Delay Line Filter Research Articles

Trisection Microstrip Delay Line Filter With Mixed Cross-Coupling

It has been discovered that a trisection bandpass filter with mixed cross-coupling K 13 has flat group delay if the condition K 13 = 0 is satisfied, which occurs when magnetic Km and electric |K e | components of the coupling are equal. It has been proven that the group delay of the filter increases as the values K m = |K e | increase. The microstrip construction of the trisection delay line filter is proposed. The analysis of this construction has been carried out, which allows controlling the values Km = |Ke| at the zero of cross-coupling. The results of the measurements and the simulation are presented.

Few Mode Fiber-Based Microwave Photonic Finite Impulse Response Filters

Single-source few mode fiber-based microwave photonic finite – impulse response filters, which exploit the few mode fibers’ differential mode group delays as the separate optical delay lines of the filter, are experimentally demonstrated and compared to theoretical predictions. These microwave photonic filters exhibit excellent stability compared to equivalent conventional optical delay line filters in the coherent regime. The advantages and disadvantages of these robust photonic devices with extremely simple architectures are discussed.

Analysis and Design of Bang-Bang PD-Based Phase Noise Filter

In this paper, we present a bang-bang phase detector (BBPD) and a delay-line frequency discriminator-based phase noise filter (PNF). With a larger phase detection gain, the BBPD-based PNF enhances the sensitivity by suppressing the charge pump noise. A time-amplifier and a five times voting machine are introduced together with the sense-amplifier-flip-flop to minimize the BBPD noise to make its effects negligible in the PNF sensitivity. At 1-MHz offset, the PNF demonstrates 15-dB phase noise suppression with −120.2-dBc/Hz sensitivity. Its phase noise suppression offset frequency is from 100 kHz to 8 MHz with 10–10.1-GHz input frequency range. The circuit is fabricated in a 65-nm CMOS technology, and dissipates 98-mW power.

A wide range delay locked loop for low power and low jitter applications

SummaryIn this paper, a design of analog delay locked loop is introduced in which new techniques are applied to eventually increase operating frequency range and reduce jitter considerably. In this design, all blocks of a delay locked loop including a voltage controlled delay line, charge pump, and loop filter are accurately designed. A new delay cell is proposed with wide delay range, in which increase of delay range results in using fewer cells, and consequently the power consumption will decrease. Current mirror techniques and feedback in the proposed charge pump also cause higher current matching and better jitter performance. This delay locked loop, which is designed with TSMC 0.18‐μm CMOS technology, has a wide frequency range from 217 to 800 MHz. It consumes maximum 3.4‐mW and minimum 2.6‐mW power dissipation in source voltage of 1.8 V, which is suitable for low power applications. It also has an appropriate lock time that is at least equal to 3 clock cycles at 217 MHz and at most 25 clock cycles at 800 MHz. Jitter performance in this delay locked loop is improved significantly: RMS jitter is 0.65 ps at 800 MHz and 2.54 ps at 217 MHz. Moreover, its maximum peak‐to‐peak jitter is equal to 5.17 ps, and its minimum peak‐to‐peak jitter is equal to 1.39 ps at 217 and 800 MHz, respectively.

A Taylor Series Approximation of Self-Interference Channel in Full-Duplex Radios

The fundamental problem in the design of a full-duplex radio is the cancellation of the self-interference (SI) signal generated by the transmitter. Current techniques for suppressing SI rely on generating a copy of the SI signal and subtracting it partly in the radio frequency (RF) and digital domains. A critical step in replicating the self-interference is the estimation of the multipath channel through which the transmitted signal propagates to the antenna. Since there is no prior model on the number of multipath reflections, current techniques assume a tap delay line filter (in the RF and digital domain) with a large number of taps, and estimate the taps in the analog and the digital domain. In this paper, using a linearization technique, we show that the self-interference channel in an indoor environment can be effectively modeled as $H(f)=C_{0} - C_{1}f$ in the frequency domain. Thus, the effective self-interference channel can be represented by two parameters $C_{0}$ and $C_{1}$ , irrespective of the multipath environment. We also provide experimental evidence to verify the above channel model and propose novel low-complexity designs for self-interference cancellation.

Beamforming system based on paralleled variable chirped microwave signal generators

Optically controlled beamforming technology has attracted a lot of research interest for its unique advantages and application in phased array antennas (PAAs). In this paper, a novel scheme of an optically controlled beamforming system based on an array of chirped microwave signal generators is proposed. In the proposed system, an array of photonic microwave delay line filters (PMDLFs) with quadratic phase response is configured, and chirped microwave signals, which are then applied to the antennas, are generated by processing a chirped-free Gaussian pulse by those filters, and the relative delay among those chirped microwave signals can be controlled by tuning the optical carriers’ wavelength in each path. Therefore, the system can realize optically controlled beamforming by successfully combining photonic generation of a chirped microwave signal with optical true time delay (OTTD). As the PMDLFs’ frequency response can be flexibly varied, the generated microwave signal waveforms can be adjustable to suit the needs of different applications. A theoretical analysis of the proposed beamforming system is carried out and its feasibility is verified by numerical simulations.

Reconfigurable photonic delay line filter working in Ku band

In this work, we experimentally demonstrate a tunable microwave photonic filter working in ‘Ku’ frequency band (12–18 GHz). We followed three different schemes: double side band (double-SB), single side band (single-SB) and optical-carrier suppression (optical-CS) for our proposed photonic link. We also derived and numerically solved the transfer function for each case. Re-configurability (change in transfer function) of the filter is achieved by using laser switching (ON/OFF) and carefully windowing (using a higher order cosine window—the Blackman window) of the time samples in the range of 1–20 GHz. Moreover, we also investigate the amplitude comparison function (difference of power fading function) with the help of a vector network analyzer. Our experimental and simulation investigations are in good agreement with the theoretical analysis.

Performance Evaluation of Broad Band CDMA Signal Using Beam Forming Antenna Technology for Next Generation Communications

<p>In order to accommodate various multimedia services, next generation wireless networks are characterized by very high transmission rates. Thus, in such systems and networks, the received signal is not only limited by noise like Additive White Gaussian noise (AWGN) but especially with increasing data transmission rate by the Intersymbol Symbol Interference (ISI) due to time dispersion of channel. A number of techniques such as rake receiver in CDMA systems and equalizers in GSM systems have been proposed to combat the effect of fading so as to improve the performance of wireless communication network. In this paper we evolve the performance of uncoded uplink transmission in broadband CDMA using beam forming technique under multipath conditions. The beam-former has been implemented using Transport Delay Line (TDL) filters. An expression for the optimal weights of a TDL based beam former has been derived. A carrier frequency of 2 Ghz has been used in this work as they are useful for next generation wireless systems. Simulation results show that TDL beamformer can reduce the multipath fading and Multiple Access Interferance (MAI). It has been shown that if SNR (related with Variance of the channel) is maintained at 10 db and if a 3 ray based beamformer having 3 antennas with 3 taps is used, the Error Rate of 0.1was found without using channel coding.</p>

Tunable microwave photonic transversal filter

We present a tapped tunable delay line filter for radiofrequency (RF) photonic filtering applications, capable of rapid tunability over a wide RF bandwidth limited only by the optical components’ losses, while maintaining independence from polarization state. Multiple fiber taps with contrasting dispersion slopes are used in intensity-modulated direct detection microwave photonic links. A temporal delay is generated between the signals within each arm of the link. Once a signal is received using balanced differential detection, nulls are generated as a function of the laser's operating wavelength. Tuning of the laser allows for a rapid shifting of the nulls in the RF spectrum to dynamically mitigate co-site interference. Through this method we demonstrate the potential for rapid tunability over the RF spectrum by the variation of the operating wavelength of the optical carrier.

Variable-chirped microwave waveform generator based on reconfigurable microwave photonic filter

An optical approach to generating chirped microwave signal using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response is proposed and demonstrated. In this scheme, a narrow band Gaussian pulse is used as the original signal. In order to eliminate the need for a wideband original microwave chirped-free signal, a mixer and a radio frequency signal are used to up-convert the spectrum of the original signal and the dispersion curve is tuned to minimize the attenuation caused by the fiber dispersion. Then the required frequency response can be reconstructed by a nonuniformly spaced PMDLF. Since the majority of the power of the original signal can bypass the filter, the power of the generated chirped microwave signal will be increased. A reconstruction example of a desired frequency response with a central frequency of 10 GHz is provided, and the generation of the corresponding chirped microwave signal is demonstrated by numerical simulations.

Hybrid technique for enhanced optical ranging in turbid water environments

A hybrid approach is described that enhances the performance of an underwater optical ranging system. This approach uses high-frequency modulation and a spatial delay line filter to suppress unwanted backscatter. A dual frequency approach is also implemented to reduce the effects of forward scatter and remove the ambiguity associated with using the phase of the single, high-frequency modulation envelope to measure range. Controlled laboratory experiments were conducted to evaluate the effectiveness of the hybrid technique to reject multiple scattered light and improve range precision. The experimental results were compared with data generated from a theoretical model developed to predict the performance of the technique as a function of system and environmental variables. Model and experimental results are shown that reveal the ability of the approach to provide accurate ranging to an underwater object in a variety of water environments. Model predictions also indicate that advancements in transmitter and receiver technology will extend the range and improve the accuracy of the technique beyond what has been achieved thus far.

A Nonuniformly Spaced Microwave Photonic Filter Using a Spatially Discrete Chirped FBG

We report an experimental demonstration of a nonuniformly spaced photonic microwave delay-line filter implemented using an incoherent broadband optical source and a spatially discrete chirped fiber Bragg grating (SD-CFBG). The SD-CFBG performs simultaneously three functions: 1) to slice the spectrum of the broadband optical source for generating the filter taps; 2) to provide nonuniform time delays; and 3) to control the weights of the filter taps. Since negative or complex coefficients are equivalently generated based on the nonuniform sampling, a filter with an arbitrary spectra response is achieved. To verify the effectiveness of the proposed method, a flat-top bandpass microwave filter with seven all-positive nonuniformly spaced taps at 12 GHz is experimentally demonstrated. The proposed method offers a cost-effective and easy-to-implement solution for photonic microwave filters having arbitrary frequency responses.

Elimination of Pre-Steering Delays in Space-Time Broadband Beamforming Using Frequency Domain Constraints

One of the most popular methods in broadband beamforming is the Frost space-time processing. In this method, a pre-steering delay is followed by a tapped delay line (TDL) filter in each branch of the beamformer. Pre-steering delays are used to compensate for the effect of misalignment between the array geometry and the look direction. However, any error in implementing these delays drastically degrades the performance of the array. In this letter, a new set of constrains are introduced to substitute the pre-steering delays. These constraints are defined in frequency domain and adjust the beamformer weights such that the desired signal is passed without any distortion. Setting nulls at interference directions can also be incorporated in these constraints and can further improve the performance of the beamformer.

A new technique for 100-fold increase in the FSR of optical recirculating delay line filters using a time compression unit

A new technique that increases the free spectral range (FSR) of a recirculating delay line filter, is presented. The concept is based on a time-compression unit, which is used in conjunction with a frequency-shifting recirculating loop that generates multi-spectral characteristics, and the idea exploits the optical wavelength domain by wavelength-to-time mapping of the taps using an oppositely time-oriented dispersive element so that the taps travel different lengths, to time compress the tap separation. This technique solves, for the first time, the long-standing problem of the small FSR limitation in recirculating microwave photonic delay line filters, opening the way to realize the main functionalities required in microwave photonic filters. Experimental results are presented which demonstrate a large 100-fold increase in the FSR of the bandpass filter response.

Highly precise micro-retroreflector array fabricated by the LIGA process and its application as tapped delay line filter

We report on the fabrication of a one-dimensional micro-retroreflector array with a pitch of 100 μm. The array was fabricated by x-ray lithography and the lithographie, galvanik und abformung (LIGA) process in a 1 mm thick poly(methyl methacrylate) (PMMA) layer and subsequently covered with Au. The area of the array is 1 mm×10 mm. The high precision of the LIGA-based fabrication process allows one to use the element in spectrometers. Here, it is suggested to apply it to the implementation of a transversal filter for femtosecond pulses. We present a theoretical description of the performance of the retroreflector array as a filtering device and show experimental results.

Continuously Tunable Chirped Microwave Waveform Generation Using a Tilted Fiber Bragg Grating Written in an Erbium/Ytterbium Codoped Fiber

An optical approach to generating continuously tunable chirped microwave waveforms using a tilted fiber Bragg grating (TFBG) written in an erbium/ytterbium (Er/Yb) codoped fiber is proposed. By pumping the TFBG, the magnitude and group delay responses of the cladding mode resonances are changed, which can be used to implement a photonic microwave delay-line filter with increasing or decreasing tap spacing. If an ultranarrow pulse is sent to the photonic microwave delay-line filter, a pulse burst with increasing or decreasing pulse spacing is generated. The photodetection of the pulse burst would lead to the generation of a chirped microwave waveform. The proposed technique is demonstrated by an experiment in which a chirped microwave waveform with a tunable chirp rate from 1.8 to 7 GHz/ns is generated.

A Continuously Tunable Microwave Fractional Hilbert Transformer Based on a Nonuniformly-Spaced Photonic Microwave Delay-Line Filter

A continuously tunable microwave fractional Hilbert transformer (FHT) implemented based on a nonuniformly spaced photonic microwave delay-line filter is proposed and demonstrated. An FHT has a frequency response with a unity magnitude response and a phase response having a phase shift between 0 and π at the center frequency. A seven-tap photonic microwave delay-line filter with nonuniformly spaced taps is designed to provide such a frequency response. The advantage of using nonuniform spacing is that an equivalent negative coefficient can be achieved by introducing an additional time delay leading to a π phase shift, corresponding to a negative coefficient. An FHT operating at a center frequency around 8.165 GHz with a tunable order between 0.24 and 1 is implemented. A classical HT operating at a center frequency of 7.573 GHz with a bandwidth greater than 4.5 GHz is also implemented. The use of the classical HT to perform temporal Hilbert transform of a Gaussian-like electrical pulse is demonstrated.

Erratum to: “Small-Sized Microstpip Delay Line Filters on the Substrates with High Permittivity”

Erratum to: “Small-Sized Microstpip Delay Line Filters on the Substrates with High Permittivity”

Broadband beamforming using Laguerre filters

Space–time processing is a well-substantiated method for designing broadband beamformers. In the conventional Frost space–time beamformer, tapped delay line (TDL) filters are used in each branch of the array to create a wideband response for interference suppression. In this article a new space–time beamforming method is introduced in which Laguerre filters replace the traditional TDL filters in the Frost beamformer. The Laguerre filters are fundamentally IIR filters but with only one pole in their structure. Unlike other IIR-based space–time beamforming methods, the proposed method does not need an adaptive procedure for the pole adjustment and is inherently stable. Simulation results show superior performance of the proposed method compared to the Frost beamformer and comparable results against other IIR-based beamformers with much less computational complexity and guaranteed stability.

A Microwave Bandpass Differentiator Implemented Based on a Nonuniformly-Spaced Photonic Microwave Delay-Line Filter

A microwave bandpass differentiator implemented based on a finite impulse response (FIR) photonic microwave delay-line filter with nonuniformly-spaced taps is proposed and experimentally demonstrated. To implement a microwave bandpass differentiator, the coefficients of the photonic microwave delay-line filter should have both positive and negative coefficients. In the proposed approach, the negative coefficients are equivalently achieved by introducing an additional time delay to each of the taps, leading to a π phase shift to the tap. Compared with a uniformly-spaced photonic microwave delay-line filter with true negative coefficients, the proposed differentiator features a greatly simplified implementation. A microwave bandpass differentiator based on a six-tap nonuniformly-spaced photonic microwave delay-line filter is designed, simulated, and experimentally demonstrated. The reconfigurability of the microwave bandpass differentiator is experimentally investigated. The employment of the differentiator to perform differentiation of a bandpass microwave signal is also experimentally demonstrated.