Antenna Miniaturization Techniques: A Review of Topology- and Material-Based Methods

Antenna miniaturization has been the subject of numerous studies for almost 70 years. Early studies showed that a decrease in the size of an antenna results in a direct reduction in its bandwidth and efficiency ηr. The size limitation translates into a lower boundary on the achievable radiation quality factor (Q factor) and consequently on the maximum achievable impedance bandwidth. Recently, many new investigations have been conducted to reduce the form factor (or the overall size) of different types of antennas while trying to maintain acceptable matching properties and operating bandwidth. These miniaturization techniques are generally related to changing the electrical and physical properties of an antenna