LCP for passive components

Abstract

It has become increasingly apparent that LCP provides an ideal form, fit, and function for many broadband passive components. Since LCP is available in thicknesses less than 1 mil with low dielectric constant, this enables easy design of varying controlled impedances. Further, LCP’s property of being its own adhesive layer provides for a high layer count in a multilayer stack while simultaneously maintaining high-frequency performance that otherwise would be detuned by poor electrical ply layers. This chapter provides design and development examples of broadband passives that benefit from LCP. In section 6.1 we describe a broadband Marchand balun implemented on multilayer LCP covering 4–20 GHz and in section 6.2 a broadband Wilkinson power divider–combiner operating over 2–18 GHz. Section 6.3 presents a novel hybrid coupler using multilayer LCP to achieve a broadband design within a compact area. Broadband LCP Marchand balun A balun converts differential “balanced” signals into single-ended “unbalanced” signals, and vice versa. Marchand baluns are found in numerous microwave circuit designs owing to their characteristically wide bandwidth, low imbalance, and symmetric balanced ports. To achieve a wide bandwidth ratio, a Marchand balun is realized with multilayered broadside coupled microstrip lines implemented on LCP. A novel twin-thickness thin-film [1] structure has been devised specifically to reduce balun conduction loss without sacrificing operation bandwidth.