Compact Antennas for Wireless Communications and Terminals: Theory and Design

Chapter 1General Information About Printed Antennas ¹

 

 

 

1.1. Physical characteristics

The basic printed antenna consists of a thin layer of metal (patch) positioned over a ground plane, both being etched on the two sides of a substrate of permittivity ε_r and thickness h (Figure 1.1). Typically, h ≪ λ₀ and 0.003λ₀ < h < 0.05λ₀. The length L of the patch is of the order of , where ε_eff is the relative permittivity of the patch.

The terms printed, plated, or patch antenna are used interchangeably to describe planar antennas produced using photolithographic techniques. Note that there are planar antennas that are not produced using these techniques. For example, this is the case with PIFA antennas or their variants in 1 GHz mobile telephony, the substrate here being made up of air with metallic parts produced using copper or aluminum foil that has been folded and machined (Figure 1.2).

Planar antennas can equally be produced under clean conditions over silicon (Figure 1.3) or glass substrates using microtechnological manufacturing processes. Because of the given antenna dimensions (of the order of 1 cm), the manufacturing costs and patterning tolerances, the applications planned are typically beyond the Ka band (about 20 GHz).

Figure 1.1. Geometry of a printed antenna excited by microstrip line

Figure 1.2. PIFA antenna modified for a portable telephone (Ericsson T65)

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