Lambda/6 Suspended Patch Antenna

Abstract

This work introduces a novel, compact antenna design based on a lambda-6th suspended patch configuration that is particularly suited for small-size wireless sensor nodes. The proposed design meets key requirements such as compactness, omnidirectionality, robust source matching over a designated bandwidth, interference immunity, and low costs by evolving the conventional square patch antenna. With a footprint of only 20-by-20 mm, the antenna incorporates a grounded metal shield to both reduce its effective dimensions below one-half wavelength and mitigate interference from nearby circuitry. Simulation results, conducted on a cost-effective FR4 substrate, demonstrate a resonance at 2.45 GHz with a return loss of -32.5 dB and a bandwidth of 50 MHz (at the -10 dB level), making this design an attractive candidate for integration into densely populated wireless sensor networks.

Figures (8)

• Figure 1: Top view of the PCB layout. $\lambda$ is the free space wavelength at the resonance frequency (2.45 GHz). The bottom ground plane has the same size of the top structure bit it is not visible in the figure.
• Figure 2: Finite elements simulation of the superficial current density distribution $[A/m]$ at resonance (2.45 GHz). The highest density is reached on the vertical conducting rods. The depicted coordinate system is is identical to that used in all the simulations presented in this article.
• Figure 3: Simulation of the Return Loss as function of the frequency observed with a $50\,\Omega$ signal source. S11 refers to the reflected power at the input of a two-ports network.
• Figure 4: Simulation of the antenna's input impedance magnitude seen by the signal source as a function of the frequency. Blue: overall impedance. Green: real component. Red: imaginary component. The reactance exhibits a predominantly inductive behavior, as indicated by its positive slope with frequency. This characteristic behavior is associated with the current density through the vertical rods. At resonance, the capacitive component offsets the inductive component, resulting in a minimal net reactance.
• Figure 5: Side view of the simulated tridimensional radiation pattern at resonance ($2.45\,$GHz). The azimuth $\varphi$ and zenith $\theta$ angles are shown as well. The desired hemispherical configuration is obtained for positive z, whereas the radiation along negative z is minimized.