Free Microstrip Patch Antenna Calculator
The 310th Tool Milestone! Calculate physical patch width (W), resonant length (L), effective dielectric constant (εeff), and 50Ω inset feed notch depth.
📡 Operating Frequency & Substrate
Effective Dielectric (ε_eff): 4.09 • Fringing Extension (ΔL): 0.74 mm
• Ground Plane Length: ≥ 48.0 mm (L + 6h)
• Ground Plane Width: ≥ 56.6 mm (W + 6h)
• Directivity Gain: ~5.5 to 6.5 dBi broadside hemisphere pattern.
Fringing Field Extension (ΔL): Electric field lines extend beyond the physical copper patch into the surrounding air before terminating on the ground plane. This fringing effect makes the patch appear electrically longer by $2 Delta L$. You must shorten physical $L$ to stay resonant!
Recommended Tools & Equipment
Tested hardware and components for high reliability
Physics of the Rectangular Microstrip Patch
A microstrip patch antenna behaves as a resonant cavity with radiating magnetic dipoles along its two outer edges:
Effective Perm: ε_eff = [(ε_r + 1)/2] + [(ε_r - 1)/2] × [ 1 + 12 (h/W) ]^-0.5
Fringing ΔL: ΔL = 0.412 × h × [ (ε_eff + 0.3) × (W/h + 0.264) ] / [ (ε_eff - 0.258) × (W/h + 0.8) ]
Resonant Length: L = [ c / (2 f_0 × √ε_eff) ] - 2 × ΔL
Why the 50Ω Inset Feed is Required
The impedance at the radiating outer edge of a patch is very high—typically 150 Ω to 300 Ω. To match a standard 50 Ω transmission line with low SWR (< 1.2:1), designers cut an inset notch into the patch. As you move inward toward the center, impedance drops cosinusoidally to zero, hitting a perfect 50 Ω at depth $y_0 approx 0.34 imes L$.
Frequently Asked Questions
Why does FR-4 have lower efficiency at 5.8 GHz than Rogers RO4350B?
Standard FR-4 fiberglass has a high dielectric loss tangent (tan δ ≈ 0.02) that dissipates RF energy as heat inside the resin matrix at microwave frequencies. Low-loss substrates like Rogers RO4350B (tan δ ≈ 0.0037) boast > 90% radiation efficiency.
What is the bandwidth of a microstrip patch antenna?
Single-layer patch antennas are inherently narrowband, with typical 2:1 SWR bandwidths of only 2% to 4% of center frequency (e.g. 50 to 90 MHz at 2.4 GHz). Using a thicker substrate (h) or lower dielectric constant (εr) widens bandwidth.
Can I circularly polarize a patch antenna?
Yes! By making the patch nearly square and either truncating two opposite corners or feeding two adjacent edges with a 90° hybrid coupler, the antenna radiates Right Hand Circular Polarization (RHCP), standard for GPS antennas.