Marcel Ruf

A 4 th harmonic schottky diode mixer - facilitated access to THz frequencies

This paper will present first measurement results of a 4th harmonic Schottky diode mixer operating at 600 GHz. The mixer design compromises a rectangular waveguide based splitblock with an integrated quartz based mixer circuit. A low parasitic planar antiparallel Schottky diode pair is used to downconvert a 600 GHz signal by mixing with the 4th harmonic of the local oscillator. The local oscillator for the presented mixer consists of a 150 GHz PLL-locked frequency doubled Gunn oscillator providing a frequency and phase stabilized LO source for accurate measurements of the magnitude and phase of the RF signal. Simulations predict conversion losses well below 20 dB. Current evaluations of the mixer performance are proving the suitability for short range applications like material characterization and testing as well as for life sciences and medical applications.

Beam Position and Energy Monitoring in Compact Linear Accelerators for Radiotherapy

The experimental verification of a novel sensor topology capable of measuring both the position and energy of an electron beam inside a compact electron linear accelerator for radiotherapy is presented. The method applies microwave sensing techniques and allows for the noninterceptive monitoring of the respective beam parameters within compact accelerators for medical or industrial purposes. A state space feedback approach is described with the help of which beam displacements, once detected, can be corrected within a few system macropulses. The proof-of-principle experiments have been conducted with a prototype accelerator and customized hardware. Additionally, closed-loop operation with high accuracy is demonstrated.

Design of a 4 th harmonic Schottky diode mixer for THz frequencies

This paper focuses on the benefits of subharmonic mixers in the sub-mm wavelength range. To demonstrate the possibility to extend the advantages of 2nd harmonic mixers with respect to local oscillator requirements the paper discusses higher order subharmonic mixers. Simulation results are presented to show the achievable performance and limitations of higher order subharmonical mixing. For an exemplary 4th harmonic mixer operating at 600 GHz the circuit simulations predict a conversion loss of around 15 dB. Results of 3D-EM field simulations are presented to demonstrate a very compact split-block realization of the mixer circuitry.

A Heterostructure Barrier Charge Swing device for frequency multiplication at 306 GHz

A new type of frequency multiplier which is called Heterostructure Barrier Charge Swing (HBCS) is proposed. It concerns a bunch of charge carriers swinging in a trough between heterojunction barriers. The behavior of the device is simulated and experimentally verified. Efficiencies of 27% for tripler and 14% for quintupler operation are predicted. A split-block mount with planar circuitry is presented to prove tripler operation capabilities from 102 GHz to 306 GHz.

Beam Position Monitoring in Electron Accelerators

Beam Position Monitoring (BPM) systems are crucial in particle acceleration facilities for maintaining stable movement of the beam. Beam displacement, information about synchrotron oscillations and betatron movements can be derived from data gathered in BPM systems. Medical electron accelerators also employ BPM measurements to ensure optimal generation of treatment radiation. The article gives an overview about electron beam characteristics, BPM concepts and signal processing methods used in particle accelerators. Moreover, experimental results on electron beam position are presented. Index Terms – Linear Accelerators, Beam Position Monitoring, BPM

Heterostructure equivalence of step-recovery diodes for ballistic and diffusive electron resonance - a new concept for THz signal generation

A heterostructure equivalent to the well-known step recovery diode principle, arranged as a double structure gives a new nonlinear device for highly efficient harmonic THz signal generation. Like in the case of step recovery diodes, these devices exhibit promising performance especially for the generation of higher order harmonics. Theoretical and experimental results will be presented.