Antennas for low power applications

AN4190

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Doc ID 023812 Rev 1

An example of a microstrip antenna is shown in Figure 17. The patch antenna, microstrip

transmission line and ground plane are made of high conductivity metal. The patch is of

length L, width W, and sitting on top of a substrate of the thickness h with permittivity

Typically, the thickness h is much smaller than the wavelength of operation, but not much

smaller than 0.05 of a wavelength. The length L determines the operative frequency; the

width W controls the input impedance. Larger widths can also increase the bandwidth. The

width also controls the radiation pattern. The directivity of patch antennas is approximately 5

- 7 dB.

The patch elements radiate primarily linearly polarized waves if conventional feeds are used

with no modification. However, circular and elliptical polarizations can be obtained using

various feed arrangements or slight modifications. Figure 18 shows an example of a patch

antenna designed at 5.8 GHz left-hand circular polarized used for the Italian and European

toll payment systems.

Figure 17.

Rectangular microstrip antenna

L

W

Microstrip

Transmission

line

Substrate

AM16441v1