True Time Delay Research Articles

A Programmable Phased Array with Time-Delay Units and its Applications

In this paper, a phased array antenna schematic using true time delays is proposed and suitable time-delays are inserted by switching ON/OFF the RF switches. Using this concept, one can generate SUM pattern, DIFFERENCE pattern, as well as a combination of these two. It is shown that SUM-DIFFERENCE pattern has interesting applications in radar, namely, calibration of beam pointing accuracy and blind speed elimination in a delay line cancellation method. The proposed method can also be formatted to requirements of conical scan as well as shaped beam generation. The proposed method is validated using existing knowledge.

Opto-VLSI-based photonic true-time delay architecture for broadband adaptive nulling in phased array antennas

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.

Design and development of a broadband amplitude compensated long time delay circuit on thin‐film liquid crystal polymer

AbstractA 2‐bit long time delay circuit capable of 0 to 600 ps relative delays has been developed to operate from DC to 10 GHz. This circuit implements an amplitude compensation scheme through use of carefully designed attenuation coefficients on true time delay components that have been developed on a multilayer stack of thin‐film liquid crystal polymer. Minimal insertion losses are achieved by using prototype microelectromechanical system SP4T switches. Insertion losses are measured to be less than 4.3 dB across the band for all delays. Amplitude imbalance is measured to less than ±0.5 dB across the band. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1060–1063, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24231

Real-time all-optical performance monitoring using optical bit-shape correlation

A new optical performance monitoring technique of an optical link in real time is experimentally demonstrated. Rather than comparing bit streams or analyzing eye diagrams, we use a novel optical correlator to compare the shapes of the individual received bits to a standard. The all-optical correlator outputs a pulse whose strength directly measures the degradation of the bit during transmission. Results are produced within three bit periods in real time instead of requiring statistical analysis of long data streams. The correlator is based on a simplified White cell-based true-time delay device.

Microwave Photonics

Broadband and low loss capability of photonics has led to an ever-increasing interest in its use for the generation, processing, control and distribution of microwave and millimeter-wave signals for applications such as broadband wireless access networks, sensor networks, radar, satellite communitarians, instrumentation and warfare systems. In this tutorial, techniques developed in the last few years in microwave photonics are reviewed with an emphasis on the systems architectures for photonic generation and processing of microwave signals, photonic true-time delay beamforming, radio-over-fiber systems, and photonic analog-to-digital conversion. Challenges in system implementation for practical applications and new areas of research in microwave photonics are also discussed.

Noise analysis in photonic true time delay systems based on broadband optical source and dispersion components

The noise in photonic true time delay systems based on broadband optical source and dispersion components is investigated. It is found that the beat noise induced by the optical source begins to dominate and grows far larger than other noise terms quickly, as long as the detected optical power is above some certain value P(thr). When the system dispersion is nonzero, the output carrier-to-noise ratio (CNR) will change periodically with the optical bandwidth due to the noise power increment and the dispersion induced radio frequency signal power degradation. The maximum CNR is the peak value of the first period. For a set of specified system conditions, the P(thr) is calculated to be -21 dBm, and the optimal optical bandwidth is 0.8 nm, at which the maximum CNR is 93.3 dB by considering the noise in a 1 Hz bandwidth. The results are verified experimentally.

Rotman lens design and simulation in software [Application Notes

Since its invention in the early 1960s (Rotman and Turner, 1963), the Rotman Lens has proven itself to be a useful beamformer for designers of electronically scanned arrays. Inherent in its design is a true time delay phase shift capability that is independent of frequency and removes the need for costly phase shifters to steer a beam over wide angles. The Rotman Lens has a long history in military radar, but it has also been used in communication systems. This article uses the developed software to design and analyze a microstrip Rotman Lens for the Ku band. The initial lens design will come from a tool based on geometrical optics (GO). A second stage of analysis will be performed using a full wave finite difference time domain (FDTD) solver. The results between the first-cut design tool and the comprehensive FDTD solver will be compared, and some of the design trades will be explored to gauge their impact on the performance of the lens.

Photonic dual RF beam reception of an X band phased array antenna using a photonic crystal fiber-based true-time-delay beamformer

We report dual RF beam reception of an X band phased array antenna using a photonic crystal fiber (PCF)-based delay network. Each incoming RF signal can be independently received, and the angle of arrival can be determined based on the delay time-dependent wavelength. Two RF signals with frequencies 8.4 and 12 GHz impinge upon an X-band antenna array from -7.4 degrees and -21.2 degrees . These signals are detected, and the angle of arrival is determined with a very good degree of accuracy using PCF-based true-time delay. The total number of RF beams that can be simultaneously detected is limited by the hardware availability and the bandwidth of the wavelength differentiation capability of the system.

Improved Photonic True Time Delay Unit for a Ku-Band Phased Array Antenna Demonstration

In this letter, a Photonic True Time Delay (PTTD) unit for phased array antennas is experimentally demon- strated. The PTTD unit, employing a single wavelength laser source, exploits the distributed photonic bandgap offered by a Linearly Chirped Fiber Bragg Grating (LCFBG) to attain different time delays by properly actuating the physical and geometrical features of the LCFBG through temperature changes. The time delay response of the TTD unit has been measured experimentally revealing multiband operation capability (S, C, X and Ku bands) with ps time delay resolution and a maximum dynamic range of 250ps. The time steering demonstration has been performed by characterizing in the Ku band an array prototype within a Near Field range.

Bandwidth Improvement in Large Reflectarrays by Using True-Time Delay

A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size.

Distributed transmission line phase shifter using MEMS switches and inductors

Distributed MEMS transmission line (DMTL) phase shifter has been developed using planar inductors. The design consists of a coplanar waveguide line capacitively and inductively loaded by the periodic set of electrostatic force actuated microelectromechanical system switches as capacitors and inductors. By applying a single bias voltage on the line, the characteristic impedance can be changed, which in turn changes the phase velocity of the line and creates a true time delay phase shift. The governing equations for the impedance and loss are derived. The ABCD matrix is defined for a unit and multi-cell DMTL phase shifter to extract scattering parameters equations. The device containing 15 cells calculated, simulated, and fabricated. Fabricated results show that the device can be considered as a new type of the DMTL phase shifter with small size, higher phase shift and acceptable scattering parameters.

Multilayer Organic Multichip Module Implementing Hybrid Microelectromechanical Systems

We present the design and development of an organic package that is compatible with fully released RF microelectromechanical systems (MEMS). The multilayer organic package consists of a liquid-crystal polymer film to provide near hermetic cavities for MEMS. The stack is further built up using organic thin-film polyimide. To demonstrate the organic package, we have designed and implemented a 2-bit true-time delay X-band phase shifter using commercially available microelectromechanical switches. The packaged phase shifter has a measured insertion loss of 2.45 plusmn 0.12 dB/bit at 10 GHz. The worst case phase variation of the phase shifter at 10 GHz is measured to less than 5deg. We have also conducted temperature cycling (-65degC to 150degC) and 85/85 to qualify the packaging structures.

Complex analytic signals applied on time delay estimation

In this paper, we present the concept of the time delay estimation based on the transformation of real sensor signals into analytic ones. We analyze the differential time delay values obtained using real seismic signals, simulated complex analytic signals and simulated complex analytic signals with real parts coming from real seismic signals. The simulation results indicate that the application of complex analytic signals leads to reliable computation of the differential time delay. The influence of specific signal parameters on spectral coherence threshold in systems for passive localization and proposed methods for lowering the threshold is analyzed. The computation of all differential time delays with respect to the reference sensor (geophone) is based on the application of Generalized Cross-Correlation (GCC) applied on corresponding analytic signals. The difficulties to select a peak of cross-correlation function that corresponds to true differential time delay when dealing with real signals are significantly reduced if GCC is applied on analytic signals. The efficiency of the proposed technique on differential delay estimation is performed on deterministic and real-life signals.

SMALL SIZE KA-BAND DISTRIBUTED MEMS PHASE SHIFTERS USING INDUCTORS

MEMS phase shifter has been developed using inductors. The design consists of a CPW line capacitively and inductively loaded by the periodic set of inductors and electrostatic force actuated MEMS switches as capacitors. By applying a single bias voltage on the line, the characteristic impedance can be changed,which in turn changes the phase velocity of the line and creates a true time delay phase shift. The governing equations for the impedance and loss are derived. The ABCD matrix is defined for a unit cell and multi-cell DMTL phase shifter to extract scattering parameters equations. The MEMS switch is actuated by a 39 voltage waveform using a high resistance bias line. Estimated spring constant and switching time is 22 N/m and 3 µs,respectively. The structure is designed for Ka-band frequency range. The acceptable frequency range for the design containing 21 cells is between 26 GHz and 27 GHz and optimum condition occurs at 26.3 GHz. For the whole structure and optimum condition the un actuated position results in a return loss −16 dB and insertion loss of −1.65 dB. The actuated position results in a return loss −12.5 dB and insertion loss of −1.6 dB. The phase shift for the whole structure is 190 degree. The optimum condition can be easily changed by modifying the design parameters. The spacing in the proposed structures is S = 250 µm. The structure is also low loss. The length and the loss per bit with the phase shift of 270 ◦ are decreased by 37.5 percent and 21 percent respectively.

RF MEMS Extended Tuning Range Varactor and Varactor Based True Time Delay Line Design

MEMS varactors are one of the important passive MEMS devices. Their applica- tions include use in VCOs, tunable impedance matching networks, tunable fllters, phase shifters, and true time delay lines. The shunt capacitive structure has been employed in most of the conventional MEMS varactor designs because of its simplicity. However, the capacitance ratio of this conventional shunt capacitive MEMS varactor is limited to 1.5 because of the MEMS Pull- In efiect, which happens when the de∞ection between the MEMS top and bottom metal plates increase beyond 1/3 of the airgap between the two metal plates. At that time, the top metal plate will quickly snap down. This efiect is the major limitation in MEMS varactor designs and can cause nonlinearity and mechanically instability. In order to eliminate this Pull-In efiect, the author employed the so-called MEMS extended tuning range structure. This structure utilizes a variable height top metal beam with separate actuation parts. The airgap between the center part of the top beam and the bottom plate has been designed to be less than 1/3 of the airgap between the top beam and the bottom actuation pads. When DC bias is applied to the actuation parts, the entire top beam will move down together. Consequently, before the Pull-In efiect happens at the actuation parts, the center part has already traveled through its entire tuning range, which means that the capacitive ratio of this kind of MEMS varactor can go to inflnity. A fabrication process employing a GaAs substrate has been designed based on surface micro- machining technology. The maximum capacitance ratio of the designed MEMS extended tuning range varactor is 5.39 with a Cmax value of 167fF. Based on this MEMS varactor design, a Ka-band MEMS varactor based distributed true time delay line has been designed. This dis- tributed true time delay line includes a high impedance CPW transmission line with 70› un- loaded impedance at 28GHz and eight MEMS extended tuning range varactors based on the varactor design periodically loaded on the CPW line. The testing results show that a 56 - phase delay variation has been achieved at 28GHz. The measured insertion loss at 28GHz is i1:07dB at the up-state and i2:36dB at the down-state. The measured return losses, S11 and S22, are both below i15dB at 28GHz and below i10dB over the entire tested frequency range of 5GHz to 40GHz.

The Effects of Imbalanced Phase Shifters Loss on Phased Array Gain

In the presence of imbalanced insertion loss of phase-shifters, satisfying phase conjugate condition does not necessarily lead to the maximum phased array gain. This paper introduces noncoherent beamforming and uses lab-measured characteristics of varactor-based phase shifters to prove that by perturbing coherency partially, the array gain can increase significantly, e.g., 1.6 dB for a 12 element array. Moreover, it is shown that reduction in the average insertion loss increases the array efficiency by almost the same amount. These results are extendible to the optical beamforming networks where different lengths of fiber are used to make true time delay lines.

Designing a next-generation waveguide by geometry

Planar lightwave circuits (PLCs) have broad application in areas ranging from space to telecommunications to sensing. For example, PLC technology can be used in optical true-time delays for phased array antennas. These delays make possible a simpler, less-expensive control system and improved performance that could benefit wireless communication in space and air.1 PLCs also have utility in integrated-optic network components, such as optical add-drop multiplexers (OADMs).2 These devices help achieve high system functionality in fiber-to-thehome networks. Finally, PLC techniques can be used for optical sensors and emerging visible applications, since they enable integration of mode filters, interferometric principles, and other optical functions required for compact, highly sensitive and selective devices. Figure 1 gives an overview of optical integration technologies. Integrating functions has several advantages over discrete solutions. Lower costs, mass production, stability, and form factor (footprint area and volume) are all well-known drivers for integration. Achieving integration in the field of optics will require meeting a number of specifications. First, to ensure tight bends and consequently small structures, the technology must offer high contrast in refractive index between the light-guiding layer and the surroundings. Second, there must be a way of correcting for additional losses owing to the greater number of functions. Third, because polarization is so important, there must be a way to control it. Finally, transparency for a large range of wavelengths is essential to guarantee the maximum flexibility required of an industrial standard for integration. We have developed the TriPleX waveguide technology, which is capable of meeting these requirements. It consists of alternating layers of silicon nitride (Si3N4) and silicon dioxide (SiO2) formed by CMOS-compatible low-pressure chemical vapor deposition (LPCVD). TriPleX is fully transparent for wavelengths Figure 1. Examples of optical integration: (from left to right) optical beam forming for phased array antennas, microring resonator filter for R-OADMs, and spiral waveguide for optical sensor. R-OADMs: Reconfigurable OADMs.

An Integrated Ultra-Wideband Timed Array Receiver in 0.13 $\mu{\hbox{m}}$ CMOS Using a Path-Sharing True Time Delay Architecture

A fully integrated CMOS ultra-wideband 4-channel timed array receiver for high-resolution imaging application is presented. A path-sharing true time delay architecture is implemented to reduce the chip area for integrated circuits. The true time delay resolution is 15 ps and the maximum delay is 225 ps. The receiver provides 11 scan angles with almost 9 degrees of spatial resolution for an antenna spacing of 3 cm. The design bandwidth is from 1 to 15 GHz corresponding to less than 1 cm depth resolution in free space. The chip is implemented in 0.13 mum CMOS with eight metal layers, and the chip size is 3.1 mm by 3.2 mm. Measurement results for the standalone CMOS chip as well as the integrated planar antenna array and the CMOS chip are reported.

Fast Evaluation of the Radiation Patterns of True Time Delay Arrays With Beam Steering

A multilevel algorithm for the computation of the transient radiation patterns of true time delay (TTD) conformal arrays over a range of observation and beam steering directions is presented. The multilevel algorithm is based on hierarchical decomposition of the array into smaller sub-arrays of elements. At the finest level of decomposition, the angular-temporal radiation patterns of single-element sub-arrays are obtained over a sparse angular grid of directions and short temporal duration, by either measurement or calculation. Subsequent steps of the algorithm comprise multilevel aggregation of delayed sub-array contributions. This process continues until the transient radiation pattern of the whole array is obtained. At each level, the radiation pattern is interpolated to a finer angular grid of observations and steering directions followed by temporal delay compensation. The multilevel array decomposition algorithm attains a computational complexity substantially lower than that of the direct evaluation. Furthermore, the algorithm is particularly efficient for large arrays with large numbers of elements.

Slow Light in a Semiconductor Waveguide for True-Time Delay Applications in Microwave Photonics

We have investigated the slow and fast light properties of a semiconductor waveguide device employing concatenated gain and absorber sections. This letter presents the experimental results as well as theoretical modeling. A large phase shift of 110deg and a true-time delay of more than 150 ps are demonstrated. The combination of amplitude and phase control of the modulated signal shows great promise for applications within microwave photonics.