A robust method of calculating the effective length of a conductive strip on an ungrounded dielectric substrate

Abstract

Dipole antennas on a substrate without a ground plane are common in wireless sensor networks and RFID applications. This paper reviews a number of theoretical approaches to solving for the effective permittivity when the substrate material is thin. The surface impedance and slab waveguide propagation techniques are compared to a capacitive solution and an insulated wire antenna. The insulated wire method gives most accurate results (< 3.5%) and was verified using numerical modeling and experimental work. Measurements on a planar straight dipole on FR4 (fc = 1.50 GHz) compare favorably with the antenna modeled without the substrate and scaled using the insulated wire technique at (fc = 1.49 GHz). The method can be readily incorporate the effect of an RFID antenna on a thin plastic film placed on a wide variety of lossy and lossless objects.