Miniaturization of a Spiral Antenna Using Periodic Z-Plane Meandering

A new approach for miniaturizing an ultra-wideband spiral antenna, called the periodic spiral antenna (PSA), is presented. The combination of z-directed meandering of the antenna element and a tapered substrate profile provides a volumetric style of miniaturization. In this design, the distributed inductance and capacitance, and therefore the impedance match, are tightly controlled as the footprint is reduced. The effectiveness of z-directed meandering is confirmed through a loop antenna study that demonstrates a footprint reduction of 76.7% compared to the 57.1% reduction using planar meandering. Numerical simulations and measurements show that the PSA maintains similar performance as a traditional Archimedean spiral antenna with a miniaturization factor up to 1.2 prior to dielectric loading. A sinusoidal variation in the sidewall height of the back cavity is also shown to contribute to improved antenna performance. A 0.8-3 GHz cavity-backed PSA fabricated using a tapered ULTEM (ε_r = 2.75) substrate and 0.81 mm diameter copper wire is described.