Jouko Heikkinen

A novel dual-frequency circularly polarized rectenna

A novel dual-frequency circularly polarized shorted ring-slot rectenna (rectifying antenna) for wireless power transmission at 2.45 and 5.8 GHz is proposed. The rectenna is composed of two nested microstrip-fed shorted annular ring-slot antennas and two rectifier circuits. Output DC voltage of over 2 V at the lower frequency band and over 1 V at the higher frequency band is achieved at a transmission distance of 2 m.

Low-profile circularly polarized rectifying antenna for wireless power transmission at 5.8 GHz

Portable devices operating without batteries are sometimes desired in wireless applications such as RFID (Radio Frequency Identification) and telemetry. A novel circularly polarized shorted annular ring-slot rectenna (rectifying antenna) on a 0.5 mm thick flexible microwave laminate is proposed for the powering of these devices. Output dc voltage of 1.3 V and axial ratio of 1.5 dB were measured when 32 dBm microwave power was transmitted at 5.8 GHz over a distance of 2 m. Comparing the results with a rectenna designed on a thick rigid laminate, similar performance was observed.

Wearable antennas for FM reception

The effect of human body on wearable 100 MHz antennas is studied by measurements. At that frequency, the body is very thin compared to the wavelength, but about half a wavelength tall. Antenna performance is most affected by the posture of the antenna wearer, second matter being antenna position on body. Physical traits of the wearer have only a slight effect on the antenna performance. A ¿13 dBi gain was achieved by the constructed dipole-like antennas, and letting one¿s arms hang down reduces this by 5 to 15 dB. Most of the power delivered to the antennas is absorbed by the human body, but some is radiated not only by the antenna but also by the body. Wearable antennas need to be shortened by 15 to 25 % from the free-space length to achieve the desired resonance frequency.

Body-Worn Antennas Making a Splash: Lifejacket-Integrated Antennas for Global Search and Rescue Satellite System

The Cospas (Cosmicheskaya Sistyema Poiska Avariynich Sudov)-Sarsat Search-and-Rescue (SAR) satellite system provides distress alert and location data to assist rescue operations at sea, in the air, or on land. This paper summarizes the design, development, and verification for a body-worn antenna system interfaced with commercial Cospas-Sarsat personal locator beacons (PLBs), where the implemented system is integrated within an inflatable live vest. The modular approach adopted in the work allows different antenna configurations for different platforms. The electrical and mechanical requirements for antenna materials and antennas were derived from the Cospas-Sarsat system requirements, possible antenna platforms, and the maritime operational environments. The antennas were used in field tests organized in cooperation with the local Cospas-Sarsat search-and-rescue authorities. The field tests were a success. In both cases, low-earth orbit search-and-rescue (LEOSAR) satellites detected the distress signal within minutes, and accurately resolved the location. An additional detection by Geostationary Orbit Search and Rescue (GEOSAR) satellite confirmed the successful operation of the body-worn antenna system.

Planar rectennas for 2.45 GHz wireless power transfer

Three planar rectennas (rectifying antennas) on different PCB materials have been designed. Patch antennas were designed with a MoM (method of moments)-based simulator while in RF-to-DC conversion circuits microstrip and discrete rectifier diode models were utilized in circuit simulations. The goal was to achieve maximum antenna and conversion efficiency at the desired reception power level. 80% antenna efficiency and 70% conversion efficiency was achieved in simulations. The terms for achieving a sufficient reception power level were considered and compared to the performance of the designed antennas. The accuracy requirements for the realization of these rectenna structures were also defined with the aid of both simulation and measurement results.

Effects of bending GPS antennas

The effect of antenna bending on return loss, impedance bandwidth, and radiation pattern is studied, taking four antennas as examples. These include a patch, slot, inverted-F, and dipole antenna. Some of them exhibit circular polarization and one is broadband. Impedance is seen to be fairly constant regardless of bending, though if circular polarization is excited by careful antenna shaping, the circular polarization and corresponding resonance are easily lost. The axial ratios of all examined antennas degrade quickly with decreasing bend radius. Linearly polarized antennas are more tolerant to bending effects, though their polarization may twist and main lobe direction change.

Flexible antennas for GPS reception

Flexible antennas for GPS reception have been designed and their performance on two different substrates has been evaluated. Two antenna types, a corner-truncated square patch and a planar inverted F-antenna were studied. Antenna patterns were manufactured using conductive pastes and silk screen printing technique. Two different silver pastes and several mixing ratios of silver and carbon pastes were evaluated. It was found that the electrical performance of 25/75% carbon/silver paste mixture does not significantly differ from that of 100% silver paste, whereas the losses of 50/50% mixture are considerably higher. Furthermore, the printing substrate strongly affects the electrical performance of the other studied silver paste.

Flexible fabric-base patch antenna with protective coating

Antennas on a flexible substrate were designed and fabricated in order to study their feasibility for GPS reception. The focus of the experiments was on the design of fabric- base antennas and their manufacturing methods. Corner-truncated square patch antennas were fabricated by wet-etching copper-clad PI and PET film and then attaching the film on a fabric covered with a thermoweldable plastic. Four different coatings were applied to protect the patch antenna surface - silicon spray, parylene C, heat seal/dielectric paste, and PET-film. Only minor effects of coating on antenna characteristics were discovered - the effect of fabrication tolerances was far more significant.

Directive dual-band CP shorted ring-slot antenna

In order to maximize the power captured from incident wave a directive antenna is required. As an example, high directivity is desired for rectifying antenna (rectenna) operating at low power densities, because the rectifier efficiency decreases at lower input power levels. Ring-slot antennas-being attractive for their simplicity and ease of integration, among others-are, however, bidirectional by their nature. Unidirectional radiation pattern can be achieved e.g. by reflector- or cavity-backing. In this paper, improved broadside CP performance of a microstrip-fed dual-band circularly polarized shorted ring-slot antenna is demonstrated when a single reflector is added to the structure.

Comparison of electromagnetic band-gap structures for microstrip antenna arrays on thin substrates

The isolation properties of four different EBG structures are compared in planar antenna arrays. A novel 2-D fork-like structure proposed in this work is found to be the most efficient for the reduction of the mutual coupling between E-plane coupled antennas. The simulation results are validated by measurements