3. LTCC-Based Multilayer Composite Right/Left-Handed Transmission Lines for Super-Compact Distributed Circuits

In this chapter, multilayered composite right/left-handed (ML CRLH) transmission lines (TLs) are discussed briefly, along with examples of super-compact ultra-wideband (UWB) band pass filters, that are constructed with LTCC-based ML CRLH TL architecture. In the conventional RH microwave devices, the coupling between inner components of a device is undesirable since it degrades the performance. In contrast, in ML CRLH structure, a strong coupling between unit cells is desired since it can enhance the left-handedness and leads to significant size reduction of devices and components. It is shown here that overall dimensions of the typical ML CRLH transmission lines with three unit cells are only 1.5 × 1.5 × 0.95 mm. In theory, they can be made as small desired; the constraints on the dimensions such as line width, spacing, via diameter, thickness of sheet, etc., comes only from the design restrictions of the LTCC technology itself. Successful design examples of a few size-reduced devices, UWB filter, impedance transformer, and a Wilkinson power divider/combiner are presented.