Audio acquisition and recording can benefit from directional reception of the acoustic signals. Current acoustic designs of highly-directional microphones are bandwidth limited and physically large. A microphone array used in conjunction with a beamforming algorithm can acquire and spatially filter the signal, but traditionally this has suffered from limitations similar to those of the purely acoustic designs. The work presented in this paper attempts to overcome these limitations by producing and analyzing three atypical techniques for broadband beamforming. The last and most successful technique employs an algorithm which calculates the difference in group delay of the acquired signals and uses that information to determine the direction of the incoming signals as a function of frequency.

The analysis and design of passive broadband negative group delay (NGD) transmission line phase shifters is presented. By extending the metamaterial transmission line concept to include loss, a NGD unit cell is proposed. Phase shifters are supplemented with NGD unit cells to produce a flattened phase response significantly increasing phase bandwidths. The design methodology of a NGD phase shifter is presented with consideration of nominal phase, frequency, impedance, maximum insertion loss and bandwidth. The relation between gain, bandwidth and group delay signifies a fundamental design limitation and tradeoff. A significant application of NGD phase shifters for removing beam squint in series fed antenna arrays is discussed. Several NGD phase shifters are fabricated and experimentally verified in the UHF band upwards of 1 GHz using planar microstrip transmission lines loaded with passive surface mount RF components with both positive and negative phase shifts.

The analysis and design of passive broadband negative group delay (NGD) transmission line phase shifters is presented. By extending the metamaterial transmission line concept to include loss, a NGD unit cell is proposed. Phase shifters are supplemented with NGD unit cells to produce a flattened phase response significantly increasing phase bandwidths. The design methodology of a NGD phase shifter is presented with consideration of nominal phase, frequency, impedance, maximum insertion loss and bandwidth. The relation between gain, bandwidth and group delay signifies a fundamental design limitation and tradeoff. A significant application of NGD phase shifters for removing beam squint in series fed antenna arrays is discussed. Several NGD phase shifters are fabricated and experimentally verified in the UHF band upwards of 1 GHz using planar microstrip transmission lines loaded with passive surface mount RF components with both positive and negative phase shifts.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Group delay variations are a potential problem in many communication systems. This paper is slanted towards the effects of group delay variations in analog magnetic recorder/reproducer systems but the results are applicable in general. Because it is difficult to get an arbitrary group delay profile at the output of a recorder/reproducer, a method of generating arbitrary group delays for bit error probability (BEP) testing was developed. A 32-bit pattern in which all five-bit sequences appear with equal probability was selected as the test signal. The amplitude and phase of the discrete Fourier components were calculated for both non-return-to-zero-level (NRZ-L) and biphase-level (BI -L) waveforms. Filtering and group delay variations were computer generated by varying the amplitude and phase of the Fourier components. The modified signals were then programmed into an arbitrary waveform generator. Noise was added and the composite signal was applied to a bit synchronizer and bit error detector. BEPs were measured for various noise levels and group delay profiles.

No description available.

In modern wireless communication systems, such as satellite communications and wireless networks, the need for higher data rates without the need for additional transmit power has made Continuous Phase Modulation (CPM) one of the most attractive modulation schemes in band limited channels. However, as the data rates keep increasing, the spectral width of the CPM signal increases beyond the channel bandwidth and performance becomes constrained by the intersymbol interference (ISI) that results from band-limiting filters. We propose two approaches to the problem of equalization of band-limited CPM signals. First, our efforts are focused on shortening the channel impulse response so that we can use a low complexity MLSE equalizer. We implement the channel truncation structure by Falconer and Magee and adapt it to work with CPM signals. This structure uses a, a more derivable, pre-filter to shape the overall response of the channel, so that its impulse response is of shorter duration. Simulation results show that near-MLSE performance can be obtained while dramatically reducing MLSE equalizer complexity. In our second approach, we focus on eliminating the group-delay variations inside the channel passband using an FIR pre-filter. We assume the channel to be time-invariant and provide a method to design an FIR filter so that -when convolved with the band limiting filter - it results in more constant group-delay over the filter passband. Results show that eliminating the group-delay variations in the band limiting filter passband reduce the amount of ISI and improve bit error rate performance. / Master of Science

In this thesis, the m-arity tree networks have been investigated to derive equations for their nodes, links and required wavelengths. The relationship among all parameters such as leaves nodes, destinations, paths and wavelengths has been found. Three situations have been explored, firstly when just one server and the leaves nodes are destinations, secondly when just one server and all other nodes are destinations, thirdly when all nodes are sources and destinations in the same time. The investigation has included binary, ternary, quaternary and finalized by general equations for all m-arity tree networks. Moreover, a multicast technology is analysed in this thesis to transmit data carried by specific wavelengths to several clients. Wavelengths multicast switching is well examined to propose split-convert-split-convert (S-C-S-C) multicast switch which consists of light splitters and wavelengths converters. It has reduced group delay by 13% and 29% compared with split-convert (S-C) and split-convert-split (S-C-S) multicast switches respectively. The proposed switch has also increased the received signal power by a significant value which reaches 28% and 26.92% compared with S-C-S and S-C respectively. In addition, wavelengths allocation algorithms in multicast technology are proposed in this thesis using tree networks topology. Distributed scheme is adopted by placing wavelength assignment controller in all parents’ nodes. Two distributed algorithms proposed shortest wavelength assignment (SWA) and highest number of destinations with shortest wavelength assignment (HND-SWA) algorithms to increase the received signal power, decrease group delay and reduce dispersion. The performance of the SWA algorithm was almost better or same as HND-SWA related to the power, dispersion and group delay but they are always better than other two algorithms. The required numbers of wavelengths and their utilised converters have been examined and calculated for the researched algorithms. The HND-SWA has recorded the superior performance compared with other algorithms. It has reduced number of utilised wavelengths up to about 19% and minimized number of the used wavelengths converters up to about 29%. Finally, the centralised scheme is discussed and researched and proposed a centralised highest number of destinations (CHND) algorithm with static and dynamic scenarios to reduce network capacity decreasing (Cd) after each wavelengths allocation. The CDHND has reduced (Cd) by about 16.7% compared with the other algorithms.

In a communication system, the group delay variation (GDV) causes the distortion of signal and the degradation of symbol error rate. Usually, the compensation of group delay (GD) utilizing positive group delay (PGD) results in further propagation delay. Therefore, this research studies the negative group delay (NGD) behavior of metamaterial. Through analyzing the effects on GD caused by poles and zeros of circuit, the group delay circuit capable of switching between NGD and PGD is presented. Further, adjustable negative group delay circuits (NGDCs) are designed based on the concept of poles and zero. The NGD generated by NGDC is used to achieve the equalization of GD and recover the distorted signal in time domain. Additionally, owing to the limited frequency band of communication, a filter with high selectivity is required to utilize the available bandwidth. The character of left-handed metamaterial is applied to the design of filter for reducing the size and cost of traditional microstrip line filters with high selectivity. Under the balanced condition, composite right/left-handed (CRLH) transmission line behaves right- and left- handed characteristics in different frequency bands. Thus, a coplanar waveguide (CPW) filter with high selectivity, size reduction and low cost is presented utilizing such a CRLH structure.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: An ultra-fast laser pulse can be described in the time or frequency domain. If the timebandwidth product of an ultra-fast pulse is not satisfied, then the pulse is stretched. Stretching can be described in the time or frequency domain. In the time domain, it is called a chirp and in the frequency domain, it is known as the group delay dispersion GDD. Various techniques can be used to stretch and compress laser pulses. In this project, a prism pulse compressor used for compressing stretched pulses was built. A 200nm supercontinnum generated in an all normal dispersion photonic crystal fibre (ANDi-PCF) was compressed using the prism pulse compressor from 2ps to 140fs. The experiment and physical interpretation presented in this project suggest that a shorter pulse duration less than the measured 140fs of the compressed supercontinnum can be obtained. / AFRIKAANSE OPSOMMING: 'n Ultra-vinnige laser puls kan beskryf word in tyd of frekwensie. As die tyd-bandwydte produk van ‘n ultra-vinnige puls nie bevredig is nie, dan is die puls uitgerek. Hierdie uitrekking kan beskryf word in tyd of frekwensie. In tyd word dit tjirp genoem en in frekwensie groep vertraging dispersie. Verskeie tegnieke kan gebruik word om ‘n laser puls te rek of saam te pers. In hierdie projek is ‘n prisma puls kompressor gebou om uitgerekte pulse saam te pers. ‘n 200nm bre e bandwydte puls (“supercontinuum”) is gegenereer in ‘n fotoniese kristal optiese vesel wat uitsluitlik normale dispersie toon (ANDI-PCF) en die puls is toe saamgepers met behulp van die prisma puls kompressor van‘n oorspronklike 2ps na 140fs. Die eksperiment en fisiese interpretasie wat in hierdie projek aangebied word dui daarop dat ‘n nog korter puls, minder as die gemete 140 fs, verkry kan word deur die bre e bandwydte puls verder saam te pers.

This thesis presents the results for the temperature variation of the Differential Group Delay (DGD) measurements of a Dispersion Compensation Module (DCM) and interprets the results with a theoretical DGD model based on glass viscoelastic properties and estimated values of some of glass parameters. The results of our analysis demonstrate the existence of long birefringence relaxation times on the order of many hours in response to temperature changes. These results could be of significance in interpreting the behavior of optical fiber systems.