Microstrip antenna

Lore & Background

The microstrip antenna is fabricated by etching a metal patch pattern on a dielectric substrate, with a continuous ground plane on the opposite side. The most common type is the rectangular patch, which behaves like a truncated microstrip transmission line approximately one-half wavelength long. Fringing fields at the edges slightly increase the electrical length, so the resonant length is slightly shorter than a half-wavelength. An early model treated the antenna as a section of microstrip transmission line with equivalent loads representing radiation loss. The cavity model, introduced in 1973, better explained the relationship between dielectric loading, bandwidth, and Q factor. Some patch antennas omit the dielectric substrate and use a metal patch mounted above a ground plane with dielectric spacers, resulting in wider bandwidth but less rugged construction.

Reader's Guide

Microstrip antennas are notable for their low profile, mechanical ruggedness, and ability to conform to curved surfaces, making them common on aircraft, spacecraft, and mobile radio devices. They are relatively inexpensive to manufacture due to their simple two-dimensional geometry. A single patch provides a maximum directive gain of around 6–9 dBi, but arrays of patches on a single substrate can achieve much higher gains at little additional cost. Such arrays enable dynamic beamforming and phased array operation. Polarization diversity is an inherent advantage, allowing designs for vertical, horizontal, or circular polarization using multiple feed points or asymmetric patch structures. The half-wave rectangular patch can be modified into a quarter-wavelength half-patch by adding a physical shorting plane, which reduces gain and bandwidth. The planar inverted-F antenna (PIFA), derived from the quarter-wave half-patch, is common in cellular phones due to its compact size and omnidirectional pattern. The defected ground structure (DGS) technique, introduced in 2005, uses small slots in the ground plane to control cross-polarized radiation and reduce mutual coupling in arrays, without adding extra components or cost.

Did You Know?

• Microstrip antennas are also known as printed antennas.
• The most common type of microstrip antenna is the patch antenna.
• Patch antennas can be designed for vertical, horizontal, or circular polarization.
• The planar inverted-F antenna (PIFA) is derived from a quarter-wave half-patch antenna.