Jan Hesselbarth

Comparison of electromagnetic field solvers for the 3D analysis of plasmonic nano antennas

Plasmonic nano antennas are highly attractive at optical frequencies due to their strong resonances - even when their size is smaller than the wavelength - and because of their potential of extreme field enhancement. Such antennas may be applied for sensing of biological nano particles as well as for single molecule detection. Because of considerable material losses and strong dispersion of metals at optical frequencies, the numerical analysis of plasmonic antennas is very demanding. An additional difficulty is caused when very narrow gaps between nano particles are utilized for increasing the field enhancement. In this paper we discuss the main difficulties of time domain solvers, namely FDTD and FVTD and we compare various frequency domain solvers, namely the commercial FEM packages JCMsuite, Comsol, HFSS, and Microwave Studio with the semi-analytic MMP code that may be used as a reference due to its fast convergence and high accuracy. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.

Large Stroke Staggered Vertical Comb-Drive Actuator for the Application of a Millimeter-Wave Tunable Phase Shifter

This paper presents the design, fabrication, and characterization of a MEMS actuator with large static deflection as a waveguide-mounted variable millimeter-wave phase shifter. The actuator is composed of a pair of interdigitated microplates actuated by vertical comb-drives and suspended by SU-8 torsional springs. The SU-8 spring possesses a thin metallization top layer and a reverse-T-shaped cross-section enabling low torsional stiffness and high in-plane stability. A maximum mechanical deflection of 10.3° is obtained under a dc actuation voltage of 35 V. The dynamic characterization of the device shows that the resonance frequency of the torsional mode is well separated from the other three bending modes, confirming the designed low torsional stiffness and high in-plane stability. The torsional viscoelastic creeping is measured as a function of time at different loads and shows a maximum of 0.5° for an applied voltage of 27.5 V. A high operation cycle test is conducted and the metalized SU-8 spring withstands 800 million cycles without showing fatigue. RF measurements show that a variable mechanical deflection angle between 0° and 8.2° results in a variable transmission phase shift up to 58.0°. The measured insertion loss is always below 5.1 dB at 98 GHz, corresponding to a figure of merit of 11.5°/dB.

A microdevice with large deflection for variable-ratio RF MEMS power divider applications

In this paper, we present the design and fabrication of a large deflection MEMS actuator directly integrated as a variable-ratio radio frequency (RF) power divider in a waveguide. The device is based on a tilting microplate suspended by SU-8 springs and driven by a vertical comb drive actuator. The fabricated device is characterized by laser Doppler vibrometer and white light interferometer measurements. The dynamic measurement confirms the resonance frequency of the torsional mode being around 370 Hz, from which the spring stiffness has been extracted and used for static modeling of the device. The fabricated microplate devices achieved deflection angles of 5.9° with a dc actuation voltage of 30 V. First RF transmission measurements show good agreement with results from electromagnetic field simulations. A variable power split ranging from equal division up to a ratio of more than 1:2 is measured at 82.5 GHz whilst keeping the amount of dissipated power below 25%. This is the first reported actuated RF MEMS device integrated in a metal waveguide operating at such high frequency.

Leakage suppression in coplanar waveguide circuits by patterned backside metallization

Microwave circuits based on coplanar offer advantages compared to microstrip-based designs, but also introduce unwanted coupling or radiation effects due to the excitation of surface waves or parallel plate modes. Special measures must be introduced to suppress these modes. This paper illustrates the effect of substrate waves on coupling between parts of the circuitry. It details the influence of resonances of the substrate modes on this unwanted coupling. A method is proposed to suppress substrate modes and is supported by experimental results.

Millimeter-Wave Chip-to-Chip Transmission Using an Insulated Image Guide Excited by an On-Chip Dipole Antenna at 90 GHz

A millimeter-wave chip-to-chip transmission link operating at 90 GHz is presented. It uses an insulated image guide and on-chip dipole antennas positioned in the entrance of the waveguide for excitation and reception. The on-chip dipole antenna couples to the higher-order Ex11 mode of a synthesized insulated image waveguide. This field coupling avoids the need for conductive connections such as wire-bonds or flip-chip technology. The measured insertion loss of such a field-coupled dipole-to-image guide transition is 0.46 dB at 90 GHz.

Surface-Moount High-Q Resonators for Millimeter-Wave LTCC Oscillators

We report small-size high-Q resonators suitable for Ka-band oscillators based on alumina ceramic and temperature-compensated by using rutile material. The resonators can be mounted onto LTCC boards by means of surface-mount pick-and-place technology. The influence of tolerances is investigated. Unloaded Q-factors of more than 600 can be obtained at 33 GHz. This performance is compared, with regard to volume and cost, with other resonator structures.

A 32-element frequency-steered array antenna for reflectometry in W-band

In fusion plasma experiments, Doppler reflectometry is used as a contactless diagnostic to evaluate density fluctuations and plasma rotation profiles. It demands a steerable beam that provides a defined spot-size for the wave plasma interaction and multiple frequencies to probe plasma regions of different densities. In this paper, the suitability of a frequency-scanned phased array as a front-end for a Doppler reflectometry system is demonstrated.

Millimeter-wave on-chip solenoid inductor by on-demand three-dimensional printing of colloidal nanoparticles

Millimeter-wave on-chip solenoid inductor structures with wire diameters of O(1 μm) are investigated. The wires are formed by on-demand three-dimensional printing of nanoparticle laden droplets with known droplet size, deposition frequency, and evaporation time. After thermal annealing and morphological characterization, the solenoids are evaluated using two-port S parameter based electrical transmission measurements. The measurements over 0.1–110 GHz, combined with finite-element based electromagnetic field modeling, reveal a quality factor of 0.8 at 110 GHz for an 80 pH coil resulting in an inductance-per-area value of 80 nH/mm2, which is the highest reported value at these scales.

Surface-mount cavity filter technology

A method is proposed to realize cavity resonator filters for cellular frequencies in surface-mount technology. The cavity resonators can be produced by molding techniques and subsequently soldered onto a circuit board, where a stripline structure in the circuit board makes the coupling between the resonators. The molded parts for all resonators of a given filter can be identical. Means are proposed for dealing with the alignment accuracy of the mounting process. Temperature effects due to thermal expansion can be accounted for. Three- and five-resonator band-pass filters have been designed using combined field and circuit simulation techniques, built, and measured.

W-band tunable reflective type phase shifter based on waveguide-mounted RF MEMS

A novel concept for a continuously variable W-band phase shifter is proposed. It is based on a ridge waveguide resonator tuned by MEMS-actuated conductive fingers that interact with the fields beneath the ridge. The rotation of anti-parallel oriented MEMS conductive fingers of about half wavelength size realize a distributed interaction with the purposely structured waveguide ridge. In such a way, large transmission phase variations are obtained. By cascading an additional resonator and a waveguide short, a reflection type phase shifter is created with a single MEMS. For MEMS finger deflection angles between 0° and 7.5°, this device realizes reflection phase shift variation of 381° and a reflection coefficient magnitude of better than −1.65 dB at a frequency of 106.5 GHz. This corresponds to a figure of merit of 230°/dB.