The spiral as a traveling wave structure for broadband antenna applications

The spiral has been limited to applications for receive only because it is invariably loaded dissipatively, with a typical 3-dB loss and the resulting low efficiency. In this article, we treat the spiral as a traveling-wave (TW) structure that has unique ultra-broadband, complex, multi-facet radiation characteristics, and report development of spirals with efficient transmit performance suitable for all applications such as telecommunications and radar. Its excellent form factor and its size reduction potential are discussed. The spiral's unique geometry is also shown to allow easy and powerful switching, control and various manipulations, etc., to achieve performance and special features that are difficult or even impossible by antennas of other geometries. These unique multimode, multi-polarization, and inherent phase patterns are utilized to achieve ultra-broadband phased arrays and smart antennas for applications involving multifunction, real-time switched modes, among others.