Far-Field Radiation Characteristics of Folded Monopole Antennas over a Conducting Ground Plane

Ashanthi Maxworth

doi:10.3390/eng3010012

Abstract

Folded monopole structures have been used for many applications, including low-frequency electromagnetic wave transmission and reception. However, the literature on these antenna types is quite limited. Folded monopole antennas are mathematically complex compared to conventional monopole or dipole antennas since every fold introduces a new set of design parameters. This work studied the far-field radiation characteristics of multi-folded monopole antennas operating at 75 MHz in terms of their radiated power concerning the frequency, the far-field directivity of the electric field, and the effect of each design parameter on the far-field radiation power. According to the results, folding a monopole antenna multiple times increases its effective length, making this antenna a suitable candidate for applications where the antenna height is restricted. Additionally, the ground-to-wire separation has the biggest effect on radiated power. In both single-fold and two-fold cases, doubling the ground-to-wire separation increased the radiated power by 0.2 W compared to the other models with the same number of folds. As for the challenges, the impedance mismatch between the source and antenna causes a significant amount of power reflection; hence, suitable impedance matching is required to reduce reflected power.

Highlights

Monopole Antennas over aIt is well known in electrical engineering that the dimensions of an antenna should be comparable to the wavelength of the resonance signal
The goal of this study is to test the effect of each design parameter on the radiation power and reflection coefficient
For the sake of comparison, we initially modeled a quarter-wavelength monopole antenna resonating at 75 MHz

Summary

Introduction

It is well known in electrical engineering that the dimensions of an antenna should be comparable to the wavelength of the resonance signal. Based on this principle, there is a wide range of antennas designed starting from single monopoles, dipoles, loop antennas, and microstrip antennas [1–3], to name a few, and the dimensions of these are factors of the signal wavelengths of interest (quarter-wave, half-wave, etc.). Within the last few decades, all electromagnetic applications became miniaturized. With this size reduction, all electromagnetic instruments—most importantly, cell phones—became very compact devices. The dimensionality challenge comes when it comes to dealing with low frequencies. In the field of biomedical applications, it is a frequent challenge to build an antenna that matches the required wavelength while maintaining sufficient directivity

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