, the fourth inductive coupling window is close to the short-circuit end of the waveguide input section, and the fifth inductive coupling window The coupling window is attached to the short-circuit end of the waveguide output section. 7 . The terahertz waveguide cavity filter according to claim 1 , wherein the planar structure of the waveguide cavity can be designed to be symmetrical with respect to a center line perpendicular to the signal transmission direction. 8. The terahertz waveguide cavity filter according to claim 1, characterized in that, the waveguide cavity adopts the overall structure of the waveguide cavity processed on the silicon substrate by etching, and then the waveguide cavity structure is formed by sputtering gold plating process. Gold plated on top. 9. The terahertz waveguide cavity filter according to claim 8, wherein the thickness of the gold-plated layer is 2.5-3.5 μm. 10. The terahertz waveguide cavity filter according to claim 8, wherein the waveguide cavity is filled with air.

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