RESEARCH ON MICROSTRIP COUPLER DESIGNER FOR ELECTRONIC WIRED TRANSMISSION
Pankaj Kumar
Research Scholar, K. K. University,
Berauti, Nepura, Deep Nagar, Biharsharif, (Nalanda), Bihar – 803115 Dr. Mukesh Kumar
Assistant Professor, K. K. University, Berauti, Nepura, Deep Nagar, Biharsharif, (Nalanda), Bihar – 803115 1 INTRODUCTION
Directional couplers are essential circuits in many optical communication systems and microwave bands. A directional coupler is a device that can extract part of the signal traveling on a transmission line or waveguide, and the rest of the power is not directly coupled at the output. Key applications include power measurement, standing wave measurement, control signal sampling, and microwave signal combinations. They can also be used to perform signal processing tasks. It is part of balanced amplifiers, mixers, phase shifters, modulators and demodulators.
Consider a "microwave directional coupler" with several variations. In the first chapter, we will start with a waveguide system and look for solutions to Maxwell's equations. Maxwell's equations are a set of four PDEs that relate electric and magnetic fields to their source, charge density, and current density. You can combine these equations to show that light is an electromagnetic wave. To introduce the microstrip lines used to transmit microwave signals, we first need to look at the TEM transmission lines. It consists of conductive strips separated from the ground plane by a dielectric layer called the substrate. The first chapter describes those solutions by solving the equations and describing the connected lines. Realizes the representation of mathematically obtained equations in MatLab. The next chapter describes combined microstrip lines. Its configuration is shown in the work. Some of the more important parameters that characterize combined microstrip lines, and some of the key techniques used to analyze combined lines, are design. It also describes the join mode formulation and how to use even and odd modes. The final chapter contains a simulation of microstrip lines. These were implemented in the CST STUDIO SUITE ™ program, which we believe is suitable for further
investigation. Bringing one line closer to the other creates a coupling effect. You can observe the proportional transfer of power based on fixed parameters. Work ends with the completion of the simulation and an attachment showing the most important simulation results.
2. BASIC PROPERTIES 2.1. Four-Port Networks
The S matrix of the reciprocal and mathed four-port network has the following form:
(2.1) If the network is matched at every port,
It is important to understand that “matched” means all other ports are terminated in Z0).
If the network is reciprocal, then
3 What is CST STUDIO SUITE™?
The electromagnetic simulation software CST STUDIO SUITE ™ is the result of years of research and development into the most efficient and accurate computing solutions for electromagnetic design. It includes CST tools for designing and optimizing devices that operate at a wide range of frequencies, from static to optical. The analysis can include thermal and mechanical effects as well as circuit simulation. All programs are accessible through a common interface that facilitates co-simulation of circuits and multiphysics.
CST STUDIO SUITE consists of different modules for different applications. The following simulation uses the CST MWS module to investigate the directional coupler of the coupled microstrip lines.
CSTMICROWAVESTUDIO® (CST MWS) is a special tool for fast and accurate 3DEM simulation of high frequency problems.
3.1 A Microstrip
To introduce you to the topic of simulating microstrip lines using CST, let's run a simple example that simulates a single microstrip line. To get the physical parameters of a microstrip line, you can use a tool called TXLine (Transmission Line Calculator). TXLine is a free and easy-to-use interactive power line calculator for analysis and synthesis of power line structures. TXLine allows the user to enter either the physical or electrical characteristics of a typical transmission medium.
Fig. 3.1 TX-Line (Transmission Line Calculator).
This program provides physical properties by inputting material parameters and electrical properties to use. The reverse is also true. In the figure above, you can see the data used to simulate the program window and microstrip lines.
Fig. 3.2 A microstrip line in CST.
Use the CTS program to design the structure of lines in 3D space. Copper with effective permittivity in all simulations using standard conductors and dielectric materials .
The red area shown in Figure 3.2 represents the input and output ports.
This allows you to get graphs of S-matrix coefficients, Smith charts, electric and magnetic fields, and more. [Appendix 4.4.1] has a graphic of the coefficients of the S-matrix for simulating microstrip lines.
3.2 Two Coupled Lines
As we saw in the previous chapter, we introduced graphics to illustrate the characteristics of directional couplers.
These graphs are extracted from the following CST-simulated example (Figure 3.4).
Fig. 3.3 Coupled microstrip lines.
To make the study of this directional coupler, we decided to set three parameters (Fig 3.3). We can used as realistic values, the same used in the simulation of a microstrip line:
and copper
dielectric constant
The possible values of S and W, which is available in coupled microstrip lines are as follows (look [5]):
(3.1) The following figure is three-dimensional representation of two microstrip transmission lines coupled with
Fig. 3.4 Coupled microstrip lines in CST.
To understand how the designed directional coupler works (Figure 3.4), we must first consider the coefficients of the S-matrix S31 [Appendix 4.4.2.1]. This graph was described in the previous chapter to illustrate the coupling. The frequency, which have the largest coupling is . The operating band of the directional coupler depend on how strict we are with the coupling, if we can tolerate a 3 dB of coupling, we will be a operation band about 4.4GHz.
To Once you know what is happening at the differential output of the directional coupler, you can look at the other coefficients of the S-matrix. For example, the value of S11 [Appendix 4.4.2.1] is small. Another important factor is insertion loss. The loss incurred on the highway between the input directional coupler and the egress directional coupler P1P2 is related to the transmission medium connecting the two ports S21.We can see in the figure below that these are taking minimum values in the frequency but increase as we move of frequency.
Fig. 3.5 The insertion loss of the coupled microstrip lines.
The program CSTMWS can be used to simulate magnetic and electric fields along power lines. Therefore, there is an idea of joining between lines and the behavior of fields through lines. The program can also animate the magnetic and electric fields of power lines.
The following figure shows a picture of an animated magnetic field at frequency f = 6.73GHz. Here you can see the full transmission power from one microstrip line to another.
Fig. 3.6 Magnetic field of the coupled microstrip lines.
I implemented all the simulations with the same entry signal. CSTMWS has a standard excitation signal. As you can see in the figure below, this signal represents a unitary Gaussian function.
Fig. 3.7 Default excitation signal.
You can use CST MWS to study the behavior of magnetic and electric fields at a given point in time. In the following graph, you can observe the electric field at point.
Fig. 3.8 Electrical field of the coupled microstrip lines in a point l (2 lines).
At that distance l, a signal delay of 31010 seconds or more can be seen. In this case, the signal is not exactly the same as the original signal. Also, since the two lines have almost the same electric field signal, l can be said to be the midpoint of the line. At the end of the line, you can see that line 2 has virtually full capacity.
3.2.1 Length of the line (parameter l)
The following figure shows a simulation of a directional coupler, but only one variation doubles the length of the transmission line.
Fig. 3.9 Coupling/Frequency value.
Looking at Figure 3.9, the operating frequency is f = 6.73 GHz, and doubling the length of the line yields the second minimum of the function.
This effect has succeeded in doubling the function of the new directional coupler and the frequencies of S21 and S31 [Appendix 4.4.2.2].
Responses from these functions are always regular.
To see the effect, we doubled the magnetic and electric field frequencies to the same operating frequency f = 6.73 GHz, as shown in the figure below.
Fig. 3.10 Magnetic field of a coupled microstrip lines.
In Figure 3.10, you can see how the magnetic field is transmitted to half of the line, just like any other directional coupler (Figure 3.6). In this experiment, it can be said that this directional coupler behaves like half the length to collect (Figure 3.6).
3.2.2 Separation between lines (parameter S)
To determine the effect of varying the distance between the coupled lines, we present the most significant example, where we increase the separation between lines to S=h4, to see the results.
Fig. 3.11 Coupling/Frequency value.
As you can clearly see in the graph above S31, the most important effect of increasing S is to reduce the coupling by about 13dB. All other graphics for this simulation can be found in [Appendix 4.4.2.3].
In this experiment, the directional coupler was designed to be relatively small relative to the distance between the coupled lines for all other parameters such as input signal, dielectric height, etc.
3.2.3 Width of transmission lines (parameter W)
We did some simulations with different line widths and found that the most important effect was a change in the behavior of the ribbon directional coupler.
The following figure shows the coefficients of the matrix S31 in dB for an example of increasing the width W = 4h of two equal lines.
Fig. 3.12 Coupling/Frequency value.
In this example we can see that we have a coupling of 1 dB, a wide band of frequencies, from 6.7GHz to about 12GHz.
3.3 Three Coupled Lines
I have examined the connecting line of three lines, but I would like to add another line to investigate the operation.
In this section, you will perform a similar simulation.
This design required the addition of two ports for the new transmission line.
The following figure is a three- dimensional representation of three microstrip transmission lines coupled at W = 1.5h and S = 0.7h.
Fig. 3.13 Three coupled microstrip transmission lines.
The following figure shows the bond when the 2-wire directional coupler is not the third strand. The one we saw earlier (Figure 3.4) is designed with the same parameters, but with only two lines.
Looking at the directional coupler coupling [Appendix 4.4.2.1], you can see how changing the minimum 20dB from 13.5GHz to 9GHz will change the
functional format. This allows the coupler to operate and design at 9GHz.
Fig. 3.14 S41 parameter
As can be seen in [Appendix 4.4.3.1], parameter S21 indicates that the design has low insertion loss at a frequency of 9.8 GHz. The parameter S61 can be defined as coupling a three-wire coupler.
Fig. 3.15 Coupling/Frequency value.
Comparing usually with the coupling of traces, we will see how the layout has a chief band we will see how the layout has a better running band.
These 3 coupled microstrip transmission traces have a chief coupling on the frequency of running of 9GHz. In the subsequent discern we will have a look at how on this frequency, there may be transmission of strength from the primary line to the third.
Fig. 3.16 Magnetic field of the coupled microstrip lines (f =9GHz)
For the connection of the coupler of this 3-line coupling, the same simulation as the connection of the 2-line coupler was performed. Some tests have the same effect, such as changing the length parameter. The most important simulations are listed in [Appendix 4.4.3].
Some of them are shown below.
3.3.1 Separation between lines (parameter S)
In one of the tests, we found that the distance between the lines increased, so increasing the distance lost more connections than joining two lines.
The following figure shows a simulation of the previously presented design (Figure 3.13), with the parameter S
= 4h modified.
Fig. 3.17 Magnetic field of the coupled microstrip lines (f=6.73GHz)
You can see that the signal is not coupled to the third line and stays on port 2 of the first line at maximum power. As you can see in the parameter S61 [Appendix 4.4.3.2] in the figure, we have implemented a magnetic field simulation at this frequency because there is a coupling of up to 20 dB at a frequency of 6.73 GHz.
3.3.2 Width of transmission lines (parameter W)
Perform the same experiment as a two- line coupler. Change the value of the transmission line to see the effect on the output of the port. Waiting for a similar effect.
The following figure shows parameter S21 for a 3-line microstrip coupler with W = 3h and S = 0.7h.
Fig. 3.18 S21 parameter.
It has been found that the wider the line width, the better the three microstrip transmission lines work at higher frequencies. You can also see that the insertion loss is small because there is a 35dB S21 at a frequency of 12GHz. In
[Appendix 4.4.3.3] we can see that there is a significant improvement in the coupler due to the coupler signal S61, which is 0.9 dB higher than the other cases. This is because all other outputs of the operating frequency are of little importance.
The following figure shows the electric and electromagnetic fields to help visualize good coupling.
Fig. 3.19 Magnetic field of the coupled microstrip lines (f=12GHz) 3.4 Four Coupled Lines
We give some details of the simulation with four coupler lines. In this design is needed a number of eight ports, like we can see.
Fig. 3.20 Four coupled microstrip transmission lines.
You can see the results obtained in [Appendix 4.4.4]. Designs don't work as well as others, and they are more difficult to design. By changing the fish parameters, as we did in other designs, there are some major differences between the results and we can observe the functional bias of the S-matrix parameters.
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