A 1×4 linear microstrip patch antenna array designed for 2 GHz and conformally bent onto a cylindrical surface with a radius of 300 mm (30 cm). The array was designed and simulated in CST Studio Suite 2025, with phase-corrected feeding used to compensate for the curvature and steer the main beam from broadside toward wide scan angles.
The project includes the analytical design of the patch element, effective dielectric constant and fringing calculations, feed design, curvature-related phase correction, beam-scanning phase calculations, and CST simulation results.
The complete analytical derivation and design calculations are available in the Design Calculations Report.
The array consists of four inset-fed microstrip patch elements arranged along a cylindrical surface. The element spacing is selected as 0.5λ₀ at the 2 GHz design frequency.
The cylindrical geometry introduces different path lengths between the individual elements and the far-field observation direction. Phase corrections are therefore applied at the array ports to compensate for the curvature and control the beam direction.
| Parameter | Value |
|---|---|
| Design frequency | 2 GHz |
| Substrate | FR-4 (lossy) |
| Relative permittivity (εᵣ) | 4.3 |
| Substrate height (h) | 1.6 mm |
| Copper thickness | 0.035 mm |
| Substrate size per element | 300 mm × 56 mm |
| Patch dimensions (W × L) | 45.5 mm × 32.4 mm |
| Feed type | Inset-fed microstrip |
| Feedline width | 3.1 mm |
| Inset notch depth | 10 mm |
| Inset gap | 1 mm |
| Element spacing | 75 mm |
| Cylindrical bend radius | 300 mm |
The initial analytical calculation produced a patch length of 35.85 mm. During CST simulation, the patch length was re-optimized to 32.4 mm to account for feed-pin loading, impedance changes, and the effects of conformal bending.
The complete CST parameter set is provided in docs/Parameter_list.png.
Bending the array introduces a physical path-length difference between the elements. For broadside radiation, phase compensation is applied to the outer elements to restore the required phase relationship across the curved aperture.
| Port | Position on Cylinder | Applied Phase |
|---|---|---|
| Port 1 — Outer Left | -21.48° | +44.4° |
| Port 2 — Inner Left | -7.16° | 0.0° |
| Port 3 — Inner Right | +7.16° | 0.0° |
| Port 4 — Outer Right | +21.48° | +44.4° |
Additional phase shifts were applied to steer the main beam away from broadside.
| Target Angle | Port 1 | Port 2 | Port 3 | Port 4 |
|---|---|---|---|---|
| 0° | +44.4° | 0.0° | 0.0° | +44.4° |
| 10° | +44.4° | -31.3° | -62.5° | -49.4° |
| 20° | +44.4° | -61.6° | -123.1° | -140.3° |
| 30° | +44.4° | -90.0° | -180.0° | -225.6° |
| 40° | +44.4° | -135.0° | -250.0° | -310.0° |
| 50° | +44.4° | -160.0° | -295.0° | -375.0° |
The phase values for the 40° and 50° cases were manually refined in CST because the analytical phase relationship alone did not produce the desired beam direction at these wider scan angles.
The following table summarizes the main CST simulation results for the different steering conditions.
| Target Angle | S11 | Resonant Frequency | Gain | Actual Main Lobe | 3 dB Beamwidth | Sidelobe |
|---|---|---|---|---|---|---|
| 0° | -10.92 dB | 2.070 GHz | 7.08 dBi | 0.0° | 26.2° | -11.5 dB |
| 10° | -11.41 dB | 2.072 GHz | 6.94 dBi | 9.0° | 26.5° | -11.0 dB |
| 20° | -12.03 dB | 2.072 GHz | 6.54 dBi | 19.0° | 27.0° | -10.1 dB |
| 30° | -12.76 dB | 2.072 GHz | 5.89 dBi | 27.0° | 27.7° | -9.1 dB |
| 40° | -13.74 dB | 2.068 GHz | 4.84 dBi | 35.0° | 28.5° | -8.7 dB |
| 50° | -14.01 dB | 2.068 GHz | 3.8 dBi | 42.0° | 29.6° | -6.5 dB |
Individual S11, gain, radiation-pattern, and efficiency plots for each scan condition are available in the corresponding folders under results/.
Across the simulated scan conditions, the input reflection coefficient remains below -10 dB, ranging from -10.92 dB to -14.01 dB. The resonant frequency remains close to the 2 GHz design target, between approximately 2.068 and 2.072 GHz.
The re-optimized 32.4 mm patch length therefore provides the required impedance response for the conformally bent configuration.
The array maintains close beam-pointing accuracy at smaller scan angles:
- 0°: actual beam at 0°
- 10°: actual beam at 9°
- 20°: actual beam at 19°
At wider steering angles, the difference between the commanded and simulated beam direction increases. The 40° and 50° cases produce main-lobe directions of approximately 35° and 42°, respectively.
The wider-angle cases also show a reduction in gain and an increase in sidelobe level. Gain decreases from 7.08 dBi at broadside to 3.8 dBi at the 50° target, while the sidelobe level changes from -11.5 dB to -6.5 dB.
This behavior is consistent with the limitations of wide-angle scanning in a small, curved four-element array, where the element radiation pattern and effective aperture increasingly affect the achievable beam direction.
Results for the broadside configuration are available in:
Additional VSWR results are available in:
1x4-cylindrical-patch-antenna-array/
├── design/
│ └── CST Studio Suite project files
│
├── docs/
│ ├── Design_Calculations_Report.pdf
│ ├── Parameter_list.png
│ └── Scanned_Target_phases.png
│
├── results/
│ ├── overview/
│ │ └── 1x4_Cylindrical_antenna.png
│ │
│ ├── broadside/
│ ├── scan_10deg/
│ ├── scan_20deg/
│ ├── scan_30deg/
│ ├── scan_40deg/
│ ├── scan_50deg/
│ └── vswr/
│
└── README.md
- CST Studio Suite 2025
- Electromagnetic simulation
- Microstrip antenna design
- Phased-array analysis
- Beam-steering analysis
- Designed a 1×4 conformal microstrip patch antenna array
- Designed for a 2 GHz operating frequency
- Implemented a 300 mm cylindrical bending radius
- Applied phase correction to compensate for curvature
- Investigated beam steering from 0° to 50°
- Re-optimized patch dimensions through CST simulation
- Analyzed S11, gain, beam direction, beamwidth, and sidelobe level
- Documented analytical calculations and simulation results
Habib Ur Rehman
Electronics Engineering University of Engineering and Technology, Peshawar