Group Delay Fluctuation Research Articles

Balanced bandpass filter with common-mode reflectionless and linear-phase characteristics based on negative group delay circuit

In this paper, a balanced bandpass filter (BPF) with common-mode reflectionless and linear-phase characteristics is proposed, which consists of a balanced 3-order bandpass filtering network and two common-mode absorptive networks to obtain the common-mode reflectionless and suppression performance. The negative group delay circuits are loaded on the proposed balanced BPF to realize the full-passband linear-phase filtering performance. The flatter the group delay of the BPF (the fluctuation of the group delay within the passband tends to 0), the better the phase-frequency linearity, which will realize the undistortion transmission of the communication systems. For demonstration, a balanced linear-phase BPF prototype operating at 1.5 GHz is designed, simulated, and manufactured. The results demonstrate that the group delay fluctuation is reduced from 1.20 ns to 0.11 ns by 90.8 %, the differential-mode insertion loss is 1.04 dB, the minimum common-mode suppression is 59.3 dB within the passband and the common-mode reflectionless band is 1.22–1.91 GHz. The developed topology requires high precision in the processing, and the proposed balanced BPF can be applied to digital microwave communication systems to improve the transmission quality and reduce the bit error rate.

Compact and Wideband Flat Negative Group Delay Circuit Investigation

This paper introduces a dual transmission structure with bandpass (BP) negative group delay (NGD) wideband flat behavior. The flat BP-NGD topology is analytically modelled from equivalent circuit composed of transmission line (TL) and stepped-impedance resonator connected by two resistors. As proof of concept (POC), by tuning TL characteristic impedances, the influences of circuit physical variables on NGD flatness are illustrated by parametric study. The flat BP-NGD POC circuit with a size of 48.2 mm×90.8 mm (0.2λg 0.38λg) is designed, fabricated, and measured. A very good agreement is confirmed by simulation and experimentation results of 680 MHz over 290 MHz (42.6%) NGD bandwidth (BW) around 0.7 GHz NGD center frequency. Also, the flat BP-NGD BW reaches 223 MHz (31.8%) over 569 MHz to 792 MHz with ±0.05 ns group-delay fluctuation with insertion and reflection losses better than 14 dB.

Analysis and Design of a DC-12-GHz Distribution Power Amplifier for Quantum Key Distribution Application

A CMOS distributed power amplifier (DPA) for quantum key distribution (QKD) system to drive an electro-optical phase modulator is developed. Due to the requirement of amplifying high-speed non-return-to-zero (NRZ) signal, our design is supposed to provide enough bandwidth, including dc. To achieve sharp roll-off performance, the m-derived filter section is applied to realize the artificial transmission line rather than the constant-k section. Combining the theory analysis and simulation, the bridges between gain ripple, group delay fluctuation, or maximum linear output power and the parameters of time domain waveform are established. Furthermore, through analyzing the attenuation and delay of the transmission line, approaches to improving the frequency performance, such as gain variation and group delay fluctuation, are provided. The DPA is implemented in the 0.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process and achieves a bandwidth of dc-12 GHz, a gain of 11.54 dB with variation of ±1.34 dB, a group delay of 400 ps with fluctuation of about 100 ps, and a maximum output 1-dB compression point of 20.6 dBm. When a 1-Gb/s NRZ signal is applied to the DPA, the rise and fall times are both about 90 ps. The amplifier occupies an area of 2.8 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.94$ </tex-math></inline-formula> mm including pads and adopts the flip-chip package with low-temperature co-fired ceramic (LTCC) substrate.

Wideband Flat Negative Group Delay Circuit With Improved Signal Attenuation

A novel wideband flat negative group delay (NGD) circuit with improved signal attenuation is proposed. The proposed negative group delay circuit (NGDC) is composed of three transmission lines and two parallel branches, which are consisted of two series transmission lines with a resistor linking to a T-type stub. The complete closed-form design equations are presented. For verification, an NGDC is designed, fabricated, and measured at the center frequency of 2.14 GHz. From the measured results, NGD time of −1.11 ns at the center frequency is obtained with an insertion loss of 9.75 dB and return loss of 22.3 dB. The flat-NGD bandwidth reaches 6.1% from 2.072 to 2.202 GHz with ±11.5% group-delay fluctuation.

Reconfigurable negative group delay circuit with tunable group delay flatness

A reconfigurable negative group delay circuit (NGDC) with tunable group delay flatness is presented. The proposed NGDC is composed of an amplifier, three series resistors connecting with two transmission lines, two varactors, and a diode. By shorting different resistors through the diode, different negative group delay (NGD) times can be obtained. Two varactors are utilized to tune the flatness of the group delay. For verification, an NGDC is designed, fabricated, and measured at the center frequency of 1.0 GHz. The measured NGD time is tuned from −2.0 to −5.8 ns. The flat-NGD bandwidth varies from 2.2% to 8.8% with ±8% group-delay fluctuation. And the insertion loss varies from 6.5 to 13.8 dB.

Group delay flatness and bandwidth enhancement of wideband negative group delay microwave circuit

A wideband negative group delay (NGD) microwave circuit with group delay flatness and bandwidth enhancement is proposed. The proposed negative group delay circuit (NGDC) is composed of a resistor connected by two transmission lines and a parallel branch consisted of a resistor linking with a stepped-impedance transmission line and two open stubs. By tuning the characteristic impedance of the transmission lines, the flat-NGD bandwidth is enhanced. For verification, an NGDC with a size of 0.24λg × 0.34λg is designed, fabricated, and measured. The measurement shows that an NGD time of −0.5 ns at the center frequency of 1.0 GHz is obtained with the NGD bandwidth of 68.6% over 0.668 to 1.365 GHz. Also, the flat-NGD bandwidth reaches 46.3% or 0.776 to 1.243 GHz with ±8% group-delay fluctuation while the insertion loss is less than 18.8 dB and return loss is greater than 21 dB.

Influence of linear coupling and group delay fluctuations on intermodal four wave mixing in few mode fiber

We present numerical and experimental study on the origin of fluctuations in the idler power in partially degenerate intermodal four wave mixing in a 1 km long few mode graded index fiber where both the fundamental and higher order modes are excited in both pump and signal wavelengths. Numerical simulation is carried out in the presence of different types of mode coupling processes and group delay fluctuations in order to independently predict the influence of these phenomena by considering the appropriate statistics of the corresponding processes. We propose a quasi-distributed model by choosing the locations of specific coupling events statistically, in correspondence to their correlation lengths. Idler conversion efficiency is experimentally evaluated for different detuning frequencies between the signal and pump through multiple trials, and it is found that even though distinct features of maxima and minima are retained, there are fluctuations in frequencies corresponding to maxima and minima. These experimental results are compared with those from numerical simulations in order to identify the origin of fluctuations.

A Novel Configuration for Compact HTS CQ Structure Linear Phase Filter Design

In this paper, a novel trapezoidal meander-line resonator (TMLR) is proposed to design compact high-order high-temperature superconducting (HTS) linear phase bandpass filters with cascaded quadruplet (CQ) structures. By changing the conventional rectangle half-wavelength meander-line microstrip resonator into a trapezoidal resonator, unnecessary cross coupling between nonadjacent resonators in the CQ units can be avoided. And using the proposed TMLR to design the CQ unit, electric field cross coupling or magnetic field cross coupling can be easily achieved and tuned without the cross-coupling line. To further demonstrate the feasibility of using this configuration for miniaturized circuit design, an 8-order HTS linear phase filter with one pair of transmission zeros was designed. The measured responses agree very well with the simulated results. The physical HTS filter has a center frequency of 1935 MHz and bandwidth of 70 MHz. The out-of-band rejection is greater than 50 dB, and the effective bandwidth of group delay fluctuation less than ±3 ns takes up more than 65% in the whole passband.

Impact on Antijamming Performance of Channel Mismatch in GNSS Antenna Arrays Receivers

The performance of antijamming is limited by channel mismatch in global navigation satellite system (GNSS) antenna arrays receivers. Only when the amplitude and phase characteristics of each array channels are the same is the interference likely to be completely suppressed. This paper analyzes the impact on antijamming performance of channel mismatch. We built the model of channel mismatch and derived the impact on transfer function with space-time adaptive processor (STAP) of channel mismatch in theory. The impact factor of channel mismatch is proposed by the fuzzy transfer function, which could directly reflect the antijamming performance under channel mismatch. In addition, every characteristic in the channel mismatch model is analyzed. The analysis results show that the greatest impacts on antijamming performance are the range of amplitude wave and the group delay bias, while the influence of the number of amplitudes is next. As for the effect of group delay fluctuation is the smallest.

Group delay measurement method based on narrow‐band spread spectrum signals

The group delay fluctuation of navigation equipment will cause signal distortion, thus bringing on ranging bias, and therfore needs to be measured and compensated. The vector network analyser method commonly adopted cannot satisfy high measuring accuracy and high frequency resolution at the same time; the higher the frequency resolution, the bigger the measuring error. To resolve this problem, a new group delay measurement method based on narrow-band spread spectrum signals is proposed. Theoretical analysis and simulation results indicate that this method can implement high measuring accuracy with any frequency resolution, and the system bias of the method is much less than 0.1 ns.

Performance characterization of components with group delay fluctuations

A variety of components in optical communication systems exhibit group delay fluctuations, which degrade the quality of transmitted signals. In this letter, we present a method to derive two independent figures-of-merit, based on the measured group delay, which accurately determine the system performance degradation caused by any type of group delay fluctuations in a component. These two parameters can be used to estimate the performance of concatenated components and are, therefore, suited for component specifications.