Comparative Assessment of Patch Antennas with Magneto-Dielectric and Nanofilm Materials

Abstract

This study presents a theoretical and practical comparison of microstrip patch antennas made on two types of engineered 
substrates: magneto-dielectric polymer nanocomposites (PNCs) and thin nanofilm coated dielectric substrates. The 
magneto-dielectric substrate is created by dispersing Fe3O4 nanoparticles (average synthesised diameter $\approx$ 8.3 
nm) in a Polydimethylsiloxane (PDMS) host matrix at 40 weight percent and 70 weight percent loading. The nanofilm 
substrate was a 450 nm titanium oxide nanofilm deposited by sol-gel on a low loss dielectric carrier to increase the effective 
permittivity observed by the radiating patch. Four multilayer patch antenna prototypes were constructed and characterised 
to a common 4 GHz resonance throughout the 2–6 GHz range: a plain-PDMS baseline, two Fe3O4-PDMS nanocomposite 
designs, and a nanofilm-coated design. With an unbiased gain of 1.48 dBi and total efficiency of 13.1%, the 70 weight 
percent magneto-dielectric nanocomposite antenna outperformed the other four designs in terms of miniaturisation 
(48.9%, patch area reduced from 614 mm2 to 314 mm2) and impedance bandwidth (26.9%, over 5.6× the 4.8% bandwidth 
of the plain-PDMS baseline). By introducing an external DC magnetic bias field of around 0.22 T, a post-fabrication 
trade-off not available for the passive nanofilm substrate, this device was able to attain a gain of 4.31 dBi and 38.6% 
efficiency with a constricted bandwidth of 9.4%. Despite having a relatively small 20.8% miniaturisation and 8.7% 
bandwidth, the nanofilm-coated antenna with the lowest intrinsic material loss had the greatest gain (4.65 dBi) and 
radiation efficiency (43.8%) out of the three engineered-substrate designs. Between these extremes was the 40 weight 
percent nano composite antenna (30.0% miniaturisation, 14.9% bandwidth, 2.97 dBi gain, and 29.8% efficiency). The 
findings establish a performance envelope where magneto-dielectric substrates are best suited for applications where size 
reduction, bandwidth enhancement, and post-fabrication tunability are the primary design drivers, while nanofilm 
substrates are best suited for applications where radiation efficiency, gain, and ease of fabrication are the most important 
design drivers. As a useful foundation for substrate selection in RF and microwave antenna design, a common fabrication 
and characterisation framework that combines PDMS moulding, controlled nanoparticle dispersion, and thin-film 
deposition compatible with standard PCB and wafer-level manufacturing processes is also presented. This framework 
includes a schematic of the multilayer antenna stack, a combined process-flow diagram for both substrate routes, and a 
consolidated bar-chart comparison of all six measured substrate conditions.