Design of a compact, fully-autonomous 433 MHz tunable antenna for wearable wireless sensor applications

• Published in: IET microwaves, antennas & propagation Vol. 11; no. 4; pp. 548 - 556
• Main Authors: Buckley, John L, McCarthy, Kevin G, Gaetano, Domenico, Loizou, Loizos, O'Flynn, Brendan, O'Mathuna, Cian
• Format: Journal Article
• Language: English
• Published: The Institution of Engineering and Technology 18.03.2017
• Subjects: antenna equivalent circuit model; antenna testing; antenna under test; Antennas; AUT impedance matching; body sensor networks; Circuit boards; circuit simulator; compact fully‐autonomous tunable antenna design; Computation; Design analysis; equivalent circuits; free‐space impedance variation; frequency 433 MHz; FR‐4 material; human body; human test subject; Impedance; impedance characteristics analysis; impedance matching; load voltage standing wave ratio; loss 0.84 dB; Matching; matching loss; microstrip antennas; power delivery; printed circuit board; printed circuits; Research Article; Sensors; total on‐body AUT impedance variation; tunable matching network characterisation; UHF antennas; Wearable; wearable antennas; wearable wireless sensor application; wearable wireless sensor application; compact fully-autonomous tunable antenna design; printed circuits; frequency 433 MHz; equivalent circuits; FR-4 material; total on-body AUT impedance variation; free-space impedance variation; power delivery; tunable matching network characterisation; loss 0.84 dB; matching loss; UHF antennas; body sensor networks; AUT impedance matching; load voltage standing wave ratio; antenna under test; human body; printed circuit board; microstrip antennas; human test subject; impedance matching; antenna testing; antenna equivalent circuit model; impedance characteristics analysis; circuit simulator; wearable antennas
• ISSN: 1751-8725; 1751-8733
• DOI: 10.1049/iet-map.2015.0712

The authors present the design of a tunable 433 MHz antenna that is tailored for wearable wireless sensor applications. This study first presents a detailed analysis of the measured impedance characteristics of a chosen antenna under test (AUT) in varying proximity to a human test subject. Instead of limiting the analysis to the head and hand only, this analysis measures the AUT impedance at varying distances from 11 different body positions. A novel antenna equivalent circuit model is then developed that enables both the free-space and total on-body AUT impedance variation to be rapidly computed using a circuit simulator instead of the requirement for computationally intensive finite-element methods for example. The design and characterisation of a tunable matching network that enables AUT impedance matching for 11 different positions on the human body is then outlined. Finally, a fully-autonomous 433 MHz tunable antenna is demonstrated. The antenna occupies a small printed circuit board area of 51 × 28 mm and is printed on standard FR-4 material with the tuner completely integrated into the antenna itself. Prototype measurements show an improvement of 3.9 dB in power delivery to the antenna for a load voltage standing wave ratio of 17:1, with a maximum matching loss of 0.84 dB and S11 (−10 dB) ≥ 18 MHz for all load conditions.