AppCAD calculates the characteristic impedance of the antenna signal line

When designing a GPS receiver, the characteristic impedance of the antenna signal line is required to be 50 ohms to achieve impedance matching with the antenna. If calculated manually, the calculation is cumbersome and prone to errors. Therefore, our company has launched software for calculating characteristic impedance and other parameters during high-frequency design.

AppCAD is easy to use and is a unique RF design tool software that is suitable for engineering calculations in many RF, microwave and wireless design applications. The calculations are simple and fast. AppCAD can be used for the calculation and design of many circuits, signals and systems using discrete crystal chips, diodes to silicon and GaAs integrated circuits. The software shortcut keys are also very easy and fast to use.

In the routing of GPS antenna signal lines, microstrip lines, striplines or coplanar waveguides may be used. The following uses microstrip lines as an example to introduce how AppCAD calculates the characteristic impedance of signal lines.

After starting the software, press "Passive Circuits" in the buttons on the left, and press "Microstrip" in the options that appear, as shown in the figure above. In the window that appears, set the relevant parameters.

As shown in the figure below, set the dielectric constant of the PCB board, the frequency of the transmission signal and the unit of the PCB length in the options on the lower left. To set the dielectric constant (Dielectric Er), just select the material of the PCB board in the selection box below, such as FR-4 in the figure below; or select "Enter Custom Er Value" in the selection box below, and then directly enter the dielectric constant value above. In GPS design, the civil frequency is 1.57542GHz, and the frequency value can be directly entered, or calculated using 1.6GHz. There are several options for the length unit, and micrometers (um) are selected as the unit in the figure below.

In the upper left corner of the above figure, the following parameters need to be set: line width "W", as shown in the figure, it is 254 microns; the thickness of a single-layer PCB board "H", such as the thickness of an 8-layer board is 1.2mm, then each layer is about 150 microns, so enter 150 in the figure. The thickness of the line "T", the thickness of a 1OUNCE line is about 35 microns, and the thickness of a 0.5OUNCE line is about 18 microns, so enter 18 microns in the figure. If gold or tin plating, you need to add another 25 microns. The length of the line "L" line has little effect on the characteristic impedance, so you can ignore the length of the line and use the default value.

After entering and setting the parameters on the left, press "Caculate Z0" on the right or the shortcut key F4 to calculate. At this time, Z0 below will display the calculated characteristic impedance value of 50.75 ohms.