Conventional wireless applications are often characterized by a large distance in terms of wavelengths between the transmitting antennas and the receiving antennas or scatterers, allowing the application of far-field approximations, as well as standard antenna characteristic parameters. Nonetheless, an increasing number of wireless systems have been recently proposed, where the far-field condition is not met and specific coupling models and ad-hoc antenna design criteria must be necessarily adopted to the end of optimizing system performance. As far as near- field applications are concerned, it is worth mentioning wireless power transfer, near-field communications (NFC), radio frequency identification, antenna measurements, non-destructive sensing, chip-to-chip wireless links, biomedical applications, body-centric communications, microwave imaging, among many others. This talk is aimed to present an overview of the basic working principles of near-field focused antenna arrays and the main design criteria proposed for near-field shaping around the focal point. A brief overview of the applications requiring such class of antennas is also provided. Among others, specific attention will be given to RFID (Radio Frequency IDentification) technology.
Reconfigurable metasurfaces can be used with antennas for dynamic beam forming and beam steering. These metasurfaces are designed by incorporating switching components within subwavelength unit cells. Recently, our group has designed a metasurface and developed its controller for directly modulating the data in the channel. This design employs a compact metasurface unit cell with maximum difference between its switching states. Meandered line segments whose resonant frequency is changed by switching a PIN diode embedded in the unit cell ON or OFF, have been employed for this design. The array is placed directly in front of a microstrip antenna in its nearfield. Several parametric studies have been conducted to design of this transmitarray metasurface and a unique communication scheme has been demonstrated using this, where the data is used to modulate the channel directly, unlike conventional approaches of modulating the carrier. An extension of this configuration with a wideband antenna may be employed for computational microwave imaging. Our recent research indicates that the overall variation in the complex field for illuminating the imaged object can be improved with some modifications to the primary radiator used with this transmitarray metasurface. A preliminary co-design approach for the antenna-metasurface configuration for maximizing the overall performance will also be presented.
Smart cars with vehicular advanced driver assistance systems (ADASs) have become an important industrial trend. The functionality of ADASs is to detect the surrounding targets at near- and far distances to increase driving safety. Conventional ADASs install several different sets of phased arrays of antennas that are excited to produce high-directional gain with narrow beamwidths, and low gain with broad beamwidths for long and short-range coverages, respectively. These long- and short-range detections appear simultaneously in the front-view coverage pointing directly to the vehicles’ broadside lane and two adjacent side lanes. In this case, the broadside far-field focused (FFF) beam is angularly narrow, while the defocused beams for the two side-lane coverages are very broad. Thus, from a system point of view, the ADAS simultaneously operate in three modes for front-view coverage by alternatively exciting different antenna arrays for long- and short-range detection purposes. Large antenna arrays may produce good radiation characteristics of beam radiation, and inter-beam overlapping with dramatic coverage cutoff to avoid detection ambiguity in the inter-beam overlapping region, which may cause oversize when three large antenna arrays are used. To reduce the system complexity, sharing a common large antenna array appears to be the most effective for compactness, which may produce multiple beams as the desired operational modes by using a proper beamforming circuit (BFC), such as the Butler matrix, Blass matrix, Rotman lens, and Luneburg lens.
Conventionally available multi-beam BFC excites the common antenna array to radiate either sole FFF beams, or near-field focused (NFF) beams by using the Luneburg lens or Rotman lens. These multi-beam BFCs are not applicable to the ADAS systems that need to simultaneously produce both far-field focused and defocused beams with relative beam controllability for different range detections. A new Rotman lens BFC design is thus proposed in this paper, which may excite the antenna array to radiate far-field focused, NFF (far-field defocused beam), and shaped beams by selecting different beam ports of the BFC (referred to as the different modes of operation). This new Rotman lens BFC was made possible by generalizing the three design equations, arising from the equal-time-delay ray propagations inside the BFC with respect to the three different beam ports, to phase-matching to the desired array excitations of different beams. This introduction of excitation phase matching allows the excitations of the antenna array to be relative arbitrarily specified for either FFF, NFF, or shaped beams, as required in the ADASs for different range coverages. In other words, this new Rotman lens BFC may produce array excitations to radiate different beam characteristics of hybrid combining FFF, NFF, and shaped beams by using the common set of antenna arrays. This multi-beam design concept with FFF and NFF/shaped beam capability is applied to design a practical antenna system for ADAS applications, especially for transmitting (TX) antennas.
This antenna system consists of three TX antenna ports and four receiving (RX) antenna ports for MIMO applications. The three TX antenna ports behave like the three radiation modes of ADASs to provide a high-gain, narrow FFF beam for broadside target detection inside the front lane and two NFF/shaped beams of broad beam widths for short-range detections on both side lanes. On the other hand, the four RX antenna ports allow the DSP of received signals to estimate the angle of arrival (AoA). This antenna array has been realized by using various series- fed column arrays of patch antennas to form the multi-beams. Both full-wave simulation and measurement over the antenna array prototype were compared with good agreements. The new Rotman lens BFC can also be applied to various communication applications requiring flexible.
Phased array antenna systems (PAAS) for radars need to consider the effect of the surrounding environment and the platform for mounting to correctly assess its performance in the field scenario. This paper discusses these aspects of the design and development of PAAS. A substrate integrated waveguide technology (SIW) based U-slot microstrip patch antenna (SIW_MPA) is designed with wide beam width and wide band performance and used for realizing the antenna array for PAAS. The design cycle of PAAS includes the single element design (isolated), element performance in array environment, followed by the effect of platform and surrounding structures on array performance. A hybridization of finite element method (FEM) and shooting bouncing ray (SBR) modules in electromagnetic (EM) solver, Ansys HFSS are utilized to carry out the various simulations. The results are quite informative and useful for mast mounted phased array antenna systems.
