GPS Spoofing Detection System

Project Overview

Department: Electronic & Telecommunication Engineering, University of Moratuwa
Role: RF & Hardware Engineer

GNSS spoofing on the GPS L1 band (1575.42 MHz) poses a critical threat to navigation systems, autonomous vehicles, and timing infrastructure worldwide. Our final-year project addresses this security challenge by developing a complete spoofing detection system that integrates custom RF hardware with machine learning algorithms.

The system combines three key components: a custom-designed RHCP patch antenna optimized for GPS L1, a high-performance RF front-end for signal acquisition and conditioning, and a machine-learning pipeline for intelligent spoofing detection. My contribution focuses entirely on the RF hardware domain, encompassing antenna design, electromagnetic simulation, and front-end PCB development.

My Contributions

1. RHCP Patch Antenna Design (GPS L1 – 1575.42 MHz)

I designed and optimized a Right-Hand Circularly Polarized microstrip patch antenna specifically for GPS L1 reception. This antenna serves as the critical first element in the signal chain, capturing satellite signals with optimal polarization matching and minimal interference.

Key Design Aspects:

• Substrate Selection: Precise material characterization considering dielectric constant (εᵣ), thickness, and loss tangent for optimal performance
• Patch Geometry: Calculated and refined patch dimensions for resonance at 1575.42 MHz with tight frequency tolerance
• Circular Polarization: Achieved RHCP through carefully designed perturbation techniques (corner truncation/dual-feed)
• Impedance Matching: Designed 50 Ω matching network using quarter-wave transformers and inset feed optimization
• Axial Ratio Optimization: Achieved axial ratio < 3 dB across the L1 band for high-quality circular polarization
• Radiation Pattern: Tuned far-field pattern for maximum gain in the zenith direction, ideal for overhead satellite reception

Simulation & Optimization:

Performed comprehensive electromagnetic analysis using Ansys HFSS, including parametric sweeps, optimization routines, and near-field/far-field pattern analysis.

Antenna Performance Achieved:

• Return Loss (S₁₁): < -20 dB at 1575.42 MHz
• Axial Ratio: < 3 dB across GPS L1 bandwidth
• Radiation Pattern: Stable RHCP with minimal cross-polarization
• Gain: Optimized for satellite link budget requirements
• Efficiency: Maximized through substrate and conductor loss minimization

2. GPS L1 RF Front-End PCB Design

I developed the complete RF front-end circuitry responsible for conditioning the L1 signal before digitization and processing by the machine learning pipeline. This subsystem amplifies, filters, and conditions the weak satellite signals for reliable detection and analysis.

Design Responsibilities:

• LNA Selection & Design: Selected low-noise amplifier with optimal noise figure, gain, and linearity; performed DC biasing network design and stability analysis
• RF Circuit Simulation: Used Keysight ADS for S-parameter analysis, noise figure simulation, and stability verification (K-factor, μ-factor)
• Bandpass Filter Design: Designed narrow bandpass filter centered at L1 frequency for out-of-band interference rejection
• Impedance Matching Networks: Implemented distributed/lumped element matching for 50 Ω system impedance throughout the signal chain
• RF PCB Layout: Executed controlled impedance microstrip/stripline routing with precise trace width calculations and length constraints
• Grounding Strategy: Implemented solid ground plane, via stitching, and compartmentalized grounding for EMI/EMC compliance
• Power Distribution: Designed low-noise power delivery network with decoupling capacitors and filtering for RF stability
• Gerber Generation: Finalized fabrication-ready files including drill files, stackup documentation, and assembly drawings

Tools & Workflow:

• Keysight ADS: RF circuit co-simulation, matching network synthesis, and performance verification
• Altium Designer: Complete schematic capture, multi-layer PCB layout, and design rule checking (DRC)

3. Current Project Status (December 2025)

• ✅ RHCP patch antenna design completed and prototype fabricated
• ✅ Full RF front-end PCB design finalized in Altium Designer
• ✅ Gerber files submitted for professional PCB fabrication
• 🔄 Project currently in PCB manufacturing stage
• ⏳ Upcoming: Hardware testing, S-parameter measurements, and system calibration
• ⏳ Planned: Integration with DSP/ML pipeline and end-to-end system validation

Technical Skills Demonstrated

Tools & Technologies

Project Significance

This final-year project strengthens my core expertise in multiple critical areas of RF engineering:

• RF & Microwave Engineering: Hands-on experience with real-world RF system design from concept to fabrication
• GNSS/L-Band Development: Deep understanding of satellite navigation systems and L-band antenna engineering
• RF Front-End Systems: Complete signal chain design including LNA, filtering, and signal conditioning
• Secure Navigation Hardware: Addressing critical cybersecurity challenges in navigation infrastructure

Career Positioning

This project positions me strongly for future opportunities in:

• RF/Microwave Design: Communication systems, radar, and wireless infrastructure
• GNSS Receiver Development: Navigation systems for automotive, aerospace, and consumer electronics
• Aerospace Electronics: Satellite communication, avionics, and space-grade hardware
• Defence Systems: Secure communication, electronic warfare, and navigation security
• Communication Hardware R&D: Next-generation wireless systems and IoT connectivity

Key Learnings

• Comprehensive understanding of RHCP antenna design principles and circular polarization techniques
• Advanced electromagnetic simulation methodology and optimization workflows in HFSS
• RF circuit design fundamentals: LNA stability, noise analysis, and gain-bandwidth optimization
• High-frequency PCB design best practices: controlled impedance, via stitching, and EMI suppression
• System-level thinking: integrating RF hardware with digital signal processing and ML algorithms
• Project management in multidisciplinary team environment with hardware/software integration
• GNSS signal characteristics, satellite link budgets, and navigation system vulnerabilities