// Antennas › Patch Antenna

Patch Antenna Calculator

Design a rectangular microstrip patch antenna. Computes patch width, effective length, resonant frequency, feed position (inset or edge), input impedance, bandwidth and gain using the transmission line model.

// Parameters

Design Frequency (fr)

Patch Length (L)

Patch Width (W)

Substrate Height (h)

Relative Permittivity (εr)

—

Loss Tangent (tan δ)

—

Substrate Presets

⚠ Please check your inputs.

// Results

📡

Enter parameters and click Calculate

Patch Dimensions

Patch Width (W)—mm

Effective Length (Leff)—mm

Physical Length (L)—mm

End Extension (ΔL each end)—mm

Electrical Parameters

Resonant Frequency (fr)—GHz

Effective Permittivity (εeff)—

Edge Impedance (Zedge)—Ω

Inset feed distance (y₀) for 50Ω—mm

Antenna Performance

Bandwidth (approx, VSWR≤2)—%

Bandwidth (MHz)—MHz

Gain (approx)—dBi

Radiation efficiency (approx)—%

Transmission Line Model
W = c/(2fr) · √(2/(εr+1)) · εeff = (εr+1)/2 + (εr−1)/2·(1+12h/W)^−0.5
ΔL = 0.412h·(εeff+0.3)(W/h+0.264)/((εeff−0.258)(W/h+0.8))
L = c/(2fr√εeff) − 2ΔL
Zedge ≈ 90·εr²/(εr−1)·(L/W)² · Bandwidth ≈ 3.77(εr−1)/εr²·(h/L)

About the Patch Antenna Calculator

The rectangular microstrip patch antenna is the most widely used planar antenna in modern wireless products. It consists of a rectangular conducting patch on top of a grounded dielectric substrate. Its low profile, ease of fabrication and compatibility with PCB manufacturing processes make it the standard choice for WiFi, GPS, Bluetooth, cellular and IoT applications.

Resonant Frequency and Dimensions

The patch resonates when its length L is approximately half a wavelength in the effective dielectric medium. The effective permittivity is lower than the substrate permittivity because the fringing fields at the edges extend into the air above the patch. This fringing effect also makes the electrical length slightly longer than the physical length â€” accounted for by the end extension delta_L in the transmission line model.

Patch Width

The width W affects radiation resistance, bandwidth and cross-polarisation. The standard starting point is W = (c / 2f) * sqrt(2/(er+1)), which gives approximately 50% bandwidth efficiency. Wider patches have lower radiation resistance and broader E-plane beamwidth. The width does not strongly affect the resonant frequency.

Inset Feed for 50 Ohm Matching

The edge impedance of a patch is typically 100-300 ohm depending on the L/W ratio. To match to a 50 ohm feed line, the feed point is moved inward from the edge by a distance y0. At position y0 the input impedance equals 50 ohm: y0 = (L/pi) * arccos(sqrt(Zin/Zedge)). This inset feed is the simplest matching technique and requires no separate matching network.