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The analysis, simulation and testing of an experimental travelling- wave tube.Reynolds, Christopher Garth. January 1994 (has links)
As a design and analysis aid for the development of an
experimental TWT, a computer program is written which
allows the small-signal gain to be computed for various
operating conditions, such as various conditions of tube
bias (beam voltage and current) and frequency. In order to
arrive at a value for the gain, a number of parameters
need first to be defined or calculated.
Using the method (Approach II) of Jain and Basu [17] which
is applicable to a helix with a free-space gap between it
and circular dielectric support rods surrounded by a metal
shell, the dielectric loading factor (DLF) for the
structure is found and the dispersion relation then solved
to obtain the radial propagation constant y and axial
propagation constant B. The method is tested for a helix
with measured data and found to be acceptably accurate.
Helix losses are calculated for the low-loss input and
output sections of the helix, using the procedures
developed by Gilmour et al [14,18], from which values are
found for the helix loss parameter d. Another value for d,
obviously much larger, is also found for the lossy
attenuator section of the helix. Here measured data for
the attenuator is used as a basis for a polynomial which
models the attenuator loss as a function of frequency.
The Pierce gain parameter C is found using the well-known
equations of Pierce [21,22,26], and then the space-charge
parameter Q. Here knowledge of the space-charge reduction
factor F is required to find Q, and a simple non-iterative
method is presented for its calculation, with some
results. From the other parameters already calculated the
velocity parameter, b, is then found.
since sufficient information is now available, the
electronic equations are solved. These equations are in a
modified form, better accounting for the effects of space-charge
than the well-known standard forms. Results are
compared and slight differences found to exist in the
computed gain. Now that the x's and y's (respectively the
real and imaginary parts of the complex propagation
constants for the slow and fast space-charge waves) are
known the launching loss can be calculated. Launching
losses are found for the three space-charge waves, not
just for the gaining wave.
The gain of the TWT is not found from the asymptotic gain
equation but from a model which includes the effects of
internal feedback due to reflections at the ports and
attenuator. Values of reflection coefficients are modelled
on the results of time-domain measurements (attenuator)
and found by calculation (ports). This model permits the
unstable behaviour of the tube to be predicted for various
conditions of beam current and voltage and anticipates the
frequencies at which instability would be likely. Results
from simulations are compared with experimental
observations.
The need to pulse the experimental tube under controlled
conditions led to the development of a high-voltage solid state
pulse modulator providing regulated output pulses of
up to 5000V and 200mA directly, without the use of
transformers. The pulse modulator design embodies two
unusual features a) its operation is bipolar, delivering
positive or negative output pulses, depending only on the
polarity of the rectifier input, and b) the use of
multiple regulating loops and stacked pass elements to
achieve high-voltage operation. Some results are
presented. / Thesis (Ph.D.)-University of Natal, Durban,1994.
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Travelling-wave frequency conversion.Ham, Ronald Edgar. January 1985 (has links)
Travelling-wave distributed amplifiers are providing gain over broad
frequency ranges for microwave applications. Similar concepts are
applicable to distributed mixers and, with the use of controlled feedback,
to a multifunction component simultaneously emulating a mixer, amplifier
and an oscillator. The concept of this new travelling-wave frequency
converter is introduced and data for a discrete component test circuit is
presented. To facilitate the converter operation a new three-port
travelling-wave mixer is introduced and characterized. Four-port
scattering and wave scattering transformations are derived as a method of
analysis of the four-port distributed structure. This enables sequential
circuit analysis on a small computer.
Practical applications unique to the advanced automatic network
analyser, including time domain measurements, are presented to
characterize test circuits as well as to develop ancillary equipment such
as a transistor test fixture. Automated error corrected transistor
measurements and de-embedding are also discussed.
A piecewise linear quantum mechanical method of modelling the
conduction channel of a short gate field effect transistor is given to aid
the extrapolation of the distributed frequency converter concept to
submicron and heterojunction structures. / Thesis (Ph.D.)-University of Natal, Durban, 1985.
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Análise multi-sinal e caracterização experimental de válvulas de ondas progressivas (TWT) para aplicação em amplificadores de micro-ondas / Multi-signal analysis and experimental characterization of travelling-wave tubes for microwave amplifiersLOPES, DANIEL T. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:34:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:48Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:08/05286-1
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Análise multi-sinal e caracterização experimental de válvulas de ondas progressivas (TWT) para aplicação em amplificadores de micro-ondas / Multi-signal analysis and experimental characterization of travelling-wave tubes for microwave amplifiersLOPES, DANIEL T. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:34:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:48Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho apresenta o desenvolvimento de uma plataforma para o estudo teórico e experimental de dispositivos amplificadores de micro-ondas do tipo válvula de ondas progressivas (TWT). A plataforma é composta por um modelo matemático e uma bancada de testes. O modelo matemático descreve a TWT como uma linha de transmissão acoplada a um feixe eletrônico unidimensional, onde as forças de carga espacial AC e DC são calculadas auto consistentemente, eliminando-se a necessidade de um cálculo separado para o fator de redução de carga espacial. O modelo matemático deu origem a dois códigos para a simulação da TWT. Ambos foram comparados com resultados experimentais e teóricos disponíveis na literatura especializada para uma pré-validação. O nível de concordância entre os presentes resultados e aqueles de referência foi acima de 90%, o que atendeu as expectativas de exatidão do modelo, tendo em vista que nem todos os parâmetros de entrada estavam disponíveis na referência. A bancada de testes construída é composta por uma TWT com banda de operação de 6,0 a 18 GHz e potência saturada máxima em torno de 55 dBm (316 W) em 13 GHz, um circuito de polarização para a mesma e a instrumentação necessária para a realização das medidas pertinentes aos amplificadores de potência. A TWT em questão foi caracterizada segundo seu comportamento mono-sinal e multi-sinal. As curvas de ganho e potência foram obtidas em função da frequência utilizando a voltagem de aceleração do feixe eletrônico e a potência de entrada como parâmetros. As curvas de transferência de potência, de fase e compressão de ganho foram obtidas para frequências escolhidas ao longo da banda, tendo novamente a voltagem de aceleração como parâmetro. Adicionalmente, a produção de produtos de intermodulação de terceira ordem foi caracterizada no ponto de 1 dB de compressão de ganho ao longo da banda analisada. Um teste de linearização por injeção de sinais, que estava previsto no plano de trabalho, não apresentou o desempenho esperado devido a problemas no funcionamento do circuito linearizador. Esses problemas foram analisados e listou-se uma série de passos para saná-los. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:08/05286-1
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A gridless, variable perveance Pierce electron gun.Foulis, Bruce David. January 1994 (has links)
This thesis covers the design and development of a modulated Pierce electron gun
used in the construction of experimental travelling wave tube (TWT) amplifiers. The
gun incorporated an open aperture switching electrode, positioned mid-way between
anode and cathode, to pulse the beam. This method of modulation did not have the
same adverse effects on electron trajectories as in the case of a conventional mesh
grid, but rather the electrode could be used to alter the focus conditions within the
gun and subsequently improve certain beam characteristics. Ion focusing effects
could also be eliminated with the electrode, allowing dual mode operation of the guns
without the complications normally associated with such a practice.
The switching electrode was simulated to ascertain its effect on electron trajectories
within the gun, using finite element analysis as well as an electron optics design
program. A test gun was constructed in a glass envelope in order to investigate the
performance of the new design. The glass gun allowed a beam analysis to be
performed, as well as thermal measurements to be made. Results from this gun
compared favourably with earlier simulations. The results of two metal/ceramic
construction TWTs are presented, showing the beneficial effects of the switching
electrode on the performance of the tubes as a whole, and the electrode's potential
to compensate for constructional anomalies.
The joining of metals to ceramic using active brazing techniques is also an important
aspect tackled by the thesis, with several innovative ideas being implemented in the
construction of the devices. A simple yet reliable electrical feed-through was
developed for those guns having a ceramic envelope.
Extensive work was also performed on the manufacture of impregnated tungsten
cathodes for use in the electron guns. Several test diodes, including a water-cooled
demountable test vehicle, were constructed to test the performance of the cathodes.
An analysis was performed on the patchy behaviour of some of the initial cathodes
to improve the preparation methods used in the laboratory. The emission results
obtained from the cathodes are documented, as is the successful incorporation of
several of them into the new modulated gun design. / Thesis (Ph.D.)-Univesity of Natal, Durban, 1994.
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The development of an experimental, low profile, broadband travelling wave tube amplifier.Vassilopoulos, Nicolaos. January 1994 (has links)
An experimental, field replaceable travelling wave tube (TWT) with low profile, TEM
transitions has been developed with the aim of combining the cost advantages of field
replaceable TWTs with the bandwidth advantages of TEM transitions. Field replaceable
TWTs are cheaper because their periodic permanent magnet (PPM) stacks (which are
expensive) are easier to produce and can be reused. Standard TEM transitions have a
high profile and prevent TWTs from being plugged into PPM stacks. The stacks of
packaged TWTs are therefore built onto the tubes, using split ring magnets, before the
tubes are potted. Upon failure, such tubes are discarded together with their focusing,
coupling and cooling structures.
Two types of low profile, TEM transitions were investigated: a ring and a plug transition.
In the former, the helix was joined to a metal ring that was sandwiched between two
ceramic rings in the vacuum envelope. Due to its high shunt capacitance, this transition
was narrowband. In the plug transition, the helix was joined to a small metal plug in the
wall of a ceramic tube. Plug transitions with a return loss of better than 10 dB over an
octave were made but some technological difficulties were encountered. Metal/ceramic
joining with active solder is therefore discussed.
The development of graphite attenuators was attempted but graphite of high enough
resistivity to achieve the attenuation and matching required was not available. Thin film
attenuators were therefore used instead. Some good attenuators were made but the
molybdenum films were sensitive to processing conditions.
An empirical procedure was developed to magnetize PPM stacks to a wanted profile.
The stacks that were designed and built resulted in good beam focusing. TWT tests
were made using an automated test station that was built. Maximum RF gains and
output powers of 20 dB and 43 dBm respectively were measured.
The TWT design, construction and testing was a combination of materials science and
microwave work. Some simulations were used to solve electromagnetic problems but
much of the work was practical, involving trial and error and many measurements. / Thesis (Ph.D.)-University of Natal, Durban, 1994
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Caracterização de estruturas de ondas lentas helicoidais para utilização em, TWT de potênciaLOPES, DANIEL T. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:53:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:44Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP / FAPESP:05/03612-0
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Análise via simulação computacional de uma estrutura de ondas lentasTENORIO, EIK 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:25:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:37Z (GMT). No. of bitstreams: 1
11319.pdf: 9882365 bytes, checksum: 8fb38bd7d12d728bb49c46d11e58f0a1 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:99/06087-1
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Caracterização de estruturas de ondas lentas helicoidais para utilização em, TWT de potênciaLOPES, DANIEL T. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:53:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:44Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho, desenvolveu-se um modelo matemático e um aparato de medidas, que têm como objetivo auxiliar no projeto e na caracterização de estruturas de ondas lentas para válvulas de ondas progressivas. O objetivo é obter as características de velocidade de fase e de impedância de interação de uma dada estrutura de ondas lentas. Modelou-se matematicamente uma estrutura de ondas lentas do tipo ringbar como uma hélice dupla contraposta, de forma que se obteve uma série de resultados teóricos já publicados e outros inéditos. Desenvolveu-se um aparato de medida em microondas para a caracterização experimental da estrutura de ondas lentas sob análise. Apresentam-se os procedimentos de medida e os resultados experimentais obtidos, comparando-os com as predições do modelo matemático. Os resultados experimentais apresentaram boa reprodutibilidade e distaram dos teóricos de acordo com o esperado. Considerou-se que o modelo matemático e o aparato de medida, bem como as técnicas experimentais, já constituem uma importante ferramenta que será de fundamental importância no projeto e fabricação de válvulas de ondas progressivas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP / FAPESP:05/03612-0
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Análise via simulação computacional de uma estrutura de ondas lentasTENORIO, EIK 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:25:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:37Z (GMT). No. of bitstreams: 1
11319.pdf: 9882365 bytes, checksum: 8fb38bd7d12d728bb49c46d11e58f0a1 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:99/06087-1
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