Milan Polivka

UHF RF Identification of People in Indoor and Open Areas

The performance of an ultra-high-frequency RF identification (ID) system operating at 869 MHz, intended for the ID of persons in both indoor and open areas, has been validated using the propagation models, as well as the series of practical measurements. A two-ray propagation model and the 3-D ray-tracing model were used for calculations of all important system parameters in open and indoor areas, respectively. For the application mentioned above, a novel (electrically small and, at the same time, low-profile) wearable TAG antenna was designed. It was used in order to carry out the necessary tests as well. The antenna in question is based on an artificial-like surface. The latter provides an important screening effect and avoids detuning. Another virtue of the surface used is represented by the fact that it ensures the minimum loss of the antenna efficiency (resulting from the presence of a nearby human body). The simulations and measurements show that the optimized system can guarantee a reliable ID at distances up to 9 m in open areas and up to 16 m in corridors.

A Dual Band Leaky Wave Antenna on a CRLH Substrate Integrated Waveguide

This communication presents the results of an investigation of a new version of a leaky wave antenna designed on a CRLH substrate integrated waveguide. The antenna operates in two frequency bands and its main beam can be steered from backward to forward direction by changing the frequency. The antenna structure is planar and can be fabricated by a standard PCB technology, so it is suitable for mass production. An efficient method for determining the complex dispersion characteristic of periodic 1D structure is proposed.

A Novel Microstrip Patch Antenna Miniaturization Technique: A Meanderly Folded Shorted-Patch Antenna

A novel microstrip patch antenna miniaturization technique based on multilayer meanderly folded shorted- patch structure is introduced. The technique enables a decrease of the original shorted (quarter-wavelength) patch dimension by the factor l/N where N is a number of vertically placed patch plates above the ground plane while maintaining a quarter wavelength resonant length. The antenna operational principle is explained via both E-field distribution inside the antenna structure and the surface current distribution on the conductive parts of the antenna. Two variants of the miniaturized patches with the footprint dimension approx. ~ lambda0/12 and lambda0/16 are simulated, realized and measured.

Collinear Microstrip Patch Antennas

The original idea of the collinear principle in the antenna design comes from Franklin (Franklin, 1925). He faced the problem of resonant long wire antennas. In principle, the standing wave current distribution on the long straight wire produces n radiation lobes of the same level, depending on the number n of half-wave antenna sections. Employing nonradiating quarter-wave stubs Franklin converted the original out-phase current distribution into an in-phased distribution of currents on collinear segments (represented by solid red arrows in Fig. 1), thus producing only one major radiation beam. A key advantage of such arrangement is represented by the high gain of the antenna with the properties of series antenna array, whereas the simplicity of the single feeding point is maintained. All antenna structures based on this principle are known as collinear arrays (CoA). The latter are composed of in-phase fed radiating elements that lie in the straight line. Their radiation is typically broadside and perpendicular to the axis of collinear elements. Since Franklin’s times many collinear antenna structures have been proposed. The principle representatives of the CoA are described later on.

Impedance Properties and Radiation Efficiency of Electrically Small Double and Triple Split-Ring Antennas for UHF RFID Applications

This letter is targeted at investigation of electrically small planar antennas, formed by double and triple split rings that are intended to serve as tag antennas operated within the European UHF RFID band. An extensive systematic study of possible geometrical configurations demonstrates the range of their achievable input impedances (complex conjugate to typical UHF RFID integrated circuits) in the case that both structures electrically decrease below the limit for electrically small antennas, i.e.,

Matching Technique for an On-Body Low-Profile Coupled-Patches UHF RFID Tag and for Sensor Antennas

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Improvement in Robustness and Recognizability of RCS Response of U-Shaped Strip-Based Chipless RFID Tags

. The advantage of the triple split-ring version over the standard double split-ring one consists in reduction in its electrical size and concurrent maintenance of the required range of input impedances and high radiation efficiency. Samples of both structures were manufactured and measured, and their electrical properties were critically compared.

Stepped Impedance Coupled-Patches Tag Antenna for Platform-Tolerant UHF RFID Applications

This paper introduces a novel impedance matching technique for extremely low-profile on-body UHF RFID tag antennas based on coupled shorted-patch antennas. The approach employs a novel arrangement of comb-notches perpendicular to the central radiation slot that excites the close higher order mode that affects the field distribution of the fundamental mode and sets the input impedance to the required complex values of UHF RFID chips over the range of 5-50 Ω for the real part and 100-200 Ω for the imaginary part, or directly to 50 Ω impedance. A set of parametric studies shows the flexibility of the proposed technique for achieving complex input impedances. To verify the proposed technique, we have developed and measured two antenna samples of relative size 0.3 × 0.17 × 0.0022λ0. A first antenna is matched to 50 Ω, and is intended to be used as an on-body antenna sensor for mapping the received signal strength in applications of the European UHF RFID band. The second antenna operates as an RFID tag antenna with input impedance in Zin = 22 + j195 Ω, and reaches a read range of 7.3 m.

A dual band SIW leaky wave antenna

This letter presents significant improvement in robustness and recognizability of radar cross section (RCS) response of the two topologically rearranged 20-bit U-shaped strip-based tags for spectral signature-based chipless RFID systems. The space rearrangement of individual tag scatterers in the array reduces the interelement mutual coupling and, thus, significantly enhances the frequency and amplitude robustness of their RCS. In comparison to the original arrangement of scatterers, the measurement of tags designed for 2-4-GHz frequency band showed a significantly improved homogeneity of the RCS curve, which results in a more reliable recognition of coded information.

Planar version of Collinear Microstrip Patch Antenna

We introduce a low-profile platform-tolerant UHF radiofrequency identification (RFID) tag antenna composed of a pair of three-step impedance sections of shorted patches coupled by a slot, which is differentially fed by an RFID chip. Its input impedance is analytically investigated using transmission line (TL) modeling. A further set of parametric studies using electromagnetic simulation shows good flexibility for achieving the required complex input impedance for typical UHF RFID chips. The selected antenna topology has been manufactured and measured, and good agreement with the analytical values has been found.