MMW/60GHz liquid crystal tuneable periodic filters

This thesis presents a design method for liquid‑crystal–tuneable periodic microstrip filters at 60 GHz built around a three‑stage synthesis. (1) Odd–even mode analysis provides closed‑form starting dimensions for a symmetric unit cell on an anisotropic, voltage‑biased LC substrate, placing the shunt/series resonances, target impedances and coupling needed for compact selectivity. (2) Reflection‑coefficient (Γ) optimisation then refines the geometry using an analytical Γ expression for the unit cell, improving matching across the intended passband/stopband while preserving manufacturability; the criterion naturally incorporates the LC’s bias‑dependent effective permittivity. (3) Periodic cascade prediction forms the full filter by chaining optimised cells via the ABCD matrix to extract the Bloch propagation constant, locate the Bragg edges, and forecast insertion and return loss versus the high‑level targets (centre frequency, selectivity and tuning range). Validation relies on full‑wave electromagnetic simulation in two independent platforms, Keysight ADS (Momentum) and CST Studio Suite, with harmonised substrate stacks, metallisation and bias conditions. The results show continuous, voltage‑controlled frequency tuning around 60 GHz, low insertion loss in the passband and strong return loss, with close agreement between matrix‑based predictions and EM responses. Cross‑tool correlation substantiates the robustness of the synthesis and the practicality of biasing LC substrates at millimetre‑wave. The contribution is an LC‑aware, synthesis workflow that unifies odd–even sizing, Γ‑based optimisation and ABCD/Bloch prediction, together with a reproducible cross‑platform validation protocol. The method provides a tractable path to reconfigurable 60‑GHz front‑end filtering and is readily extendable to other periodic topologies and frequency bands.