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|Title: ||Broadband radio frequency active quasi-circulator|
|Other Titles: ||Kuan dai she pin you yuan ban huan xing qi|
|Authors: ||Mung, Wai Yin (蒙偉賢)|
|Department: ||Department of Electronic Engineering|
|Degree: ||Master of Philosophy|
|Issue Date: ||2008|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Circulators, Wave-guide.|
Broadband communication systems.
|Notes: ||CityU Call Number: TK7871.65 .M86 2008|
x, 75 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references.
|Abstract: ||Wireless communication standards can cover several frequency bands spread over
quite a wide range, e.g. GSM, WiFi, GPS, Bluetooth, etc. With global roaming, it
becomes necessary to use wideband RF front-end circuits to cover these different
global standards. Applications of wideband directional components in particular
circulators will be an avenue to explore for future wireless communication
components because it enables simultaneous signal transmission and reception at
different frequencies due to good port to port isolation. The conventional ferrite
circulator, however, suffers from narrow bandwidth, large size and weight, which
make these circulators impractical. In this thesis, two different wideband
equalization techniques (self-equalization technique and phase equalization
technique) are proposed to enable wideband operation in active quasi-circulator so
that the RF front-end circuit components will be fewer, smaller and, more
importantly, the unit will be transparent to changing standards such as the
proposed future RF architecture called software defined radio.
A self-equalization technique is proposed for the distributed quasi-circulator, which is comprised of a distributed balun and combiner. The self-equalization is
necessary in order to realize wideband isolation. Experimental results show that
the distributed quasi-circulator can operate over the frequency range 0.8-2.2 GHz.
The minimum isolation obtained between ports 1 and 3 is around 20 dB using the
self-equalization technique, with greater than 20 dB between the other ports due to
the FET unilateral characteristic.
The phase equalization technique is proposed for a simple active quasi-circulator,
which it is formed by configuring three transistors together with a complimenting
phase shifter. Experimental results show that it can operate over the frequency
range 0.8-2.2 GHz. The return losses of the three ports are all greater than 10 dB
while the minimum isolation between ports 1 and 3 is 15 dB, and with greater than
30 dB between the other ports over the frequency range of 0.8-2.2 GHz. The
insertion losses, S21 and S32 are around 0 ± 1.5 dB.
Past works on the design of the active quasi-circulator was limited to narrow band
operation. The main contribution of the research presented in this thesis is to
increase the bandwidth of the quasi-circulator using active devices in a way that it maintains its advantages of small size, light weight and compatibility with
monolithic microwave integrated circuit (MMIC) technology compared to
previously presented work on active and passive circulators. The simultaneous
operation at several different frequency bands, therefore, will be adaptable to the
current multi-band standards and foreseeable standards in future.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2374844|
|Appears in Collections:||EE - Master of Philosophy |
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