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A patch antenna is a type of radio antenna with a low profile, which can be mounted on a flat surface. It consists of a flat rectangular or circular sheet or "patch" of metal, mounted over a larger sheet of metal called a ground plane. Patch antennas are a common type of microstrip antenna, which means they're often fabricated by etching the antenna elements out of a flat sheet of metal, such as the copper layer on a printed circuit board (PCB).

Here are some key characteristics of a patch PCB antenna:

•Design and Implementation: A patch antenna is usually designed as a rectangular or circular conductive patch on a ground plane. The antenna is usually fed by a probe (a soldered wire) or by a microstrip line (a thin strip of copper).

•Resonant Frequency: The resonant frequency of a patch antenna is determined primarily by its size. For a rectangular patch, the length of the patch is approximately half of the wavelength in the dielectric medium of the frequency it's intended to receive or transmit.

•Polarization and Directionality: Patch antennas produce linearly polarized waves, with the electric field oriented perpendicular to the ground plane. They are usually designed to be directional and emit towards the area above the ground plane, making them useful for surface mounted applications.

•Applications: Due to their low profile and ease of fabrication, patch antennas are used in various applications where size, weight, and cost are critical. These include wireless communication devices like mobile phones, WiFi routers, and GPS receivers.

Designing a patch antenna on a PCB requires knowledge of RF circuit design, and careful consideration of factors like the dielectric constant of the substrate, the thickness of the substrate, and the operating frequency. The performance of the antenna should be validated in a real-world environment to ensure optimal performance.