Modeling of Broadband Antennas for Room Temperature Terahertz Detectors

The purpose of this chapter is to present modeling investigations dedicated to planar broadband antennas with nearly frequency-independent characteristics. These antennas are used to couple efficiently terahertz radiation to semi-conducting YBCO bolometers of high impedance (kΩ range). Both detector and antenna structures are attached on thin substrates to avoid losses due to substrate high-order modes. The antenna properties (radiation diagram, reflection coefficient, input impedance) have been investigated by software modeling with regard to the need of high impedance and high bandwidth. By modifications of conventional concepts (spiral antenna, log-periodic dipole array), an impedance increase of about 50% could be achieved while maintaining wideband properties at the same time. For extreme high antenna impedance we propose a novel design of a grounded multi-tail dipole antenna. The reached antenna impedance maximum for this structure is 2 kΩ for a bandwidth of 10% at the center frequency f = 2 THz. All concepts were proven by measurements of large-scale models in anechoic chambers (in the 1–4 GHz range, typically).