This paper discusses the prospects of millimeter-wave beam steering antennas, such as tuneable high-impedance surface, dielectric rod waveguide with an integrated phase shifter, tuneable leaky-wave antenna, active reflectarray, and shaped lens antenna with an integrated switched feed array. In these antennas the necessary phase change for antenna elements can be achieved using various electronically tuneable elements, but in our case MEMS are used. Some early results of our investigations are presented.

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.

In many emerging applications of millimeter waves, electronic focusing and beam steering is needed. We present a survey of mm-wave beam steering antennas, where the necessary phase change for antenna elements is achieved using various electronically tuneable elements, e.g. microelectromechanical systems (MEMS), such as tuneable leaky-wave antennas, shaped lens antennas with integrated switched feed array, active reflectarray, tuneable high-impedance surface, and dielectric rod waveguides with integrated phase shifters. Some early results of our own relevant investigations are also presented.

The reflection properties of the MEMS-based HIS illuminated from oblique angles of incidence have been characterized numerically, and a quasi-optical measurement setup has been built for experimental characterization. The resonance frequency and the relative bandwidth are slightly increasing with the increase of the angle of incidence. The comparison between the simulated and measured results is discussed.

This thesis focuses on the development of novel microelectromechanically tuneable high-impedance surfaces (HIS) for millimetre wave beam steering applications. Microelectromechanical systems (MEMS) provide good functional parameters, e.g., low loss even at millimetre wave frequencies and excellent reliability, and can effectively compete with conventional technologies, e.g., ferroelectrics and ferrites. At the same time MEMS enable tuneability of the HIS, which can be used for developing reconfigurable devices with decreased system complexity, high level of integration and even as a system-on-a-chip, which dramatically reduces cost of the high frequency devices. The proposed MEMS tuneable HIS consists of a two-dimensional periodical arrangement of MEMS varactors, with a period much smaller than the wavelength of the interacting electromagnetic field, placed on an electrically thin grounded dielectric substrate. Being embedded in a waveguide, the structure can be used as an analogue type phase shifting element controlled by a bias voltage connected to the MEMS varactors. Alternatively, the MEMS tuneable HIS can be used as a smart electronic beam steering reflective surface, if a reconfigurable gradient of the effective surface impedance is induced throughout the structure by applying different programmed bias voltages to the different rows of the MEMS varactors. The methodology used in this study is a combination of analytical analysis, numerical simulations and electromagnetic measurements. A precise analytical model of the MEMS tuneable HIS is derived and used for designing of the structures operating in the W-band. Numerical simulations of different types of HIS and phase shifters based on the tuneable impedance surface embedded in rectangular metal waveguides and dielectric rod waveguides are carried out. Results of the numerical simulations correspond very well with the analytical calculations. Several prototypes of the multi-layered and MEMS-based HIS are fabricated and characterised. Measurements of the reflection coefficient show clear resonant high-impedance behaviour in the designed frequency range with reflection phase changing from almost 180° at lower frequencies to 0° at the resonance and to almost 180° at higher frequencies. The measured phase shifter based on a MEMS tuneable HIS placed adjacent to a dielectric rod waveguide exhibits an analogue type phase shift of up to 70° when the bias voltage is applied to the MEMS varactors.

Microelectromechanical (MEMS) technology is being used for many purposes in reconfigurable devices due to its advantages compared to other technologies, e.g., varactors. In this paper MEMS are suggested to be used for the development of leaky-wave antenna for 77 GHz. Antenna comprises a right left handed transmission line, where a microstrip is used as the right handed transmission line. The left handed loading comprises series reconfigurable MEMS capacitors and shunt narrow strip inductors. Analytical design, simulation and measurement of a planar leaky-wave antenna structure are carried out and compared.

Beam steering with a MEMS-based high impedance surface has been studied in W band. The steering mechanism is based on the principle of a phase gradient array. Reflection phase properties of a single unit cell structure are analyzed. Radiation pattern of a strip consisting of elements with different impedance is analyzed numerically for two beams of normal and oblique incidence. The steering range is achieved from -45 degrees to 45 degrees with respect to the normal direction.

The authors suggest and theoretically study an efficient leaky-wave antenna (LWA) with beam scanning governed by micro-electromechanical systems (MEMS) capacitors. The use of MEMS instead of varactors or magnetised ferrite substrate allows one to significantly decrease losses. The LWA is implemented as a periodically loaded transmission line (PLTL). In order to obtain maximal possible dispersion of a PLTL, resonant loads combining variable capacitors and stub strap inductors are applied. Analysis of dispersion properties and design of a unit cell of the PLTL are based on the analytical model with further numerical optimisation. Full-wave simulations are carried out for a realistic beam-scanning LWA, where the radiated beam can transit from forward to backward directions for a practical MEMS design.

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.

MEMS varactors and switchers used as a key element for the phase shifters on dielectric rod waveguides are presented. The 32 degree phase shift due to capacity change in MEMS is demonstrated in W band. New approach of the reconfigurable phase shifter with MEMS switchers is discussed in this work.

This paper presents study of controllable leaky wave modes in various planar transmission lines operating at millimetre wavelengths. Leaky wave regime is achieved by exploitation of periodic inclusions. The main goal is to obtain the scanning of the radiation angle from forward to backward direction and rather broad range of scanning angles at a given operation frequency corresponding to the mm-wave range. For this purpose, we suggest to use MEMS capacitors combined with shunt strap inductors. This design solution allows one to significantly reduce the losses in the loaded line compared to known scanning leaky-wave antennas based on varactors, or on magnetized ferrites. The design of the unit cell is done using global optimization method, and the dispersion is investigated analytically. After that, full wave analysis is done using Ansoft HFSS v.11 environment. After the leaky wave regimes are verified, an example of a leaky-wave antenna is introduced in order to confirm possibility of beam scanning.

In this paper, design, analytical analysis and numerical analysis of beam-steering possibilities of the planar transmission line loaded with microelectromechanical systems (MEMS) capacitors and stub inductors is presented. First, the design and analysis of a single unit cell comprising antenna structure is carried out. By stacking certain number of these unit cells leaky-wave structure is obtained, which is then analyzed. As a result, effective beam-steering structure (controlled by MEMS capacitance variation) is obtained.