Design and modeling of terahertz Schottky diode harmonic mixers
Typ
Examensarbete för masterexamen
Program
Wireless, photonics and space engineering (MPWPS), MSc
Publicerad
2019
Författare
Jayasankar, Divya
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Compact, efficient and reliable frequency converters, preferably operating at room temperature are necessary for frequency stabilising far infra-red optical sources in order to achieve high spectral resolution. Future air and space-borne instrumentation requirements are driven by the need to accommodate compact LO sources for detection of atomic oxygen (OI) and hydroxyl radical (OH) lines at 3.5 THz, and 4.7 THz as they provide valuable information in atmospheric and planetary sciences. The main objective of this work is to design and model Schottky diode-based harmonic mixers for phase locking of quantum cascade laser operating at 3.5 THz. Detailed large-signal analysis of the four basic single-ended Z-, H-, G-, and Y-mixers was carried out using a standard Schottky-diode model to determine the optimum diode embedding impedances and mixer performances. Conversion nulls were observed in Y-mixers due to destructive interference among the mixing products. It is noticed that for low local oscillator pump power, Y-mixer has low conversion loss. However, as the local oscillator pump power increases, Z-mixer provides reduced conversion loss due to the associated power dissipation in the idler circuits. Based on the ideal simulation study, a 3D electromagnetic model of planar single-ended Schottky diode with sub-micron anode size, integrated with suspended strip-lines on an ultra-thin GaAs membrane was designed. The estimated conversion loss for x6 harmonic mixer operating at 3.5 THz is around 35 dB for −4dBm local oscillator pump power including the waveguide losses. The designed x6 harmonic mixer is intended to be a part of the quantum cascade laser frequency stabilization scheme operating at 3.5 THz in the proposed European Space Agency’s mission LOCUS (Linking Observations of Climate, the Upper atmosphere, and Space weather) targeting the mesosphere and lower thermosphere region (MLT). This thesis also provides initial guidelines for a x8 harmonic mixer design operating at 4.7 THz.
Beskrivning
Ämne/nyckelord
Conversion efficiency, far-infrared, frequency converters, frequency stabilization, harmonic mixers, phase-locking, Schottky diodes, diode mixers