Antonio A. Moreira

A Novel, Low-Profile, Vertically-Polarized UWB Antenna for WBAN

This paper proposes a novel, low-profile UWB antenna for wireless body area network (WBAN) applications. The antenna has a polarization perpendicular to the body-free-space interface, which is interesting in order to minimize the coupling into the body. Its structure comprises a modified mono-cone with a top-cross-plate and is coaxially fed through the ground plane. The higher frequency band |S11| performance is due to the mono-cone while the top-cross-plate is responsible for the lower frequency band. This plate also leads to a height reduction when compared to conventional mono-cone antennas. A comprehensive parametric study is done to provide design guidelines. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the antenna operates from 3.06 to beyond 12 GHz based on |S11| ≤ -10 dB, radiates omni-directionally in the H-plane, and has a radiation efficiency over 95%. The system-fidelity factor for UWB signals is adequate for pulse transmission. Finally, the influence of the human proximity on the antenna matching was tested. Results show that its impedance is nearly unchanged as compared to free-space.

A Novel Compact CPW-Fed Polarization Diversity Ultrawideband Antenna

A new compact coplanar-fed antenna suitable for polarization diversity in ultrawideband (UWB) applications is presented. The antenna consists of two identical monopoles that are printed on a low-loss substrate with 3 mm spacing and positioned perpendicular to each other. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the proposed antenna has not only ultra-wide bandwidth ( ~115% for port 1 and ~107% for port 2), but also good port isolation above 22 dB over the entire band of interest. Moreover, radiation patterns demonstrate good orthogonal polarization operation. Furthermore, the system fidelity factor is adequate for pulse transmission with averages of 85% and 75% for port 1 and 2, respectively. Finally, the envelope correlation coefficient (ρe) has been calculated to evaluate the diversity performance. Results indicate that ρe ≤ -20 dB across the ultra-wide bandwidth. These results show the suitability of the proposed antenna for future UWB diversity applications.

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.

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.

Belt antenna for wearable applications

In this paper a microstrip fed belt antenna, using leather as substrate, was designed and tested in wearing scenario including the influence of the human user. Measurements have shown that the antenna can be used in the GSM (900 and 1800), UMTS and IEEE802.11b-g operating bands. The measured input reflection coefficient is bellow −10dB in all bands considered. It was observed that a possible contact between the belt central wire and a metal button causes no significant perturbation in the antenna performance.

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.

Ultra Wideband ring monopole miniaturization using dielectric loading sandwich

A simple miniaturization technique using dielectric loading was applied to the design of Ultra Wideband (UWB) microstrip fed ring monopoles. The method consists of gluing a commercially available substrate layer to each metallization side. Two antenna prototypes were built and tested to validate the concept. The larger prototype covers the whole UWB bandwidth with |S11| ≪ −10dB. The smaller has considerable reduced size, making it suitable for use in a Universal Serial Bus (USB) dongle. The larger structure was further investigated by testing the influence of a close metallic box on antenna matching.

Omnidirectional wrapped microstrip antenna for WLAN applications in laptop computers

An omnidirectional low profile microstrip antenna for WLAN applications in laptop computers is presented. By wrapping the patch antenna around the screen edge, very good omnidirectionality is achieved. The designed structure, fed by a microstrip inverted line, can be easily integrated inside the display plastic cover. An antenna prototype has been fabricated and tested. Good agreement has been obtained between simulations and experimental results. An adequate coverage of the whole 2.4 GHz ISM band has been achieved.