ENGR 227 Electromagnetic Laboratory Exercise 2024
You will design, build and test your own PCB patch antennae. Students will work in pairs and make a joint submission. Each pair will undertake design at a different frequency between 1.58 GHz and
2.75 GHz. Frequencies will be assigned during the first Lab session.
The PCB substrate will be 1.6 mm thick FR-4 with relative permittivity εr = 4.6 and loss tangent
tan(δ) = 0.015. The copper layer thickness is 0.035 mm. Design your patch antenna to fit on a 60 mm by 60 mm PCB. Those pairs assigned lower frequencies may require a slightly larger PCB, if you cannot fit your design on the 60 x 60 mm board, then please contact Amos Dexter.
Week 17 Investigation of Microstrip
Your feed line must have an impedance of 50 Ohms. Initially calculate the required width of the microstrip track using the formula in Lecture 9. Plot impedance vs width in the range of interest using Excel and read the ideal width from a graph rather than inverting the formula.
Follow the instructions on using CST Microwave Studio in MOODLE to model a microstrip line. When drawing the geometry in CST microwave studio you must parameterise dimensions (i.e. use names not numbers for dimensions). Perform. simulations. Investigate how the impedance depends on mesh size. Investigate how the impedance depends on the relative permittivity of the substrate. Adjust the track width from your initial value (chosen using the analytic formula) to improve your design value for the track width getting the impedance to 50 Ohms (see instructions on MOODLE)
Remember to take screenshots for your report.
Week 18 Antenna Design
Use the simple equations from lecture 10 to define the width, length and feed insertion depth of your antenna at your given frequency. Draw your geometry in CST microwave studio, remembering to parameterise it (i.e. use names not numbers for dimensions). Add a far-field monitor at your desired frequency (see below). Simulate using the frequency domain solver.
Perform. a mesh convergence study to find an appropriate mesh size and use it for subsequent simulations. Do this by parametrising the meshing as shown in the previous lab and setting a parameter sweep. Investigate how the S11 plot changes with mesh density by plotting the resonant frequency versus mesh size. A finer mesh gives a more accurate simulation but takes longer to run. Consider what mesh size is optimum.
Determine the frequency and S11 (reflection coefficient) of your simulated antenna. Consider the quality of matching to the feed. Aim for the S11 minima to be less than -20 dB (0.1) at the resonant frequency, (it may not always be possible to achieve this).
Vary the antenna parameters using parameter sweeps to get S11 and frequency to determine dependencies. Consider which parameters have the strongest effects on frequency and S11. Utilise data from parameter sweeps to get the correct frequency and to minimise reflection (S11) at this frequency.
Finally, look at the gain select Far-field. Then right-click on the file and select far-field plot properties, now you can do 2D polar plots of gain.
Week 19 Finalisation
Finish the antenna optimisation. Export your geometry as a 2D Gerber file (change the working plane to be across the top of the board then select Modelling/ Import/Export/Gerber). Import the Gerber file into Eagle and complete any missing lines. Alternatively, you can draw your Antennae in Eagle using the instructions on Moodle. Check your board layout in Eagle before sending it off to be made. Name the file with your names and indicate that you need the ground plane.
If you need to draw a rectangle in Eagle in the command line is
RECT R0 (x1 y1) (x2 y2);
where the coordinates are the corners of the rectangle.
The space around the board should be the same as in your simulation. Adding your name on the dielectric will add extra capacitance so is not recommended. Remember the microstrip input should go to the edge of the board without a gap.
Finally send the eagle .brd file to our electrical technician Thomas Clayton ([email protected]) for manufacture no later than 11:00 am on Monday 11th March.
Week 20 TEST
On receipt of your board, you may need to solder on the SMA coaxial to PCB connector if this has not been done for you. You will measure the resonant frequency and gain of your antenna. If the board is off frequency then you should adjust the permittivity in CST, and find the real permittivity of the board. You should then re-adjust the antenna dimensions in CST to bring the frequency back to the desired frequency.
Write everything up in a report including dimensional calculations, screenshots of the mesh analysis & optimisation graphs, and S11 measurements. Discuss the mesh analysis and the agreement between your final results and simulations, discussing any disagreement. Submit online in Moodle to meet the advertised deadline.