CN108172958A - A Periodic Slow Wave Transmission Line Unit Based on Coplanar Waveguide - Google Patents

Abstract

The present invention relates to a kind of cyclic slow wave transmission line units based on co-planar waveguide, belong to microwave technical field.It includes medium substrate (5), metal micro-strip is provided on one surface of medium substrate (5), metal micro-strip includes center conduction band (1), short transmission line (2), folded transmission lines (3) and metal ground (4)；Center conduction band (1) is connected to folded transmission lines (3) by short transmission line (2), metal (4) be irregular shape, metal (4) and center conduction band (1) it is mutually isolated, and metal (4) each detail prominent to center conduction band (1) direction be parallel to the corresponding folded transmission lines of each detail (3), the spacing distance between each detail and folded transmission lines (3) is equal.Conventional co-planar waveguide transmission line is substituted by the transmission line unit of the present invention, realizes the purpose that size significantly reduces in the case where transmission line performance is constant.

Description

A Periodic Slow Wave Transmission Line Unit Based on Coplanar Waveguide

technical field

The invention belongs to the field of microwave technology, and relates to a periodic slow-wave transmission line unit based on a coplanar waveguide.

Background technique

Transmission lines are widely used in the field of radio frequency and microwave circuits. They are not only the medium of electromagnetic power transmission, but also the basic components of microwave radio frequency devices.

The coplanar waveguide circuit, whose central conduction strip and ground plane are on the same plane, is a single-plane transmission line, which avoids the need for microstrip lines to be plated with metal on the back of the dielectric layer. Therefore, using the coplanar waveguide circuit instead of the original microstrip circuit can reduce the production cost. Moreover, the coplanar waveguide circuit has the advantages of easy short circuit at the end without via holes, easy integration with active devices and lumped parameter components, easy realization of compact balanced circuits, and improved integration of integrated circuits. However, with the development of radio frequency communication circuits towards miniaturization and integration, traditional radio frequency microwave devices, such as power splitters and couplers, often have relatively high performance due to the limitation of quarter-wavelength transmission lines in their structures. Large size, this defect is especially obvious when the working wavelength in the low frequency band is long, which is not conducive to the miniaturization of radio frequency communication systems.

Contents of the invention

In view of this, the object of the present invention is to provide a periodic slow-wave transmission line unit based on coplanar waveguide, which can replace the traditional coplanar waveguide transmission line, solve the problem of excessive transmission line size in the prior art, and realize the reduction of microwave device size. Performance is largely unchanged.

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

A periodic slow-wave transmission line unit based on a coplanar waveguide, comprising a dielectric substrate 5, one surface of the dielectric substrate 5 is provided with a metal microstrip, and the metal microstrip includes a central conduction strip 1, a short transmission line 2, folded Transmission line 3 and metal ground 4;

The central conduction strip 1 is connected to the folded transmission line 3 through the short transmission line 2, the metal ground 4 is irregular in shape, the metal ground 4 is isolated from the central conduction strip 1, and the metal ground 4. Each branch protruding toward the central guide belt 1 is parallel to the folded transmission line 3 corresponding to each branch, and the distance between each branch and the folded transmission line 3 is equal.

Further, the number of the short transmission lines 2 is two, the number of the folded transmission lines 3 is two, and the number of the metal grounds 4 is two.

Further, the two sections of the short transmission line 2, the two sections of the folded transmission line 3 and the two parts of the metal ground 4 are all mirror-symmetrical about the central conductive strip 1, and the central conductive strip 1, the two sections of the folded transmission line 3 and the two sections of the metal ground 4 are all mirror-symmetrical to the connecting line of the two short transmission lines 2 .

Further, the equivalent characteristic impedance of the transmission line unit is:

Among them, L _t is the equivalent series inductance of the transmission line unit, C _t is the equivalent ground parallel capacitance of the transmission line unit;

The phase propagation constant of the transmission line element is:

Among them, ω is the working angular frequency.

Further, the dielectric substrate is made of polytetrafluoroethylene.

Further, by changing the width of the central conductive strip 1, the distance between the central conductive strip 1 and the metal ground 4, the length and width of the two short transmission lines 2, the length and width of the two folded transmission lines 3 or the two folded transmission lines 3 and the The distance between the metal ground 4 is used to change the characteristic impedance and electrical length of the transmission line unit.

Further, a slow-wave transmission line whose electrical length is an integral multiple of the electrical length of a single transmission line unit is obtained by cascading a plurality of the transmission line units.

The beneficial effect of the present invention is that: the transmission line unit of the present invention uses a periodic slow-wave transmission line unit based on a coplanar waveguide to replace a traditional coplanar waveguide transmission line, so that the size of the transmission line is greatly reduced while the performance of the transmission line remains unchanged.

Description of drawings

In order to make the purpose, technical scheme and beneficial effect of the present invention clearer, the present invention provides the following drawings for illustration:

Fig. 1 is the structural representation of transmission line unit of the present invention;

Fig. 2 is a dimensional drawing of a sample of a specific embodiment of the transmission line unit of the present invention;

Figure 3 is a sample dimension diagram of an existing traditional coplanar waveguide transmission line with a characteristic impedance of 50 ohms and an electrical length of 22.5 degrees;

Fig. 4 is the characteristic impedance and phase graph of the sample of the specific embodiment of the transmission line unit of the present invention;

Fig. 5 is the simulated S parameter curve diagram of the sample of the specific embodiment of the transmission line unit of the present invention;

Fig. 6 is a schematic structural view of a sample of a specific embodiment in which two units of the transmission line unit of the present invention are cascaded;

Fig. 7 is the simulated characteristic impedance and phase curve diagram of the specific embodiment sample of two units cascaded in the transmission line unit of the present invention;

Fig. 8 is the simulated S-parameter curve diagram of the specific embodiment sample of two units cascaded in the transmission line unit of the present invention;

Fig. 9 is a schematic structural view of a specific embodiment sample of a transmission line unit of the present invention in which four units are cascaded;

Fig. 10 is the simulated characteristic impedance and phase curve diagram of a sample of a specific embodiment in which 4 units of the transmission line unit are cascaded according to the present invention;

Fig. 11 is a simulation S-parameter curve diagram of a sample of a specific embodiment in which four transmission line units are cascaded in accordance with the present invention.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The present invention is a periodic slow-wave transmission line unit based on a coplanar waveguide, as shown in FIG. 1 , including a dielectric substrate 5, and a metal microstrip is arranged on one surface of the dielectric substrate. The metal microstrip part includes a central conduction strip 1 , two short transmission lines 2 , two folded transmission lines 3 , and two metal grounds 4 .

The two parts of the metal ground 4 are isolated from the central conductive strip 1 from each other. The two parts of the metal ground 4 are irregular in shape, and the branches protruding from the floor toward the central guide belt 1 are parallel to each section of the folded transmission line 3 , and there is an equal distance between each branch and the folded transmission line 3 . The central conduction belt 1 is connected with two folded transmission lines 3 through two short transmission lines 2 respectively. Two sections of short transmission lines 2 , two sections of folded transmission lines 3 , and two sections of metal ground 4 are mirror-symmetrical about the central conduction band 1 . The central conduction strip 1 , two sections of folded transmission lines 3 , and two sections of metal grounds 4 are mirror-symmetrical to the connection between the two sections of short transmission lines 2 .

The equivalent characteristic impedance calculation formula of each transmission line unit is

The phase propagation constant of each transmission line element is

Among them, ω is the operating angular frequency, L _t and C _t are the equivalent series inductance and equivalent parallel capacitance to ground of each transmission line unit, respectively. The width of the central conduction band 1 is smaller than that of the traditional coplanar waveguide transmission line, which increases the equivalent series inductance of the unit. The two sections of folded transmission line 3 are respectively located between the central conduction band 1 and the metal ground 4, which increases the equivalent parallel capacitance to ground of the unit. In order to increase the equivalent parallel capacitance to ground as much as possible, the metal ground 4 is designed as an irregular pattern to couple as much as possible with the two folded transmission lines 3 to increase the equivalent parallel capacitance to ground.

In the case of the same electrical length, compared with the traditional coplanar waveguide transmission line, since the periodic slow-wave transmission line unit per unit length can obtain larger equivalent series inductance L _t and equivalent parallel capacitance C _t to ground, Therefore, the phase propagation constant is larger, and each periodic slow-wave transmission line unit can obtain a smaller physical size, thereby reducing the size of the entire circuit.

By changing the width of the central conductive strip 1, the distance between the central conductive strip 1 and the metal ground 4, the length and width of the two short transmission lines 2, the length and width of the two folded transmission lines 3, the distance between the two folded transmission lines 3 and the metal ground 4 The pitch can change the characteristic impedance and electrical length of the periodic slow wave transmission line unit.

The specific dimensions of the example sample of the transmission line unit of the present invention are shown in FIG. 2 . The sample of this embodiment is a periodic slow-wave transmission line unit based on a coplanar waveguide with an operating frequency of f=0.9 GHz. It is made on a domestic polytetrafluoroethylene dielectric substrate with a relative dielectric constant of 2.65 and a substrate thickness of 1mm. The circuit size is 10.9mm×5.8mm, that is, 4.1% _λg ×2.2% _λg , where _λg represents the waveguide wavelength on the dielectric substrate at 0.9GHz.

For comparison, the sample structure size of a traditional coplanar waveguide transmission line with a characteristic impedance of 50 ohms and an electrical length of 22.5 degrees is shown in Figure 3. In the case of using the same dielectric substrate as the sample in the example, working at the same center frequency, and having the same distance between the center transmission line and the metal ground, the circuit size of the traditional coplanar waveguide transmission line is 10.9mm×16.7mm, which is 4.1% λ _g ×6.3% λ _g , λ _g represents the waveguide wavelength on the dielectric substrate at 0.9 GHz. It can be seen that the unit size of the periodic slow-wave transmission line based on the coplanar waveguide of the embodiment sample of the present invention can be reduced by about 65.3%.

The simulation software IE3D is used for simulation, and the characteristic impedance and phase curves obtained from the simulation of the embodiment sample of the periodic slow-wave transmission line unit based on the coplanar waveguide of the present invention are shown in FIG. 4 . At 0.9GHz, the real part of the characteristic impedance is 49.97 ohms, the imaginary part is -0.17 ohms, and the phase delay is -22.50 degrees, that is, the electrical length of this transmission line unit is 22.50 degrees.

The S-parameter curve obtained from the simulation of the sample of the embodiment of the transmission line unit of the present invention is shown in FIG. 5 . In the figure, |S ₁₁ | represents the modulus value of the reflection coefficient of port 1, and |S ₂₁ | represents the modulus value of the unit transmission coefficient of the periodic slow-wave transmission line. In the embodiment sample of the present invention, the periodic slow-wave transmission line unit based on the coplanar waveguide is within the bandwidth range of 0 GHz-4.29 GHz, and |S ₁₁ | is less than -10 dB, which proves that the impedance matching of the transmission line unit port is good. |S ₂₁ | is greater than -0.5dB, which proves that the transmission line unit has the characteristic of low loss. The relative bandwidth of the sample of the embodiment of the present invention reaches 476.7%.

Example 2:

In this embodiment, two units of the transmission line unit are cascaded to realize the transmission line function with a characteristic impedance of 50 ohms and an electrical length of 45 degrees.

Fig. 6 is a schematic structural diagram of cascading two units of the periodic slow-wave transmission line unit based on the coplanar waveguide of the present invention. Fig. 7 is the simulation characteristic impedance and the phase curve diagram of 2 units cascaded. At 0.9GHz, the real part of the characteristic impedance is 49.96 ohms, the imaginary part is -0.15 ohms, and the phase delay is -44.96 degrees, that is, the electrical length of the structure formed by cascading two units is 44.96 degrees.

Fig. 8 is a simulation S-parameter curve diagram of cascading two units. In the bandwidth range of 0GHz-4.16GHz, |S ₁₁ | is less than -10dB. Since two units are cascaded, there are two resonant frequencies within the bandwidth, which are 0.9GHz and 3.35GHz. At 0.9GHz, |S ₁₁ | is -53.09dB and |S ₂₁ | is -0.02dB.

Example 3:

In this embodiment, four units of the transmission line unit are cascaded to realize the transmission line function with a characteristic impedance of 50 ohms and an electrical length of 90 degrees.

FIG. 9 is a schematic structural diagram of cascading four units. Fig. 10 is the simulated characteristic impedance and phase curve diagram of 4 units cascaded. At 0.9GHz, the real part of the characteristic impedance is 50.09Ω, the imaginary part is -0.13Ω, and the phase delay is -90.01°, that is, the electrical length of the structure formed by cascading four units is 90.01 degrees. The cascaded structure of four units can be better equivalent to a quarter-wavelength transmission line with a characteristic impedance of 50Ω.

Fig. 11 is a simulation S-parameter curve diagram of 4 units cascaded. When |S ₁₁ | is less than -10dB, the bandwidth ranges from 0GHz to 4.35GHz. Since 4 units are cascaded, there are four resonant frequencies in the bandwidth range, namely 1.0GHz, 1.76GHz, 3.24GHz, 4.16GHz. At 0.9GHz, |S ₁₁ | is -50.11dB and |S ₂₁ | is -0.04dB. It can be seen that as the number of cascaded units increases, the insertion loss increases.

Combined with the accompanying drawings and the above analysis, it is shown that the periodic slow-wave transmission line unit and multi-unit cascaded embodiment samples of the present invention are compared with the traditional coplanar waveguide transmission line while reducing the size by 65.3%. Similar good performance to conventional coplanar waveguide transmission lines.

Finally, it is noted that the above preferred embodiments are only used to illustrate the technical solutions of the invention and not limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that it may be possible in form and details. Various changes can be made to it without departing from the scope defined by the claims of the present invention.

Claims (7)

1. a kind of cyclic slow wave transmission line unit based on co-planar waveguide, it is characterised in that：It is described comprising medium substrate (5) Metal micro-strip is provided on one surface of medium substrate (5), the metal micro-strip includes center conduction band (1), short transmission line (2), folded transmission lines (3) and metal ground (4)；

The center conduction band (1) is connected to the folded transmission lines (3) by the short transmission line (2), the metal (4) be Irregular shape, the metal (4) and the center conduction band (1) it is mutually isolated, and the metal (4) led to the center Each detail that band (1) direction protrudes is parallel to the corresponding folded transmission lines of each detail (3), each detail and the folding Spacing distance between folded transmission line (3) is equal.

2. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 1, it is characterised in that：Institute It is 2 to state the quantity of short transmission line (2), and the quantity of the folded transmission lines (3) is 2, the metal the quantity of (4) be 2.

3. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 2, it is characterised in that：Two Duan Suoshu short transmission lines (2), two sections of folded transmission lines (3) and two parts metal (4) about center conduction band (1) mirror As symmetrical, and the center conduction band (1), two sections of folded transmission lines (3) and two parts metal (4) it is described short about two sections The line mirror symmetry of transmission line (2).

4. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 3, it is characterised in that：Institute The equivalent characteristic impedance for stating transmission line unit is：

Wherein, L_tFor the equivalent series inductance of transmission line unit, C_tEquivalent shunt capacitance over the ground for transmission line unit；

The phase propagation constant of transmission line unit is：

Wherein, ω is work angular frequency.

5. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 1, it is characterised in that：Institute Medium substrate is stated to be made of polytetrafluoroethylene (PTFE).

6. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 3, it is characterised in that：It is logical Cross the width for changing the center conduction band (1), the spacing of center conduction band (1) with metal (4), the length of two sections of short transmission lines (2) Degree, width, the spacing of the length of two sections of folded transmission lines (3), width or two sections of folded transmission lines (3) with metal (4), to change Become characteristic impedance and the electrical length of the transmission line unit.

7. a kind of cyclic slow wave transmission line unit based on co-planar waveguide according to claim 3, it is characterised in that：It is logical Cross the unit cascaded slow wave transmission line for obtaining electrical length as single transmission line unit electrical length integral multiple of multiple transmission lines.