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This paper deals with the implementation of a compact frequency reconfigurable antenna in a challenging environment being embedded in a laptop. The antenna structure is designed to be restricted in a volume of 3.3 cm3 (70mm∗12mm∗4mm). The antenna structure was originally developed through EM simulations using CST Microwave Studio and later prototyped and tested in a Laptop mockup. The antenna structure presented is a frequency reconfigurable structure and provides 4 tuning states to cover the low band from 698 MHz to 960 MHz and provides an instantaneous bandwidth with good efficiency characteristics across the high band from 1710 MHz to 2690 MHz.

This paper presents a miniaturized right hand circularly polarized antenna design for operation at the GPS frequency [1575 MHz]. This antenna structure utilizes a pair of planar Isolated Magnetic Dipole [IMD] antennas collocated on a square ground plane and fed 90 degrees out of phase to generate right hand circular polarization. The antenna design provides axial ratio of less than 1.5 dB at zenith.

A dual capacitive feed antenna solution is proposed to address the new challenges, on the RF front end, that LTE Carrier Aggregation has introduced. The antenna covers the frequency bands 690 MHz to 964 MHz and 1700MHz to 2700 MHz. The antenna has two feeding elements that are capacitively coupled to the same grounded folded loop, allowing an efficient use of the total volume allocated to the antenna, and saving the need for an additional diplexer circuit.

With the growing use of M2M [Machine to Machine] communication in the industry, it has become essential to have antennas in devices that cover a wide frequency range from 700MHz to 2700 MHz and work efficiently by being impedance matched under various environmental effects. This paper proposes a closed loop impedance matched antenna system solution to tackle this challenging issue. A novel and compact plug and play solution is proposed that can include an antenna with a dynamic tuning range of up to a few 100 MHz.

We present a detailed study of two-dimensional (2D) photonic crystals based on macroporous silicon technology, showing a broad range of wavelengths accessible for applications with this material. In this work, we have reached 1.55 /spl mu/m, this certainly represents a decisive issue for this technology. First, the reflection performances of a hexagonal and a triangular lattice of air holes are compared. The triangular lattice reduces technological requirements because the complete photonic bandgap (PBG) results from the overlap of broader forbidden bands of lower order. Second, a combined experimental and theoretical study is presented of the reflection properties of a 2D photonic crystal in a three-dimensional (3D) optical environment. This reveals the critical parameters that can degrade the performances of such 2-D structures. Reflection coefficients up to 98% are obtained with optical quality interfaces. Finally, a complete PBG centered at 1.55 /spl mu/m is demonstrated with a submicrometer period triangular lattice defined by holographic lithography. The influence of the air filling factor on the band position and the interface quality is analyzed by reflection measurements. The overall results show the high flexibility of the macroporous silicon technology and its applicability to integrated optics at telecommunication wavelengths.

In this paper, we present several experimental and theoretical studies showing the feasibility of active photonic crystal controlled either by electrical elements or by light. The controllability of photonic crystals at centimeter wavelengths is proposed with the periodic insertion of diodes along the wires of a two-dimensional (2-D) metallic structure. For only three crystal periods with commercially available devices, more than 30 dB variations of the crystal transmission are predicted over a multigigahertz range by switching the diodes. From calculation models, a tight analogy is shown between these crystals and those consisting of discontinuous metallic rods with dielectric inserts. The numerical models as well as the proposed technology are validated by experimental measurements on 2-D crystals with either continuous or discontinuous metallic rods. The partial control of a 3-D layer-by-layer dielectric structure at millimeter wavelengths is also demonstrated in the second part of the work. A laser light is used to modulate the transmission level of defect modes by photo-induced free carrier absorption. The overall results are expected to contribute to further developments of switchable electromagnetic windows as well as to tunable waveguide structures in the microwave and millimeter wave domains.

An electrically small, low-profile, antenna structure suitable for mobile devices is presented. An example of GPS implementation inside a cellular phone shows high antenna efficiency and integration flexibility. High isolation is shown by little detuning from various phone holding positions and high out of band rejection. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 449–451, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20167

The far infrared behavior of doped semiconductors is dominating by the free carrier response and it is well described by the simple Drude model. As the free carriers can be photogenerated in high resistivity semiconductors, the electromagnetic response of these semiconductors can be changed, via laser excitation, from a dielectric behavior to a metallic one. Using terahertz time-domain spectroscopy, we have checked this Drude-like behavior with several silicon wafers of different doping, and with a high resistivity silicon sample photo-excited by a Ti:Sa laser beam. Then we benefited of this effect to photo-modify the transmission of a photonic band-gap crystal in the terahertz range. The photonic band-gap crystal is a woodpile structure, which exhibits a complete forbidden band around 265 GHz. Silicon- made defects are introduced in interstitial sites of the lattice of the photonic crystal in order to create a defect mode inside the photonic band-gap of the crystal. This defect mode then acts as a narrow bandpass filter at the frequency of 253 GHz. Under 400-mW laser excitation power, the resonance peak associated to the defect mode completely vanishes.

We report a low cost and material independent fabrication technique to reproduce sub-millimeter 3D photonic crystals. The crystal is made by stacking mechanically machine dielectric substrates. Interstitial defects can be introduced in the structures. This technique is illustrated by experimental studies with highly resistive silicon based crystals with and without defects. A terahertz time-domain spectroscopy set-up is used for broad band transmission characterization of the crystals. Systematic measurements of the transmission characteristics for different crystal thicknesses and incident angles were performed. A wide compete photonic band gap centered at 265 GHz with a 19 percent band-gap to mid-gap frequency ratio, and excellent filtering properties are observed with only six crystal periods. The influence of the defects was experimentally studied and an external control of their mode's transmission coefficients is demonstrated. The transmission coefficient of the defect modes is controlled by illuminating the interstitial silicon defects with a 330 mW laser beam. Numerical simulations reproduce this behavior by modeling the illumination as an increase of the defect absorption.

The authors report the fabrication of sub-millimetre three dimensional photonic crystals by a new, simple, low cost and material independent mechanical machining technique. A high quality photonic crystal was fabricated in silicon and characterised with a time extended THz spectroscopy setup. A complete bandgap was observed around 265 GHz as well as higher order bands.