Frequency Division Multiplexer With Directional Filters in Multilayer LCP Films at - and -Band

A quasi-reflectionless frequency division multiplexer (FDM) with directional filters (DFs) in multilayer liquid crystal polymer (LCP) substrates is proposed for
$E$
- and
$W$
-band applications. The in-series cascaded DFs are designed at 74, 84, and 94 GHz, each of which comprises two microstrip lines in the first layer, two pairs of coupling slots in the second layer, and loop resonators in the third layer. The distance between DFs is optimized for suppressing reflection and insertion losses, and the asymmetric distribution of DFs is designed to obtain a low profile. The experimental data demonstrate a 3-dB passband of 8.3%, 8.8%, and 9.7% centered at 74, 84, and 94 GHz, respectively, for the proposed FDM, showing a good match with the simulation. The corresponding insertion loss is measured as 3.63, 3.4, and 2.72 dB at 74, 84, and 94 GHz, respectively. The proposed device may find many applications in multiband and ultrawideband communication and radar systems.