Davor Bonefačić

Considerations on Embroidered Textile Antennas for Wearable Applications

Planar inverted-F antennas (PIFAs) made of woven conductive textiles and of patterns embroidered with conductive threads are investigated. The influence of conductive thread density on antenna properties is considered in both cases. The effect of lockstitch on antenna resonant frequency is quantified. A metallic button is proposed as the transition between textile antennas and classical circuits. A full-textile prototype of a PIFA is designed and shown to operate properly in the ISM 2.4 band.

Modified rectangular patches for self-oscillating active-antenna applications

Two modifications to a rectangular-patch antenna, suitable for the integration of active devices, are presented. In the first modification, the impedance inverter was placed in the rectangular opening formed by removing the central part of the patch. This modification allows optimal matching of the active device by changing the position, width, and length of the impedance-line transformer. An oscillating antenna, using this modified patch and a Gunn diode, showed a high EIRP, higher spectral purity, and substantially lower cross-polarization levels, in comparison with the reference active antenna with an unmodified patch. Because of the higher overall Q, this modification is recommended for active-antenna applications with active devices that have a narrower negative-resistance bandwidth. In the second modification, an active device (Gunn diode) was integrated directly into a rectangular opening inside the patch, without the use of a line transformer. This reduced the overall Q of the antenna, thus allowing wide-band frequency tuning by changing the bias voltage. A clear spectrum, with no spurious components of the free-running oscillating antenna, was observed. Radiation patterns in the E and H planes were measured. Low levels of cross-polarization, as for the first modification, were obtained. Injection-locking properties were investigated throughout the tuning range. A relatively wide locking range, with a good locking gain, was achieved. Such a miniaturized wide-band VCO antenna is applicable for integration in injection-locked active arrays, and spatial power combiners.

ENZ-based shortened horn antenna - an experimental study

Recent numerical study predicted phenomenon of a gain increase of a shortened horn antenna with the help of embedded double-thin-wire ENZ metamaterial slab. Here, we perform an experimental investigation of shortened horn antenna (length of which spans 52% of the length of optimal horn) with much simpler single-wire ENZ slab operated in 10 GHz band. Measurements revealed gain increase of more than 2 dB (comparing to the gain of a bare shortened horn) in 12% fractional bandwidth, with return loss better than -13 dB.

Modified Rectangular Patch Radiator for Microstrip Active Antennas

The applicability of a modified rectangular microstrip patch radiator for active antenna with one-port active element has been demonstrated. The modified rectangular patch antenna, designed for the operating frequency of 3.4 GHz, was manufactured and tested. The inverter line was placed inside the rectangular opening in the central part of the patch. The active patch element for the 9.1 GHz frequency was realized. Co-polar and cross-polar radiation patterns, spectral purity and EIRP have been measured. Oscillating antenna using modified patch showed a higher spectral purity and substantially lower cross-polar levels in comparison with the active patch antenna realized with unmodified rectangular patch.

Numerical and experimental investigation of horn antenna with embedded ENZ metamaterial lens

Recent numerical study indicated possibility of use of a double thin-wire metamaterial slab as a flat lens that can be embedded into a horn antenna. This led to the construction of the horn, the gain of which is almost equal to the gain of an optimal horn across the moderate bandwidth, but with the substantially shorter length (down to 52% of the original length). Here, we perform both numerical and experimental investigation of such shortened horn antenna operating in 10 GHz band. Simulation showed that both the single thin-wire media and double thin-wire media indeed increase the gain of the shortened horn antenna by 2 dB in 10% fractional bandwidth with return loss better than -13 dB. Qualitatively similar results were obtained for the lens made out of fictitious continuous ENZ material with Drude dispersion model, which indicates that theory of the continuous media can be used for the initial design. Finally, measurements of the gain of experiential antennas verified existence of the phenomenon of gain increase.

The circularly polarized cylindrical patch

The paper presents a new type of antenna with a dipole-like radiation pattern and circular polarization. The antenna is a cylindrical patch antenna fed by a coaxial line, with a special geometry which generates the circular polarization. The configuration was optimized so it would generate the minimum axial ratio in the azimuthal plane where the pattern is omnidirectional. The antenna proposed is a simple and inexpensive solution for any wireless communication system where omnidirectional pattern and circular polarization are required.

Textile antennas for on-body sensors

Guidelines for modification of conventional antenna design to yield efficient operation in body-centric environment are presented. The interaction of the antenna and human body is investigated by modeling the wave propagation around torso. Two types of wearable antennas based on modifying quarter-wavelength shorted patch are designed and manufactured, while integration of the antennas and RFID sensors into the everyday clothes is addressed.

Voltage controlled self-oscillating microstrip patch antenna

An active rectangular microstrip patch antenna for quasi-optical power combining arrays is hereby described. Part of the patch metallization was removed to form a rectangular opening where a Gunn diode was placed. This modification lowered the Q and allowed the oscillating patch to perform VCO capabilities. Patch parameters were optimized using a moment method procedure. A tuning range of more than 300 MHz at 9.85 GHz and EIRP of 208 mW was obtained. A clear spectrum with no spurious components of the free running oscillating antenna was observed. Injection locking experiments were performned. At 9 V bias, a locking gain of 40.9 dB with locking bandwidth of 5.9 MHz was obtained. Radiation patterns in E and H plane were measured. Low levels of cross-polarisation were observed.

Embroidered textile logarithmic spiral antenna and its energy efficiency

The paper presents the parametric analysis of logarithmic spiral antenna which is followed with prototype design by embroidering conductive yarn into denim material. To match the antenna, exponentially tapered microstrip balun has been designed. The antenna exhibits stable properties across wide frequency band which makes it suitable for collecting the energy from outside sources.

Waveguide calibration for measuring electric properties of textile materials

The paper presents the adaptation of so-called transmission-reflection procedure for measuring constitutive parameters of textile materials by using rectangular waveguide in L-band. Waveguide is calibrated using transmission-reflection-line procedure, while the focus is put on analysis of thin samples with low losses and permittivity. This poses a particular challenge due to high precision requirements both in magnitude and phase measurements.