KR102418661B1 - Method for determining impedance matching circuit of vehicle radar - Google Patents

Abstract

A method for determining an impedance matching circuit of a vehicle radar according to the present invention is disclosed. A method for determining an impedance matching circuit according to the present invention comprises: selecting a plurality of points spaced apart by a preset distance from among points corresponding to a preset return loss based on an origin on a Smith chart as a matching point; designing an impedance matching circuit corresponding to the impedance characteristic value for each of the origin and preset matching points; and determining a PCB substrate having the lowest insertion loss among PCB substrates including each of the designed impedance matching circuits as a PCB substrate of a frequency band to be used.

Description

METHOD FOR DETERMINING IMPEDANCE MATCHING CIRCUIT OF VEHICLE RADAR

The present invention relates to a vehicle radar, and more particularly, to a method for determining an impedance matching circuit of a vehicle radar.

Recently, automotive radar usually uses a very high frequency band of 77 GHz or higher. Even if the matching circuit in the very high frequency band is designed using a simulation tool, frequency shift and characteristic change appear depending on the dielectric constant, thickness, and pattern tolerance of the substrate.

In order to manufacture a substrate of such a very high frequency band, it is necessary to process it using a special substrate, but this method takes a long time and has a problem in that the cost is also increased.

In addition, the dielectric constant of the 77 GHz band used in the vehicle radar is not provided by the board maker, so you have to check the dielectric constant through additional production of the board.

Laid-Open Patent Publication No. 10-2013-0093996, 2013.08.23. open

Therefore, in order to solve the problems of the prior art, an object of the present invention is to specify impedance corresponding to a preset number of points located in different directions among points having a preset return loss based on the origin in the Smith chart. An object of the present invention is to provide a method for determining an impedance matching circuit of a vehicle radar that implements an impedance matching circuit having an impedance matching circuit and selects an impedance matching circuit having the smallest insertion loss among the implemented impedance matching circuits.

However, the object of the present invention is not limited to the above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above objects, a method for determining an impedance matching circuit according to an aspect of the present invention includes a plurality of points spaced apart by a preset distance among points corresponding to a preset return loss based on the origin on the Smith chart. selecting them as matching points; designing an impedance matching circuit corresponding to the impedance characteristic value for each of the origin and preset matching points; and determining a PCB substrate having the lowest insertion loss among PCB substrates including each of the designed impedance matching circuits as a PCB substrate of a frequency band to be used.

Preferably, the selecting includes: drawing a circle connecting points corresponding to a preset return loss based on the origin on the Smith chart; and selecting a plurality of points dividing a quadrant on the drawn circle as a matching point.

Preferably, the return loss is characterized in that -10dB or less.

Preferably, the designing step is characterized in that the length and width of the matching end in the impedance matching circuit are adjusted according to the impedance characteristic value for the origin or the matching point.

Preferably, the determining comprises: generating PCB substrates including each of the designed impedance matching circuits; measuring the insertion loss of the generated PCB substrates; and comparing the measured insertion loss of the PCB substrates and determining the PCB substrate having the lowest insertion loss as the PCB substrate of the frequency band to be used as a result of the comparison.

A method for determining an impedance matching circuit according to another aspect of the present invention includes the steps of: identifying a frequency band to be used and checking the dielectric constant of the PCB substrate in the identified frequency band; If the PCB substrate permittivity is not known as a result of the check, selecting a plurality of points spaced apart by a preset distance from among points corresponding to a preset return loss based on the origin on the Smith chart as a matching point; designing an impedance matching circuit corresponding to the impedance characteristic value for each of the origin and preset matching points; and determining a PCB substrate having the lowest insertion loss among PCB substrates including each of the designed impedance matching circuits as a PCB substrate of a frequency band to be used.

Through this, the present invention implements an impedance matching circuit having impedance characteristics corresponding to a preset number of points located in different directions among points having a preset return loss based on the origin in the Smith chart, and the implemented impedance matching circuit By selecting an impedance matching circuit having the least insertion loss among them, there is an effect of reducing the return loss.

In addition, since the present invention can reduce the return loss of the impedance matching circuit, the output power and the reception gain of the RF module are increased, so that the radar performance can be improved.

In addition, since the present invention does not need to weed an additional substrate for measuring the dielectric constant, convenience can be improved and additional manufacturing costs can be reduced.

1 is a diagram showing the structure of a vehicle radar according to an embodiment of the present invention.
2 is a diagram illustrating a pattern of an impedance matching circuit according to an embodiment of the present invention.
3 is a diagram illustrating a method for manufacturing an impedance matching circuit according to an embodiment of the present invention.
4 is a diagram illustrating a structure of a transmission line used in an ultra-high frequency circuit.
5 is a diagram illustrating points having a preset return loss on a Smith chart.
6A to 6E are diagrams illustrating the shape of an impedance matching circuit with respect to a matching point.

Hereinafter, a method for determining an impedance matching circuit of a vehicle radar according to an embodiment of the present invention will be described with reference to the accompanying drawings. It will be described in detail focusing on the parts necessary to understand the operation and operation according to the present invention.

In addition, in describing the components of the present invention, different reference numerals may be assigned to components of the same name according to the drawings, and the same reference numerals may be assigned even though they are different drawings. However, even in such a case, it does not mean that the corresponding components have different functions depending on the embodiment or that they have the same function in different embodiments, and the function of each component depends on the corresponding implementation. It will be judged based on the description of each component in the example.

In particular, in the present invention, an impedance matching circuit having impedance characteristics corresponding to a preset number of points located in different directions among points having a preset return loss based on the origin in the Smith chart is implemented, and among the implemented impedance matching circuits We propose a new method to select an impedance matching circuit with the least insertion loss.

1 is a diagram showing the structure of a vehicle radar according to an embodiment of the present invention.

As shown in FIG. 1 , the vehicle radar according to the present invention is a very high frequency radar, and may largely include an antenna 100 , an RF module 200 , and a signal processing module 300 .

The antenna 100 may include a transmit antenna and a receive antenna. The transmitting antenna radiates the signal transmitted from the RF module, and the receiving antenna receives the signal reflected by the object and transmits it to the RF module.

In this case, the antenna 100 may be manufactured in a WR-10 size waveguide type to transmit a signal of 77 GHz, and precise processing is required to prevent signal loss.

The RF module 200 may include a monolithic microwave integrated circuit (MMIC) and a phase locked loop (PLL). The PLL generates a chirp waveform and transmits it to the transmit antenna through the MMIC. The MMIC down-converts a signal received through a reception antenna into a baseband signal and transmits the down-converted signal to the signal processing module.

In this case, in order to prevent signal loss in the connection from the transmit MMIC to the transmit antenna and the connection from the receive antenna to the receive MMIC, an optimal design of a transition and matching circuit is required. In particular, the 77 GHz high-frequency signal is very sensitive to slight distortion and process errors, so the connection structure with the antenna is very important.

The signal processing module 300 processes the PLL control of the RF module 200 and the baseband signal transmitted from the RF module 200 , and supplies power to the MMIC and various ICs of the RF module 200 . The baseband signal transmitted from the RF module is converted into a digital signal through the ADC, and an object in front is detected based on the converted digital signal.

At this time, since the signal transmitted from the RF module 200 to the signal processing module 300 is a relatively low frequency signal compared to the signal transmitted from the antenna to the RF module, there is little loss.

The reason that matching is important in the RF module is to transmit and receive signals without loss through transitions connected to the antenna at the output end of the transmitting MMIC and the input end of the receiving MMIC.

The impedance of the input and output terminals of MMIC is very different from the 500hm used in circuit design. 500hm is generally used as a reference point for circuit design, and 500hm is generally used. A separate matching stage is used to connect the distorted impedance with the 500hm line connected to the transition. This matching stage compensates for the impedance difference by reducing the reflection caused by the impedance difference between the two different connection terminals.

2 is a diagram illustrating a pattern of an impedance matching circuit according to an embodiment of the present invention.

As shown in FIG. 2 , the pattern of the impedance matching circuit includes a first connection terminal 10 connected to the MMIC, matching terminals 20 and 30 for impedance matching, and a second connection terminal 30 connected to a transition. is composed of

At this time, the impedance difference is corrected by adjusting the width and length of the matching stages 20 and 30 .

3 is a diagram illustrating a method for determining an impedance matching circuit according to an embodiment of the present invention.

As shown in FIG. 3 , first, the frequency band to be used, for example, the 77 GHz band of the vehicle radar may be identified, and the permittivity of the PCB substrate in the frequency band may be checked ( S310 ).

Next, if the substrate dielectric constant is not known as a result of the check, a circle connecting points corresponding to a preset return loss, for example, -10 dB (VSWR 2:1) based on the origin on the Smith chart can be drawn (S320).

Next, a plurality of points in different directions spaced apart by a preset distance on a circle drawn based on the origin in the Smith chart, that is, a plurality of points dividing a quadrant with respect to the origin may be set as matching points (S330) ). That is, the lines connecting the matching points and the origin have an angle of 90 degrees with the adjacent lines.

At this time, in the present invention, the impedance characteristic is changed using the Smith chart. The principle of changing the impedance characteristic in this way will be described in detail as follows.

4 is a diagram illustrating a structure of a transmission line used in an ultra-high frequency circuit.

Referring to FIG. 4 , a transmission line is used in an ultra-high frequency circuit, and the relationship between impedances for the transmission line can be expressed as the following [Equation 1].

[Equation 1]

At a low frequency, the signal transmission characteristic does not change due to Equation 1 above. On the other hand, at high frequencies, the impedance characteristics change depending on the line length (l) due to the shortened wavelength (λ).

In consideration of these characteristics, impedance matching of the transmission line must be performed to accurately design a matching circuit. The return loss is checked to check whether the impedance matching is correct, and the return loss RL can be expressed as in [Equation 2] below.

[Equation 2]

The return loss represents a value obtained by converting the reflection coefficient Г into a log scale of power. Here, the reason why we multiply by 20 instead of 10 when taking dB is that the reflection coefficient value itself is a ratio of voltage. That is, we multiply by 20, not 10, because we have to consider the square of the voltage to calculate the dB of the power reference. The larger the calculated return loss, the smaller the reflection, meaning better impedance matching.

At this time, the reflection coefficient Г represents an index calculated by simply calculating the amount of reflection caused by the impedance difference at a certain connection end as the ratio of the input voltage to the reflected voltage. That is, the reflection coefficient is a numerical value indicating how much the reflection amount is with respect to the input amount, and the smaller the value, the smaller the reflection amount.

In general, a Smith chart is used for impedance matching. For accurate matching, it is considered that matching is achieved only when it is located at the origin in the desired frequency band.

5 is a diagram illustrating points having a preset return loss on a Smith chart.

Referring to FIG. 5 , assuming that the origin of the Smith chart is 500hm, and connecting points corresponding to reflection loss of about -10dB (VSWR 2:1), a circle is drawn as shown in the figure.

At this time, the point dividing the circle into quadrants on the circle of -10dB of return loss centered on the origin is set as a matching point and 4 matching points. The reason for drawing a circle with a return loss of -10 dB in this way to obtain a matching point is to minimize loss due to mismatch of matching.

Here, an example in which the point dividing the quadrant is set as the matching point is described, but the present invention is not limited thereto, and the point dividing the n quadrant may be set as the matching point.

Since the reflection coefficient Г has a value of 0≤Г≤1 as a voltage ratio, and the return loss RL has a value of 0≤RL≤∞, the smaller the reflection, the closer the reflection coefficient approaches 0 and the return loss approaches ∞.

Usually, after measuring the VSWR value with a vector network analyzer, the reflection coefficient is obtained from the measured VSWR value, which can be expressed as in [Equation 3].

[Equation 3]

Since the reflection coefficient is a voltage ratio, it must be expressed as a power ratio to obtain a loss. Since the reflection coefficient represents the reflected amount, the power value of the non-reflected signal appears as an insertion loss, and the insertion loss IL can be expressed as in Equation 4 below.

[Equation 4]

The reason for squaring the reflection coefficient in [Equation 4] is to represent the reflection coefficient as a voltage ratio and the insertion loss as power. That is, the square of the voltage can be expressed as power.

If the insertion loss obtained as a result of this calculation is converted into dB, the loss according to the reflection coefficient can be known. [Table 1] below shows the insertion loss according to the VSWR.

VSWR 1.50 2.00 2.50 3.00 reflection coefficient 0.20 0.33 0.43 0.50 Return loss [dB] -13.98 -9.54 -7.36 -6.02 Insertion loss [dB] -0.35 -1.02 -1.76 -2.50

As can be seen from [Table 1], the insertion loss varies greatly depending on the VSWR.

On the other hand, the radar detection distance R can be expressed as in the following [Equation 5].

[Equation 5]

Here, P _S represents transmit power, G represents antenna gain, λ represents wavelength, σ represents RCS, and P _E represents receive power.

As the output changes by 1dB, the radar detection range changes by about 20m. Considering that the normal radar specifications are 200m for LRR (Long Range Radar) and 160m for MMR (Middle Range Radar), it can be seen that a 1dB difference has a large effect on radar performance.

Therefore, in the present invention, the reason for matching a circle with a return loss of -10 dB (VSWR 2:1) is to bring a loss within 1 dB due to a mismatch of the matching. If the loss due to matching is less than 1dB, the final radar detection range performance will be around ±20m.

Next, an impedance matching circuit corresponding to the impedance characteristic value for each of the origin and preset matching points may be designed ( S340 ).

6A to 6E are diagrams illustrating the shape of an impedance matching circuit with respect to a matching point.

6A, when the origin in the Smith chart is the matching point, the first connection end of the impedance matching circuit is formed to have a length of 260 μm and a width of 150 μm, and the matching end is formed to have a length of 150 μm and a width of 700 μm, The second connection end may be formed to have a width of 300 μm.

6B, when a point in the Smith chart is used as a matching point, the first connection end of the impedance matching circuit is formed to have a length of 260 μm and a width of 150 μm, and the matching end is formed to have a length of 150 μm and a width of 1 mm, The second connection end may be formed to have a width of 300 μm.

Referring to FIG. 6C , when another point in the Smith chart is used as a matching point, the first connection end of the impedance matching circuit is formed to have a length of 260 μm and a width of 150 μm, and the matching end is formed to have a length of 150 μm and a width of 450 μm. and the second connection end may be formed to have a width of 300 μm.

Referring to FIG. 6D , when another point in the Smith chart is used as a matching point, the first connection end of the impedance matching circuit is formed to have a length of 260 μm and a width of 150 μm, and the matching end has a length of 100 μm and a width of 550 μm. is formed, and the second connection end may be formed to have a width of 300 μm.

Referring to FIG. 6E , when another point in the Smith chart is used as a matching point, the first connection end of the impedance matching circuit is formed to have a length of 260 μm and a width of 150 μm, and the matching end is formed to have a length of 200 μm and a width of 550 μm. is formed, and the second connection end may be formed to have a width of 300 μm.

As such, since the impedance characteristics are different according to each matching point, it can be seen that the sizes, eg, lengths and widths, of the matching terminal patterns forming the impedance matching circuit are changed.

Next, a PCB board including each of the impedance matching circuits designed according to the origin and the matching point may be generated ( S350 ), and an insertion loss of each of the generated PCB boards may be measured ( S360 ).

Next, the measured insertion loss is compared, and as a result of the comparison, the PCB board having the lowest insertion loss may be determined as the PCB board in the frequency band to be used ( S370 ).

The embodiments described above are examples thereof, and various modifications and variations may be made by those of ordinary skill in the art to which the present invention pertains without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: antenna
200: RF module
300: signal processing module

Claims (5)

confirming, by the simulation tool, the dielectric constant of the PCB substrate in the frequency band to be used;
If the PCB substrate permittivity is not known, the simulation tool draws a circle connecting points corresponding to a preset return loss based on the origin on the Smith chart, and selects a number of points dividing n quadrants on the drawn circle as matching points to do; and
designing, by the simulation tool, an impedance matching circuit corresponding to the origin and impedance characteristic values for each of the selected matching points
A method for determining an impedance matching circuit comprising:
According to claim 1,
After designing the impedance matching circuit,
Determining an impedance matching circuit, characterized in that the simulation tool further comprises the step of determining, by the simulation tool, the PCB substrate having the lowest insertion loss among the PCB substrates including each of the designed impedance matching circuits as the PCB substrate of the frequency band to be used. way for.
3. The method of claim 2,
The determining step is
generating PCB boards including each of the designed impedance matching circuits;
measuring the insertion loss of the generated PCB substrates; and
Method for determining an impedance matching circuit comprising the step of comparing the insertion loss of the measured PCB boards and determining the PCB board having the lowest insertion loss as the PCB board of the frequency band to be used as a result of the comparison .
According to claim 1,
The return loss is
A method for determining an impedance matching circuit, characterized in that it is less than or equal to -10 dB.
According to claim 1,
The design step is
A method for determining an impedance matching circuit, characterized in that the length and width of a matching end in the impedance matching circuit are adjusted according to the impedance characteristic value for the origin or the matching point.

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