Open AccessDesign of a compact, fully‐autonomous 433 MHz tunable antenna for wearable wireless sensor applications
Author(s) -
Buckley John L.,
McCarthy Kevin G.,
Gaetano Domenico,
Loizou Loizos,
O'Flynn Brendan,
O'Mathuna Cian
Publication year - 2017
Publication title -
iet microwaves, antennas and propagation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.555
H-Index - 69
eISSN - 1751-8733
pISSN - 1751-8725
DOI - 10.1049/iet-map.2015.0712
Subject(s) - antenna (radio) , antenna tuner , impedance matching , electronic engineering , electrical impedance , electrical engineering , antenna factor , engineering , input impedance , antenna measurement , acoustics , computer science , physics
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 S 11 (−10 dB) ≥ 18 MHz for all load conditions.