True Time Delay Research Articles

Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis.

Design of ultra large negative dispersion PCF with selectively tunable liquid infiltration for dispersion compensation

A systematic analysis of the dispersion characteristics of a selectively liquid-filled dual-core PCF by varying different geometrical parameters towards achieving ultra negative dispersion values around a desired wavelength has been carried out. The dependence of PCF parameters along with the infiltrating liquid upon dispersion has been investigated. Our analysis establishes that with the increase of Λ, the total dispersion is red-shifted with a reduction of the negative dispersion. Again, the dispersion is red-shifted but with an increment of negative dispersion and narrower FWHM for an increase of d. In contrary to the above dependence of Λ and d, with an increase of nL, the dispersion gets blue-shifted with an increase of negative dispersion at the cost of reduced FWHM. Our numerical study establishes a high negative dispersion of −52,100ps/nm/km around 1550nm through an optimized design. Three such designs of selectively liquid filled dual-core PCF demonstrating a negative dispersion from −28,700ps/nm/km to −52,100ps/nm/km around the wavelength of 1550nm with available practical liquids have been presented to demonstrate the effectiveness of the method. Our optimized structures demonstrate excellent tunable properties with temperatures for various optical communication systems based devices. Our proposed PCF will be an excellent candidate for dispersion compensation in long-haul data transmission as being thousand times more than the available DCFs. Our approach of dispersion engineering will be helpful for dispersion engineering related applications like true time delay instruments, Raman amplifier, ASE suppression, Four-wave mixing etc.

Spatial Filtering in a Broadband In-Home OFDM Radio-Over-Fiber Network

The spatial filtering in an orthogonal frequency division multiplexing (OFDM) radio-over-fiber network is proposed to boost its capacity using broadband optical true time delay enabled microwave beam steering. The observed suppression ratio of the spatial filtering is 19.4 dB. The optical delivery and directional wireless transmission of 3.975 Gb/s OFDM data on a 19-GHz microwave carrier is studied. The observed beam directing-induced bit error ratio improvement is more than four orders of magnitude.

Tunable slowing, storing, and releasing of a weak microwave field

We study the slowing, storing, and releasing of microwave pulses in a superconducting circuit composed of two coplanar waveguide resonators and a superconducting transmon-type qubit. The quantum interference analogy to electromagnetically induced transparency is created in two coupled resonators. By tuning the resonance frequency of the transmon, we dynamically tune the effective coupling between the resonators. Via the modulation of the coupling, we show the tunable true time delay of microwave pulses at the single-photon level. We also store the microwave field in a high-$Q$ resonator and release the signal from it to the output port. Our scheme promises applications in both quantum information processing and classical wireless communications.

Estimation of delay time difference through space for phased array antennas with true time delay

Estimation of delay time difference through space for phased array antennas with true time delay

A prototype high-speed optically-steered X-band phased array antenna

We develop a prototype of optically-steered X-band phased array antenna with capabilities of multi-band and multi-beam operations. It exploits high-speed wavelength tunable lasers for optical true-time delays over a dispersive optical fiber link, enabling agile, broadband and vibration-free RF beam steering with large angle.

Demonstration of complementary apodized cascaded grating waveguides for tunable optical delay lines

High-speed, tunable integrated silicon photonic delay lines are demonstrated by cascading complementary apodized silicon grating waveguides. The cascaded grating waveguides, with inward and outward super-Gaussian apodization profiles, compensate each other's dispersion and allow high-speed operation. Characterization of the compact delay lines shows that they have low loss, offer true time delays of 82 ps and a tuning range of 32 ps, and can potentially operate at bit rates as high as 107 Gb/s.

Microwave photonic signal processing

Photonic signal processing offers the advantages of large time-bandwidth capabilities to overcome inherent electronic limitations. In-fibre signal processors are inherently compatible with fibre optic microwave systems that can integrate with wireless antennas, and can provide connectivity with in-built signal conditioning and electromagnetic interference immunity. Recent methods in wideband and adaptive signal processing, which address the challenge of realising programmable microwave photonic phase shifters and true-time delay elements for phased array beamforming; ultra-wideband Hilbert transformers; single passband, widely tunable, and switchable microwave photonic filters; and ultra-wideband microwave photonic mixers, are described. In addition, a new microwave photonic mixer structure is presented, which is based on using the inherent frequency selectivity of the stimulated Brillouin scattering loss spectrum to suppress the carrier of a dual-phase modulated optical signal. Results for the new microwave photonic mixer demonstrate an extremely wide bandwidth operation of 0.2 to 20 GHz and a large conversion efficiency improvement compared to the conventional microwave photonic mixer.

Generating, multiplexing/demultiplexing and receiving the orbital angular momentum of radio frequency signals using an optical true time delay unit

A scheme for generating and/or eliminating the orbital angular momentum (OAM) of radio frequency (RF) signals based on the true time delay (OTTD) system is proposed for the first time. The central structure of the scheme is the OTTD unit connected with a circular antenna array which can provide or compensate the helical phase variation precisely, and therefore can form or eliminate the OAM radio beam with different states (the topological charges) conveniently. Other prominent advantages of the proposed system are support for multiplexing/demultiplexing the OAM states carried on the RF signals with the same frequency and support for exchange of the OAM states carried on two RF signals. This can be regarded as the analog of various other multiplexing technologies for increasing the capacity and efficiency in radio communication systems. Theoretical analysis and numerical simulations demonstrate the feasibility of the proposed scheme.

Demonstration of tunable optical delay lines based on apodized grating waveguides

High-speed and tunable integrated optical delay lines are demonstrated based on silicon grating waveguides apodized by the super-Gaussian function. The submicron channel waveguides with inward-apodized gratings are fabricated by deep-ultraviolet optical lithography. Characterization of the compact delay lines shows that they offer true-time delays as long as 132 ps, tuning range of ~86 ps, and a minimum bit rate of ~13 Gb/s. For lower bit rates, delays as high as 220 ps and tuning range of 174 ps are feasible.

Design and Analysis of the Millimeter-Wave SPDT Switch for TDD Applications

This paper presents a low-loss and high Tx-to-Rx isolation single-pole double-throw (SPDT) millimeter-wave switch for true time delay applications. The switch is designed based on matching-network and double-shunt transistors with quarter-wavelength transmission lines. The insertion loss and isolation characteristics of the switches are analyzed revealing that optimization of the transistor size with a matching-network switch on the receiver side and a double-shunt switch on the transmitter side can enhance the isolation performance with low loss. Implemented in 90-nm CMOS, the switch achieves a measured insertion loss and Tx-to-Rx isolation of 1.9 and 39 dB at 60 GHz, respectively. The input 1-dB gain compression point is 10 dBm at 60 GHz, and the return loss of the SPDT switch ports is greater than 10 dB at 48-67 GHz.

A 5-20 GHz 5-Bit True Time Delay Circuit in 0.18 ㎛ CMOS Technology

This paper presents a 5-bit true time delay circuit using a standard 0.18 ㎛ CMOS process for the broadband phased array antenna without the beam squint. The maximum time delay of ~106 ps with the delay step of ~3.3 ps is achieved at 5-20 ㎓. The RMS group delay and amplitude errors are ＜ 1 ps and ＜2 ㏈, respectively. The measured insertion loss is ＜27 ㏈ and the input and output return losses are ＜12 ㏈ at 5-15 ㎓. The current consumption is nearly zero with 1.8 V supply. The chip size is 1.04 × 0.85 ㎟ including pads.

A novel millimetre wave EBG-SIW wideband delay line

A novel millimetre wave wideband time delay line based on substrate integrated waveguide (SIW) is proposed in this article to achieve true time delay. The delay line is formed by loading the SIW with cross electromagnetic bandgap (EBG) unit. The higher delay time can be obtained by adjusting the structure size without affecting its transmission characteristics. A simulation software HFSS is utilised for the optimisation to achieve a better performance. ,, delay lines have been designed and measured in Ka band. All delay line is implemented in this article in Rogers Duroid5880. Compared to the microstrip of the same length, the average delay time is about four times of microstrip on the same substrate in the whole bandwidth from 27.7 GHz to 37.7 GHz. The simulation and measurement show good consistency.

Robert Cell-Based Optical Delay Elements for White Cell True-Time Delay Devices

A low-loss and compact optical delay element is devised to be integrated into existing White cell-based true-time delay systems. The delay element is based on a multiple-bounce cell that consists of simple optical components, which was initially described by Claude Robert for spectroscopy. We hereby provide a comprehensive analysis of the Robert cell and propose that it can be modified in a number of ways to produce discrete and variable time delays up to hundreds of ns. The Robert cell show appealing traits compared to traditional optical delay devices because it relies on reflections within a system of mirrors to produce time delays, and this mechanism reduces the physical size and optical losses compared to traditional approaches for long delays. We also illustrate how modified Robert cells can be designed such that they can be compatibly combined with White cell-based true-time delay systems.

Hybrid Photonic True-Time Delay Modules for Quasi-Continuous Steering of 2-D Phased-Array Antennas

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.

A 15–40 GHz CMOS True-Time Delay Circuit for UWB Multi-Antenna Systems

A CMOS true-time delay (TTD) circuit operating from 15 to 40 GHz is presented for integrated UWB multi-antenna systems. The TTD circuit employs a distributed active switching structure in which eight cascode switches are distributed along transmission lines, leading to 3-bit variations of the group delay. The size of the switches and the characteristic impedance of the transmission lines are carefully scaled so as to minimize loss variation among the different delay states, while maintaining flat delay performance over a wide bandwidth. The circuit is implemented in a bulk 0.13-μm CMOS technology and exhibits a total variable group delay of 40 ps with an average resolution of 5 ps from 15 to 40 GHz. The insertion loss was 14 dB with a maximum RMS variation of 1.6 dB, while the input and output return loss was better than 10 dB over the operating bandwidth.

Electronically scanned Rotman lens antenna with liquid crystal phase shifters

The performance of a Rotman lens, which forms fixed beams at 0°, ±15° and ±30°, is augmented using liquid crystal phase shifters to simultaneously steer each beam by up to ±7.5°. Measured results are used to demonstrate that the true time delay property of the antenna and voltage controlled phase shifters can be exploited to provide continuously scanned beams with full coverage over an angular range of ±37.5°, and with operation over the band 6–10 GHz.

Reconfigurable liquid metal fiber-optic mirror for continuous, widely-tunable true-time-delay

This paper reports the demonstration of a widely-translatable fiber-optic mirror based on the motion of liquid metal through the hollow core of a photonic bandgap fiber. By moving a liquid metal mirror within the hollow core of an optical fiber, large, continuous changes in optical path length are achieved in a comparatively small package. A fiber-optic device is demonstrated which provided a continuously-variable optical path length of over 3.6 meters, without the use of free-space optics or resonant optical techniques (i.e. slow light). This change in path length corresponds to a continuously-variable true-time delay of over 12 ns, or 120 periods at a modulation frequency of 10 GHz. Wavelength dependence was shown to be negligible across the C and L bands.

The LWA1 Radio Telescope

LWA1 is a new radio telescope operating in the frequency range 10-88 MHz, located in central New Mexico. The telescope consists of 258 pairs of dipole-type antennas whose outputs are individually digitized and formed into beams. Simultaneously, signals from all dipoles can be recorded using one of the instrument's "all dipoles" modes, facilitating all-sky imaging. Notable features of the instrument include high intrinsic sensitivity (about 6 kJy zenith system equivalent flux density), large instantaneous bandwidth (up to 78 MHz), and 4 independently-steerable beams utilizing digital "true time delay" beamforming. This paper summarizes the design of LWA1 and its performance as determined in commissioning experiments. We describe the method currently in use for array calibration, and report on measurements of sensitivity and beamwidth.

THE DESIGN OF AN OPTICAL TIME STEERED ANTENNA BASED ON A NEW INTEGRATED TRUE TIME DELAY UNIT

In the framework of wide-band and ultra wide-band array antennas, an Optical Time Steered Antenna (OTSA) is presented, by considering the design strategies of a new True Time Delay (TTD) Control Unit in the Beam Forming Network (BFN). The unit has high reliability, low crosstalk, low switching time and potential low cost, being based on a low cost technology. Furthermore, due to its compactness and modularity, it can be easily grouped with other ones to make a control unit of large arrays. Difierent strategies and working conflgurations of the TTD control unit are presented as a trade-ofi among hardware complexity, insertion loss reduction and beam control capability. The design of an OTSA prototype is discussed by considering a realistic model simulating the behavior of a real world antenna and accounting for unavoidable non-realities, such as random, periodic and systematic errors introduced by each device exploited in the OTSA as well as mutual coupling between radiating elements. An optimal trimming strategy, able to compensate at best for BFN errors and based on the use of suitably located trimmers, is presented. Among other cases, to enlighten the potentialities of the OTSA, an all optical architecture providing a difierence beam squint free pattern is also proposed.