Design of Integrated Antenna Arrays for MIMO Enabled Laptops

Design of Integrated Antenna Arrays for MIMO Enabled Laptops J. Guterman(1,2)*, D.W. Browne(2), Y. Rahmat-Samii(2), A.A. Moreira(1) and C. Peixeiro(1) (1) Instituto de Telecomunicações, Instituto Superior Técnico Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal e-mail: {jerzy.guterman, antonio.moreira, custodio.peixeiro}@lx.it.pt (2) University of California, Los Angeles, CA 90095-1594 USA e-mail: {decibel, rahmat}@ee.ucla.edu Abstract This paper presents a novel antenna array for MIMO enabled laptops that is designed to preserve channel capacity. The antenna-level performance of this array is compared with the performance of a simple microstrip patch antenna array. This comparison is made with both arrays fully integrated within a realistic laptop structure. Introduction Multiple-Input Multiple-Output (MIMO) radio communications offers a significant increase in throughput and range without an increase of bandwidth or overall transmit power. The separation of antenna elements allows MIMO techniques to get the above benefits by exploiting multipath diversity across space. Physical MIMO implementation can be divided into two layers: (i) the antenna array interface to the multipath channel, and (ii) space-time signal processing. The search for MIMO array designs that are integrated into the terminal and provide an adequate multipath interface to allow system performance near the capacity of the radio channel still remains an open problem. Recent experimental work has confirmed what characteristics MIMO arrays must have so that the multipath interface is capacity preserving [1]. These characteristics include: (i) arrays of omnidirectional elements and (ii) low mutual coupling between elements. These characteristics have been shown to be satisfied by a pair of circular arrays of dipoles whose radius was 1 wavelength. However, in the majority of real mobile unit designs, the size restrictions do not allow such large element spacing. Moreover, dipole antennas are sensitive to the proximity of the terminal's housing and are impractical for mobile terminals. Therefore the design of compact arrays that are both highly integrated with the mobile terminal and are MIMO capacity preserving is a challenging task. This paper presents a novel four-element dual band (2.4/5.2 GHz) MIMO array integrated into a laptop screen housing. In spite of the integration with electrically large laptop structure, each of the radiators has quasi-omnidirectional horizontal plane radiation pattern in both operating frequency bands. The antenna-level performance of the proposed design is compared with the performance of traditional microstrip patch antenna array. The comparison is made with the arrays integrated into a laptop screen housing. The system-level performance of above mentioned arrays is experimentally evaluated and compared in [2] where measurements are performed with MIMO radios over a full range of multipath scenarios in an indoor environment.

Laptop Antenna Arrays Design and Measurement A. Linear Array of Quasi-omnidirectional Dual-band Back-to-back E-shaped Elements A quasi-omnidirectional dual-band back-to-back E-shaped patch element [3], has been designed to be mounted within laptop screen rim. It embraces conformally a ground plane edge, constituted by a TFT panel metallic case, Fig. 1c. In spite of integration with large conducting parts, it features quasi-omnidirectional far field total gain horizontal patterns in both operating bands. In this work a 2.4/5.2 GHz back-to-back patch has been used as a MIMO array element. Four radiators are integrated along the top screen edge forming a uniform linear array with spacing 0.66λ (@2.44GHz), as shown in Fig. 1b. B. Simple Microstrip Patch Array A simple microstrip 0.66λ spaced uniform linear patch array operating in the ISM 2.4GHz band has been designed as a reference antenna. Four square patch elements of dimensions L = W = 46.6 mm have been printed on a Duroid 5880, 1.57 mm thick microwave substrate, attached to the metal plate which simulates a 14” TFT panel (Fig. 1a). In order to fulfill bandwidth requirements an additional 1.57mm air gap has been introduced between metal plate and substrate. Microstrip inverted lines, printed on the back side of the substrate have been used to feed the patches. C. Antenna Prototypes and Measurement The simple patch and back-to-back patch array prototypes have been built and attached to the real Toshiba Satellite keyboard chassis, to mimic the realistic antenna operating conditions, Fig. 1a,b. A 1mm thick metal plate has been used to model a 14’ display panel. Measured scattering parameters are presented in Fig. 2 (left column). For both arrays all antenna elements are matched (Sii