Design and fabrication of a small microstrip patch antenna
COMPACT MICROSTRIP ANTENNA
Microstrip antennas consist of a very thin (t<<λ0, whereλ0 is the free-space wavelength) metallic strip (patch) placed a small fraction of a wavelength (h << λ0, usually 0.003λ0 ≤ h ≤ 0.05λ0) above a ground plane. For a rectangular patch, the length L of the element is usually λ0/3 < L < λ0/2. The strip (patch) and the ground plane are separated by a dielectric sheet (referred to as the substrate). There are numerous substrates that can be used for the design of microstrip antennas, and their dielectric constants are usually in the range of 2.2 ≤ ε0 ≤ 12. Often microstrip antennas are also referred to as patch antennas. The radiating elements and the feed lines are usually photoetched on the dielectric substrate. The radiating patch may be square, rectangular, thin strip (dipole), circular, elliptical, triangular, or any other configuration.
Coaxial-line feeds, where the inner conductor of the coax is attached to the radiation patch while the outer conductor is connected to the ground plane, are also widely used. The coaxial probe feed is also easy to fabricate and match, and it has low spurious radiation. However, it also has narrow bandwidth and it is more difficult to model, especially for thick substrates (h > 0.02λ0