Custodio Peixeiro

Miniaturization of rectangular microstrip patches using genetic algorithms

This paper presents a new procedure for the miniaturization of rectangular microstrip patches based on genetic algorithms. The shape of a typical rectangular patch is modified in order to reduce its resonance frequency keeping the physical volume of the antenna constant. As an example, the resonance frequency of a square microstrip patch is reduced from 3 to 1.8 GHz. The patch is divided in 9/spl times/9 square cells. The genetic algorithm optimization procedure is subsequently used to remove some of the metallic cells. To validate the procedure an antenna prototype has been fabricated and tested. Good agreement is obtained between theoretical and experimental results.

Integration of omnidirectional wrapped microstrip antennas into laptops

The integration of a novel quasi-omnidirectional low-profile microstrip antenna element into laptop computers is proposed. The antenna structure is obtained by wrapping a patch element around the top edge of the laptop screen. The antenna is fed by a microstrip inverted line, which can be easily integrated inside the plastic display cover. Experimental results show that very good total power radiation pattern omnidirectionality and an adequate coverage of the whole 2.4-GHz ISM band are achieved. An antenna with six elements and low-mutual coupling, aiming at multiple-input¿multiple-output (MIMO) arrangements, has been fabricated and tested. Experimental results confirm the fulfillment of the requirements for MIMO applications in laptops.

Single-Layer Quad-Band Printed Reflectarray Antenna with Dual Linear Polarization

A novel single layer, dual linear polarized unit cell is introduced for a quad-band reflectarray antenna in the Ku-band centered around 12, 13, 14, and 15.5 GHz. The unit-cell design is such that the resultant reflectarray antenna can be considered as four different reflectarray antennas, each with a specific beam shape, sharing one aperture. As proof-of-concept, two quad-band reflectarray antenna prototypes having a plate size of 20 × 20 cm2 have been designed and fabricated each with a certain beam direction versus frequency. Measurement and simulation results show satisfactory performance of both reflectarray antennas at each frequency.

Circularly polarized aperture coupled stacked patch antenna element for Ka-band

This paper presents the design and implementation of a circularly polarized stacked patch antenna element for Ka-band applications. The printed element has been developed to be used in a LEO satellite antenna array. Two circular stacked patches, with air gaps, are placed inside a circular cavity. A suspended stripline is used to feed the patches through a cross slot cut in the bottom of the cavity. Broadband input impedance, radiation pattern and axial ratio characteristics have been obtained. The numerical simulations have been validated with experimental results.

Tri-Band, Polarization-Independent Reflectarray at Terahertz Frequencies: Design, Fabrication, and Measurement

In this paper, two THz reflectarray surfaces have been designed and fabricated in order to deflect a plane wave with any polarization and with a specific incident angle to three different specific directions each at distinct three frequencies of 0.7, 1.0 and 1.5 THz. The surface is composed of an array of 100 ×100 cells, each comprised of gold crosses and parasitic dipoles printed on thin grounded high resistivity silicon. Finite-element method (FEM) simulations are in line with the measurement results obtained using THz time-domain spectroscopy (THz TDS) showing the intended deflections for the two fabricated samples each with an arbitrary frequency-vs-deflection angle relationship. In addition, the use of silicon as the substrate paves the way for the integration of reconfigurable technologies which enhances the reflectarray versatility.

Reconfigurable E-shaped patch antennas

This paper discusses the potential of E-shaped patches to be used in reconfigurable antennas. It is shown that the application of a PIFA configuration to dual-band E-shaped patches gives the freedom of independently tuning two resonances in a very wide frequency range, without affecting the antenna general structure and external dimensions. An application of these features to reconfigurable quasi-omnidirectional back-to-back E-shaped patch for laptops is demonstrated. To prove the concept a very simple model of RF MEMS switches is used in a dual-band laptop reconfigurable antenna prototype. In spite of frequency bands toggling (between IEEE 802.11b/g /2.44 GHz/ or WiMAX /3.45 GHz/ and IEEE 802.11a /5.25 GHz or 5.775 GHz/) the radiation pattern is always almost omnidirectional.

Compact triple-band microstrip patch antenna element for cellular and WLAN systems

A new small triple-band microstrip patch antenna element is presented. It has been developed to be used in handsets of future mobile multi-standard cellular and WLAN communication systems. The research effort has been focused in miniaturisation and adequate multi-band behaviour at the GSM9000, UMTS and HiperLAN2 frequency bands. A prototype has been designed, fabricated and tested. Good agreement has been obtained between numerical simulations and experimental results providing validation of the design procedure.

Radiation Pattern of a 2.4/ 5.2GHz Laptop Internal Antenna: Near Field Spherical Range Measurements and Full Wave Analysis

The omnidirectionality of a laptop internal antenna can be severely affected by the laptop electrically large structure. Therefore, an accurate evaluation of the radiation pattern requires a proper modelling of the laptop housing effects. Due to the large laptop dimensions, this antenna-PC integrated approach leads to a minimum far field distance of at least 12 meters at the WLAN frequency bands. Such a large distance is not easily accommodated in indoor far-field measurement ranges. A near field measurement technique seems appropriate to solve the problem. This study reports 2.4/5.2 GHz laptop internal antenna housing effects on the far field radiation pattern. The full wave simulations are compared with measurement results obtained in UCLA near field spherical range. A very good agreement obtained for all the investigated scenarios confirms that the near field technique is adequate to deal with this type of measurement problems.

Design of integrated antenna arrays for MIMO enabled laptops

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.

Radiation from Commercially Viable Antennas for PCMCIA Cards Housed in Laptops

This study evaluates laptop terminal housing effects on the radiation patterns of popular 2.4 GHz antennas mounted on PCMCIA cards: sleeve dipole and inverted-F antenna (IFA). The antennas far field patterns of freestanding WLAN/WPAN wireless cards are compared for cards inserted in different positions in a laptop chassis. Our results show that IFAs are more robust to housing effects and keep fair omnidirectionality in the horizontal plane whereas sleeve dipoles patterns are notably altered.