A new electrically small antenna with size ka = 0.415 is presented, fabricated and measured in this work. This is intrinsically matched to 50 Ω, has omni-directional and linear-polarized radiation pattern in the horizontal plane with maximum directivity of 1.75 dBi and simulated radiation efficiency of 93%. The antenna in combination with a low-complex and co-planar rectifier with one single diode forms a high efficient and sensitive electrically small rectenna with ka = 0.53 at 868 MHz (UHF RFID-band in Europe). The latter has measured efficiency 22.5% for −19 dBm power input and sensitivity of −44 dBm (or equivalently 0.00028 μW/cm2 power density), while at 2.25 μW/cm2 is able to supply continuously, i.e., without a boost converter or use of any energy tank, a small electrical device with 118 μW. In order to increase the dc output voltage and the delivered dc power to the load for lower power density levels, rectenna-array configuration is exploited. Application to batteryless, backscatter wireless sensor node powering is discussed. Specifically, for a power density of 0.1237 μW/cm2 the RF energy harvesting system delivers 172 μW at 2.85 V every 22.5 s.
A new type of printed rectangular loop or 100-51 transmission line. The unidirectional antenna with capacitive loads is proposed for radiation pattem is achieved by introducing two -unidirectional radiation pattern production. The arrangement presented here is shown to have a current distribution with balanced magnitude and 90' phase difference on parallel radiating edges of the loop. As a result, the printed loop is equivalent to an .gaps into ;he loop in order to produce capacitive phasing elements. It is experimentally demonstrated that a front-to-back ratio of than 2o dB and a 4.5-dBi gain can be achieved.array of two dipoles with quarter-wavelength space separation and 90' phase excitation difference.
II. ANTENNA CONFIGURATIONSimulated and measured results for 1 GHz center-The geometry and optimised sizes of the frequency operation show that the new unidirectional unidirectional rectangular loop antenna are depicted printed loop antenna can achieve a front-to-hack can he easily matched. GHz. The loop is made of etched copper strips of width w=6 mm and thickness F17.5 pm printed on an RT/duroid 5880 dielectric substrate (thichess=0.254 mm, er =2.2). The antenna is centre-fed by a quafier-wavelength folded balun constructed from 5 0 0 coaxial cable.ratio of more than 20 dB, power gain of 4.5 dBi, and in l'ig. The antenna is designed to Operate at
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AbstractA novel type of microwave probes based on the loaded aperture geometry has been proposed and experimentally evaluated for dielectrics characterization and high-resolution near field imaging.Experimental results demonstrate the possibility of very accurate microwave spectroscopic characterization of thin lossy dielectric samples and biological materials containing water. High resolution images of the subwavelength lossy dielectric strips and wet and dry leaves have been obtained with amplitude contrast around 10-20dB and spatial resolution better than one tenth of a wavelength in the near field zone. A microwave imaging scenario for the early-stage skin cancer identification based on the artificial dielectric model has also been explored. This model study shows that the typical resolution of an artificial malignant tumour with a characteristic size of one tenth of a wavelength can be discriminated with at least 6dB amplitude and 50 degrees phase contrast from the artificial healthy skin and with more than 3dB contrast from a benign lesion of the same size. It has also been demonstrated that the proposed device can efficiently deliver microwave energy to very small, subwavelength, focal areas which is highly sought in the microwave hyperthermia applications.
Abstract-A super-resolution defect characterization technique based on near-field resonance reflectometry and cross-correlation image processing is proposed in this paper. The hardware part of the microwave imaging system employs a novel loaded aperture (LA) probe which allows collimation of the electromagnetic field to approximately λ/10 focal spot(s) at λ/100 to λ/10 stand-off distances, λ being the wavelength of radiation in free space. The characteristic raw image spatial resolution of the LA probe is around λ/10 in one dimension with amplitude contrast/sensitivity exceeding 10-20dB. It is demonstrated that the LA spatial resolution can be at least two times enhanced in two dimensions in the image plane using basic crosscorrelation image processing while retaining a very high level of amplitude contrast of at least 10dB.
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