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|Title: ||A waveguide-based coupled oscillator array integrated with a voltage-tunable frequency selective surface for spatial power combining|
|Other Titles: ||Ji yu bo dao de dian ya ke tiao pin lü xuan ze biao mian ji cheng ou he zhen dang qi zhen lie de kong jian gong lü he cheng ying yong|
|Authors: ||Lou, Yu (樓彧)|
|Department: ||Department of Electronic Engineering|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2009|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Oscillators, Microwave -- Design and construction.|
Frequency selective surfaces.
|Notes: ||CityU Call Number: TK7872.O7 L68 2009|
xi, 130 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2009.
Includes bibliographical references (leaves 120-130)
|Abstract: ||In recent years, research on quasi opt ical or spat ial power
combining techniques becomes more and more attract ive due to the
burgeon of wireless communicat ions, such as telecommunicat ion,
satellite communicat ion and radar systems, which t rends to operate
at higher frequency bands due to the exponent ially increasing
demands on bandwidth and high data rate. Due to the physical
limitations of semiconductor devices, power from many devices
should be combined together to meet the system requirements.
However, as a matter of fact , the loss of any transmission structures
at such frequency bands is really a serious issue which limits the use
of convent ional incorporating power combining approaches such as
Wilkinson power combiner and compels the advent of new power
combining methods. One of them is the quasi optical or spat ial
power combining technique in either free space or a closed cavity
filled with air or dielectric materials, for which the combining is
conducted in a low-loss medium, employing act ive circuit element
such as amplifier, oscillator or mixer.
In this work, a spat ially combined oscillator array is discussed.
For this waveguide-based design, oscillators are coupled together
within a common cavity resonator for synchronizat ion and
efficient ly combined at the output waveguide. Both input and
output sides of the oscillators are coupled using wideband
waveguide-to-microst rip t ransit ion array, to conduct the power
combining in a spatial way in a standard WR90 rectangular waveguide.
The oscillation cores are designed with the negative resistance
method. The MESFETs are properly biased and terminated so that
the negat ive resistance of the act ive devices is large enough to
cancel the loss of the resonator to meet the oscillat ion condit ion in
both small signal and large signal cases.
In this research, the spatially combined oscillator array is
synchronized using a common cavity resonator. To build a voltage
cont rolled oscillator, a voltage-tunable frequency select ive surface
(VTFSS) is integrated within the cavity as a reflect ion phase tuner
so that the elect romagnetic characterist ics of the common cavity
resonator are electrically controllable. This spatially tunable
design is advantageous in terms of simplicity especially for the
waveguide design where available space is rather limited, because
all the oscillators are tuned by a single voltage bias instead of the
applicat ion of bias tuning upon each one of them.
To further enhance the output power level of the oscillators, a
buffer stage is added at the outputs of the oscillator MESFETs.
Not only does the buffer act as a gain block to the circuits, it also
provides isolat ion, e.g. S12 of a BFP740F transistor is around -15
to 20 dB, between oscillators so that the only significant coupling
between oscillators is the one conducted through the common
resonator with voltage-tunable FSS integrated.
The thesis is arranged as follows. Firstly, a brief introduct ion will
be given in Chapter 1, followed by a research background with
previous work by other researchers in Chapter 2.
After the background informat ion on spat ial power combining, all
the components of the system will be discussed in detail through
Chapter 3-6. The tolerance and fabricat ion problems are covered in Chapter 7 for complet ion and conclusion will be drawn in
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2374860|
|Appears in Collections:||EE - Doctor of Philosophy |
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