Patch Antenna
Understanding Patch Antennas
Patch antennas have become ubiquitous in modern wireless systems due to their low profile, ease of manufacture, and natural compatibility with printed circuit board technology. They can be designed for any frequency from hundreds of MHz to millimeter-wave, and are easily arranged in arrays for higher gain and beam steering.
Patch Antenna Design
- Dimensions: Patch length is approximately lambda/2 in the substrate, determining the resonant frequency.
- Substrate: Lower dielectric constant gives wider bandwidth; higher dielectric constant gives smaller size.
- Feed methods: Microstrip edge feed, coaxial probe feed, aperture coupling, or proximity coupling.
- Bandwidth: Typically 1-5% for single-layer patches. Stacked or thick substrates achieve 10-30%.
Polarization
- Linear: Standard rectangular patch radiates linear polarization.
- Circular: Truncated corners, dual feed with 90-degree phase shift, or nearly square patch with slight perturbation.
Typical gain: 5-9 dBi (single element)
Bandwidth: 1-5% (single layer)
Array gain: G_array = G_element + 10 x log10(N)
N=4: +6 dBi, N=16: +12 dBi, N=64: +18 dBi
Example at 10 GHz (Rogers 4350B, er=3.66):
L = 30/(2 x 10 x sqrt(3.1)) = 8.5 mm
Frequently Asked Questions
What is a patch antenna?
A patch antenna is a flat, low-profile radiating element made from a metallic patch on a dielectric substrate over a ground plane. It is compact, lightweight, easily fabricated on PCBs, and commonly used in arrays for mobile devices, GPS, radar, and 5G systems.
What is the bandwidth of a patch antenna?
Standard single-layer patches have 1-5% impedance bandwidth. Stacked patches, thick substrates, U-slot designs, or parasitic elements can increase bandwidth to 10-30%. For wideband applications, patch arrays may use multiple resonant elements or aperture coupling.
How do you make a circularly polarized patch?
Methods include: truncated corners on a square patch, dual orthogonal feeds with 90-degree phase shift, or a slightly rectangular patch with one corner chamfered. Each method excites two orthogonal modes with equal amplitude and 90-degree phase difference to produce circular polarization.