Citation: Oller, B.; Andújar, A.; Anguera, J. Antenna Booster Versus a Spiral Monopole Antenna for Single-Band Operation at 900 MHz. Electronics 2023, 12, 2067. https://doi.org/10.3390/ electronics12092067 Academic Editors: Yiming Huo and Flavio Canavero Received: 10 January 2023 Revised: 11 March 2023 Accepted: 24 April 2023 Published: 30 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). electronics Article Antenna Booster Versus a Spiral Monopole Antenna for Single-Band Operation at 900 MHz Bernat Oller 1 , Aurora Andújar 2 and Jaume Anguera 1,2, * 1 Telecommunication Engineering, Universitat Ramon LLull, 08022 Barcelona, Spain; bernat.oller@salle.url.edu 2 Ignion, 08174 Barcelona, Spain; aurora.andujar@ignion.io * Correspondence: jaume.anguera@ignion.io or jaume.anguera@salle.url.edu Abstract: The number of devices connected to the internet has grown exponentially through the last decade, making IoT and connection worldwide more possible every year, enabling an incredible number of applications. This calls for better and more efficient methods for designing wireless devices. An efficient and small antenna is needed to ensure connectivity, range, and battery life. Under these circumstances, antenna booster technology is proposed, which uses a tiny component called an antenna booster to excite currents in the ground plane of the IoT device. This allows the antenna booster to be as small as 12 mm × 3 mm × 2.4 mm, representing only ~λ/30 at 863 MHz. The antenna booster is matched across the frequency range using a matching network. The paper compares an antenna booster and a monopole antenna regarding bandwidth for a design using a 120 mm × 60 mm ground plane in the 863 MHz to 928 MHz frequency range. Afterwards, the same designs are analysed when the ground plane size changes from 20 mm × 30 mm to 200 mm × 200 mm using steps of 10 mm to determine which approach can be reused across 53.8% of the ground planes with S 11 < −6 dB without making any changes to the antenna system; for contrast, the monopole antenna can be reused only 4.6%. In addition, the antenna booster features better total efficiencies of up to 2.3 dB. A physical prototype with the antenna booster validates the numerical analysis. Keywords: IoT; antenna boosters; monopole antennas; matching network; ISM 1. Introduction The revolution of the Internet of Things (IoT) connected era enables an endless field to invent new applications for tracking devices, intelligent sensors and agriculture, smart home, etc. The connectivity, range, and battery longevity of those devices depend upon antennas. Antennas for wireless devices mainly rely on shaping the geometry of the antenna to make them small enough to fit in the device and multiband to provide operation across several frequency bands [1–10]. Spiral, meander, and loops are typical for designing an antenna to a particular frequency. In [11], a meandered monopole is proposed for a mobile phone. Although the bandwidth is 101.7%, the size is too big (100 mm × 44 mm, 0.3 λ at 900 MHz) to fit in a small IoT device (Table 1). In [12], a spiral monopole is proposed for covering 900 MHz, 1800 MHz, and 2200 MHz, having a size of 24 mm × 22.75 mm (λ/14 at 900 MHz). In [13], a meandered monopole is designed for 900 MHz, with a large size of 42.2 mm × 70 mm (0.21 λ at 900 MHz). In [14], a multi-spiral monopole is analysed for 900 MHz, with a size of 22.9 mm × 10 mm (λ/14 at 900 MHz). In some cases, a simple matching network comprising lumped components such as capacitors and inductors is used for fine-tuning the frequency response of the antenna. Other cases use a tuneable component, such as a digitally tuneable capacitor with a meandered monopole of a compact size of 20 mm × 18 mm [15]. Electronics 2023, 12, 2067. https://doi.org/10.3390/electronics12092067 https://www.mdpi.com/journal/electronics