Terahertz low-pass filter based on cascaded resonators formed by CPS bending on a thin membrane

Abstract

A membrane-based coplanar-stripline (CPS) transmission-line platform has recently enabled implementation of diverse THz system-on-chip (TSoC) components. In this paper, we demonstrate an elliptic-function THz low-pass filter (TLPF) using cascaded λ/4 resonators between the right-angle bending of a CPS transmission line defined on a 1 μm-thin membrane. We investigated the effect of bending the CPS transmission line with different angles that introduces a frequency response similar to a simple LC low-pass filter (LPF) and facilitates the design of a desired roll-off performance using traditional methods. ANSYS HFSS was used to provide a full-wave analysis and characterize the effective parameters of the TLPF with a designed cutoff-frequency around 0.6 THz. Using 7 sections of right-angle CPS bending with total length 1.4 mm, we demonstrate experimentally an elliptic-function TLPF characterized by a low-ripple at passband, a roll-off transition with zero transmission near the cutoff frequency and a wide stopband with −60 dB rejection.

Demonstration of a terahertz coplanar-strip spoof-surface-plasmon-polariton low-pass filter

“…The experiment involved utilizing a femtosecond pulsed laser with a wavelength of 780 nm focused on PCSs placed on the waveguide to generate and detect a broadband THz pulse signal. The transmitted signal was reconstructed by translating the mechanical delay line measuring the receiver current using a lock-in amplifier (alike THz-TDS) 26 , 35 . The fluctuations in the measurement are the result of uncorrelated system noise sources (laser, electric, environmental, etc.).…”

Demonstration of a Terahertz Coplanar-Strip Spoof-Surface-Plasmon Polariton Low Pass Filter

“…The experiment involved utilizing a femtosecond pulsed laser with a wavelength of 780 nm focused on PCSs placed on the waveguide to generate and detect a broadband THz pulse signal. The transmitted signal was reconstructed by translating the mechanical delay line measuring the receiver current using a lock-in amplifier (alike THz-TDS) 25,30 .…”

Terahertz Power Divider Using Symmetric CPS Transmission Line on a Thin Membrane

“…First, HFSS was used to obtain the characteristic impedance and propagation constant of the CPS transmission line used for the input and output ports and λ/4 impedance transformers. The optimal geometry of the CPS transmission line for the input and output ports minimizes attenuation of the CPS transmission lines for stripline width W 0 = 45 µm and separation between striplines S 0 = 70 µm [53]. The geometry of the λ/4 impedance transformer Z m1 is W 1 = 45 µm, S 1 = 25 µm, while the geometry of Z m2 is W 2 = 10 µm, S 2 = 70 µm.…”

“…We then tapered the narrow CPS to a wider CPS (W 0 = 45 µm, S 0 = 70 µm) to minimize the attenuation of the transmission line. More details were described in [53]. The optimal tapering length which introduces an acceptable reflection is 0.5 mm.…”