Focusing RF-on demand by logarithmic frequency-diverse arrays

The radiating systems exploiting the frequency diversity of the antennas are powerful architectures, that can have a big impact on wireless power transmission applications, but their characterization is merely theoretical. This paper offers a deep and critical numerical analysis of frequency- diverse arrays and shows the advantages of the family with logarithmic distribution of the frequency for radio-frequency energy focusing goals. For the first time, these systems are analyzed through a Harmonic Balance-based simulation combined with the full-wave description of the array made of eight planar monopoles: the rigorous results confirm the potentialities of these complex radiating systems, in particular show how the time-dependency of the radiating mechanism can be favorably deployed

Dual-polarized aperture-coupled patch antennas with application to retrodirective and monopulse arrays

An isolation technique, which does not require conventional circulators, is proposed for the realization of a simple and low-cost aperture-coupled circularly polarized antenna for application to full-duplex devices. The approach is based on the use of slotlines loops to provide surface current cancellation in specific regions of the antenna structure, leading to improved axial ratio and isolation between the ports in excess of 50 dB. Circular polarization is achieved by introducing a double-box hybrid coupler, which is optimized to obtain good matching and isolation of the quadrature signals. On this basis, both right- and left-hand circularly polarized beams are achieved by interchanging the transmitting and receiving antenna ports, enabling full-duplex operation and reconfigurability. While the antenna structure is designed for 2.45 GHz operation, one can take advantage of the proposed approach to tune the frequency of maximum isolation. Both single-element prototypes as well as a 2 × 2 array are fabricated and measured, showing good agreement with the simulations and validating the proposed isolation approach. The beam steering capabilities as well as the application to a Van Atta retrodirective antenna array and the possibilities of achieving delta and sum patterns for monopulse operation are also reported. The proposed full-duplex antenna can also represent an excellent solution for narrowband wireless power transmission systems

Dual-Polarized Aperture-Coupled Patch Antennas With Application to Retrodirective and Monopulse Arrays

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Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

Time-Range FDA Beampattern Characteristics

Current literature show that frequency diverse arrays (FDAs) are able of producing range-angle-dependent and time-variant transmit beampatterns, but the resulting time and range dependencies and their characteristics are still not well understood. This paper examines the FDA transmission model and the model for the FDA array factor, considering their time-range relationship. We develop two novel FDA transmit beampatterns, both yielding the auto-scanning capability of the FDA transmit beams. The scan speed, scan volume, and initial mainlobe direction of the beams are also analyzed. In addition, the equivalent conditions for the FDA integral transmit beampattern and the multiple-input multiple-output (MIMO) beampattern are investigated. Various numerical simulations illustrate the auto-scanning property of the FDA beampattern and the proposed equivalent relationship with the MIMO beampattern, providing the basis for an improved understanding and design of the FDA transmit beampattern.Comment: 10 pages, 9 figure

Next-generation IoT devices: sustainable eco-friendly manufacturing, energy harvesting, and wireless connectivity

This invited paper presents potential solutions for tackling some of the main underlying challenges toward developing sustainable Internet-of-things (IoT) devices with a focus on eco-friendly manufacturing, sustainable powering, and wireless connectivity for next-generation IoT devices. The diverse applications of IoT systems, such as smart cities, wearable devices, self-driving cars, and industrial automation, are driving up the number of IoT systems at an unprecedented rate. In recent years, the rapidly-increasing number of IoT devices and the diverse application-specific system requirements have resulted in a paradigm shift in manufacturing processes, powering methods, and wireless connectivity solutions. The traditional cloud-centering IoT systems are moving toward distributed intelligence schemes that impose strict requirements on IoT devices, e.g., operating range, latency, and reliability. In this article, we provide an overview of hardware-related research trends and application use cases of emerging IoT systems and highlight the enabling technologies of next-generation IoT. We review eco-friendly manufacturing for next-generation IoT devices, present alternative biodegradable and eco-friendly options to replace existing materials, and discuss sustainable powering IoT devices by exploiting energy harvesting and wireless power transfer. Finally, we present (ultra-)low-power wireless connectivity solutions that meet the stringent energy efficiency and data rate requirements of future IoT systems that are compatible with a batteryless operation

Lens Based High Directivity Simultaneous Transmit and Receive Systems

Simultaneous transmit and receive (STAR) has the potential to theoretically double the capacity of wireless networks making it a highly desirable technology for modern wireless systems. Self interference (SI) is the chief challenge and high Tx/Rx isolation (greater than 100 dB) is required to mitigate this issue and realize STAR operation. The required isolation level is typically achieved by using a multi-layer cancellation approach across the antenna, analog, and digital domains. A well-designed antenna or propagation layer can provide a significant portion of the SI cancellation (SIC) enabling simplified and more practical transceiver realization. For typical wireless networks and electronic warfare systems, monostatic or shared-aperture STAR antennas are often required to maintain the aperture compactness. At millimeter waves, high directivity and beam steering characteristics are highly desired; particularly for access point and backhaul antennas, to overcome the path loss, achieve the required communication range, and improve the signal-to-noise ratio in dynamic multi-user environments. A co-polarized, co-channel STAR antenna system utilizing a two-layer, spherically stratified lens with nominal directivity of 24.3 dBic is demonstrated in the 27 to 29 GHz frequency band. The STAR operation is achieved with a WR28 waveguide-implemented balanced circulator beam forming network (BC-BFN), which relies on two 90deg hybrids and two circulators along with antenna symmetry to cancel the circulator leakages and achieve theoretically infinite isolation between the transmit and receive ports. The sensitivity of the BC-BFN to alignment and other imperfections is studied. To comply with the BC-BFN's symmetry requirements, a highly symmetric WR28 waveguide ortho-mode transducer (OMT) is developed. Tx/Rx isolation of 30 and 34 dB is measured with and without the lens, respectively, indicating acceptable impact of the lens on system isolation. To demonstrate STAR with the beam steering in an equatorial field of view, the proposed configuration is modified into a mechanically rotated half spherical lens over a ground plane. The experiments show that the isolation of the rotating half-lens system degrades compared to the full-lens counterpart due to the break of the geometrical symmetry. However, respectable isolation greater than 27 dB and high quality circularly polarized radiation patterns are still maintained over the operational bandwidth. Another co-polarized, co-channel, lens-based STAR system based of the same BC-BFN and OMT subsystem but using a compact planar graded index (GRIN) lens is also introduced. The compact lens achieves broadside directivity greater than 24 dBic in the band centered about 28 GHz. The beams are steered by mechanically rotating the proposed compact lens, maintaining the focal point on the antenna's phase center. A maximum scan loss of 4.5 dB is seen in an 80deg conic field of view while preserving system isolation. The measured system maintains 30 dB of isolation with at most 2 dB degradation in isolation at the more severe inclination angles. Finally, closed-form expressions are derived for the component of the radar cross section (RCS) due to the BFN in the context of retrodirective systems. The ability to accurately predict the effect of feedback and infinite reflections is shown with numerical simulations. The derived equations allow calculating the bounds for the maximum loop gain for the system before feedback leads its response into the non-linear domain. The potential of using STAR to improve the performance of retrodirective systems is evaluated with the spherical lens antenna and BC-BFN subsystem. Improvements of 20 dB are obtained when data from the fabricated STAR system is used in the equation and compared to passive lens reflectors.</p