Continuously tunable true-time delay lines based on a one-dimensional grating waveguide for beam steering in phased array antennas.

We review our last work on dispersion-engineered heterogeneous multicore fiber links designed to act as tunable true time delay lines for radiofrequency signals. This approach allows the realization of fiber distributed signal processing in the context of fiber-wireless communications, providing both radiofrequency access distribution and signal processing in the same fiber medium. We show how to design trench-assisted heterogeneous multicore fibers to fulfil the requirements for sampled true time delay line operation while assuring a low level of crosstalk, bend sensitivity and tolerance to possible fabrication errors. The performance of the designed radiofrequency photonic delay lines is evaluated in the context of tunable microwave signal filtering and optical beamforming for phased array antennas.

A simple miniaturized ultra-wideband true time delay line (TTD) is demonstrated using Indium Phosphide (InP) MMIC technology. An unprecedented bandwidth from close to dc to beyond 110 GHz is measured. The TTD has around 200 ps delay, a maximum insertion loss of only ~4.5 dB at 110 GHz, and better than 15 dB return loss across the majority of the band. This configuration significantly reduces the chip size, weight and cost. It demonstrates that wideband large time delay line is viable for planar IC implementation. To the authors' knowledge, this is the widest bandwidth ever reported for MMIC true time delay lines with relatively large time delay and compact size.

A high performance bias tee is designed in microstrip line technology. It is shown that a single capacitor and a section of high impedance line are enough to achieve an RF isolation of at least 30 dB over 40% bandwidth. The bias tee is used to implement a switchable true time delay (TTD) line over 2–3 GHz frequency band with a delay difference variation less than 0.025 ns.

Summary form only given, as follows. A millimeter wave phased antenna array (PAA) has been proposed for use in plasma imaging reflectometric diagnostics and is currently under design and fabrication. To account for the rapid changes of the cutoff layer with plasma density variation, a true time delay (TTD) controlled phased antenna array (PAA) is being developed as an artificial lens with controllable focal length for launching the illumination beam of the microwave imaging reflectometry (MIR) system. The beam shaping concept illustrates that programming the PAA generates concave (focusing/beam narrow) or convex (defocusing/beam broaden) wavefronts by properly arranging the time delay (or phase shift), therefore, the PAA functions like a real optical lens. The focal properties can be easily changed by different time delay arrangement at high speed so that real time control is possible on time scales significantly faster than plasma changes. The operation frequencies for the first implementation of beam shaping antenna array are set as 45-55 GHz based on the NSTX MIR system requirements. The time delay unit utilizes a piezoelectric translator (PET)-driven perturber to vary the propagation velocity along low loss microstrip lines. Tapered slot antenna will be used in the system as array element. To overcome the system loss and scattering loss from the plasma, the beam shaping array system is designed with an output power of at least 50 mW, and with a desired variable 3-dB beam width extending from 15/spl deg/ to 25/spl deg/.

We experimentally demonstrate, for the first-time to our knowledge, tunable true-time delay line operation over a few-mode fiber link, in which the time delay can be continuously and widely tuned, from 46.3 to 105.6 ps, by simply sweeping the operating optical wavelength over the 35-nm range of the C-band. This has become possible thanks to the particular modal dispersion properties of the developed double-clad step-index few-mode fiber, as it features relatively evenly-spaced incremental chromatic dispersion values among 5 spatial modes. To date, it is the first time a dispersion-diversity FMF with this property has been experimentally reported. We assess the performance of this true-time delay line when applied to microwave signal filtering in both space and wavelength diversities, where a variety of reconfigurable 5, 7 and 10-tap microwave filters with free spectral ranges ranging from 7.7 to 27.1 GHz are experimentally demonstrated.

Photonic‐assisted terahertz (THz) wireless communication is a promising solution for future high‐capacity wireless networks. However, the low output power and severe propagation loss of THz waves limit transmission distance. To overcome these challenges and support dynamic multi‐user connectivity, we demonstrate an integrated photonics‐assisted THz beamformer enabling broadband, beam‐squint‐free beam steering in the D‐band, based on silicon four‐channel tunable optical true‐time delay lines (OTTDLs). Each OTTDL combines an 8‐bit switchable delay and a continuously tunable delay unit, achieving a total continuous delay range of 0–394.24 ps. By providing true time delays, the proposed beamformer maintains a consistent beam direction across a wide operating bandwidth, thereby fundamentally eliminating beam squint. Leveraging this chip and a 1 × 4 dielectric rod antenna array, we achieve beam steering with a total beam switching time of 120 ns and a maximum angle of ±20.19°. We demonstrate wireless transmission with a line rate of 100 Gb/s at two distinct angles. To the best of our knowledge, this is the first integrated THz beamforming system that realizes broadband, beam‐squint‐free operation using OTTDLs. This work represents a significant step toward scalable, low‐latency, and high‐speed THz wireless networks, offering a viable pathway for dynamic beam management in future 6G systems.

Optical phased arrays occupy the predominant position in the solid-state light detection and ranging; however, their applications are limited by high insertion loss, complex control, and the need for tunable lasers. Here, by assembling a quadratic silicon metalens onto the end face of a single-mode fiber array to form a metafiber, we propose an all-solid-state beam steering module. With the introduction of the flat metalens, the module is highly compact, and the field of view may be extremely wide. A large field of view up to about 60° is testified experimentally based on a one-dimensional module. The application for parking space monitoring is also demonstrated based on a two-dimensional module. The beam steering module can be switched between the scanning mode and the flash mode compatibly and can also be extended to a larger scale with a higher scanning precision by increasing the size of the fiber array and scaling the metalens. The presented scheme featured with high compactness, high performance, and good compatibility provides a distinctive beam steering candidate for light detection and ranging or optical wireless communication applications.

This paper demonstrates the use of hybrid beam steering components for wideband electronic scanning. A unidirectional multifunction monolithic microwave integrated circuit (MMIC) core chip is combined with three numbers of single pole double throw (SPDT) switches to realize bi-directional TTD units for transmit and receive operation. The realized bi-directional TTD unit is characterized for its functionality at the four-element subarray for true-time delay beam steering. The 6-bit digitally controlled phase shifters and a 6-bit true-time delay (TTD) units are used in a hybrid configuration to realize an X-band wideband 16-element linear array. The element level phase delay (limited to a maximum 360º) and subarray level time delay in steps of 3.125 ps (maximum delay of 197ps) is applied for the array calibration and beam steering. The radiation pattern is measured at the center operating frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , and the beam is steered at f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> + 0.5 GHz to validate squint-free beam scanning. The proposed configuration with a two-stage hybrid phase/time delay demonstrates the wideband beam steering and eliminates the beam squint for wide instantaneous signal bandwidth for high-resolution imaging active phased array radars.

Enhancing signal quality, minimizing interference, allowing high-speed data transmission, and beam steering in phased array antennas are pivotal in today's wireless communication systems.In terms of global optimality, low side lobe levels, and fast convergence, conventional optimization methods often fail to deliver.The ease and adaptability of metaheuristic algorithms, such as the Whale Optimization Algorithm (WOA), have rendered them desirable solutions for managing such complex optimization problems.However, traditional WOA may still suffer from premature convergence and failure to exploit the search space fully.This study proposes a Chaos-Enhanced Whale Optimization Algorithm (CWOA) in intelligent beam steering for phased array antennas.A significant enhancement is that the algorithm can now escape local optima more effectively and attain higher global convergence due to the integration of chaos theory into the WOA framework.Chaotic maps such as the logistic and tent maps generate dynamic control parameters that guide the search for a more balanced exploration-exploitation trade-off.To reduce side lobe levels and give accurate main lobe steering, the proposed CWOA is employed to enhance phase excitation of the antenna elements in a uniform linear array (ULA).Beam direction accuracy, side lobe suppression, and convergence speed are three domains where the CWOA performs better in simulations than normal WOA, PSO, and GA.By comparing various approaches, we realize that chaotic integration significantly enhances the performance of WOA in adaptive beamforming and real-time applications.Innovative and self-adaptive beam steering in dynamic environments like 5G, radar, and satellite communications can be built on this research's efficient and resilient optimization framework for next-generation antenna systems.

One of the key elements for modern microwave circuits is a delay line, which is widely utilized for the signal generation as well as processing. Spin-wave delay lines based on ferrite films provide a high delay time and small dimensions. Typically, the performance characteristics of such lines are tuned by the variation of an externally applied magnetic field characterized by some drawbacks. The phenomenon of a metal–insulator transition (MIT) in the phase change materials permits to improve the performance characteristics of the spin-wave delay lines. In particular, this concept allows to reduce the power consumption and improve the control speed of a delay time. Aim. Development of a tunable spin-wave delay line based on ferrite and vanadium dioxide films, as well as the study of its performance characteristics. Methods. Experimental investigations were carried out for the delay line composed of the yttrium iron garnet (YIG) and vanadium dioxide (VO2) films. The ferrite waveguide was fabricated from a single-crystal YIG film grown on a gallium gadolinium garnet substrate. A vanadium dioxide film was formed on a silicon dioxide substrate by DC reactive magnetron sputtering. The microwave measurements were carried out using the vector network analyzer R&amp;S®R ZVA40. Results. It was shown that heating of the VO2 film induces a sufficient drop of its resistance that causes the transformation of the spin-wave dispersion characteristic. This leads to the decrease in the group velocity of the propagating waves providing a growth of a delay time. Namely, experimental structure of 5-mm length offers a tunable time delay range from 130 up to 150 ns at the operating frequency of 4.33 GHz. Conclusion. A proof-of-principle for the MIT control of the delay time composed on the YIG-VO2 structure has been presented. It was shown that a switch of VO2 film from the isolating into conducting state produces a 15% change in the delay time. The considered microwave delay lines look favorable for applications as a complimentary part to the traditional approach for general computing and microwave signal processing.

Bifurcation analysis on a turning system with large and state-dependent time delay

Hybrid photonic true-time delay modules for phased-array antennas are designed and demonstrated. Continuously tunable true-time delay network based on highly dispersive photonic bandgap fiber (up to 2135 ps/nm/km at 1570 nm), combined with a programmable true-time delay network utilizing optical waveguide delay line and optical switches, provides the antenna with quasi-continuous steering ability. Far-field patterns are simulated and measured to confirm the squint-free beam steering.

This paper proposes a novel Opto-VLSI-based tunable true-time delay generation unit for adaptively steering the nulls of microwave phased array antennas. Arbitrary single or multiple true-time delays can simultaneously be synthesized for each antenna element by slicing an RF-modulated broadband optical source and routing specific sliced wavebands through an Opto-VLSI processor to a high-dispersion fiber. Experimental results are presented, which demonstrate the principle of the true-time delay unit through the generation of 5 arbitrary true-time delays of up to 2.5 ns each.

A cognitive antenna array, which is designed by using deep reinforcement learning (DRL) is proposed in this article to adapt to the complex electromagnetic environment. Specifically, the phased array antenna is utilized as the manipulatable component to achieve the characteristic of beam steering with the help of the DRL algorithm. We begin by establishing a DRL-based framework, which is comprised of a microprogrammed control unit, power divider, digital phase shifter, and the patch antenna array. In the DRL algorithm, the desired beam steering is obtained through trial-and-error interactions with the environment, which is required to observe predefined rewards based on the current state and action. Next, the system is trained to perform beam steering, and a set of hyperparameters of the deep neural network are obtained and stored for practical usage. A good agreement is achieved between the simulated and measured radiation patterns of the planar phased array antenna, which validates the DRL-based phase distribution regulation algorithm. Finally, the algorithm is implemented in the design process of a conformal phased array antenna, and it is shown that the measured radiation performance of the array is satisfactory for different beam scan angles.

Thin glass provides attractive solutions for emerging high frequency applications and particularly those related to the rollout of 5G. The electrical and physical properties of glass enable low RF loss, the ability to adjust thermal expansion properties, and low roughness with excellent flatness to achieve fine L/S and smaller form factors. The scalability of glass also provides opportunities to establish cost-effective solutions. There have been a number of research articles published over the past several years showing the advantages that glass based solutions can bring to packaging and systems integration including RF front ends, interposers, MEMs devices, and integrated photonics. [1-10]. RF applications of glass in particular are gaining interest for use as a substrate for filters, switches, true time delay modules, and millimeter antenna arrays. The advantages include low insertion loss relative to Si-based solutions and higher integration density compared with laminates and ceramics. Furthermore, numerous articles have shown the ability of glass to provide reliable solutions. These tests have included, HAST, thermal shock and drop tests [e.g. 5, 8]. The biggest challenge to adopting glass-based solutions has been the existence of gaps in the supply chain, caused primarily by the difficulty in handling large, thin glass substrates using standard automation and processing equipment. A new thin glass handling approach, Viaffirm TM, has been recently developed. [12,13] The approach utilizes a thin inorganic adhesion layer to temporarily bond a thin glass wafer to a silicon or glass handle wafer (Si handle wafer is the primary approach). The thin glass substrate, which may contain through-glass vias (TGVs), is then processed through downstream steps such as via fill, CMP, RDL/passive deposition, lithography and bumping. The bond is stable (remains temporary and without outgassing) to over 400 °C. Utilizing a Si handle wafer allows the thin glass to be processed leveraging existing equipment and process flows, with only a mechanical de-bond to yield finished substrates. In previous publications, the basic process has been described. Here, we will show advancements and application of this technology, with and without TGV, to seamlessly interface with the supply chain to fabricate next generation thin glass solutions for applications including photonic substrates, RF filters and antennas. The process is available for multiple glass types including alumino-borosilicate glasses with coefficient of thermal expansion that matches silicon, as well as ultra-low loss materials like fused silica (FS). Leveraging the precision bond Viaffirm allows you to fabricate FS wafers down to 100 um thick. The approach is enabling low loss solutions in electronically steerable antenna (ESA), radar arrays, MEMS, sensors and packaging substrates. A particularly attractive use for glass is in 5G applications due to its material properties, especially at high frequencies including mm-Wave applications. First, it is stable with respect to environmental changes (e.g. temperature and humidity). Also, glass is an isotropic material by nature, which means its properties are stable in all 3 axes. This can be very important in applications such as phased array antennas where you might have an 8x8 array of patch antennas, and require them all to perform predictably and with minimal variation to achieve desired results, such as in beam steering. Recent work was done to fabricate a multi-layer glass based Electronically Steerable Array (ESA) antenna with a design transmit signal of approximately 29.5 GHz. Additional architectural enhancements in this novel approach enable a dramatic reduction in the number of controllable elements in the array and therefore reduce the number of MMICs needed for antenna steering, resulting in a design with reduced size, weight, power and cost relative to more conventional approaches. [14] The approach utilized a multi-layer glass-based feed network to control 8x8 patch arrays. Analysis shows that by utilizing glass instead of PCB solutions, dramatic reduction in electrical loss are realized. By leveraging Viaffirm technology, thin glass solutions are available to address these and other mmWave applications important in 5G and beyond.