This paper presents a study of planar silicon lens antennas with up to three stepped-impedance matching regions. The effective permittivity of the matching regions is tailor-made byetching periodic ...

This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric-rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry-defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from 3.2-j2.3 to 7.2-j8.0, loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6 × 0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor.

This paper presents the recent achievements in a project on micromachined millimeter-wave near-field medical sensors, in particular for skin cancer diagnosis. Micromachining enables sensor probes which achieve both high sensitivity and high lateral resolution through a drastically miniaturized probe tip. Two different design strategies are investigated: a broad-band, non-resonating, tapered dielectric-rod probe, and a resonance slot sensor. For probe characterization micromachined silicon test and calibration samples with tailor-made permittivity were fabricated. Characterization of fabricated prototypes show that the tapered probe can clearly and reproducibly distinguish silicon test samples of permittivity corresponding to healthy and cancerous skin tissue at 100 GHz. For the resonance slot probe the simulated response to materials of different permittivity is shown. Furthermore, the paper presents the design of phantom materials for probe evaluation on soft-matter dielectrics.

This paper describes the main results of the EU FP7 project TUMESA - MEMS tuneable metamaterials for smart wireless applications. In this project, we studied several reconfigurable antenna approaches that combine the new technology of MEMS with the new concept of artificial electromagnetic materials and surfaces (metamaterials and metasurfaces) for realisation of millimetre wave phase shifters and beam-steering devices. MEMS technology allows to miniaturise electronic components, reduce their cost in batch production, and effectively compete with semiconductor and ferroelectric based technologies in terms of losses at millimetre wavelengths. Novel tuneable materials and components proposed in this project perform as smart beam steering devices. Fabricated with MEMS technology in batch and on a single chip, proposed tuneable devices allow substituting of larger and more complex sub-system of, e. g., a radar sensor. This substitution provides a dramatic cost reduction on a system level.

Characterization of high-resolution millimeter-wave measurement probe for skin tissue analysis

This paper presents an overview on novel microwave micro-electromechanical systems (MEMS) device concepts developed in our research group during the last 5 years, which are specifically designed for addressing some fundamental problems for reliable device operation and robustness to process parameter variation. In contrast to conventional solutions, the presented device concepts are targeted at eliminating their respective failure modes rather than reducing or controlling them. Novel concepts of MEMS phase shifters, tunable microwave surfaces, reconfigurable leaky-wave antennas, multi-stable switches, and tunable capacitors are presented, featuring the following innovative design elements: dielectric-less actuators to overcome dielectric charging; reversing active/passive functions in MEMS switch actuators to improve recovery from contact stiction; symmetrical anti-parallel metallization for full stress-control and temperature compensation of composite dielectric/metal layers for free-standing structures; monocrystalline silicon as structural material for superior mechanical performance; and eliminating thin metallic bridges for high–power handling. This paper summarizes the design, fabrication, and measurement of devices featuring these concepts, enhanced by new characterization data, and discusses them in the context of the conventional MEMS device design.

Dielectric rod waveguide antennas of rectangular cross section have a number of advantages over conventional waveguide and horn antennas as an antenna array element. Dielectric rod waveguide antennas have relatively low cost, low losses, a broadband input match and a high packing potential. Additionally the radiation pattern of such antennas is almost frequency independent. In this paper the suitability of Sapphire rod waveguides for an antenna array is studied with simulations and prototype measurements at W band. Strong mutual coupling is observed when the elements are close to each other.

Microelectromechanical systems (MEMS) are proposed as a technological solution for fabrication of metamaterials. This enables tunability of metamaterials effective properties and allows using metamaterials in wide range of applications. Low loss of the MEMS devices allows the metamaterials application to be extended to millimeter and submillimeter wave frequencies without compromising on performance. Electronic beam steering by MEMS tunable metamaterials at millimeter wavelength is considered and a prototype of a W band analog tunable phase shifter is demonstrated. The insertion loss of the fabricated MEMS tunable metamaterials surface varies from 0.7 dB to a maximum of 3.5 dB (at a resonance frequency). MEMS varactors have shown reliable and repeatable analog operation over 108 cycles.

Analogue type millimetre wave phase shifter based on a dielectric rod waveguide with adjacent MEMS tuneable high-impedance surface is proposed. Applying bias voltage to the MEMS varactors of the high-impedance surface allow controlling its effective impedance and consequently the phase factor of the propagation constant inside the waveguide. The measured phase difference between the phase shifter with adjacent high-impedance surface and phase shifter with low impedance surface is up to 378°. The insertion loss of the high-impedance surface as phase shifting element at 80–90 GHz is 0.5–2.7 dB depending on the distance to the dielectric rod waveguide.

Possibility of compact low loss analog type millimeter wave phase shifter was demonstrated. The phase shifter is controlled by a MEMS tunable high-impedance surface placed, e.g., as a backshort or as sidewall inclusions of a rectangular metal waveguide. Reflection type phase shifter can provide differential analog phase shift from 0° to up to 240°. Reliable and tunable MEMS based high-impedance surface has been demonstrated for the first time. The insertion loss of the fabricated MEMS tunable high-impedance surface varies from 0.7 dB to a maximum of 3.5 dB (at a resonance frequency), which is a dramatic improvement over our previous non-tunable prototype.

Overview of recent research activities of MilliLab and SMARAD at mm- and submm-wavelengths is presented. These activities include MEMS-tunable high-impedance surfaces, passive and active dielectric rod waveguide components, indirect holographic imaging, and measurement techniques for high-gain antennas.

In this work we propose a novel millimetre-wave phase shifter targeted on thin ferroelectric film technology. Architecture of the phase shifter is proposed to use a dielectric rod waveguide with a periodic printed array of electrically small dipoles loaded with a ferroelectric varactor (pin diode, Schottky diode, etc.) with the function of control the phase of the propagating wave. The proposed architecture of the phase shifter is verified by measuring two prototypes, where the tuneable elements (ferroelectric varactor) are replaced by non-tuneable capacitors with 10 fF and 15 fF respectively. The measurements revealed a considerable phase shift and small insertion losses. It is demonstrated that the proposed periodic structure using the dielectric rod waveguide allows to fully realize a potential of known tuneable elements at millimetre-wavelengths.

This letter presents a planar omnidirectional antenna structure with wide beam for applications in the 60-GHz band. The antenna was designed using only one metal layer on top of a quartz substrate, which is very cost efficient. The optimal structure, of size 4.5 times 4.3 mm2, exhibits a gain of 1.4 dBi plusmn 0.5 dBi in the omnidirectional plane and a half power beam width of about 75 deg in the perpendicular plane. The bandwidth with return loss at least 10 dB covers the 57-64-GHz license-free band, which is commonly considered for very high data rate communications. The consistency of the simulated results was successfully checked with measurements.

In this paper travelling wave amplification is experimentally demonstrated in the dielectric rod waveguide at W band. An AlGaAs/GaAs heterostructure chip is inserted in the waveguide, and the applied electric field causes an electron drift. Due to the energy transfer from the drifting electrons the electromagnetic wave travelling in the periodic structure is amplified. A maximum of about 8 dB/cm electronic gain was observed in the measurements with the electric field of 150 V/cm.