Sébastien Palud

A Novel Broadband Eighth-Wave Conical Antenna

A novel antenna is composed of a conical monopole with metallic parasitic elements and a capacitive disk placed above a ground plane. A dielectric substrate is used in order to optimize the performances. This antenna provides broadband characteristics and omnidirectional radiation patterns over the whole bandwidth with a height limited to a one eighth wavelength associated to the lowest frequency. Simulations and experiments demonstrate that this structure exhibits a 2.9:1 impedance bandwidth with VSWR below 2:1 and very good radiation patterns and gain in spite of a size extremely reduced.

Scattering of Spherically and Hemispherically Stratified Lenses Fed by Any Real Source

An analytical method to compute the scattering of spherically and hemispherically stratified lens antennas is described. The expansion of any real source on spherical wave functions is detailed and validated by comparison to commercial software simulations and measurements at both 50 GHz and 77 GHz. A mode matching technique (MMT) based on spherical wave functions is first used to analyze the scattering by spherically stratified lens antennas. The far field patterns and directivity obtained are in excellent agreement with commercial software simulations and measurements for a six-shell Luneburg lens at 6 GHz. This MMT is then extended to hemispherically stratified lens antenna analysis. Its validation is also carried out by comparisons to both commercial software and measurements for a three-shell half Maxwell fish-eye lens fed by an open-ended waveguide at W-band. The expansion on spherical modes gives direct access to the field everywhere. To highlight the progressive focusing effect of inhomogeneous lens antennas, the electric field is mapped in terms of magnitude and phase in the neighborhood of the entire structure. One of the originalities of this work is the quantification of the reaction created by the scatterer on the feed. Narrowing the scatterer to a stratified lens does not affect the generality of the presented procedure. While providing controlled accuracy, the MMT tremendously reduces both computation time and memory load in comparison to commercial software.

Wideband Omnidirectional and Compact Antenna for VHF/UHF Band

A wideband omnidirectional and compact (WIBOC) antenna is proposed in this letter. The antenna is constructed with a combination of an upper metallic plane with an elliptic shape, a rectangular metallic plane placed underneath, and a discone monopole antenna used as an excitator located between these metallic planes. This antenna provides broadband characteristics and omnidirectionnal radiation patterns in the azimuth plane over the whole bandwidth with a height limited to λLF/29, where λLF is the lowest frequency of the operating band.

Circuit Modeling of a Small Broadband Conical Antenna

Equivalent circuit modeling methodology is proposed in this letter for a small broadband antenna composed of a conical monopole with metallic parasitic elements, a capacitive disk, and a dielectric substrate around the feed region. This omnidirectional antenna provides broadband performances over the whole bandwidth with a height limited to a one-eighth wavelength associated to the lowest frequency. The proposed modeling procedure presents excellent agreement with electromagnetic and experimental results.

Millimeter Wave Reconfigurable Antenna Based on Active Printed Array and Inhomogeneous Lens

This paper deals with radiation pattern reconfigurable antenna in millimetre wave range. An active printed antenna array is designed in 24 GHz band and feed an inhomogeneous lens (Half Maxwell Fish Eye) to obtain reconfigurable patterns and in particular sectorial and directive cases. In the first part, the authors describe a four patches multilayer active array which allows achieving radiation pattern control by associating a commutator to each element and by changing the fed patches number. In a second part, this array feed an inhomogeneous lens to shape radiation pattern.

A tactical broadband omnidirectional antenna

In this paper, a vertically polarized broadband antenna with an adjustable shape for specific applications in the VHF and UHF bands is proposed. This antenna is a compact monopole with a pseudo-conical shape set on a rectangular ground plane, partially made of wire netting. A part of the radiating element is made of metallic pipes which are bent to minimize the height of the shape without deteriorating the impedance matching. The bent pipes and the wire netting of the ground plane can be removed in order to dramatically reduce the size of the antenna for applications in high-frequency range. As a result, two compact structures relatively to the wavelength are obtained with a vertical size of respectively lambdaLF/6.25 for the low-frequency mode (100-500 MHz) and lambdaLF/7.2 for the high-frequency mode (415-915 MHz) (lambdaLF is the wavelength associated to the lowest frequency of the covered bandwidth). The structures operate with good gain and radiation patterns in both E- planes and H-planes.

Measurements of Vertically Polarized Electromagnetic Surface Waves Over a Calm Sea in HF Band. Comparison to Planar Earth Theories

Radio communication over Earth along mixed-paths in the HF band is a relevant subject today. In this communication, we present measurements of electric field propagating over sea water in HF Band compared to K.A. Norton, R.W.P. King and G. Millingtons theories, thanks to a reliable measurement setup. The transmitting antennas are located on the coast while the receiver antenna is installed on a boat steering a constant course. The electric field measurements are carried out with a loop antenna and we measured the field strength attenuation versus distance between the transmitter and the boat along a sea water path. In order to take into account the media change (the coast and the sea water), Millingtons solution has been added to Kings and Nortons theories with the planar Earth model. The measurements performed at three frequencies (10 MHz, 20 MHz and 30 MHz) and the calculations are in a good agreement. At 10 MHz, the “smoothly” attenuation is shown and is very well correlated with the theory. The EM field decrease as 1/d2 has been clearly observed at 20 MHz and 30 MHz.

A Novel Reduced-Height Broadband Monopole

This paper presents a broadband omnidirectional vertically polarized antenna of only a one eighth wavelength associated to the lowest frequency. This antenna is composed of a conical monopole with metallic parasitic elements, a capacitive disk and a dielectric substrate placed above a square ground plane. This structure provides broadband performances and omnidirectional radiation patterns over the whole bandwidth. Simulations and experiments demonstrate that this structure exhibits a 2.9:1 impedance bandwidth with VSWR below 2:1 and very good radiation patterns and gains in spite of a height extremely reduced.

Intermodulation distortion and compression point measurement of active integrated antennas using a radiative method

In this paper, a measurement procedure allowing the characterization of active integrated antennas in terms of intermodulation distortion and compression point inside of a parallel plate cell is presented. The validity of the radiative measurement is shown and compared to the traditional guided procedure. A good agreement between the two methods shows that this approach allows the evaluation of the overall linearity behavior of arbitrary complex integrated antennas and can serve as a complementary tool when the traditional guided method cannot be applied.

Investigation on an Effective Magnetic Permeability of the Rod-Shaped Ferrites

In this paper, we provide full-wave numerical results concerning the effective magnetic permeability of the rod-shaped ferrites which is useful in the calculation of the inductance or the efficiency of ferrite rod antennas. This study covers the circular cross-section ferrites with a centered winding fitting the diameter of the rod. A careful attention is taken to the simulation model, and obtained results are in better agreement with the measured coils than existing solution published earlier.