How do I design a microstrip patch antenna for a specific frequency and bandwidth?
Patch Antenna Design
The microstrip patch antenna resonates when the patch length is approximately half a guided wavelength (λg/2) in the substrate. The patch radiates from the fringing fields at the two open edges (radiating slots). The substrate dielectric constant and thickness determine the bandwidth, efficiency, and radiation characteristics.
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Frequently Asked Questions
How do I increase bandwidth?
Use thicker substrate (h > 0.04λ₀), use lower εr, use stacked patches (two patches on different substrate layers), use aperture-coupled feeding, or add parasitic patch elements. A U-slot patch on thick substrate achieves 15-25% bandwidth.
What gain does a single patch provide?
A single microstrip patch: 5-9 dBi depending on the substrate and size. The gain is primarily determined by the electrically small aperture. For higher gain: use an array of patches. Gain increases by 10·log10(N) for an N-element array with proper spacing.
Can I make a circular polarized patch?
Yes. Methods: (1) square patch with two feed points at 90° spatial and 90° phase offset, (2) single-feed truncated corner patch or nearly-square patch (two modes excited with 90° phase difference), (3) single-feed slot-loaded patch. Axial ratio < 3 dB over 1-2% bandwidth for single-feed designs, wider for dual-feed.