Benito Sanz-Izquierdo

Substrate integrated folded waveguides (SIFW) and filters

A substrate integrated folded waveguide (SIFW), integrated transition to shielded stripline and a SIFW filter are demonstrated and shown to be in good agreement with X band measurements. Both the filter and waveguide are considerably smaller than their unfolded counterparts. Furthermore, the filter response is defined purely in terms of a photolithographically etched plane.

Cylindrical Slot FSS Configuration for Beam-Switching Applications

A novel design for a beam-switching antenna using active cylindrical slot frequency selective surface (ACSFSS) is presented. The antenna system is composed of an omnidirectional monopole antenna and the ACSFSS, which employs a new technique of switching slot arrays. The ACSFSS is made up of 12 columns with 8 slots each, dividing the cylinder by 30°. To steer the beam of the antenna the diodes are set off and on, so that the radiation pattern of the antenna is determined by the number of off state columns. To estimate the general dimension of the cylindrical FSS, an equivalent metallic reflector is introduced and optimized, and then parametric studies for the unit cell dimensions are discussed. The fabricated prototype works within the WLAN band, centered around 2.45 GHz, and can agilely select either a narrow-beam or wide-beam operating mode. Simulation and measurements confirm the operation of the ACSFSS antenna, with good matching and gain observed. In particular, the narrow-beam mode -3 dB beamwidth is 47° which offers enhanced angular resolution compared with other reported beam-sweeping work.

Singly and Dual Polarized Convoluted Frequency Selective Structures

Convoluting the elements of frequency selective surfaces produces resonating structures with very small unit cell dimensions. This feature is attractive when the FSS is to be used at low frequencies, mounted on a curved surface, or when placed in the proximity of compact radiators. The characteristics of single and dual polarized convoluted FSS are analyzed and measured. The development of novel convoluted elements derived from the square loop slot is traced and their performance is examined. A novel technique of interweaving convoluted loops allows for further cell size reduction, while increasing the passband width, introducing flexibility in wideband FSS design, particularly for tailoring the electromagnetic architecture of buildings, and mobile communications in the built environment. Simulated transmission responses of the convoluted structures are in good agreement with the measurements.

Dual-Band Tunable Screen Using Complementary Split Ring Resonators

Active frequency selective surfaces (FSS) based on slot-form split ring resonators are described. Switching and tuning have been achieved using two different biasing circuit configurations. The first design switches ON and OFF the two concentric rings separately, producing four distinct transmission responses. The second design is able to vary the capacitance of the two split rings, allowing independent dual-band frequency tuning. The active FSS incorporate commercially available, low cost, surface mount switched PIN diodes and varactor diodes. The operation of the surfaces covers a wide band frequency range within the UHF spectrum, which is desirable for applications such as the modification of the EM architecture of buildings. Measurements compare well with the simulations.

Single and double layer planar multiband PIFAs

A compact multiband planar inverted-F antenna (PIFA) suitable for distributed radio-over-fiber repeater networks is modified into a planar structure. It is shown that the planar antenna performance is not degraded with respect to the original PIFA and further, a two layer design is demonstrated to offer improved feed matching. The European bands for GSM, DCS-1800, DECT, UMTS, Bluetooth and HiperLAN2 are all covered. A model of the antenna is introduced as a first stage to developing an equivalent circuit

UWB wearable button antenna

A UWB antenna based on button structures will be presented in this paper. The antennas use the wearable metallic button features and its bandwidth characteristics to create body-centric UWB monopole antennas. The antenna resulted is a rigid wearable antenna structure which is able to operate within the 3.1 GHz to 10.6 GHz bandwidth required for UWB communication systems. Good omni-directional pattern were obtained for the antenna which is desirable for transmission with other wearable devices located across the body.

Dual Polarized Reconfigurable Frequency Selective Surfaces

Novel band-stop active frequency selective surfaces (FSS) capable of modifying their response for different polarizations are proposed. Geometries based on full rings, and split rings are employed. The designs using full rings are able to tune over a wide frequency range while designs using split rings tune in a narrow frequency band. Both structures use a new biasing methodology which allows independent control of rows and columns of FSS arrays, therefore permitting independent modification of the transmission responses at the vertical and horizontal polarizations. Convoluting the shape of the elements significantly reduces the sensitivity to angle of wave incidence. The aim is to demonstrate a technology that could be used for various applications including modification of the electromagnetic architecture of buildings and the control of electromagnetic wave propagation to improve the efficiency of radio spectrum use. The surfaces incorporate commercially available, low cost, varactor diodes and surface mount resistors. Theoretical and experimental results confirm the operation of the surfaces within the UHF frequency band.

3-D Printing of Elements in Frequency Selective Arrays

3-D printing is a technology that enables the fabrication of complex objects directly from a digital model. Folding the elements of Frequency Selective arrays in three dimensions gives a significant reduction in the resonant frequency for a given cell dimension, and such structures are candidates for additive manufacture. The aim in this paper is to demonstrate by example the development of novel electromagnetic structures that could be fabricated in parallel and integral with the additive manufacture of buildings, for electromagnetic architecture control. The principle is illustrated with two new geometries based on dipole and loop elements. The cores of these structures were fabricated with a 3-D printer that uses a plaster-based material. Theoretical and experimental results confirm the operation of the surfaces within the UHF frequency band.

Switchable Frequency Selective Slot Arrays

A switchable frequency selective surface (FSS) made of square loop slots and PIN diodes connected to a novel separate biasing circuit is presented. The structure uses a very thin, flexible substrate sandwiched between two physically independent metallic layers to create the active filter. An application is the modification of the EM architecture of buildings, where propagation could be controlled using active FSS. The relatively small number of elements employed creates a compact FSS structure which could fit in an aperture within a wall of a building. The Fabry-Perot approach is used to design a cascaded version for improved filter selectivity.

A Dual Band Belt Antenna

A novel wearable antenna for wireless communications is presented in this paper. This paper has discussed the possibility of employing a belt buckle as an antenna, bringing benefits such as removability and the ability to hand portable wireless devices from the belt itself. The antenna consists of a belt buckle, hinge, denim waist band and electrical connections. The antenna was fed by a microstrip transmission line on the denim substrate with the antenna placed on the other side of the textile band. The prototype achieves wide band, dual frequency operation and is able to cover the 2.45GHz and 5.25 GHz bands necessary for Bluetooth/WLAN and IEEE 802.11 standards.