This paper addresses the microwave energy harvesting on board of geostationary satellites for health satellite monitoring. To prove the feasibility of such a concept, we investigated the electromagnetic environment existing on antenna panels. Based on established cartographic maps, three designs of rectennas are proposed. Measured DC powers ranging from 0.256 mW to 1.28 mW can be harvested for electric field levels ranging from 91 V/m to 121 V/m and by using very simple and compact designs. The harvesting structures consist of only one Schottky diode per rectenna and present a total surface of 2.4 cm 2. They are suitable for powering the new generation of ultralow power transceivers, thus enabling autonomous wireless power networks for satellite health monitoring.

The design and realization of a novel wideband twolayer 4 4 Butler matrix in substrate integrated waveguide (SIW) technology are addressed. The two-layer SIW design is exploited through a two-fold enhancement approach. The two-layer topology is first explored in a simple matrix layout with minimum number of components. A space saving design is then proposed making optimum use of the two-layer topology and the SIW technology leading to a significant size reduction. A two-level, low-loss, wideband SIW transition is designed and optimized using its equivalent circuit model. The two corresponding Butler matrix prototypes are optimized, fabricated and measured. Measured and simulated results are in good agreement. Isolation characteristics better than 15 dB with input reflection levels lower than 12 dB are experimentally validated over 24% frequency bandwidth centered at 12.5 GHz. Measured transmission magnitudes and phases exhibit good dispersive characteristics of 1 dB, around an average value of 6.8 dB, and 10 with respect to the theoretical phase values, respectively, over the entire frequency band. The impact of the measured transmission phases and magnitudes on the radiation pattern of a 4-element antenna array is also investigated.Index Terms-Beam forming networks, Butler matrix, multilayer, substrate integrated waveguide (SIW) technology.

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Abstract-A novel design of a highly sensitive wireless passive RF strain transducer is presented based on a patch antenna loaded with an open loop that is capable of sensing strain independently in two directions. An original idea of utilizing a cantilever at the gap of the open loop significantly improves the sensitivity of resonant frequency shifts. The frequency shifts in two distinct resonant modes are detected based on two dominant orthogonal modes of the patch resonators. In measurements, the prototypes achieved a sensitivity of 2.35% frequency shift per 1% strain, more than twice that of existing strain transducers of the same class. In simulations, the new design achieved a theoretical sensitivity up to four times as high as existing designs of RF passive wireless strain transducers. The ground plane allows for the sensitivity of the sensor to be independent from the applied surface. An implementation example of the passive remote sensing system based on the proposed strain transducer is also discussed as a proof-of-concept case. Based on calculations, the interrogation method in the example shows a radar cross section fluctuation of 3.8 dB corresponding to the strain induced at the sensor.

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The direction finding performances of a novel passive, wideband and radiation pattern reconfigurable vector antenna are reported. Accurate estimation of the direction of arrival of incoming electromagnetic fields across the 3-D half-space is obtained over a 1.69:1 impedance bandwidth from the radiation pattern reconfigurability of a 4-port vector antenna. This antenna consists of only two orthogonal and co-located semi-circular arrays of Vivaldi antennas. Due to its reconfigurability, more radiation patterns can be used in addition to those commonly employed in standard vector antennas to estimate the direction of arrival of incoming electromagnetic fields. A new method based on the Cramer-Rao lower bound is proposed in order to select the radiation pattern diversity that improves the estimation accuracy across the overall bandwidth. Measured and simulated results are found in good agreement. The present study brings a further step towards developing new concepts of reconfigurable vector antennas.

Abstract-This article presents an equivalent electrical circuit for designing Radio-Frequency MEMS-controlled planar phase shifter. This kind of phase shifters has recently been incorporated in reconfigurable reflectarrays. The proposed equivalent circuit depends on the number, the ON/OFF state and the locations of the switches inside the unit cell. Such equivalent circuit is used for determining, with a little computational effort, the two important design parameters i.e., the number and the locations of RF-MEMS switches in the phase shifter cell. These two design parameters then allow a designer to design a phase shifter cell having a linear distribution of a given number of phases over 360 • phase range at a single desired frequency.

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