A Novel Miniaturized Quasi-Lumped Element Antenna Based on Interdigital Capacitor

The miniaturization feasibility of microstrip passives is constrained by the intrinsic electrical length limitation imposed. A few methods to attain miniaturization have been flawed with low radiative resistance, a poor link budget, poor data throughput, a high Q-factor and poor voltage standing wave ratio owing to feeding difficulty. Alternative methods that will satisfy the following design considerations must consider other ways to circumvent the electric length design requirement in order to overcome the imposed restriction. In this work therefore, we present an alternative passive whose resonance does not depend on the radiation wavelength but rather on some lumped element equivalent. We demonstrate convincingly the lumped element possibility of the proposed passive by showing its equivalent circuit. The necessary equations to de-embed the lumped element components are documented. The de-embedded component values are used to design passives etched on different board with a different dielectric constant to characterize the effect of laminate board on the reduction capability of the proposed passive. Subsequently, the miniaturization capability of the proposed passive is validated by designing antennas for frequency bands of 1-6 GHz while measuring the aperture sizes. The findings indicate that the proposed passive exhibits a compact and efficient premium, good aspect ratio diversity, design flexibility and reasonable gain.

1. Introduction

A small and light-weight antenna will be necessary to support high-mobility requirements for most wireless applications. More importantly, an antenna for wireless communication requires more than one operating band. New and emerging converged technologies in communication applications normally associate themselves with increasing data rates and a wide frequency band required for multiple integrated services such as direct digital broadcast, video-conferencing, indoor wireless and new wireless standard demands. It is currently not uncommon to use a single antenna to provide full coverage over the entire frequency range. However, the resonance frequency of resonance antennas depends on the electrical length. For instance, the resonance frequency of wire antennas is proportional to . whereas that of planar antennas is proportional to , where is the speed of light, is the radiation wavelength and is the dielectric constant. This fundamental theory of antennas imposes a limitation on the extent to which resonant antennas can be reduced below the radiation wavelength at a target frequency based on the electrical length limitation stated in the above equations.