Application of negative group delay active circuits to the design of broadband and constant phase shifters
01 Dec 2008-Microwave and Optical Technology Letters (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 50, Iss: 12, pp 3078-3080
TL;DR: In this paper, a phase shifter with a negative group delay (NGD) active circuit was proposed to achieve a constant phase of 90° ± 5° over a 75% relative bandwidth around 1.6 GHz.
Abstract: The new phase-shifter configuration described in this report uses a negative group delay (NGD) active circuit. In this topology, a classical transmission line is set in cascade with an NGD circuit whose phase slopes are alike, but opposite, to get a constant and broadband phase shift. The proposed approach was validated through the design and measurement of a phase shifter, which exhibited a constant phase of 90° ± 5° over a 75% relative bandwidth around 1.6 GHz. Moreover, as the group delay of the NGD circuit compensated the transmission line one, the overall circuit group delay was kept to a small value in the operating frequency band. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3078–3080, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23883
Citations
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TL;DR: An alternative topology for the feedforward amplifier is demonstrated, which does not use a delay element, thus providing an efficiency enhancement and a size reduction by employing a distributed-element negative group-delay circuit.
Abstract: We will demonstrate an alternative topology for the feedforward amplifier. This amplifier does not use a delay element, thus providing an efficiency enhancement and a size reduction by employing a distributed-element negative group-delay circuit. The insertion loss of the delay element in the conventional feedforward amplifier seriously degrades the efficiency. Usually, a high-power coaxial cable or a delay-line filter is utilized for a low loss, but the insertion loss, cost, and size of the delay element still act as a bottleneck. The proposed negative group-delay circuit removes the necessity of the delay element required for a broadband signal suppression loop. With the fabricated two-stage distributed-element negative group-delay circuit with 30 MHz of bandwidth and -9 ns of group delay for a wideband code-division multiple-access downlink band, the feedforward amplifier with the proposed topology experimentally achieved 19.4% power-added efficiency and -53.2-dBc adjacent channel leakage ratio with 44-dBm average output power.
126 citations
Cites background from "Application of negative group delay..."
...In [25]–[27], various applications of the NGD circuits with an active topology have been proposed....
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TL;DR: This work consolidates this non-Foster reactive element loading method with earlier efforts where NGD networks were used to implement zero-degree phase shifters for beamforming at the broadside direction, and generalizes these methods for arbitrary-angle beamforming from backfire to endfire including the broad side direction.
Abstract: Beamforming in series-fed antenna arrays can inherently suffer from beam-squinting. To overcome the beam-squinting problem, low-dispersion, fast-wave transmission lines can be employed. Such transmission lines can be designed by loading a regular transmission line with non-Foster reactive elements (e.g., negative capacitors and inductors). As a result of a recent development, these non-Foster reactive elements can be implemented using loss-compensated negative-group-delay (NGD) networks, providing a solution to the stability issues associated with conventional non-Foster networks. In this work, transmission lines augmented by loss-compensated NGD networks, representing the non-Foster reactive-element loading, are employed for designing wideband fast-wave, low-dispersion transmission lines. This work consolidates this non-Foster reactive element loading method with earlier efforts where NGD networks were used to implement zero-degree phase shifters for beamforming at the broadside direction, and generalizes these methods for arbitrary-angle beamforming from backfire to endfire including the broadside direction. Experimental results are presented for a wideband linear four-element transmitting array feed network for beamforming at 30° with respect to the broadside direction in the frequency range 1–1.5 GHz. By connecting this feed network to four wideband tapered-slot antennas, the beamforming performance is experimentally verified inside an anechoic chamber. Moreover, the antenna array is experimentally tested for transmission of a narrow pulse, where low distortion is observed at the beamforming angle over the entire operating bandwidth. The physical length of the feed network is realistic and is 0.96 wavelengths long at the center of this frequency range. In addition, switched-line phase shifters are employed for squint-free beamforming in three other angles: 60°, 0°, and $-30^{\circ}$ .
107 citations
TL;DR: A NGD-bandwidth-product limit is derived as a function of the number of stages and the out-of-band gain, which is independent of the circuit topology and can include active gain compensation.
Abstract: In this paper the asymptotic limits of negative group delay (NGD) phenomena in multi-stage RLC resonator-based circuits are discussed. A NGD-bandwidth-product limit is derived as a function of the number of stages and the out-of-band gain, which is independent of the circuit topology and can include active gain compensation. The limit is verified experimentally at microwave frequencies using a gain-compensated NGD circuit employing a parallel RLC resonator in the feedback path of a high-frequency op-amp. It is shown that, in the asymptotic limit, the NGD-bandwidth-product is proportional to the square root of the number of stages, and also to the square root of the logarithm of the out-of-band gain. The relation between the time-domain transient amplitude and the out-of-band gain is analyzed for finite-duration modulated signals, indicating an exponential increase in transient amplitudes with the square of NGD. Analysis shows that any attempt to increase the NGD of a finite-duration modulating waveform, by cascading more stages, is thwarted by the transients.
90 citations
Cites background from "Application of negative group delay..."
...The results presented here are also applicable to gain-compensated NGD circuits operating at higher frequencies [9], used in applications such as broadband baluns [12] and broadband constant phase shifters [14]....
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...Similarly, the circuits used in [8], [9], [12] and [14], can all be modeled using general expression (1), by determining from their circuit parameters....
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...2107251 constant phase shifters [13], [14], channel equalizers [15], and interconnect RC-delay and RLC-delay equalization [16]....
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TL;DR: In this article, a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delays (NGD) time is proposed. And the performance degradation of the NGD time and signal attenuation according to the temperature dependent resistance variation is also analyzed.
Abstract: This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of -7.3 ns with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.
69 citations
TL;DR: An alternative topology to greatly increase the operating bandwidth of an analog RF feedback power amplifler by introducing a negative group delay circuit (NGDC) in the feedback loop and achieving an adjacent channel leakage ratio of i53:2dBc.
Abstract: We will demonstrate an alternative topology to greatly increase the operating bandwidth of an analog RF feedback power amplifier. A limited operating bandwidth due to the group delay mismatch of a feedback loop discouraged the use of an RF feedback technique in spite of its powerful linearization performance and great tolerance capability. By introducing a negative group delay circuit (NGDC) in the feedback loop, group delay match condition could be satisfied. With the fabricated 2-stage distributed element negative group delay circuit with a 30MHz of bandwidth and a -9 ns of group delay for a wideband code division multiple access (WCDMA) downlink band, the proposed feedback amplifier with the proposed topology experimentally achieved an adjacent channel leakage ratio of -53.2 dBc with a cancellation bandwidth of over 50 MHz.
65 citations
References
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TL;DR: These experiments directly confirm the predictions of Maxwell's equations that n is given by the negative square root ofɛ·μ for the frequencies where both the permittivity and the permeability are negative.
Abstract: We present experimental scattering data at microwave frequencies on a structured metamaterial that exhibits a frequency band where the effective index of refraction (n) is negative. The material consists of a two-dimensional array of repeated unit cells of copper strips and split ring resonators on interlocking strips of standard circuit board material. By measuring the scattering angle of the transmitted beam through a prism fabricated from this material, we determine the effective n, appropriate to Snell's law. These experiments directly confirm the predictions of Maxwell's equations that n is given by the negative square root of epsilon.mu for the frequencies where both the permittivity (epsilon) and the permeability (mu) are negative. Configurations of geometrical optical designs are now possible that could not be realized by positive index materials.
8,477 citations
TL;DR: A network that synthesises negative group delay is presented and a hybrid MIC realisation of the network, operating at 1 GHz, is described and its measurements are reported.
Abstract: A network that synthesises negative group delay is presented. The conditions required for achieving negative group delay, with a simple R-L-C tuned circuit, are briefly introduced. A hybrid MIC realisation of the network, operating at 1 GHz, is described and its measurements are reported.
114 citations
TL;DR: The negative group delay in the electronic circuit shares the same mechanism with superluminal light propagation, where the group velocity exceeds the speed of light or even becomes negative.
Abstract: We present a simple electronic circuit that produces negative delays. When a pulse is sent to the circuit as input, the output is a pulse with a similar wave form that is shifted forward in time. The advance time or negative delay can be increased to the order of seconds so that we can observe the advance with the naked eye by observing two light emitting diodes that are connected to the input and the output. The negative group delay in the electronic circuit shares the same mechanism with superluminal light propagation, where the group velocity exceeds the speed of light or even becomes negative.
100 citations
TL;DR: In this article, the negative group velocity was demonstrated theoretically and experimentally in the time domain using modulated Gaussian pulses, where the output pulse peak emerged from the loaded transmission line prior to the input peak entering the line.
Abstract: We have simulated and constructed a one-dimensional metamaterial composed of a periodically loaded transmission line that exhibits both negative and positive group velocities in a band of effective negative index of refraction. The negative group velocity or, equivalently, the negative group delay, is demonstrated theoretically and experimentally in the time domain using modulated Gaussian pulses. Due to this negative delay, we can show an output pulse peak emerging from the loaded transmission line prior to the input peak entering the line, i.e., the output pulse precedes the input pulse. The fact that this surprising behavior does not violate the requirements of relativistic causality is illustrated with time-domain simulations, which show that discontinuities in the pulse waveforms are traveling at exactly the speed of light in vacuum. The pulse-reshaping mechanism underlying this behavior is also illustrated using time-domain simulations.
89 citations
TL;DR: In this paper, the design, simulation and implementation of an active negative group delay circuit that operates at 1 GHz with a group delay and a gain, respectively, around 2 ns and 2 dB.
Abstract: In this letter, we report on the design, simulation and implementation of an active negative group delay circuit that operates at 1 GHz with a group delay and a gain, respectively, around 2 ns and 2 dB. Analytical formulas are proposed to demonstrate that the adopted topology is able to simultaneously achieve negative group delay (NGD) and gain while fulfilling active device constraints. The theoretical and simulated results are both validated by frequency measurements of a two-stage active microwave circuit.
88 citations