ANTENNA
OBJECTIVE
• Design of a microstrip patch antenna with microstrip feed.
• To study input impedance matching of an antenna.
• To study the radiation characteristics of an antenna.
THEORY
A Patch antenna consists of a flat rectangular patch of metal mounted over a dielectric slab
backed by sheet of metal called a ground plane. The patch antenna is convenient for
microwave frequencies, specifically on the 2.4-GHz band and higher. It consists of a plated
geometric form (the patch) on one side of a printed circuit board, backed up on the opposite
board side by a ground plane which extends beyond the dimensions of the radiating patch.
Rectangular and circular forms are the most common, but other shapes—for example, a
trapezoid—are sometimes used. Maximum radiation is perpendicular to the board. A square
half-wave patch antenna has a directivity of 7 to 8 dB. The dimension L is approximately a half
wavelength, calculated as half the free space wavelength (λ) divided by the square root of the
effective dielectric constant (ɛ) of the board material. It must actually be slightly less than a
half wavelength because of the fringing effect of the radiation from the two opposite patch
edges that are L apart and the ground plane. As long as the feed is on the centerline, the two
other edges don’t radiate. The figure shows a microstrip feeder, which is convenient because
it is etched on the board together with the patch and other component traces on the same
side.
PART A: SIMULATION
Layout of the microstrip line
Substrate Material: RogerR04003
Calculation of Length and Width for Microstrip Line
Dielectric Constant = 3.55
Dielectric Height, h=0.813 mm
Frequency of Operation, f = 10 GHz
Characteristic Impedance, Zo = 50 Ohm
Theta = 90 degree
Using these values in the Microstrip Line Calculator, the Length and Width have been obtained
as: Length, L = 4.5 mm and Width, W = 1.82 mm
Plots of E and H Fields
E Field
H Field
S Parameter Plot
Layout of Monopole Antenna
Thickness, t = 0.017mm
Height, h = 0.813mm
Dielectric Constant = 3.55
Plots
S Parameter Plot
E Field
Monopole Radiation Pattern
At Phi = 0 Degree
At Phi = 90 Degree
3D Radiation Pattern, Polar Plot
Discussions and Conclusions
The primary focus was to simulate the S parameters of the Microstrip line and Monopole
Antenna and see how efficiently the impedance matching is taking place in terms of the power
reflected. Also, the E and H fields of both the Simulations were observed.
Reflection parameter, S11 indicates the efficiency of the antenna in terms of the power
reflected back due to impedance mismatch. A low S11 signifies good impedance matching and
indicates that most of the signal is being radiated rather than being reflected.
The observed S11 values confirm that the antenna was appropriately matched to the design
frequency of 1.8 GHz.
PART B: MEASUREMENTS
Monopole Antenna Photo
Observations
E plane: Copole
Angle (°) S11value(dB) Normalised(dB) Angle (°) S11value(dB) Normalised(dB)
0 -38.9 0 100 -39.94 -0.44
10 -41.67 -2.77 110 -42.77 -3.87
20 -42.51 -3.61 120 -44.74 -5.84
30 -45.44 -6.54 130 -42.84 -3.94
40 -47.88 -8.98 140 -41.64 -2.74
50 -51.82 -12.02 150 -42.71 -3.81
60 -50.2 -10.4 160 -45.73 -6.83
70 -47.73 -8.84 170 -43.31 -4.41
80 --44.67 -5.77 180 -46.22 -7.32
90 -41.55 -2.65
Radiation Pattern Plot
H Plane: Co-pole
Angle (°) S11value(dB) Normalised(dB) Angle (°) S11value(dB) Normalised(dB)
0 -46 0 100 -52.4 -6.4
10 -45.54 0.46 110 -50.8 -4.8
20 -45.12 0.88 120 -48.6 -2.6
30 -46.41 -0.41 130 -47 -1
40 -48.4 -2.4 140 -46.9 -0.9
50 -51.76 -5.76 150 -48.4 -2.4
60 -54.7 -8.7 160 -49.73 -3.73
70 -56.9 -10.9 170 -51.92 -5.92
80 -56.17 10.17 180 -51.43 -5.43
90 -50.24 -4.24
Radiation Pattern Plot
Overall Discussions
In the context of a Microstrip Patch Antenna Lab experiment where scattering parameters (S-
parameters) were measured, the conclusion might be framed as follows:
Objective Summary: The primary objective of the experiment was to design and evaluate a
microstrip patch antenna, with a focus on measuring and analyzing its scattering parameters
(S-parameters), specifically the reflection coefficient (S11) and, if applicable, transmission
parameters (S21).
Design and Fabrication: The antenna was designed with specific dimensions and substrate
characteristics. The fabrication process involved creating the antenna on a dielectric substrate
with defined material properties.
Scattering Parameter Measurements:
Reflection Coefficient (S11): The measured S11 values indicated the efficiency of the antenna
in terms of power reflected back due to impedance mismatch. A low S11 value (below -10 dB)
signifies good impedance matching and indicates that most of the signal is being radiated
rather than reflected.
Transmission Parameters (S21): If S21 was measured, it would show the transmission
characteristics if the setup involved coupling between multiple antennas. In many cases, this
might be less relevant for a simple patch antenna analysis.
Results and Analysis:
Resonant Frequency: The resonant frequency observed from the S11 measurements should
closely match the designed resonant frequency. Any deviations might be attributed to
fabrication imperfections or substrate dielectric variations.
Bandwidth: The bandwidth can be inferred from the frequency range over which S11 remains
below a certain threshold (e.g., -10 dB). This helps assess the operational range of the
antenna.
Impedance Matching: Effective impedance matching is reflected in the S11 results. Good
impedance matching is crucial for minimizing reflected power and improving antenna
performance.
Conclusion: The experiment demonstrated that the designed microstrip patch antenna
effectively met the targeted design specifications based on the measured scattering
parameters. The observed S11 values confirmed that the antenna was appropriately matched
to the designed frequency, with acceptable performance in terms of bandwidth and reflection
loss.
