and antti v. ra ¤isa ¤nen 1 Millimeter-wave phase shifters are important components for a wide scope of applications. An analog-type phase shifter for W-band has been designed, analyzed, fabricated, and measured. The phase shifter consists of a reconfigurable highimpedance surface (HIS) controlled by micro-electromechanical system (MEMS) varactors and placed adjacent to a silicon dielectric rod waveguide. The analog-type phase shift in the range of 0-328 is observed at 75 GHz whereas applying bias voltage from 0 to 40 V to the MEMS varactors. The insertion loss of the MEMS tunable HIS is between 1.7 and 5 dB, depending on the frequency.
I . I N T R O D U C T I O NMillimeter-wave phase shifters are important components for a wide scope of applications such as automotive radars, highcapacity communication systems, satellite communication, etc. Existing millimeter-wave phase shifters change the phase by adjusting either the geometrical parameters of the device (e.g. changing the length of a transmission line using switches), or material properties of its components (e.g. by applying magnetic or electric field). Phase shifters based on switched networks and distributed transmission lines may be inconvenient, e.g. in phased arrays due to their relatively large size. Besides they provide with a discrete phase shift only, and of no more than 4.25 bits at frequencies above 60 GHz, e.g. [1-3], which restricts their usability. Using materials with controllable parameters (e.g. ferroelectrics) for phase shifter usually results in high insertion loss at millimeter wavelength frequencies, e.g. 10 dB for a continuous phase shift up to 2208 at 60 GHz [4]. That is why we propose an approach that combines micro-electromechanical systems (MEMS) fabrication technology with the concept of artificial electromagnetic surfaces for realization of analogtype millimeter-wave phase shifters. MEMS technology allows one to miniaturize electronic components, reduce their cost in batch production, and effectively compete with semiconductor and ferroelectric technology in terms of losses. Combined with the artificial electromagnetic surfaces, MEMS varactors enable tunability of unique engineered properties of these surfaces. Previously, we proposed the design of a novel MEMS tunable high-impedance surface (HIS), analyzed its electromagnetic properties analytically and numerically, studied possible applications, and fabricated and measured several non-tunable prototypes, as well as tunable MEMS capacitors [5][6][7][8][9][10][11][12]. In this work we present for the first time the measurement results of the MEMS-based HIS that is tunable in an analog way and is employed in an analog-type phase shifter.
I I . M E M S T U N A B L E H I SConventional HIS [13] consists of a capacitive twodimensional periodic grid of electrically small metal patches placed on a thin dielectric substrate with a ground plane. As the period of the structure is much smaller than the wavelength of the field above it, an effective surface impedance model can be used to an...