Near-Field Radiation Exposure Control in Slot-Loaded Microstrip Antenna: A Characteristic Mode Approach

TL;DR

This paper uses characteristic mode analysis to understand how slot loading in microstrip antennas affects near-field radiation and SAR, aiding the design of biomedical antennas with controlled exposure.

Contribution

It introduces a characteristic mode approach to analyze the impact of slot orientation on antenna performance and SAR in biomedical applications.

Findings

Slot orientation significantly influences current distribution and radiation behavior.

Slot loading can suppress orthogonal eigenmodes, affecting impedance and gain.

Design insights for biomedical antennas with controlled SAR are provided.

Abstract

Microstip antenna topology is commonly loaded with a narrow slot to manipulate the resonance frequency or impedance bandwidth. However, the tuning of the resonance frequency or impedance bandwidth results in the variation of the current and field distributions. In this regard, this work adopts the concept of characteristic modes to gain an initial understanding of the perturbation mechanism of the rectangular patch when loaded with a slot. The performance of microstrip antennas with finite ground plane is then studied using full-wave simulation. It has been found that the distribution of the induced current density is highly dependent on the orientation of the slot The incorporation of a narrow slot suppresses the nearby orthogonal eigen mode and, as a consequence, the radiation behavior is affected. Specifically, in the presence of biological tissues in the near-field region, both antenna input impedance properties and the realized gain are dependent on the slot orientation. Different examples are included for understanding the impact of slot loading on the energy absorption by biological tissues, by calculating the the specific absorption rate (SAR). The proposed analysis facilitates the design of miniaturized antenna geometries for biomedical applications via systematic loading of narrow slots.