Modern Intelligent Transportation Systems (ITS) and IoT access points require small, low-cost antennas capable of operating across multiple frequency bands.This project covers the complete design, electromagnetic simulation, fabrication, and Vector Network Analyzer (VNA) measurement of a compact multiband planar patch antenna. To achieve dual-band resonance (targeting 2.4 GHz and 5.2 GHz) without increasing the footprint, the design utilizes a fractal-inspired patch and a Defected Ground Structure (DGS).
Technical Implementation
Design and Simulation
Substrate: Fabricated on standard double-sided FR4 (thickness: 1.6 mm, dielectric constant: 4.4, loss tangent: 0.02) for cost-effective manufacturing.
Fractal Slot Pattern: Concentric shapes etched into the top radiating copper patch lengthen surface current paths, effectively lowering the fundamental resonant frequency.
Defected Ground Structure (DGS): Dumbbell-shaped slots are etched into the ground plane directly below the feedline. This alters the line's capacitance and inductance, broadening the impedance bandwidth and creating new resonant points.
CST Microwave Studio: Used for 3D electromagnetic modeling, parametric optimization of slot sizes, and matching network alignment.
Measurement & Verification
Standard chemical wet-etching was used to manufacture the prototype.
The return loss (S11) and Voltage Standing Wave Ratio (VSWR) were measured from 1 GHz to 6 GHz using a calibrated Vector Network Analyzer (VNA).
Key Features
Multiband Resonance: Clear operating points at 2.4 GHz (ISM) and 5.1 GHz.
Improved Bandwidth: DGS implementation widened the impedance bandwidth around 2.4 GHz, keeping VSWR below 1.5.
Compact Form Factor: Metamaterial-inspired cuts kept the patch dimensions small and compatible with standard PCB layouts.
Challenges and Solutions
FR4 Dielectric Variances: Cheap FR4 substrates do not have a uniform dielectric constant, which shifted the measured resonant frequency down to 2.38 GHz. I compensated for this in subsequent design iterations by tuning the feedline matching network.
Solder Parasitics: SMA connector soldering can introduce parasitic inductance. I used a high-temperature solder profile and kept solder pads minimal to maintain signal integrity up to 6 GHz.
