Compact UWB Monopole Antenna for System-on-Package Applications

Abstract

A novel compact, dual layer UWB monopole antenna is presented. This low profile ultra-wideband antenna is fed by a 50 Ω shielded strip-line with an array of metal vias making the conducting walls. A circular shaped monopole is the radiating element. The dual layer, shielded strip line feeding design characteristic of the antenna allows for integration in multilayer System-on-Package technologies. The ultra-wideband, monopole characteristics of the antenna are confirmed experimentally. INTRODUCTION Ultrawide-band communications systems have been investigated and developed over the last few decades. The technology promises high-speed transmission rate for short-range, indoor data communications. In 2002, the Federal communications Commission (FCC) allocated the spectrum from 3.1 to 10.6 GHz for unlicensed UWB measurement, medical and communication applications [1]. The frequency allocation has prompted the development of antennas and systems capable of covering the complete UWB frequency band. Antennas have been proposed for ultrawide-band applications in three dimensional [2],[3] and planar form [4], [5]. Planar monopole antennas have been developed with different shapes such as circular [4] and half disc [6]. Multilayer technologies have also attracted strong interest in recent years. Amongst them, technologies such as photo-imageable thick-film and LTCC (Low Temperature Co-fired Ceramic) offer compact multilayer solutions. In most cases, the ideal design requires a non-radiating transmission medium such as stripline [7] or substrate integrated waveguides [8]. This paper proposes a shielded strip-line fed UWB antenna design which can be integrated into multilayer circuit devices. The walls of the shielded strip line are formed using metal vias. The antenna is the disc shape proposed in [4] though is smaller in size when fabricated on the same permittivity substrate. Also, the feedline is better isolated from radiation and other circuitry when realized as shielded stripline. ANTENNA DESIGN: Fig.1. shows the proposed compact, dual-layer strip-line fed antenna and the reference antenna proposed in [4]. Both antennas have been designed to cover the UWB frequencies 3.1 and 10.6GHz and were fabricated using RT Duroid substrate of dielectric constant 2.33. The multilayer structure consisted of two layers of thickness 1.575mm with metal etched in the two sides of each substrate. The rectangular shape of the ground plane was produced by etching the top and bottom metal clad of the top and bottom layer respectively. The antenna was fed by a 50ohm shielded strip-line as illustrated in Fig.2. The stripline ground planes were terminated in the radiation region above and below the monopole disc which was 68 0-7803-9444-5/06/$20.00 © 2006 IEEE. metal vias strip line Wl ground planes L s r Ws Lg L d located between the 2 substrate layers. The side walls of the shielded strip transmission line were fabricated using two arrays of metallised vias of diameter 0.5mm and pitch 1mm. The separation between the two via arrays was 7.5 mm. A tapered transition was used between the radiating element and the transmission line. The other dimensions of the antennas are shown in table 1. Fig.1. Proposed dual layer design for system on package applications (left) and similar single layer arrangement in [4] (right). Table I. Dimensions of the multilayer Strip-line fed UWB antenna Fig.2. Geometry of the Dual-layer UWB antenna ANTENNA ANALYSIS AND EXPERIMENTAL RESULTS: Fig 3. Shows the simulated and measured return loss (S11) of the compact UWB antenna. The measured return loss was obtained using an HP 8722 ES network analyzer with coaxial calibration and CST Microwave Studio was used for the simulations. The calculated and measured -10dB S11 bandwidth achieves more than the 3 – 10.6 GHz needed for the UWB communication systems. Parameter Dimensions (mm) Ws 20 r 7.5 Ls 20 Ld 1.5 Lg 37 x y z