Microstrip patch antennas are the most common type of printed antenna due to a myriad of advantages which encourage use in a wide range of applications such as: wireless communication, radar, satellites, remote sensing, and biomedicine. An initial design for a stacked-patch, broadband, dual-polarized, aperture-fed antenna is tested, and some adjustments are made to improve performance. The design goal is to obtain a 3 GHz bandwidth centered at 10 GHz for each polarization. Once the single-element design is finalized, it is used in a 4x1 array configuration. An array increases the gain, and by utilizing variable phase-shifters to each element, the pattern can be electronically steered in a desired direction. The phase-can be easily adjusted. The result of this new phased array design is a wide bandwidth system with dual-polarization which can be electronically steered. Rectennas (rectifying antennas) are used in wireless power transmission (WPT) systems to collect microwave power and convert this power into useable DC power. They find use in many areas such as space power transmission, RFID tags, wireless sensors, and recycling ambient microwave energy. The ability to simulate rectenna designs will allow for an easier method of analysis and tuning without the time and expense of repetitive fabrication and measurement. The most difficult part of rectenna simulation is a good diode model, and since different diodes have dissimilar properties, a model must be specific to a particular diode. Therefore, a method of modeling an individual diode is the most critical part of rectenna simulation. A diode modeling method which is based on an equivalent circuit and compatible with harmonic balance simulation is developed and presented. The equivalent circuit parameters are determined from a series of S-parameter measurements, and the final model demonstrates S-parameters in agreement with the measured data. An aperture-coupled, high-gain, single-patch rectenna is also designed and measured. This rectenna is modeled using the presented method, and the simulation shows good agreement with the measured results. This further validates the proposed modeling technique.

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In the future, space solar power transmission and wireless power transmission will play an important role in gathering clean and infinite energy from space. The rectenna, i.e., a rectifying circuit combined with an antenna, is one of the most important components in the wireless power transmission system. To obtain high power and high output voltage, the use of a large rectenna array is necessary. Many novel rectennas and rectenna arrays for microwave and millimeter-wave wireless power transmission have been developed. Unlike the traditional rectifying circuit using a single diode, dual diodes are used to double the DC output voltage with the same circuit layout dimensions. The rectenna components are then combined to form rectenna arrays using different interconnections. The rectennas and the arrays are analyzed by using a linear circuit model. Furthermore, to precisely align the mainbeams of the transmitter and the receiver, a retrodirective array is developed to maintain high efficiency. The retrodirective array is able to track the incident wave and resend the signal to where it came from without any prior known information of the source location. The ultra-wideband radio has become one of the most important communication systems because of demand for high data-rate transmission. Hence, ultra-wideband antennas have received much attention in mobile wireless communications. Planar monopole ultra-wideband antennas for UHF, microwave, and millimeter-wave bands are developed, with many advantages such as simple structure, low cost, light weight, and ease of fabrication. Due to the planar structures, the ultra-wideband antennas can be easily integrated with other circuits. On the other hand, with an ultra-wide bandwidth, source power can be transmitted at different frequencies dependent on power availability. Furthermore, the ultra-wideband antenna can potentially handle wireless power transmission and data communications simultaneously. The technologies developed can also be applied to dual-frequency or the multi-frequency antennas. In this dissertation, many new rectenna arrays, retrodirective rectenna arrays, and ultra-wideband antennas are presented for microwave and millimeter-wave applications. The technologies are not only very useful for wireless power transmission and communication systems, but also they could have many applications in future radar, surveillance, and remote sensing systems.

The agricultural sector is an emerging application area for Wireless Sensor Networks (WSNs). This requires sensor nodes to be deployed in the outdoor environment so as to monitor pertinent natural features, such as soil condition or pest infestation. Limited energy supply and subsequent battery replacement are common issues for these agricultural sensor nodes. One possible solution is to use energy harvesting, where the ambient energy is extracted and converted into usable electrical form to energise the wireless sensors. The work presented in this thesis investigates the feasibility of using Radio Frequency (RF) energy harvesting for a specific application; that is powering a generic class of wireless ground-level, agricultural sensor networks operating in an outdoor environment. The investigation was primarily undertaken through a literature study of the subject. The first part of the thesis examines several energy harvesting/ wireless energy transfer techniques, which may be applicable to power the targeted agricultural WSN nodes. The key advantages and limitations of each technique are identified, and the rationale is being given for selecting far-field RF energy harvesting as the investigated technique. It is then followed by a theoretical-based system analysis, which seeks to identify all relevant design parameters, and to quantify their impact on the system performance. An RF link budget analysis was also included to examine the feasibility of using RF energy harvesting to power an exemplar WSN node - Zyrox2 Bait Station. The second part of the thesis focuses on the design of two energy harvesting antennas. The first design is an air-substrate-based folded shorted patch antenna (FSPA) with a solid ground plane, while the second design is a similar FSPA structure with four pairs of slot embedded into its ground plane. Both antennas were simulated, fabricated and tested inside an anechoic chamber, and in their actual operating environment - an outdoor field. In addition, a power harvester circuit, built using the commercially available off-the-shelf components, was tested in the laboratory using an RF signal generator source. The results from both the laboratory and field trial were analysed. The measurement techniques used were reviewed, along with some comments on how to improve them. Further work on the RF energy harvester, particularly on the improvement of the antenna design must be carried out before the feasibility and viable implementations for this application can be definitively ascertained.

Nikolai Tesla's revolutionary experiments demonstrated the possible benefits of transmitting power wirelessly as early as 1891. Applications for the military, consumers, emergency personnel, remote sensors, and others use Tesla’s discovery of wireless power. Wireless power transmission (WPT) has the potential to be a common source of consumable energy, but it will only receive serious consideration if the transmit and receive systems are extremely efficient and capable of delivering usable amounts of power. Research has been conducted to improve the efficiency and performance of nearly every aspect of WPT systems, but the relatively new field of metamaterials (MTMs) has yet to play a dominate role in improving system performance. A gradient index (GRIN) MTM lens was designed using Ansoft’s High Frequency Structure Simulator (HFSS) to improve antenna gain and thereby increase WPT system performance. A simple WPT demonstration system using microstrip patch antennas (MPAs) confirmed the benefits of the GRIN MTM lens. The WPT demonstration system, MPAs, and GRIN MTM lens were constructed and experimentally tested near 2.45 GHz. The theoretical and experimental gain improvement of the MPA due to the GRIN MTM lens is 5.91 dB and 7.06 dB, respectively.

In the past decade, artificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in mobile communications, medical, and optoelectronics applications. To realize this potential, more research on metamaterials is needed. In this dissertation, new bandpass filter and diplexer as microwave metamaterial applications have been developed. Unlike the conventional complementary split ring (CSRR) filters, coupled lines are used to provide larger coupling capacitance, resulting in better bandpass characteristics with two CSRRs only. The modified bandpass filters are used to deisgn a compact diplexer. A new CSRR antenna fed by coplanar waveguide has also been developed as another metamaterial application. The rectangular shape CSRRs antenna achieves dual band frequency properties without any special matching network. The higher resonant frequency is dominantly determined by the outer slot ring, while the lower resonant frequency is generated by the coupling between two CSRRs. The proposed antenna achieves about 35 percent size reduction, compared with the conventional slot antennas at the low resonant frequencies. As a future alternative energy solution, space solar power transmission and wireless power transmission have received much attention. The design of efficient rectifying antennas called rectennas is very critical in the wireless power transmission system. The conventional method to obtain long distance range and high output power is to use a large antenna array in rectenna design. However, the use of array antennas has several problems: the relatively high loss of the array feed networks, difficultiy in feeding network design, and antenna radiator coupling that degrades rectenna array performance. In this dissertation, to overcome the above problems, a reflectarray is used to build a rectenna system. The spatial feeding method of the reflectarray eliminates the energy loss and design complexity of a feeding network. A high gain rectifying antenna has been developed and located at the focal point of the reflectarray to receive the reflected RF singals and genterate DC power. The technologies are very useful for high power wireless power transmission applications.

This thesis proposes a novel technique using a phase-lock loop (PLL) style phase control loop to achieve retrodirective phased array antenna steering. This novel approach introduces the concept of phase scaling and frequency translation. It releases the retrodirective transmit-receive frequency ratio from integer constraints and avoids steering approximation errors. The concept was developed to achieve automatic and precise beam steering for the solar power satellite (SPS). The testing was performed using a transceiver converting a pair of received 2.9 GHz signals down to 10 MHz, and up converting two 10 MHz signals to 5.8 GHz. Phase scaling and conjugation was performed at the 10 MHz IF using linear XOR phase detectors and a PLL loop to synthesize a 10 MHz signal with conjugate phase. A phase control loop design is presented using PLL design theory achieving a full 2π steering range. The concept of retrodirective beam steering is also presented in detail. Operational theory and techniques of the proposed method are presented. The prototype circuit is built and the fabrication details are presented. Measured performance is presented along with measurement techniques. Pilot phase detectors and PCL achieve good linearity as required. The achieved performance is benchmarked with standards derived from likely performance requirements of the SPS and beam steering of small versus large arrays are considered.

With the ever growing application requirements for wireless power transmission in recent years, use of Ultra High Frequency (UHF) band via passive RFID technology escalates quickly. However, limited read range and outdoor interference has always been a great obstacle for various RFID applications. Escalating power transmission at the tag to identify and amplify received power under flawless conditions of electromagnetic theory do not provide estimates of read-rates, which bring major limitations to RFID system performance. Therefore, discovering the reason behind these problems and assessing the performance of backscatter power to improve the system performance remains as a crying need.   Implying radar cross section (RCS) mechanism into RFID can enhance the system performance at a larger extent, as passive RFID works same as radar at far field range by detecting backscatter signal from target object. Antenna radiation pattern and co located interference effect are vital considerations for RFID propagation mechanism and tag read range optimization. Consequently, the robust performance of transmitting and receiving antenna will provide a better RCS value when we get them in good agreement with experimental results.   This thesis provides analytical framework for backscatter performance modeling and suggest techniques to enhance the efficiency of reader to tag to reader performance. It explores uncertainties associated with certain parameters like antenna far field radiation property, antenna spacing, optimal backscatter power and communication range, which implies scattering efficiency of the tag and establish a relationship between the measured and predicted values of tag read-rate probabilities. Comparing measurement patterns in both outdoor and in an-echoic chamber, finally it determines method to increase efficiency at power transmission and reception end. Obtained results will encourage the future researchers to design, analyze and enhance the backscattered passive RFID systems at a larger scenario.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(農学) / 乙第12823号 / 論農博第2796号 / 新制||農||1025(附属図書館) / 学位論文||H26||N4818(農学部図書室) / 31310 / 京都大学農学研究科農業工学専攻 / (主査)教授 清水 浩, 教授 近藤 直, 教授 飯田 訓久 / 学位規則第4条第2項該当

This thesis presents a multi-stage rectifier for wireless power transfer in biomedical implant systems. The rectifier is built using Schottky diodes. The design has been simulated in 0.5µm and 130nm CMOS processes. The challenges for a rectifier in a wireless power transfer systems are observed to be the efficiency, output voltage yield, operating frequency range and the minimum input voltage the rectifier can convert. The rectifier outperformed the contemporary works in the mentioned criteria.