Calculator Inputs
Example Data Table
| Frequency | Substrate | Height | Directors | Guided wavelength | Driven length | Estimated gain |
|---|---|---|---|---|---|---|
| 2400 MHz | FR4, εr 4.4 | 1.6 mm | 4 | 68.3 mm | 29.4 mm | 8.3 dBi |
| 5800 MHz | Rogers, εr 3.48 | 0.8 mm | 5 | 29.3 mm | 12.5 mm | 9.0 dBi |
| 915 MHz | FR4, εr 4.4 | 1.6 mm | 3 | 181.6 mm | 78.2 mm | 7.5 dBi |
Formula Used
Free space wavelength: λ0 = c / f.
Patch width: W = c / (2f) × √(2 / (εr + 1)).
Effective dielectric constant: εeff = (εr + 1) / 2 + (εr - 1) / 2 × 1 / √(1 + 12h / W).
Fringing extension: ΔL = 0.412h × ((εeff + 0.3)(W / h + 0.264)) / ((εeff - 0.258)(W / h + 0.8)).
Driven element length: L = c / (2f√εeff) - 2ΔL.
Guided wavelength: λg = λ0 / √εeff.
Reflector length: Lr = L × reflector factor.
Director length: Ld = L × (1 - taper × director number).
Reflection coefficient: Γ = |(Zin - Z0) / (Zin + Z0)|.
VSWR = (1 + Γ) / (1 - Γ).
How to Use This Calculator
Enter the antenna operating frequency and select the correct unit. Add substrate dielectric constant and board height. Choose the number of directors. Set reflector length, director taper, spacing, strip width, and board margin factors. Add feed impedance and expected input resistance. Press Calculate. Review the dimensions, gain estimate, mismatch, and element table. Use CSV or PDF buttons to export the same calculation.
Microstrip Yagi Antenna Design Guide
About This Microstrip Yagi Tool
A microstrip Yagi antenna uses printed metal strips, patches, or dipole arms on a dielectric board. It follows the same directional idea as a classic Yagi array. A driven element launches energy. A longer reflector pushes energy forward. Shorter directors guide the beam toward the target direction.
Why Guided Wavelength Matters
Printed antennas do not use only free space wavelength. The substrate slows the wave. That effect is described with effective dielectric constant. A higher dielectric value makes the guided wavelength shorter. Element lengths and spacings therefore shrink on the board. This calculator uses substrate height, relative permittivity, and practical end correction to estimate printed dimensions.
Design Choices
The driven element is based on the half guided wavelength. The reflector is longer by a selected factor. Each director is shorter by a chosen taper. Spacing is set as a fraction of guided wavelength. These settings help you compare a compact layout with a wider, higher gain layout. The estimate is useful during early design, homework, lab planning, and first prototype work.
Reading the Results
The element table lists the reflector, driven section, and every director. It gives length, width, position, and spacing. The substrate length estimate adds front and rear margins. Gain, front to back ratio, beamwidth, and mismatch are approximate. They are not a replacement for full wave simulation. They are planning values.
Practical Notes
Keep units consistent during fabrication. Use the same dielectric grade you entered. FR4 varies with frequency and supplier. Thin copper changes loss more than geometry. Nearby connectors, ground cuts, solder, and mounting screws can move resonance. After building, measure return loss with a vector network analyzer. Trim director length only in small steps. Document every change before testing again. This makes tuning safer, repeatable, and easier to explain.
Where To Improve Accuracy
For a final antenna, check the layout in an electromagnetic solver. Include the feed line, connector pad, ground plane, solder mask, and copper loss. Use manufacturer dielectric data at the operating band. Then compare simulated resonance with measured resonance. Small test coupons can confirm the real dielectric value. That step prevents repeated board spins. It also helps keep the beam direction stable during normal outdoor field use.
FAQs
What is a microstrip Yagi antenna?
It is a printed directional antenna. It uses a driven element, reflector, and directors on a dielectric substrate. The layout focuses radiation toward one direction.
Is this calculator a full wave simulator?
No. It gives planning dimensions and estimates. Final designs should be checked with electromagnetic simulation and measured with suitable RF instruments.
Why does dielectric constant affect length?
The dielectric slows the wave on the board. This lowers guided wavelength. A shorter guided wavelength makes printed elements shorter than free space dimensions.
What reflector factor should I use?
A common starting range is 1.03 to 1.08 times the driven length. Increase carefully. Too much length can reduce matching and bandwidth.
How many directors are useful?
Three to six directors are common for compact prototypes. More directors can improve gain, but board length, loss, and tuning difficulty also increase.
Why is the gain only estimated?
Gain depends on conductor loss, dielectric loss, feed structure, ground shape, and coupling. Simple equations cannot capture every physical detail.
Can I use FR4 for this design?
FR4 works for many prototypes. Its dielectric constant and loss can vary. Use measured data or supplier data when accuracy matters.
What should I measure after fabrication?
Measure return loss, VSWR, resonant frequency, pattern direction, and gain if equipment is available. Record every trim or layout change.