| dc.description.abstract | Modern satellite, wireless communications, and radar systems often demand
wideband performance for multi-channel and multi-function operations. Among these
applications, phased array antennas play an important role. This dissertation covers two
wideband phased array antennas, one produces linear polarization and one produces
circular polarization. The main difference between these two phased array antennas is
the antenna array. For the linearly polarized array, a wideband microstrip line to slotline
transition is used to feed a Vivaldi antenna. For the circularly polarized array, a
wideband microstrip line to parallel stripline transition is used to feed a spiral antenna.
From 3 to 12 GHz, the linearly polarized beam is steered over ± 15º.
Since the electromagnetic spectrum is limited and has to be shared, interference is
getting serious as more and more wireless applications emerge. Filters are key
components to prevent harmonic interference. The harmonic signals can be suppressed
by cascading additional lowpass filters or bandstop filters. A bandstop filter combining
shunt open stubs and a spurline is proposed for a compact size and a deeper rejection.
Two lowpass filters with interdigital capacitors and slotted ground structures are also studied.
Harmonic suppression can also be achieved with the modification of bandpass
filters. Three conventional bandpass filters with spurious passbands are investigated. The
first one is a dual-mode patch bandpass filter. The second passband of the proposed filter
is at 2.88fo, where fo is the fundametal frequency. The second filter is an open-loop
bandpass filter. Two open stubs are added to achieve high suppression in the second
harmonic signal. The suppression of 35 dB at the second harmonic is obtained. For the
third filter using half-wavelength open stubs, a T-shaped line is used to replace the
quarter-wavelength connecting line. The T-shaped line has the same response with the
connecting line in the passband. Furthermore, the T-shaped line works as a bandstop
filter at the second harmonic.
Finally, a new compact slow-wave resonator and bandpass filters are presented. A
simple transmission-line model is used to predict the resonant frequency. Compared with
the conventional uniform half-wavelength resonator, the slow-wave resonator shows a
25% size reduction. | en |
