Microstrip Patch Antenna — 2.45 GHz Geometry Comparison

Comparative study of five microstrip patch antenna geometries (circular, F-shaped, triangular, square, hexagonal) operating at 2.45 GHz. Each design was simulated in CST Studio Suite, fabricated on FR-4 substrate, and measured with a Rohde & Schwarz VNA.

Results

Simulation (CST Studio)

All five geometries were modeled in CST Studio Suite before fabrication. Each antenna was simulated at 2.45 GHz to evaluate return loss, impedance matching, bandwidth, and radiation characteristics. The 3D models, S11 plots, VSWR curves, radiation patterns, and far-field views are available in simulation-and-results.pdf. The CST VBA macros that build each antenna from scratch are in the cst/ directory.

Geometry	S11 (dB)	VSWR	Bandwidth (%)	Gain (dBi)	Side Lobe (dB)
Circular	−53.08	1.004	3.12	5.54	−3.7
F-shaped	−30.02	1.065	2.98	4.11	−1.6
Triangular	−18.86	1.257	2.45	4.51	−0.6
Square	−16.38	1.357	2.41	3.00	−6.7
Hexagonal	−14.78	1.446	2.12	5.54	−7.0

Measurement (VNA)

Geometry	S11 (dB)	VSWR
Circular	−31.99	1.125
F-shaped	−16.98	1.167
Triangular	−15.37	1.368
Square	−14.46	1.536
Hexagonal	−13.93	1.694

Simulation vs. Measurement

Geometry	S11 sim (dB)	S11 meas (dB)	ΔS11 (dB)	VSWR sim	VSWR meas	ΔVSWR
Circular	−53.08	−31.99	+21.09	1.004	1.125	+0.121
F-shaped	−30.02	−16.98	+13.04	1.065	1.167	+0.102
Triangular	−18.86	−15.37	+3.49	1.257	1.368	+0.111
Square	−16.38	−14.46	+1.92	1.357	1.536	+0.179
Hexagonal	−14.78	−13.93	+0.85	1.446	1.694	+0.248

Circular patch came out on top in both simulation and measurement. All five designs cleared the S11 < −10 dB threshold, confirming acceptable impedance matching at 2.45 GHz. The ranking held across simulation and measurement, though measured return loss was consistently higher (worse) than simulated. The largest delta appeared in the circular patch (21 dB), likely because its deep simulated null is sensitive to any real-world imperfection. Probable error sources include SMA connector parasitics, FR-4 permittivity variation (manufacturer spec: 4.2–4.8, simulation used 4.4), etching undercut reducing trace accuracy, and soldering losses at the SMA–feed junction.

Fabricated Antennas

Each geometry was fabricated on FR-4 with SMA connectors — two samples per design.

Circular (best performer)	F-shaped	Triangular
Square	Hexagonal

Design Parameters

Common

Parameter	Value
Operating frequency	2.45 GHz
Substrate	FR-4 (εr ≈ 4.4)
Substrate height (Hs)	1.4 mm
Conductor height (Ht)	0.036 mm
Ground plane (Wg × Lg)	75.20 × 58.76 mm
Feed line width (Fw)	2.7 mm
Feed-patch gap (Gpf)	1 mm

Geometry-Specific

Geometry	Dimensions
Circular	R = 17.0 mm
Square	S = 29.38 mm
Triangular	Tb = 37.60 mm, Th = 29.38 mm
Hexagonal	Ha = 17.0 mm
F-shaped	W = 37.60, L = 29.38, Vw = 10.0, Bh = 8.0, Sh = 3.0, Mw = 25.0 mm

Methodology

1. Design — Calculated patch dimensions for 2.45 GHz based on substrate properties
2. Simulation — Electromagnetic modeling in CST Studio Suite
3. Fabrication — PCB manufacturing via photolithography, UV exposure, and chemical etching
4. Measurement — S-parameter characterization using a Rohde & Schwarz VNA
5. Comparison — Analyzed return loss, bandwidth, and radiation patterns across all five geometries

Equipment Used

VNA (Smith chart display)	Laminator	UV Exposure Unit

UV Exposure (closed)	Etching Machine

Fabrication Process

Blank FR-4 substrate	Circular patch in NaOH developer bath

Simulation Macros

CST Studio VBA macros for each geometry — open in CST and run to build the full antenna model (substrate, ground plane, patch, feed line, port, and solver).

Macro	Patch shape
circular-patch.bas	Cylinder — R = 17.0 mm
square-patch.bas	Brick — S = 29.38 mm
triangular-patch.bas	Extruded isosceles triangle — base 37.60 mm, height 29.38 mm
hexagonal-patch.bas	Extruded regular hexagon — side 17.0 mm
f-shaped-patch.bas	Boolean union of vertical bar + two horizontal bars

Documentation

Document	Contents
methodology.pdf	Design parameters, substrate specs, VNA calibration
simulation-and-results.pdf	CST results — S11 plots, VSWR, radiation patterns, gain
fabrication-and-measurement.pdf	Step-by-step fabrication process, VNA measurements

Repository Structure

Antenna/
├── README.md
├── LICENSE
├── CITATION.cff
├── .gitignore
├── .gitattributes
├── cst/
│   ├── circular-patch.bas
│   ├── square-patch.bas
│   ├── triangular-patch.bas
│   ├── hexagonal-patch.bas
│   └── f-shaped-patch.bas
├── docs/
│   ├── methodology.pdf
│   ├── simulation-and-results.pdf
│   └── fabrication-and-measurement.pdf
└── images/
    ├── equipment/
    │   ├── vna-smith-chart.jpg
    │   ├── laminator.jpg
    │   ├── uv-exposure-open.jpg
    │   ├── uv-exposure-closed.jpg
    │   └── etching-machine.jpg
    ├── fabrication/
    │   ├── fr4-substrate-blank.jpg
    │   └── circular-patch-naoh-bath.jpg
    └── antennas/
        ├── circular-patch.jpg
        ├── f-shaped-patch.jpg
        ├── triangular-patch.jpg
        ├── square-patch.jpg
        ├── hexagonal-patch.jpg
        └── all-five-geometries.jpg

Applications

2.45 GHz microstrip patch antennas are used in Bluetooth, Wi-Fi (802.11b/g/n), ZigBee, and satellite communication systems. This study shows that patch geometry alone can noticeably improve antenna performance without increasing design complexity.

Tools

CST Studio Suite · Rohde & Schwarz VNA · FR-4 Substrate · CorelDraw

Citing This Work

GitHub provides a "Cite this repository" button via the CITATION.cff file. You can also use this BibTeX entry directly:

@misc{bose2018microstrip,
  author       = {Bose, Urme},
  title        = {Microstrip Patch Antenna: 2.45 GHz Geometry Comparison},
  year         = {2018},
  url          = {https://github.com/urme-b/Antenna},
  note         = {Comparative study of circular, F-shaped, triangular, square, and hexagonal patch geometries on FR-4 substrate}
}

References

1. C. A. Balanis, Antenna Theory: Analysis and Design, 4th ed. Hoboken, NJ: Wiley, 2016. — Chapters 14.2–14.4 cover the transmission-line model and cavity model used to derive rectangular and circular patch dimensions.
2. R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook. Norwood, MA: Artech House, 2001. — Design curves and impedance matching techniques for various patch geometries.
3. D. M. Pozar, "Microstrip Antennas," Proc. IEEE, vol. 80, no. 1, pp. 79–91, Jan. 1992. — Survey of microstrip antenna theory, design methods, and feeding techniques.
4. K. F. Lee and K. M. Luk, Microstrip Patch Antennas. London: Imperial College Press, 2011. — Geometry-specific analysis including triangular, circular, and polygonal patches.

License

This project is licensed under CC BY 4.0.