ENGR 227 Electromagnetic Laboratory Exercise 2025
You will design, build and test your own PCB patch antennae. Students will work in pairs and make a
joint submission. You partner will be usually be assigned as a person sitting next to you in the first Lab
session. 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. You are to assume its 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 estimate the required width of the
microstrip track using the formulae in the lectures, also given below.

( )
o
o
o eff
hZ
w 2h
µ
=
ε ε +

1 2
2r r
eff
1 1 h 1 w h1 12 1 H 1
2 2 w 25 h w
− ε + ε −       ε = + + + − −             

You might 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). Note that CST might give
a better answer than the approximate formula as it can account for the thickness of the copper,
electrical losses and a finite width to the base.
Remember to take screenshots for your report.
Week 18 Antenna Design
Use the simple equations from the lectures to define the
width, length and feed insertion depth of your antenna
at your given frequency. Repeating the formula here
r eff
c 2w
2f 1
=
ε +

eff
r eff
cL
2f
=
ε

h
w
effL L L= −∆
( )
( )
eff
eff
w0.3 0.264
hL 0.824h
w0.258 0.8
h
 ε + + 
 ∆ =
 ε − + 
 

7 6 5 4
eff eff eff eff
4 3 2
eff eff eff
0.001699 0.13761 6.1783 93.187LX
2 10 682.69 2561.9 4043 6697
 ε + ε − ε + ε =    ×  − ε + ε − ε + 

2
in L
XZ Z cos
L
π =  
 


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 (t.clayton@lancaster.ac.uk)
for manufacture no later than 9:00 am on Monday 17th 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.
Page Limit = 20, word limit = 2500

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