Group Delay Response Research Articles

Highly miniaturized dual-band bandpass filter with wide bandwidth and large center frequency ratio

The design of a miniaturized dual-band bandpass filter featuring a broad bandwidth and a high center frequency ratio is demonstrated in this article. A novel symmetrically loaded shunt coupled line with dual stepped impedance stubs has been investigated for the first time and it is utilized to realize a dual-band bandpass filter with seven transmission zeros. The transmission zeros frequencies of the filter response have been theoretically verified using even-odd mode analysis. For experimental validation purposes, a dual-band filter with a center frequency ratio of 4.06 covering 5G applications is implemented using Rogers RT/duroid 5870 substrate and tested. The tested filter has wide 3 dB fractional bandwidths of 53.8% and 17.9% in the first and second passbands, respectively, and has a compact topology of 0.20 × 0.09 λg 2. The full-wave simulated and tested magnitude and group delay responses of the proposed filter are in good congruence.

Measurement of Group Delay Ripples of Chirped Fiber Bragg Gratings for CPA Lasers, and Their Effect on Performance

The deleterious effect of group delay ripples (GDR) on the performance of a chirped fiber Bragg grating used as a stretcher in a chirped pulse amplification (CPA) laser is analyzed through simulations of CFBGs with various amounts of noise. We show that GDR with a standard deviation of less than one-half the transform-limited pulse duration are required for consistent good performance. We furthermore describe a simple method to measure the group delay response of such CFBGs written in polarization-maintaining fiber, using the beat spectrum of the reflections from the two polarization axes after passing through a polarizer. The method can be used to extract GDR, as well as the phase response of the CFBG, which is used to predict the pulse recompression performance of a CPA laser. The method is theoretically described, and we show that despite limitations on its spatial resolution, it can capture the most deleterious GDR. Experimental measurements of GDR as low as 161 fs in an actual CFBG are demonstrated using our method, indicating a resolution better than 50 fs and very good reproducibility, with pulse recompression performance in agreement with the measurement prediction.

Design of dispersion‐reconfigurable phaser using stepped‐impedance line

AbstractThis paper proposes a dispersion‐reconfigurable reflection‐type phaser based on the stepped‐impedance microstrip line structure. By configuring “ON” and “OFF” states of switches, the proposed phaser exhibits positive‐slope, negative‐slope, and zero‐slope linearly dispersive group delay responses. For proof‐of‐concept demonstration, we use line connection/disconnection to mimic the ON/OFF states of real switches. Three prototypes are hence fabricated to represent the three different states. The experimental results agree well with the expected responses, which finally validate the proposed concept.

A novel compact semicircular defected ground structure ultrawideband monopole antenna integrated with Ku band for breast cancer detection

SummaryA compact and novel ultrawideband (UWB) antenna integrated with Ku band for microwave imaging applications is reported. The reported antenna consists of a novel patch structure along with a tapered feed structure on top of FR‐4 substrate having a compact dimension of 16 × 22 mm2 and novel semicircular defected ground structure (SC‐DGS) etched below the substrate. The proposed antenna covers a wide impedance bandwidth of 15.07 GHz spanning from 3.51 to 18.58 GHz with a fractional bandwidth (FBW) of 136%. The intended antenna performance is analyzed for S11, peak gain, efficiency, and radiation patterns in frequency domain, and group delay, isolation (S21), and linear phase response in time domain. The simulated and measured results of reported antenna are well matched for the usage in practical portable UWB applications. More importantly, the proposed antenna system is simulated for the detection of breast cancer tissue by comparison of S21 results, current densities, and specific absorption rate with and without tumor conditions. These findings show that the radiator and the whole system work well in detecting the breast tumor.

Efficient photonics beam forming system incorporating super structure fiber Bragg grating for application in Ku band

We propose and demonstrate a photonic true-time delay beamforming system for a 1 × 4 linear phased array antenna, operating in the Ku-band, based on superstructured fiber Bragg gratings (SFBGs) with linearly rising equivalent chirps. The proposed beam-forming network operates at 18 GHz frequency, which is theoretically analyzed and simplified by simulated results. The SFBG has a distinct number of gratings in each beamforming path, which provides a large and progressive phase delay. The advantage of the proposed technique can be found in terms of its wavelength tunable scheme making the system squint-free. The proposed architecture is a true time delay optical beam forming a network, which enables squint-free beam steering of radio frequency (RF) signals. In this study, a technique known as double sideband modulation of multiple wavelengths is utilized to investigate the reflection quality of SFBG at various chirp rates. Taking into account that each segment of FBG consists of 50, 60, 70, and 80 gratings and phase shift section samples of each segment, the overall length of the SFBGs is calculated to be 2 cm, 2.4 cm, 2.8 cm, 3.2 cm, respectively, are used for calculating group delay. An equation in a closed form representing the corresponding dispersion is derived. SFBG group delay response is analyzed theoretically with required simulation to investigate the reflectance characteristics. All simulation work for designing the beam forming system is done on Optisystem version 19 and designing of Super structure fiber Bragg grating Optigrating version 4.2. The optically process wavelengths are detected by high speed dedicated photo-detector (PD) and delay response is investigated through array factor of each antenna. Errors in the fabricated SFBGs' group delay responses are examined also.

Multiple Fano Resonances in a Metal–Insulator–Metal Waveguide for Nano-Sensing of Multiple Biological Parameters and Tunable Slow Light

A surface plasmonic waveguide made of metal–insulator–metal (MIM) capable of generating triple Fano resonances is proposed and numerically investigated for multi-biological parameter sensing as well as tunable slow light. The waveguide is made up of a bus waveguide with a silver baffle, a square split-ring cavity with a square center (SSRCSC), and a circular ring cavity with a square center (CRCSC). Based on the triple Fano resonances, human blood temperature and plasma concentration are measured simultaneously at different locations in the waveguide, and the maximum sensitivities were 0.25 nm/°C and 0.2 nm·L/g, respectively. Furthermore, the two biological parameters can be used to achieve tunable slow light, and it was found that the group delay responses to human blood temperature and plasma concentration all conformed to cubic functions. The MIM waveguide may have great applications in future nano-sensing of multiple biological parameters and information processing of optical chips or bio-optical chips.

Tailoring Group Delay Dispersion of Spatial Phaser using Anisotropic Metasurface and Polarized Incident Waves

AbstractMetasurface‐based spatial phaser, exhibiting dispersive group delay responses, is able to perform real‐time analogue signal processing on the temporal spectrum of spatial electromagnetic waves, e.g., Fourier transformation, pulse chirping, pulse spread, and compression. The functionality of a spatial phaser is closely related to its group delay dispersion slope. For instance, for an up‐chirped incident pulse, the positive‐slope‐dispersion phaser spreads the pulse whereas the negative‐slope‐dispersion one compresses the pulse. Most reported spatial phasers exhibit fixed dispersion slopes and hence perform single functionality only, which cannot meet the demand of multifunctional systems in communication and sensing applications. In this paper, a new way is proposed to control and tune the dispersion slope of spatial phasers using polarization of incident waves, which is simpler and more efficient than conventional approaches based on tunable circuits. To verify the proposed method, a first‐order spatial phaser is designed and experimentally demonstrated within 9.4–10.6 GHz. It is able to generate negative‐slope, positive‐slope, and zero‐slope group delay dispersions, in case of x‐, y‐, and ±45°‐polarized waves. Such a reconfigurable phaser may find wide applications in integrated communication and sensing.

Digitally tunable dispersion controller using chirped multimode waveguide gratings

We propose a digitally tunable dispersion controller (DTDC) for dispersion management that shows potential for realizing phase correction, waveform generation, beamforming, and pulse sculpting in many photonic systems. The controller consists of N stages of cascaded chirped multimode waveguide gratings (MWGs) as well as (N+1) Mach–Zehnder switches (MZSs) on silicon. We introduce MWG technology so that the reflected light can be separated from the input signal even without a circulator, which makes it convenient for various system applications. All the chirped MWGs are identical so that the photonic circuit design is convenient, while the number, m, of the chirped MWGs in cascade for the nth stage is given by m=2(n−1). The total dispersion from the DTDC is accumulated by all the stages, depending on the states of all the 2×2 optical switches. Since there are 2 N −1 chirped MWGs in total, the total dispersion can be freely tuned from 0 to (2 N −1)D0 by a step of D0, where D0 is the dispersion provided by a single chirped MWG. As an example, we designed a DTDC consisting of four stages of chirped MWGs (N=4) and five MZSs and demonstrated its low loss as well as its high-quality group delay response. A chirped MWG with a 2-mm-long grating section has a dispersion of D0=2.82ps/nm in a 20-nm-wide bandwidth, and accordingly the maximum dispersion is given as 42.8 ps/nm by switching the MZSs appropriately. Our on-chip DTDC provides a brand-promising option for broadband flexible dispersion management in optical systems of microwave photonics and optical communications.

A 20 ns to 320 ns group delay controller and its application in long time delay self-interference cancellation system

A frequency tunable group delay controller (GDC) based on second-order reflective tunable resonant network and circulator is proposed. The GDC has continuous tunable group delay with allpass magnitude response. Trade-off between delay time and loss of general one-port lossy resonant circuit is studied, and a one-port second-order coupled-resonator structure is optimized. This proposed second-order reflective tunable resonant network is realized by microstrip resonators with optimized coupling location. A circulator is utilized to convert the reflection-type circuit to transmission type. The influence of the circulator isolation leakage upon the delay time is also analyzed. The GDC is designed, simulated and fabricated. Group delay can be tuned from 20 ns to 320 ns, and central frequency of the group delay response can be tuned from 940 MHz to 980 MHz. The insertion loss is less than 10 dB, 15 dB, 25 dB and 27 dB for 50 ns, 100 ns, 200 ns and 320 ns group delay, respectively. The figure-of-merit that the insertion loss per 1 ns delay of the GDC cell is the lowest among compared delay controllers. Two proposed GDC cells are then cascaded. The measurement demonstrates the bandwidth extension ability and the potential usage in full-duplex communication self-interference cancellation.

A Christmas Tree-Shaped Quadband Compact Antenna with Triple Slots for Various Wireless Technologies

A compact, coplanar waveguide (CPW)-fed multiband antenna is developed and analyzed in this paper for quad-band applications. Christmas tree-like monopole antennae with three symmetric slots are designed on a low-cost FR4 epoxy substrate with the overall dimensions of 0.312λ 1 × 0.364λ 1 × 0.0083λ 1 where λ 1 is the wavelength corresponding to the lower cut-off frequency. Three rectangular-shaped slots of different dimensions are etched on the three triangular-shaped stacked patches to enhance the current carrying path due to which the proposed antenna resonates at the required frequency bands. Different antenna parameters such as reflection coefficient (S 11), gain, radiation efficiency, surface current, radiation pattern, group delay and magnitude response of transfer function (S 21) are analyzed for inspecting the antenna performance. The quad-band antenna offers measured bandwidths of 3.1–3.9 GHz (22.86%), 5.46–5.98 GHz (9.1%) 9.76–11.74 GHz (18.42%) and 17.55–19.25 GHz (9.24%). The antenna shows nearly omnidirectional radiation patterns in all resonating bands with the highest gain of 4.5 dBi and measured radiation efficiency greater than 70% in all the bands. The antenna also offers stable group delay response and linear S 21 response in its operational spectrums. All these characteristics ensure the antenna’s applicability in IEEE 802.16 WiMAX band, 5.5 GHz Wi-Fi band, 5.8 GHz ISM band, terrestrial broadband, radiolocation and earth explorer satellite applications.

Simultaneous flattening of amplitude and group delay responses in narrowband bandpass filters using a novel systematic design method

Simultaneous flattening of amplitude and group delay responses in narrowband bandpass filters using a novel systematic design method

A 4-bits active inductor-based lattice 24.5–50 ps all-pass filter

In this paper, a lattice network-based second-order all-pass filter (APF) design is presented. Unlike previously published works, floating active inductors (FAIs) are used in the lattice topology. Inductance (L) and quality factor (Q) tunability of Q-enhanced FAIs are employed to ensure the designed APF is robust to process-voltage-temperature (PVT) variations and to make the filter’s group delay responses are constant for a wide frequency range. The operation of the proposed APF is verified by post-layout simulations using Cadence Design Suite in TSMC 65-nm CMOS technology. The operating frequency of the designed filter reaches 5 GHz with a delay range of 24.5-50 ps. The designed filter has a gain of -0.15 dB, which varies up to 1.47 dB in the operating frequency range. The group delay error is 114 fs, which is a 0.294% variation in the nominal case. The input-referred 1 dB compression point (P1dB) and the third-order interception point (IIP3) values are attained as -5.21 dBm and +9.19 dBm, respectively. At the nominal condition, the noise figure is achieved as 16.7 dB. The circuit occupies only 0.0189 μm2 while drawing 29 mA from a 1.5 V supply.

Optimum Chebyshev filter with an equalised group delay response

ABSTRACT The first part of the paper discusses designing of the lowpass filter that gives both a constant group delay over the passband and a sharp cut-off slope, which is one of the most difficult challenges in continuous-time signal processing. Furthermore, equalisation of the group delay distortion of the Chebyshev filter has been performed through a cascade connection of the allpass filters. The Newton–Raphson method is applied for solving the system of nonlinear equations that calculate the allpass filter parameters for equalising the constant group delay in an equiripple sense. This procedure gives nearly symmetric impulse response of the resulting filtering system, as well as a longer duration. In the second part of the paper, two solutions for synthesising polynomial filter transfer functions are discussed: filter with monotonic amplitude characteristic (LSM) and filter using Chebyshev polynomial. For the purpose of comparison, the passband ripple factor of the Chebyshev filter is necessary to be adjusted so that both filters have the same stopband insertion loss, group delay and transient response. It is shown that Chebyshev filter is preferable since the passband magnitude distortions and sensitivity to the element deviation tolerance are significantly superior.

Cascaded Dispersive Delay Structure Based on Periodic Glide Symmetric Microstrip Stubs

A novel cascaded dispersive delay structure based on a periodic glide symmetric stub-loaded microstrip transmission line is presented. Two group delay peaks are superposed to realize a group delay response that illustrates linear characteristics versus frequency. Two examples with slopes 0.83 and 2 ns/GHz, respectively, are proposed. Verified by experiments, the simulated and measured group delays show a well agreement.

Dispersive Delay Structures With Asymmetric Arbitrary Group-Delay Response Using Coupled-Resonator Networks With Frequency-Variant Couplings

This article reports the design of coupled-resonator-based microwave dispersive delay structures (DDSs) with arbitrary asymmetric-type group delay response. The design process exploits a coupling matrix representation of the DDS circuit as a network of resonators with frequency-variant couplings (FVCs). The group delay response is shaped using complex transmission zeros (TZs) created by dispersive cross-couplings. We also present an optimization-based synthesis procedure for characteristic polynomials with a prescribed group delay profile. Thus, when compared with prior-art DDS approaches, the proposed DDS solutions allow a general group delay profile to be patterned while incorporating optimization-based coupling matrix design techniques for their synthesis. The design method is validated by full-wave simulations and measurements of three built proof-of-concept prototypes of DDS devices with different shapes of group delay response in waveguide and microstrip technologies.

Compact reconfigurable antenna system for spectrum interweaved cognitive radio

This article discusses the design of a compact antenna system for spectrum interweaved cognitive radio (CR). The system consists of a sensing filtenna and three communicating antennas. The sensing ultra-wideband (UWB) antenna is a coplanar-waveguide (CPW)-fed monopole (2.2–11 GHz). The narrowband communicating patch antennas are reconfigurable through a switching mechanism, operating in six different frequency bands (5.54, 6.12, 7.60, 8.25, 9.64, and 10.29 GHz). To block the Wi-MAX and WLAN bands, the proposed design uses a meandering slot and a stepped U-slot in the monopole. Analysis of communicating antennas using the theory of characteristic mode analysis indicates good radiation in the desired frequencies. Isolation among these antennas is better than −18 dB. A constant group delay and linear phase response indicate a good time-domain performance of the proposed UWB antenna. Simulated results match closely with those from measurements on the prototype. The proposed antenna system can find applications in various sectors adopting CR like internet of things.

Hyperfine optical vector analysis of ultra- narrowband optical bandpass filters based on coherent two-tone sweeping and fixed low-frequency detection

A hyperfine optical vector analyzer (OVNA) is proposed and experimentally demonstrated to characterize ultra-narrowband optical bandpass filters (OBPFs). In this scheme, a coherent two-tone optical signal (TTOS) with a small frequency interval is generated to act as a probe light. Through finely sweeping the TTOS across the passband of the OBPF via electro-optic modulation, the magnitude and phase responses of the OBPF under test can be measured with a high signal-to-noise ratio based on fixed low-frequency detection. The frequency response measurement is immune to external disturbance. In the experiment, the magnitude and group delay responses of a fiber-based Fabry-Perot tunable filter (FFP-TF) and a fiber-based Fabry-Perot interferometer (FFP-I) with 3-dB bandwidths of 1.5 GHz and 60 MHz, respectively, are successfully measured. In addition, the measurement uncertainty is theoretically and experimentally analyzed. This method paves a way to characterize ultra-narrowband OBPFs with high out-of-band rejection ratios.

Design of low‐pass and band‐pass infinite impulse response maximally flat stable digital differentiators

Maximally flat digital differentiators (MFDDs) are very attractive for differentiation of narrowband signals. The design of infinite impulse response (IIR) MFDDs, however, is very challenging due to the non-convexity of the flatness constraints of the IIR digital differentiator (DD). This study derives a set of linear conditions that are equivalent to the non-convex flatness constraints and then utilises these conditions to design low-pass and band-pass IIR MFDDs with low and nearly constant group delay. In addition, a generalized-positive-realness-based stability constraint is incorporated in the design to ensure the robust stability of the DD. A design algorithm is presented to maximise the total flatness degree subject to the flatness conditions and the stability constraint, resulting in maximally flat stable DDs (MFSDDs). Design examples and comparisons with existing DDs demonstrate that the designed IIR MFSDDs have better magnitude and group-delay responses and lower implementation complexity.

Active Terahertz Modulator and Slow Light Metamaterial Devices with Hybrid Graphene-Superconductor Photonic Integrated Circuits.

Metamaterial photonic integrated circuits with arrays of hybrid graphene–superconductor coupled split-ring resonators (SRR) capable of modulating and slowing down terahertz (THz) light are introduced and proposed. The hybrid device’s optical responses, such as electromagnetic-induced transparency (EIT) and group delay, can be modulated in several ways. First, it is modulated electrically by changing the conductivity and carrier concentrations in graphene. Alternatively, the optical response can be modified by acting on the device temperature sensitivity by switching Nb from a lossy normal phase to a low-loss quantum mechanical phase below the transition temperature (Tc) of Nb. Maximum modulation depths of 57.3% and 97.61% are achieved for EIT and group delay at the THz transmission window, respectively. A comparison is carried out between the Nb-graphene-Nb coupled SRR-based devices with those of Au-graphene-Au SRRs, and significant enhancements of the THz transmission, group delay, and EIT responses are observed when Nb is in the quantum mechanical phase. Such hybrid devices with their reasonably large and tunable slow light bandwidth pave the way for the realization of active optoelectronic modulators, filters, phase shifters, and slow light devices for applications in chip-scale future communication and computation systems.

Switchable and simultaneous spatiotemporal analog computing with computational graphene-based multilayers

In the past few years, analog computing has experienced rapid development but mostly for a single function. Motivated by parallel space-time computing and miniaturization, we show that reconfigurable graphene-based multilayers offer a promising path towards spatiotemporal computing with integrated functionalities by properly engineering both spatial- and temporal-frequency responses. This paper employs a tunable graphene-based multilayer to enable analog signal and image processing in both space and time by tuning the external bias. In the first part of the paper, we propose a switchable analog computing paradigm in which the proposed multilayer can switch among defined performances by selecting a proper external voltage for graphene monolayers. Spatial isotropic differentiation and edge detection in the spatial channel and first-order temporal differentiation and multilayer-based phaser with linear group-delay response in the temporal channel are demonstrated. In the second section of the paper, simultaneous and parallel spatiotemporal analog computing is demonstrated. The proposed multilayer processor has almost no static power consumption due to its floating-gate configuration. The spatial- and temporal-frequency transfer functions (TFs) are engineered using a transmission line (TL) model, and the obtained results are validated with full-wave simulations. Our proposal will enable real-time parallel spatiotemporal analog signal and image processing.