KR101061873B1 - Design Method of Microstrip Directional Coupler - Google Patents

Abstract

A method of designing microstrip directional bonds is disclosed. The microstrip directional coupler of the present invention comprises: a microstrip coupling line consisting of first and second microstrip lines spaced at predetermined intervals on a dielectric and having a predetermined width and length; A first inductor connected between an intermediate point of the first microstrip line and ground; And a second inductor connected between the midpoint of the second microstrip line and ground, the design method comprising: (a) a right mode impedance of the microstrip coupling line with a given target system impedance and a target coupling degree; Obtaining a pre-mode impedance, a right mode electrical length, and a pre-mode electrical length; (b) obtaining inductances of the first and second inductors according to the obtained right mode impedance, pre-mode impedance, right mode electrical length, and pre-mode electrical length; (c) obtaining a system impedance and a coupling degree by reflecting the obtained inductance; And (d) compensating for the target system impedance and target coupling degree according to the obtained system impedance and coupling degree; (e) repeating steps (a) to (d) with the compensated target system impedance and target coupling degree.

Directional Coupler, Microstrip Bonding Line, Microstrip Directional Coupler

Description

Design method of microstrip directional coupler

The present invention relates to a microstrip directional coupler, and more particularly, to a microstrip directional coupler having improved directionality using a shunt inductor and a design method thereof.

Microstrip coupling lines form the basis for various passive components such as directional couplers, bandpass filters, and baluns. In particular, microstrip directional couplers are widely used because they are inexpensive and planar, making them compatible with other active / passive circuits.

As a technique for improving the orientation of a microstrip directional coupler using a conventional lumped device, there is a method of attaching a capacitor between the microstrip coupling lines. In the case of such a capacitor compensation technique, the required capacitance value is very small, which impairs practicality. In addition, the conventional techniques only have a design method at the circuit level, and do not take into account the various parasitic effects that appear in the actual layout process, and thus require numerous full-wave simulations depending on the characteristics of the coupler. There is a disadvantage.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a microstrip directional coupler having improved directionality and easy implementation and design using a shunt inductor and a design method thereof.

In order to solve the above technical problem, the microstrip directional coupler includes: a microstrip coupling line formed of first and second microstrip lines having a predetermined width and length and spaced apart from each other on a dielectric; A first inductor connected between an intermediate point of the first microstrip line and ground; And a second inductor connected between an intermediate point of the second microstrip line and ground.

The first and second inductors may be implemented using shunt ground stubs.

The microstrip directional coupler may further include a transmission line connected to ends of the first and second microstrip lines.

In order to solve the above technical problem, a method of designing a microstrip directional coupler according to the present invention includes (a) a right mode impedance, a pre-mode impedance, a right mode of the microstrip coupling line with a given target system impedance and a target coupling degree. Obtaining an electrical length and a pre-mode electrical length; (b) obtaining inductances of the first and second inductors according to the obtained right mode impedance, pre mode impedance, right mode electrical length, and pre mode electrical length; (c) obtaining a system impedance and a coupling degree by reflecting the obtained inductance; And (d) compensating for a target system impedance and a target coupling degree according to the obtained system impedance and coupling degree; (e) repeating steps (a) to (d) with the compensated target system impedance and target coupling degree.

Here, the process (e) may be repeated until the obtained system impedance and coupling degree converge to the given target system impedance and target coupling degree.

Also, the step (d) may be compensated for by using a ratio or a difference between the target system impedance and the target coupling degree and the obtained system impedance and the coupling degree.

In addition, the process (b) and the process (c) may obtain the inductance, the system impedance, and the coupling degree in consideration of the parasitic capacitance of the microstrip coupling line.

The microstrip directional coupler further includes a transmission line connected to ends of the first and second microstrip lines, and the parasitic capacitance is a parasitic capacitance between the first and second microstrip lines and the transmission line. Parasitic capacitances in between.

According to the present invention described above, the direction is improved by using an inductor, and since it can be easily implemented by a shunt ground stub, there is an advantage in that the implementation and design of the microstrip directional coupler are easily performed without degrading performance even at high frequency.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted. In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a circuit diagram of an existing directional coupler using a microstrip coupling line, which is referenced in one embodiment of the present invention. The illustrated directional coupler is implemented as a microstrip coupling line consisting of two microstrip lines 105 and 106 spaced apart at predetermined intervals on a dielectric (not shown). The input end of the directional coupler corresponds to port 1 (101), the output end is port 2 (102), the coupling end is port 3 (103), and the isolation end is port 4 (101). (104). The directional coupler is such a four-port circuit in which the system impedance of each port is denoted by Z ₀ . Z ₀ may be, for example, 50 Ω standard impedance. The illustrated directional coupler has an impedance Z _0e and an electrical length θ _e in the right mode, an impedance Z _0o and an electrical length θ _o in the _normal mode at the center frequency f.

Since the conventional directional coupler uses an inhomogeneous material as a substrate, the phase velocity of the even mode and the odd mode is generally different, resulting in low directionality.

2 is a circuit diagram of a directional coupler using a microstrip coupling line, according to one embodiment of the invention. Compared with the directional coupler shown in FIG. 1, the directional coupler according to the present embodiment has an inductor connected between the ground and the midpoint of each microstrip line that forms the microstrip coupling line to improve orientation. Specifically, the directional coupler according to the present embodiment, the first microstrip line 205 and the second microstrip line 206 are spaced apart at predetermined intervals on the dielectric (not shown) and have a predetermined width and length. A microstrip coupling line consisting of: a first inductor 207 connected between an intermediate point of the first microstrip line 205 and ground, and an intermediate point of the second microstrip line 206 and ground; And a second inductor 208. In FIG. 2, the first or second microstrip line 205 or 206 is shown as being divided into two parts with respect to the intermediate point to which the inductor is connected, but physically as shown in FIG. 4 described later. It is not separated. As shown, each half portion has an impedance Z _0e and an electrical length θ _e / 2 in the right mode, and an impedance Z _0o and an electrical length θ _o / 2 in the _initial mode, as shown.

The directional coupler according to the present embodiment also has an input end corresponding to port 1 201, an output end corresponding to port 2 202, a coupling end port 3 203, and isolation. ) Corresponds to port 4 204. However, in the directional coupler according to the present embodiment, the center frequency f impedance at the (angular frequency ω = 2πf) impedance at the feather de to have the maximum directivity in the Z _0e and the electrical length θ _e, group mode Z _0o electrically The length θ _o must differ from the directional coupler shown in FIG. 1 due to the added inductor and the inductance values of the first inductor 207 and the second inductor 208 must be determined.

Hereinafter, as a design method of a directional coupler according to an embodiment of the present invention, the impedance Z _0e and the electrical length θ _e in the right mode of the microstrip coupling line as a design parameter, the impedance Z _0o and the electrical length θ _o in the _idle mode , And the process of determining the inductance value L.

As an initial step to determine the design parameters of the directional coupler, in the directional coupler shown in Fig. 2, the first and second inductors 207 and 208 are ignored and the impedance, electrical length, Find the impedance and electrical length in mode. This is the same as the process of obtaining the design parameters for the directional coupler shown in FIG. In general, the system impedance and the coupling degree are given first as a design condition of the directional coupler. Given the system impedance and coupling, the impedance and electrical length in the right mode of the microstrip coupling line for the directional coupler, and the impedance and electrical length in the conventional mode can be determined using known methods. Here, the electrical length in the right mode and the electrical length in the pre-mode can be obtained from the right mode effective dielectric constant and the pre-mode effective dielectric constant. The above mentioned parameters are described, for example, in G. L. Matthaei, L. Young, and EM Jones, Microwave Filters, Impedance-Matching Network, and Coupling Structures, Artech House, Inc., Dedham, Massachusetts, 1980. This can be obtained using the simulator "LineCalc".

Initially, given the target system impedance Z ₀ and coupling degree C, this value is used to determine the right mode impedance Z _0e , the _premode impedance Z _0o , and the right mode effective relative dielectric constant ε _{r, eff, e} of the microstrip coupling line. _Calculate the physical length l of the microstrip coupling line. The right mode electrical length θ _e and the pre mode electrical length θ _o can be obtained from the right mode effective dielectric constant, the premodal effective dielectric constant, and the physical length of the microstrip coupling line using the following equation.

Here (and below), c denotes the speed of light, w = 2πf.

When the right mode impedance Z _0e , the _pre mode impedance Z _0o , the right mode electrical length θ _e and the _pre mode electrical length θ _o of the microstrip coupling line are obtained, the maximum in the directional coupler according to the embodiment of the present invention shown in FIG. The inductance value L which has the directionality of is obtained using the following equation.

In the directional coupler according to the embodiment of the present invention shown in FIG. 2, since the first inductor 207 and the second inductor 208 having such inductance values are added, the actual system impedance is different from the initially given system impedance. The combination is also different. That is, by adding the first inductor 207 and the second inductor 208, the system impedance and the coupling degree are different from the target values.

Next, the actual system of the directional coupler shown in FIG. 2 with the right mode impedance Z _0e , the _premode impedance Z _0o , the right mode electrical length θ _e , the _premode electrical length θ _o , and the inductance value L of the microstrip coupling line. Impedance and coupling are calculated according to the following equation.

In Equation 4, Z _ee , Z _eo , Z _oe , and Z _oo are calculated according to the following equations.

The actual system impedance Z ₀ and the coupling degree C thus obtained are different from the target value (the value given earlier) as described above. Therefore, the target system impedance and coupling degree are compensated according to the obtained actual system impedance and coupling degree, and with this compensated value, the right mode impedance Z _0e , the _premode impedance Z _0o , and the right mode electrical length θ of the microstrip coupling line. After calculating _e and the pre-mode electrical length θ _o , the inductance value is calculated according to Equation 2 again. The system impedance and coupling degree are calculated using the calculated impedance values and Equations 3 and 4 again. By repeating this process, the system impedance and coupling degree converge to the initial system impedance and coupling degree.

The following table shows an example of a process for obtaining a design parameter of a directional coupler having a system impedance of 50 Ω and a coupling degree of 20 dB at the center frequency f = 2.4 GHz according to the embodiment of the present invention described above.

Repeating numbers Early One 2 3 4 5 6 Design system impedance Z ₀ (Ω) 50 25.90 23.25 23.84 23.68 23.74 23.78 Design coupling
C (dB) 20 22.18 21.98 22.04 22.02 22.03 22.03 Right Mode Impedance
Z _0e (Ω) 55.28 28.00 25.18 25.81 25.63 25.70 25.75 Pre-mode impedance
Z _0o (Ω) 45.23 23.95 21.46 22.03 21.87 21.93 21.97 Right-mode effective dielectric constant
ε _{r, eff, e} 2.915 3.148 3.183 3.175 3.177 3.176 3.176 G-mode effective dielectric constant
ε _{r, eff, o} 2.516 2.770 2.801 2.794 2.796 2.796 2.796 Length of coupling line
l (mm) 18.96 18.16 18.06 18.08 18.08 18.08 18.08 inductance
L (nH) 2.885 1.336 1.228 1.251 1.245 1.251 1.252 Real system impedance
Z ₀ (Ω) 96.54 55.69 48.75 50.35 49.87 49.91 50.04 Actual coupling
C (dB) 17.82 20.20 19.94 20.02 20.00 20.00 20.00

Initially, the design system impedance Z ₀ = 50Ω, design coupling C = 20dB, the right mode impedance Z _0e , the _premode impedance Z _0o , the right mode effective relative dielectric constant ε _{r, eff, e} , the _premode effective dielectric constant ε _r The physical length l of the _{, eff, o} and microstrip coupling lines is 55.28 Ω, 45.23 Ω, 2.915, 2.516, 18.96 mm, respectively, as shown in the table above. From the right mode effective dielectric constant ε _{r, eff, e, the premodal} effective dielectric constant ε _{r, eff, o} , and the physical length l of the microstrip coupling line, the right mode electrical length θ _e and the premode electrical length θ _o are obtained. With the obtained right mode impedance Z _0e , _premode impedance Z _0o , right mode electrical length θ _e and _premode electrical length θ _o , the actual system impedance Z ₀ and the actual coupling degree C are obtained using Equations 3 and 4, respectively. 96.54 Ω and 17.82 dB. Since this value is outside the target design system impedance and design coupling, the compensated design system impedance and design coupling are obtained. This compensated value can be obtained using the ratio or difference between the target value and the calculated actual value. For example, it can obtain | require according to following Formula.

System impedance (Ω): compensation target value = initial target value × (design target value / actual value)

Coupling (dB): Compensation Target = Initial Target + (Design Target-Actual)

Then, in the first iteration (1), the design system impedance Z ₀ = 50 × (50 / 96.54) = 25.90 Ω, design coupling C = 20 + (20-17.82) = 22.18 dB. According to this value, the right mode impedance Z _0e , the _premode impedance Z _0o , the right mode electrical length θ _e and the _premode electrical length θ _o are obtained. With these values, the actual system impedance and the coupling degree are obtained. Z ₀ = 55.69 Ω and C = 20.20 dB.

In the second iteration (2), the design system impedance Z ₀ = 50 × (25.90 / 55.69) = 23.25 Ω, design coupling C = 20 + (22.18-20.20) = 21.98 dB. The actual system impedance and coupling obtained in this second iteration (2) are Z ₀ = 48.75 Ω and C = 19.94 dB.

If this process is repeated, the system impedance and coupling will converge to the initial target values of 50 Ω and 20 dB. Referring to Table 1, it can be seen that in the sixth iteration (6), the system impedance and coupling degree are 50.04 Ω and 20 dB, and converged to the target values. In other words, all the design parameters can be found to have maximum directionality with only six iteration calculations with a given system impedance and coupling degree.

According to the design method of the directional coupler according to the embodiment of the present invention, it is possible to obtain the design parameters of the directional coupler so as to have the maximum directionality only a few iterations calculation without additional optimization or simulation.

The number of repetitive calculations depends on the degree of coupling of the directional coupler and generally increases as the coupling degree increases.

3 is a graph showing the results of performing a circuit simulation with the final design parameters obtained in Table 1. Referring to FIG. 3, the isolation degree S ₄₁ shows a very good value at the center frequency of 2.4 GHz, and the coupling degree S ₃₁ is maintained precisely at 20 dB. It can also be seen that the matching degree S ₁₁ also has a very good value.

4 is a diagram illustrating an embodiment of a layout of a directional coupler according to the embodiment of the present invention shown in FIG. 2. The layout according to the present embodiment has a transmission line having an impedance equal to the system impedance (typically 50 Ω) at the ends of the first microstrip line 205 and the second microstrip line 206 for compatibility with other circuits. 411, 412, 413, and 414 are additionally connected layouts. 2 and 4, reference numeral 405 corresponds to the first microstrip line 205, reference numeral 406 corresponds to the second microstrip line 206, and reference numerals 401, 402, 403, And 404 correspond to port 1 201, port 2 202, port 3 203, and port 4 204, respectively. The first shunt stub 407 and the second shunt stub 408 correspond to the first inductor 207 and the second inductor 208, respectively. The inductor, which is connected between the midpoint of the microstrip line and ground, can be easily implemented with a shunt ground stub, so there is no difficulty in layout, especially in high frequency circuits.

Various parasitic effects occur in the actual layout of the directional coupler. Among them, parasitic capacitance between microstrip coupling lines, which only affects directionality and greatly affects directionality, is an important factor to be considered in the design process. 4, such parasitic capacitance is mainly present between two microstrip lines (point A) and between 50 Ω transmission lines (point B). FIG. 5 is a circuit diagram of adding such parasitic capacitances C _p1 and C _p2 to the directional coupler according to the embodiment of the present invention shown in FIG. 2. The higher the frequency and the greater the degree of coupling, the greater the parasitic capacitance. The parasitic capacitance needs to be reflected in the design of the directional coupler. Therefore, as a method of designing a directional coupler according to another embodiment of the present invention, a method of designing a directional coupler considering the parasitic capacitance shown in FIG. The design method of the directional coupler according to the present embodiment is the same as the design method and the process of the directional coupler according to an embodiment of the present invention described above, except that the capacitance values C _p1 , C _p2 are Replaced by the following equations 10 to 16 as reflected.

According to the design method of the directional coupler according to the present embodiment, it is possible to obtain design parameters of the directional coupler considering the parasitic capacitance through the design formula, and finally, the matters that are difficult to be considered by the formula such as the loss of the microstrip line and the discontinuity point. Since only a small number of simulations need to be performed for the directional coupler, the overall design time of the directional coupler can be greatly reduced.

FIG. 6 shows the results of performing an electromagnetic simulation (simulated) by obtaining design parameters according to the design method of the directional coupler according to the present embodiment in consideration of parasitic capacitance, and measuring the S-parameters of actual fabrication (measured). The figure shown. Referring to FIG. 6, it can be seen that the simulation results and the actual measured results are almost identical, and the isolation degree (S ₄₁ ) is very excellent at about 76 dB at 2.4 GHz.

FIG. 7 illustrates the simulation results of the directional coupler and the conventional directional coupler according to the present embodiment in consideration of parasitic capacitance, and directivity and coupling according to measured results. Referring to FIG. 7, the directional coupler according to the present embodiment is shown to have a maximum directionality measured at 56 dB, while the maximum directionality of the existing directional coupler is shown to remain below 9.5 dB in the entire measurement range. It can be seen that the performance of the directional coupler is very good.

According to the present invention described above, the directional performance is improved by connecting the inductor between the midpoint of the microstrip coupling line and the ground. In addition, design formulas for obtaining various design parameters are provided, which allows accurate design with only a few iterations and greatly shortens the optimization time through cumbersome electromagnetic simulations, which is advantageous in terms of time and economy. In addition, the actual layout is facilitated by using a shunt ground stub as the inductor.

Conventional microstrip directional couplers have relatively low directionality, so their use has been limited in certain applications. However, the microstrip directional coupler according to the present invention greatly improves the directionality, such as isolation of transmit / receive antennas. It is possible to apply a variety of applications that are difficult to use.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium. The computer-readable recording medium may include a magnetic storage medium (eg, ROM, floppy disk, hard disk, etc.), an optical reading medium (eg, CD-ROM, DVD, etc.) and a carrier wave (eg, internet Storage medium).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a circuit diagram of an existing directional coupler using a microstrip coupling line, which is referenced in one embodiment of the present invention.

2 is a circuit diagram of a directional coupler using a microstrip coupling line, according to one embodiment of the invention.

3 is a graph showing a result of performing a circuit simulation with the final design parameters obtained in Table 1.

4 is a diagram illustrating an embodiment of a layout of a directional coupler according to the embodiment of the present invention shown in FIG. 2.

FIG. 5 is a circuit diagram of adding such parasitic capacitances C _p1 and C _p2 to the directional coupler according to the embodiment of the present invention shown in FIG. 2.

FIG. 6 is a diagram showing the results obtained by performing electromagnetic simulations by obtaining design parameters according to the design method of the directional coupler according to the present embodiment in consideration of parasitic capacitance, and measuring the S-parameters by actual fabrication.

FIG. 7 shows the results of the simulation of each of the directional couplers and the existing directional couplers according to the present embodiment in consideration of parasitic capacitance and the degree of orientation and coupling according to the actual measured results.

Claims (14)

delete delete delete As a method of designing a microstrip directional coupler, The microstrip directional coupler may include: a microstrip coupling line formed of first and second microstrip lines spaced at predetermined intervals on a dielectric and having a predetermined width and length; A first inductor connected between an intermediate point of the first microstrip line and ground; And a second inductor connected between the midpoint of the second microstrip line and ground; The design method, (a) obtaining a right mode impedance, a pre-mode impedance, a right-mode electrical length, and a pre-mode electrical length of the microstrip coupling line with a given target system impedance and target coupling degree; (b) obtaining inductances of the first and second inductors according to the obtained right mode impedance, pre-mode impedance, right mode electrical length, and pre-mode electrical length; (c) obtaining a system impedance and a coupling degree by reflecting the obtained inductance; And (d) compensating for the target system impedance and target coupling degree according to the obtained system impedance and coupling degree; (e) repeating the steps (a) to (d) with the compensated target system impedance and target coupling degree. 5. The method of claim 4, The process (e) is repeated until the obtained system impedance and coupling degree converges to the given target system impedance and target coupling degree. 5. The method of claim 4, The step (b) is a microstrip directional coupler design method characterized in that to obtain the inductance using the following equation.

Where Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is the predetermined center frequency). . 5. The method of claim 4, The method (c) is a microstrip directional coupler design method, characterized in that to obtain the system impedance using the following equation.

Where L is the inductance, Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is previously Given center frequency). 5. The method of claim 4, The step (c) is a microstrip directional coupler design method characterized in that to obtain the degree of coupling using the following equation.

Here, Z ₀ represents the obtained system impedance, Z _ee , Z _eo , Z _oe , Z _oo is as follows,

Where L is the inductance, Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is previously Given center frequency). 5. The method of claim 4, And (d) the compensation using the ratio or the difference between the target system impedance and the target coupling degree and the obtained system impedance and coupling degree. 5. The method of claim 4, Step (b) and step (c), And the inductance, the system impedance, and the coupling degree in consideration of the parasitic capacitance of the microstrip coupling line. The method of claim 10, The microstrip directional coupler further includes a transmission line connected to ends of the first and second microstrip lines, respectively. And said parasitic capacitance comprises a parasitic capacitance C _p1 between said first and second microstrip lines and a parasitic capacitance C _p2 between said transmission lines. The method of claim 11, The method (b) is a microstrip directional coupler design method characterized in that to obtain the inductance using the following equation.

Where Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is the predetermined center frequency). . The method of claim 11, The method (c) is a microstrip directional coupler design method, characterized in that to obtain the system impedance using the following equation.

Where L is the inductance, Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is previously Given center frequency). The method of claim 11, The step (c) is a microstrip directional coupler design method characterized in that to obtain the degree of coupling using the following equation.

Here, Z ₀ represents the obtained system impedance, Z _ee , Z _eo , Z _oe , Z _oo is as follows,

Where L is the inductance, Z _0e is the right mode impedance, Z _0o is the _pre -mode impedance, θ _e is the right mode electrical length, θ _o is the pre-mode electrical length, and w = 2πf (f is previously Given center frequency).

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