Nonconforming implementations of the electric-field integral equation (EFIE), based on the facet-oriented monopolar-RWG set, impose no continuity constraints in the expansion of the current between adjacent facets. These schemes become more versatile than the traditional edge-oriented schemes, based on the RWG set, because they simplify the management of junctions in composite objects and allow the analysis of nonconformal triangulations. Moreover, for closed moderately small conductors with edges and corners, they show improved accuracy with respect to the conventional RWG-discretization. However, they lead to elaborate numerical schemes because the fields are tested inside the body, near the boundary surface, over volumetric subdomains attached to the surface meshing. In this letter, we present a new nonconforming discretization of the EFIE that results from
testing with RWG functions over pairs of triangles such that one triangle matches one facet of the surface triangulation and the other one is oriented perpendicularly, inside the body. This “tangential-normal” testing scheme, based on surface integrals, simplifies considerably the matrix generation when compared to the volumetrically tested approaches.
Imbert, M.; Papió, A.; de Flaviis, F.; Jofre, L.; Romeu, J. IEEE antennas and wireless propagation letters Vol. 14, p. 342-345 DOI: 10.1109/LAWP.2014.2363596 Data de publicació: 2015-01-01 Article en revista
In this letter, a practical fabrication of a novel inhomogeneous gradient-index dielectric flat lens for millimeter-wave applications is presented. A previous theoretical design of a dielectric flat lens composed of different permittivity materials is now modeled and analyzed for a practical prototype fabrication and performance evaluation at 60 and 77 GHz. The measurement results at 60 GHz show that with the novel gradient-index dielectric flat lens antenna prototype, we can achieve up to 18.3 dB of broadside gain, beam-steering capabilities in both planes from -30 degrees to +30 degrees with around 15 dB of gain, and up to +/- 45 degrees with around 14 dB of gain, with low sidelobe levels. At 77 GHz, the performance evaluation shows that we can obtain up to 18.9 dB of broadside gain, beam-steering capabilities in both planes from -30 degrees to +30 degrees with around 17 dB of gain and low sidelobe levels, and up to +/- 45 degrees with around 15 dB of gain. This novel design leads to a low-cost, low-profile, and lightweight antenna solution, easy to integrate in a compact millimeter-wave wireless communication system.
Llatser, I.; Mestres, A.; Abadal, S.; Alarcon, E.; Lee, H.; Albert Cabellos-Aparicio IEEE antennas and wireless propagation letters Vol. 14, p. 350-353 DOI: 10.1109/LAWP.2014.2362194 Data de publicació: 2015-01-01 Article en revista
Graphene is enabling a plethora of applications in a wide range of fields due to its unique electrical, mechanical, and optical properties. In this context, graphene antennas are envisioned to enable ultra-high-speed wireless communication in short transmission ranges, due to both their reduced size and their radiation frequency in the terahertz band. Despite its high potential bandwidth, the terahertz band presents several phenomena that may impair the communication and reduce the achievable data rate. In this letter, the phenomenon of molecular absorption is quantitatively analyzed, evaluating the scalability of both time-and frequency-domain performance metrics with the transmission distance. The results of this analysis show that molecular absorption creates a tradeoff between the achievable throughput and the maximum transmission distance at which short-range terahertz wireless communications can successfully take place.
Leonardo F. Yepes; Covarrubias, D.; Miguel A. Alonso; Ferrús, R. IEEE antennas and wireless propagation letters Vol. 13, p. 185-188 DOI: 10.1109/LAWP.2014.2301012 Data de publicació: 2014-01-16 Article en revista
In this letter, a new hybrid technique to synthesize sparse linear arrays is proposed. This technique is based on the combination of two methods. As a first method, a deterministic synthesis algorithm is used to resolve the nonuniform amplitude excitations and the antenna element locations. Then, the second method is an iterative optimization scheme that computes the phase of the excitation currents. This approach is proven valid to properly match diverse beam patterns (narrow-beam, flat-top, and square-cosecant) with sparse linear arrays. Three numerical experiments are reported that show the performance of the proposed technique and compare it to other outstanding methods available in the literature.
The maximum gain in on-frequency repeaters is limited by the isolation level between their two antennas due to close-loop stability conditions. In this letter, a novel pixel-layer isolator for tunable on-frequency repeaters is presented. The scattered field of the reconfigurable pixel layer is used to dynamically minimize the mutual coupling between the antennas. Insight is given on the linkage between coupling and reflection coefficients, and a useful design procedure is proposed. The optimized pixel repeater can tune the operating frequency over a 40% range, with tunable instantaneous bandwidth (1%-3%) and achieving a reliable isolation of 50 dB. The repeater has a radiation efficiency of 93% and a constant radiation pattern for the different configurations. Good agreement is obtained between simulations and measurements.
Mopidevi, H.; Damgaci, T.; Rodrigo, D.; Jofre, L.; Cetiner, B. IEEE antennas and wireless propagation letters Vol. 13, p. 1231-1234 DOI: 10.1109/LAWP.2014.2332614 Data de publicació: 2014-01-01 Article en revista
The design, fabrication, and characterization of a frequency-reconfigurable antenna for the United States Public Safety (PS) wireless communication applications are presented. This antenna is quad-band operating in the PS bands-220, 470, 800, and 4960 MHz. It is an electrically small antenna with calculated ka similar to 0.55 at 220 MHz. The antenna has two reconfigurable modes of operations. In mode 1, 220-, 470-, and 4960-MHz bands are excited. Mode 2 provides operation over 800- and 4960-MHz bands. This dynamic frequency reconfiguration is accomplished by two radio frequency microelectromechanical systems switches strategically located within the antenna architecture. The measured and simulated results for impedance and radiation characteristics agree well, where similar to 3%, 4%, 21%, and 17% fractional bandwidths have been measured in the four bands, respectively, while maintaining integrity of radiation pattern.
Mopidevi, H.; Hurneli, H.; Cagatay, E.; Biyikli, N.; Imbert, M.; Romeu, J.; Jofre, L.; Cetiner, B. IEEE antennas and wireless propagation letters Vol. 13, p. 828-831 DOI: 10.1109/LAWP.2014.2319242 Data de publicació: 2014-01-01 Article en revista
The design, microfabrication, and characterization of a broadband patch antenna capable of covering the entire IEEE 802.11ad (WiGig) frequency band (57-66 GHz) are presented in this letter. A conductor-backed (CB) coplanar waveguide (CPW)-fed loop slot couples the energy to the patch antenna, resulting in a broad bandwidth. The feed circuitry along with the loop is formed on a quartz substrate (epsilon(r) = 3.9, tan delta = 0.0002 at 60 GHz), on top of which an SU-8-based three-dimensional (3-D) structure with air cavities is microfabricated. The patch metallization is deposited on top of this 3-D structure. While the main role of the structure made out of SU-8 material is to provide a mechanical support for the patch metallization, the antenna takes advantage of the air cavities underneath, thus resulting in an antenna substrate with a very low loss. This, in turn, improves the overall antenna performances. The simulated and measured impedance characteristics agree well, showing similar to 15% bandwidth. Also, the radiation pattern results demonstrate the integrity of radiation pattern with reasonably constant gain values (average similar to 6.4 dB) in the broadside direction over the entire WiGig band.
Alonso Del, M.; Llombart, N.; Chattopadhyay, G.; Lee, C.; Jung, C.; Jofre, L.; Mehdi, I. IEEE antennas and wireless propagation letters Vol. 12, p. 84-87 DOI: 10.1109/LAWP.2013.2240252 Data de publicació: 2013-01-15 Article en revista
A silicon lens antenna suited for future integrated terahertz arrays has been proposed recently. The antenna consists of an extended hemispherical silicon lens fed by a leaky-wave waveguide feed. The primary advantage is that the antenna is compatible with silicon micro-fabrication techniques as only a small sector of the lens is actually used. Moreover, it can be easily integrated with other silicon micromachined front-end components. In this letter, the design and optimization details of such a micro-lens antenna is presented. The design is validated with a set of measurements at 550 GHz from a prototype that has been fabricated using laser micro-fabrication.
Zohur, A.; Mopidevi, H.; Rodrigo, D.; Unlu, M.; Jofre, L.; Cetiner, B. IEEE antennas and wireless propagation letters Vol. 12, p. 72-75 DOI: 10.1109/LAWP.2013.2238882 Data de publicació: 2013-01-09 Article en revista
Diaz, E.; Grau, A.; Rodriguez, J.; de Flaviis, F.; Jofre, L. IEEE antennas and wireless propagation letters Vol. 10, p. 1239-1242 DOI: 10.1109/LAWP.2011.2174330 Data de publicació: 2011-11-02 Article en revista
A novel isofrequency-reconfigurable RF repeater operating at 4.5 GHz is presented. The repeater uses a total of
eight reconfigurable parasitic dipole elements to enhance and reconfigure the isolation level between the receiving (Rx) and the transmiting (Tx) antennas. The reconfiguration of the parasitic
dipoles is achieved using p-i-n diodes as microwave switches to change their electrical length. The parasitic dipoles are dynamically reconfigured into an optimum configuration state (to make them work as either director or reflector elements) to enhance and recover the perturbed isolation level when an obstacle is placed
near the repeater, while maintaining good impedance matching and pointing the maximum of the radiation pattern at the Rx port
toward a specific base station.
Mopidevi, H.; Rodrigo, D.; Kaynar, O.; Jofre, L.; Cetiner, B. IEEE antennas and wireless propagation letters Vol. 10, p. 1224-1227 DOI: 10.1109/LAWP.2011.2174023 Data de publicació: 2011-10 Article en revista
In this letter,we present a concentric annular-ring microstrip
antenna that covers the bands of Galileo (E5a, E5b, E1, E2,
L1), GPS (L1, L2, L5), and GLONASS (L1, L3). This microstrip
antenna is fed by four apertures that improve the coupling. Broadband
phase shifters and Wilkinson power combiners are used to
generate the required circular polarization.
A dual-band enhanced-bandwidth microstrip antenna
is presented with a frequency separation of f2/f1=1.37. In
order to achieve the dual-frequency operation, a rectangular patch
antenna is reactively loaded with a stub placed along one of the
radiating edges. Then, the bandwidth is enhanced using a stacked
parasitic technique, whereas the matching and radiation characteristics
are kept constant along each band and similar at two bands.
Fernández, M.; García, F.; Gonzalez, J.; Romeu, J.; Rius, J. IEEE antennas and wireless propagation letters Vol. 2, p. 238-241 DOI: 10.1109/LAWP.2003.819694 Data de publicació: 2003-11 Article en revista
A multi-objective genetic algorithm (GA) has been
applied in conjunction with the numerical electromagnetic code
(NEC) to the optimization of wire pre-fractal Koch-like antennas
in terms of bandwidth, efficiency, and electrical size. Their performance
is compared to that of other nonfractal designs.
We present a small-size broadband antenna specifically designed for integration with RF/wireless communication systems. The antenna is built on a printed circuit board and fed by a coplanar waveguide (CPW) to allow further easy integration with active and passive components of the communication system. The compact architecture of the antenna is suitable for multi-element scenarios for diversity implementations. Theoretical and experimental results showing impedance and radiation characteristics for both single- and multi-element antenna are given and discussed
The performance of space-filling curves used as small
antennas is evaluated in terms of quality factor and radiation efficiency.
The influence of their topology is also considered. Although
the potential use of these curves for antenna miniaturization their
behavior is not exceptional when compared with other intuitivelygenerated
Puente, C.; Borja, C.; Anguera, J.; Delbene, N.; Soler, J. IEEE antennas and wireless propagation letters Vol. 2, num. 1, p. 36-39 DOI: 10.1109/LAWP.2003.811325 Data de publicació: 2003 Article en revista