MEMBRANE-SUPPORTED YAGI-UDA MILLIMETER-WAVE ANTENNAS

ABSTRACT This paper presents the design, fabrication and “on wafer” characterization of membrane-supported Yagi-Uda CPW fed antenna structures. The antennas wereattractive in term of compactness and it is considereddesigned for the 60 GHz and 77 GHz frequency operating ranges. The 60 GHz antennas were fabricated on a semi-insulating GaAs membrane using GaAs micromachining. The 77 GHz ntennas werea manufactured on 1.4 µm thin SiO 2 /Si 3 N 4 membranes obtained by micromachining of high resistivity silicon, using backside wet etching process. The design was based on electromagnetic simulations, using Zeland IE3D software package. The antenna tructures weres measured “on wafer” and have showngood experimental results in good agreement with the simulated ones. 1. INTRODUCTION The use of micromachining techniquessubstantial reduces the losses in the millimetre wave range due to the substrate removal. Additional positive effects are the reduction of dispersion effects, the suppression of higher substrate modes and the possibility of using higher transmission line characteristic impedance values in the design. These improvements are due mainly to the fact that a very thin dielectric or high resistivity semiconductor membrane is used as support for passive circuit elements that appear as being “air suspended”. In recent years, the micromachining technology has been proposed for the fabrication of millimetre waveradiation characteristics and compcircuits on very thin dielectric membranes, mostly for silicon substrates [1, 2]. Micromachining of GaAs is a less investigated alternative for manufacturing of components andmicrosystems for high performance systems. GaAs micromachining isvery interesting for the RF-MEMS field also due to the easy monolithically integration of micromachined passive circuit elements with active devices manufactured on the same chip [3]. Planar antennas are key elements in microwave and millimeter wave systems for many applications, such as wireless communications, automotive radars, remoteUda antennasensing, and survey environment.At present the tendency is to develop electronic modules featuring high electrical performance, low cost and high yield and reliability. These new requirements have motivated the emergence of the new technological concepts in order to circumvent the problem related to frequency increasing. Coplanar waveguide (CPW) fed antennae are very the opportunity to fabricate these types of antennae through collective micromachining techniques.A double folded slot antenna integrated with a Schottky diode on the same GaAs membrane in a monolithically integrated receiver is described in [3]. The Yagi-Uda antenna was invented in 1926 by Yagi and Uda and has become a standard for multi-element antenna arraysup to 500 MHz range. The Yagi-Uda antenna is a traveling-wave structure that, as the number of elements increases, has improved directivity, gain and front-to-back ratio. The Yagi-Uda array is based on principles of parasitic elements that are not directly fed by an energy source. These elements focus the radiation pattern by the currents induced in them by radiation from the driven element. According to their length and spacing from the driven element, the parasitic elements become either directors or reflectors. Directors are shorter than the driven element and result in the radiation pattern being sharplyfocused in the direction of the directors. eflectors are longer than the drivenR element and result in a radiation pattern directed away from them. The overall result is an endfire radiation pattern. Yagi-Uda antenna acquires significantly more gain and a better-controlled front-to-back ratio when they employ at least three elements. Quasi-Yagi antennas have been proposed [4]. By using the CPW ground as a reflectorthey demonstrated good actness. The quasi-Yagi antennas were fabricated on high index dielectric substrates e