CN102386470A

CN102386470A - Microstrip line, impedance converter applying microstrip line and design method of microstrip line

Info

Publication number: CN102386470A
Application number: CN2010102681396A
Authority: CN
Inventors: 邱大舜
Original assignee: Shenzhen Futaihong Precision Industry Co Ltd; Chi Mei Communication Systems Inc
Current assignee: Shenzhen Futaihong Precision Industry Co Ltd; Chi Mei Communication Systems Inc
Priority date: 2010-08-31
Filing date: 2010-08-31
Publication date: 2012-03-21
Anticipated expiration: 2030-08-31
Also published as: CN102386470B

Abstract

The invention provides a microstrip line. The microstrip line is applied in a circuit to play a role in impedance matching and is characterized in that: the microstrip line comprises an annular strip and two side strips, wherein the two side strips are arranged on the two sides of the annular strip and are respectively used for feeding in and feeding out an electromagnetic wave signal; and a groove is formed in the annular strip so as to increase an odd mode transmission route of the microstrip line. The invention also provides an impedance converter applying the microstrip line and a design method of the microstrip line; and the microstrip line designed by the method has good frequency response and greatly reduced size.

Description

Microstrip line, impedance converter using microstrip line and design method of microstrip line

Technical Field

The present invention relates to a microstrip line, and more particularly, to a microstrip line for an impedance converter and a design method thereof.

Background

With the rapid development of microwave communication technology, microstrip lines are used more and more. Microstrip lines are commonly used waveguide devices in microwave bands, and are used for microwave signal transmission, impedance conversion, band-pass filtering, phase shifting or delay lines and the like. When used for microwave propagation, microstrip lines mainly rely on Quasi-transverse electromagnetic field (QTEM) modes between metal conduction bands and metal plates to realize microwave signal transmission. QTEM has an Odd mode (Odd mode) and an Even mode (Even mode), and since transmission phase speeds of the two modes during nonlinear transmission are generally different (Odd mode transmission phase speed VO > Even mode transmission phase speed VE), the directivity of the communication device is easily deteriorated, and the frequency response of the system is further affected. In addition, the length of the existing microstrip line is mostly long, for example, when the microstrip line is used for transmitting signals with the central frequency of about 2.5GHz or 5.8GHz, the length of the microstrip line generally needs to reach about 27mm, so that the circuit layout area is easily increased, and the miniaturization of the communication device is not facilitated.

Disclosure of Invention

In view of the above, it is desirable to provide a microstrip line with a good frequency response and a short length.

In addition, it is necessary to provide an impedance converter using the microstrip line.

In addition, a design method of the microstrip line is also needed.

A microstrip line is used for playing an impedance matching role in a circuit and comprises a ring band and two side bands, wherein the two side bands are arranged on two sides of the ring band and are respectively used for feeding in and feeding out electromagnetic wave signals, and a notch is formed in the ring band so as to increase an odd mode transmission path of the microstrip line.

An impedance converter comprises a microstrip line, wherein the microstrip line comprises an annular band and two side bands, a slot is formed in the annular band to divide the annular band into a first side band and a second side band, one end of each of the first side band and the second side band forms a closed end, the other end of each of the first side band and the second side band is spaced by the slot, and the two side bands are respectively arranged at one end of the first side band and one end of the second side band which are spaced.

A design method of a microstrip line comprises an annular band and two side bands, and comprises the following steps: calculating odd-mode load admittance and even-mode load admittance of the microstrip line according to a transmission line input impedance formula; calculating two-port network parameters of the microstrip line according to the odd-mode load admittance, the even-mode load admittance and the transmission matrix; obtaining the lateral band length of the microstrip line and the parameter formulas of lateral band impedance, annular band length, annular band odd mode impedance and annular band even mode impedance according to the two-port network parameters of the microstrip line; and drawing different curves according to the specific load impedance of the microstrip line, the sizes of the side band and the annular band of the microstrip line and an impedance parameter formula.

The microstrip line is provided with the sawtooth-shaped slot on the annular belt, so that odd-mode transmission paths are effectively increased, and the frequency response of the system is improved. Meanwhile, the size of the microstrip line designed by the microstrip line design method is greatly reduced, the circuit layout area is favorably reduced, and the microstrip line design method conforms to the miniaturization development trend.

Drawings

FIG. 1 is a schematic plan view of a microstrip line according to a preferred embodiment of the present invention;

fig. 2 is an equivalent model diagram of the microstrip line shown in fig. 1;

fig. 3 is an equivalent circuit diagram of a parameter a of the two-port network of the microstrip line shown in fig. 1;

fig. 4 is an equivalent model diagram of the transmission characteristic of the microstrip line shown in fig. 1;

fig. 5 is a parameter curve diagram of the microstrip line shown in fig. 1;

fig. 6 is a design parameter diagram of the microstrip line shown in fig. 1;

fig. 7 is an insertion loss diagram of the microstrip line shown in fig. 1, wherein the load impedance is 100 ohms;

fig. 8 is an insertion loss diagram of the microstrip line of fig. 1, wherein the load impedance is 180 ohms;

fig. 9 is an insertion loss diagram of the microstrip line shown in fig. 1 applied to a bandpass filter.

Description of the main elements

Microstrip line 100

Endless belt 10

Open slot 12

Saw tooth unit 122

First horizontal groove 122a

First inclined groove 122b

Second horizontal groove 122c

Second inclined groove 122d

Third horizontal groove 122e

Primary sideband 14

Secondary side band 16

Side belt 30

Curves 1 to 6

Detailed Description

The invention discloses a microstrip line which can be applied to a circuit needing an impedance converter.

Referring to fig. 1, the microstrip line 100 is a metal sheet, which is used for impedance matching in a circuit. In the present embodiment, the center operating frequency of the microstrip line 100 is about 2.5GHz and 5.8 GHz. The microstrip line 100 includes a circular strip 10 and two side strips 30 located in the same plane, the two side strips 30 are symmetrically disposed at two opposite ends of the circular strip 10, and an electromagnetic wave signal is fed in from one side strip 30, then transmitted through the circular strip 10, and finally fed out from the other side strip 30.

The ring band 10 is substantially U-shaped, a slot 12 is formed in the middle of the ring band 10, one end of the slot 12 penetrates through one end of the ring band 10, so as to divide the ring band 10 into a first sideband 14 and a second sideband 16 which are oppositely arranged, the lengths of the first sideband 14 and the second sideband 16 are related to the operating frequency of the microstrip line 100, one ends of the first sideband 14 and the second sideband 16 are connected to form a closed end, and the other ends of the first sideband and the second sideband are spaced by the slot 12.

The slot 12 has a saw-tooth structure, which includes a plurality of saw-tooth units 122 having the same shape and connected in sequence. The sawtooth unit 122 is used to increase the odd-mode transmission path of the microstrip line 100, so that the transmission phase speeds of the odd mode and the even mode tend to be the same, thereby improving the frequency response of the system. In the present embodiment, each saw unit 122 includes a first horizontal slot 122a, and two first inclined slots 122b, two second horizontal slots 122c, two second inclined slots 122d, and two third horizontal slots 122e symmetrically disposed on two sides of the first horizontal slot 122a in sequence. The first horizontal groove 122a is adjacent to the first side band 14, the second horizontal groove 122c is disposed in the middle of the circumferential band 10, and the third horizontal groove 122e is adjacent to the second side band 16. The first horizontal groove 122a, the second horizontal groove 122c and the third horizontal groove 122e are parallel to each other, the first inclined groove 122b is parallel to the second inclined groove 122d, and the third horizontal grooves 122e of the adjacent two saw tooth units 122 are overlapped with each other. Thus, both sides of each saw tooth unit 122 are stepped, and the number of steps on both sides of each saw tooth unit 122 is 2.

The side strips 30 are of a similar size and are disposed opposite each other and perpendicular to the outer sides of the spaced ends of the primary and

secondary side strips

14, 16, respectively.

The design principle of the size of the microstrip line 100 with the girdle 10 and the sideband 30 is described with reference to fig. 2 to 4. Fig. 2 is an equivalent model of the microstrip line 100, where input impedance of the microstrip line 100 is defined as Z0, load impedance is defined as RL, length of the side band 30 is θ 1, impedance is defined as Z1, lengths of the first sideband 14 and the second sideband 16 are both θ c, odd mode impedance of the ring band 10 is Zoe, and even mode impedance is defined as Zoo. Where Z1 is related to the width of sideband 30 and θ 1 and θ c are related to the frequency of the microstrip line 100 receiving signal, the ratio of the width of the first sideband 14 or the second sideband 16 to the separation of the first sideband 14 and the second sideband 16 (i.e., the width of the slot 12) is determined by the ratio of Zoe and Zoo. Fig. 3 is an equivalent circuit of the two-port network a parameter (forward transmission parameter) of the microstrip line. Wherein, a represents a reverse transfer voltage ratio when the output port is open-circuited, B represents a reverse transfer impedance when the output port is short-circuited, C represents a forward transfer admittance when the output port is open-circuited, and D represents a reverse transfer current ratio when the output port is short-circuited. Equation 1 is obtained from the A parameter equation:

Z_{0} = \frac{{AR}_{L} + B}{{CR}_{L} + D}

CZ₀R_L+DZ₀＝AR_L+ B (formula 1)

Referring to fig. 4, the odd mode load impedance of the first sideband 14 or the second sideband 16 is defined as ZLe, and the even mode load impedance is defined as ZLo. According to the transmission line input impedance formula, the following formula is obtained:

transmission characteristic by even mode Z_LEquation 2 → ∞:

Z_Le＝-jZ_oecotθ_c (formula 2)

By the same token, the transmission characteristic Z of the odd mode_LEquation 3 is obtained when the value is 0:

Z_Lo＝jZ_ootanθ_c

(formula 3)

Thereafter, the transmission (ABCD) matrix according to the first sideband 14 and the second sideband 16 is obtained (equation 4):

(formula 4)

Wherein,

|Z|＝Z_ooZ_oe

the A, B, C, D values are calculated by substituting

equations

2 and 3 into equation 4, and are reduced by substituting the values into equation 1 to obtain equations a, b, c, d:

defining n as f1/f0(f1 and f0 are both the operating frequencies of the microstrip line 100), since the four equations of equations a, b, c, d involve five unknowns θ 1, Z1, θ c, Zoe, and Zoo, there are a plurality of solutions for θ 1, Z1, θ c, Zo e, and Zoo.

Referring to fig. 5, when the load impedance RL takes different values, the corresponding curves θ 1, Z1, θ c, Zoe and Zoo can be drawn. Where the X-axis represents the resistance of the RL, the Y-axis represents the resistance of Z1, Zoe, and Zoo, the H-axis represents the angle of θ 1 and θ c, and the ratio of Zoe/Zoo is constant. Finally, the specific dimensions of the microstrip line 100 can be obtained by extracting the values of θ 1, Z1, θ c, Zoe and Zoo through the specific load impedance RL, and then optimized by fine tuning. Since the load impedance RL is inversely proportional to the width of the microstrip line 100, the maximum value of the load impedance RL is 180 ohms in the present embodiment, which is convenient for design. Referring to fig. 6, when the load impedance RL is 100 ohms, the length of the microstrip line 100 is about 12.57mm, and when the load impedance RL is 180 ohms, the length of the microstrip line 100 is about 13.23 mm. Compared with the prior art, the length of the microstrip line 100 of the invention is obviously reduced, which is beneficial to the miniaturization development of the communication device.

Referring to fig. 7 and 8, curves 1 and 2 respectively show schematic diagrams of insertion loss (S11) obtained by the microstrip line 100 under the simulation software and the measurement fixture when the load impedance RL is 100 ohms, and curves 3 and 4 respectively show schematic diagrams of insertion loss obtained by the microstrip line 100 under the simulation software and the measurement fixture when the load impedance RL is 180 ohms. As can be seen from fig. 7 and 8, the return loss value of the microstrip line 100 meets the design requirement when the microstrip line operates in the 2.5GHz and 5.8GHz bands. Referring to fig. 9, when the microstrip line 100 is used in a dual-band bandpass filter, curves 5 and 6 respectively show the insertion loss diagrams obtained under the simulation software and the measurement tool. As shown in fig. 9, the microstrip line 100 of the present invention forms a passband in the operating frequency bands of 2.5GHz and 5.8GHz, respectively, and has low loss in the passband frequency band and high loss in the attenuation frequency band, so that a steep "transition slope" is formed between the bandpass frequency and the cutoff frequency range.

The microstrip line 100 of the present invention increases the transmission path of the odd mode by forming the slot 12 with the saw-tooth structure in the middle thereof, and effectively improves the frequency effect of the system. The microstrip line 100 can be used to design a dual-band bandpass filter, which not only greatly reduces the manufacturing cost and the product volume, but also effectively suppresses the unwanted frequency.

Claims

1. A microstrip line, which is used to perform impedance matching in a circuit, is characterized in that: the microstrip line comprises an endless belt and two side belts, the two side belts are arranged on two sides of the endless belt and are respectively used for feeding in and feeding out electromagnetic wave signals, and a notch is formed in the endless belt to increase an odd-mode transmission path of the microstrip line.

2. The microstrip line of claim 1 wherein: the slot is of a sawtooth structure and is arranged in the middle of the girdle, and one end of the slot penetrates through one end of the girdle.

3. The microstrip line of claim 1 wherein: the girdle comprises a first sideband and a second sideband which are oppositely arranged, wherein the first sideband is connected with one end of the second sideband, and the other end of the first sideband is separated by the groove.

4. The microstrip line of claim 3 wherein: the two side bands are respectively arranged outside one ends of the first side band and the second side band which are spaced apart.

5. The microstrip line of claim 3 wherein: the slotting comprises a plurality of sawtooth units which are identical in shape and are connected in sequence, and two sides of each sawtooth unit are in a step shape.

6. The microstrip line of claim 5 wherein: each sawtooth unit comprises a first horizontal groove, two first inclined grooves, two second horizontal grooves, two second inclined grooves and two third horizontal grooves, wherein the two first inclined grooves, the two second horizontal grooves, the two second inclined grooves and the two third horizontal grooves are sequentially and symmetrically arranged on two sides of the first horizontal groove, the first horizontal groove is close to the first side band, the second horizontal groove is arranged in the middle of the annular band, the third horizontal groove is close to the second side band, the first horizontal groove, the second horizontal groove and the third horizontal groove are parallel to each other, the first inclined grooves are parallel to the two inclined grooves, and the third horizontal grooves of the two adjacent sawtooth units are overlapped with each other.

7. An impedance converter, which includes a microstrip line, is characterized in that: the microstrip line comprises an annular band and two side bands, wherein a groove is formed in the annular band to divide the annular band into a first side band and a second side band, one end of the first side band and one end of the second side band form a closed end, the other end of the first side band and the other end of the second side band are separated by the groove, and the two side bands are respectively arranged at one end of the first side band and one end of the second side band which are separated from each other.

8. An impedance converter according to claim 7, wherein: the slot is in a sawtooth structure.

9. An impedance converter according to claim 7, wherein: the operating frequency of the microstrip line is 2.5GHz and 5.8 GHz.

10. A microstrip line design method is characterized in that: the microstrip line comprises an annular band and two side bands, and the design method of the microstrip line comprises the following steps:

calculating odd-mode load admittance and even-mode load admittance of the microstrip line according to a transmission line input impedance formula;

calculating two-port network parameters of the microstrip line according to the odd-mode load admittance, the even-mode load admittance and the transmission matrix;

obtaining the lateral band length of the microstrip line and the parameter formulas of lateral band impedance, annular band length, annular band odd mode impedance and annular band even mode impedance according to the two-port network parameters of the microstrip line;

and drawing different curves according to different load impedances of the microstrip line and the sizes and impedance parameter formulas of the side band and the annular band of the microstrip line.

11. The microstrip line design method of claim 10, wherein: the step of drawing different curves according to different load impedances of the microstrip line and the sizes and impedance parameters of the side band and the annular band of the microstrip line also comprises a step of extracting different sizes and impedance values of the side band and the annular band of the microstrip line according to the specific load impedance of the microstrip line.