Abstract:
Bandpass filters are the key components of the wireless communication system. Modern
applications of wireless communication need filters with low insertion loss, compact size, and
high selectivity. Traditional approaches for achieving selectivity like increasing the number of
the resonator is not a good option as both size and insertion loss is compromised. In order to meet
the demanding requirement cross coupling based approach is used which generates the
transmission zero (TZ) for improving the filter out of band rejection along with size reduction.
This thesis presents the design, simulation, and fabrication of microstrip trisection filter based on
two different topologies. In one topology a trisection filter was designed using open-loop
resonators. This filter exhibits a center frequency of 954.95 MHz, a return loss of 11.1 dB, 3dB
bandwidth of 46.3 MHz, and an insertion loss of 1.02 dB. The response of this filter is asymmetric,
and the transmission zero in this case is on the right side of the passband. Due to the sharp roll
off out of band rejection of -30 dB was achieved at 993 MHz. Another planar microstrip trisection
filter was designed at a center frequency of 775 MHz. This filter produces a single or multiple
transmission zeros by changing the tap position on the resonators. It is shown that two responses
namely asymmetric response (transmission zero on either the right or left side of the passband)
or symmetric response (transmission zeros on both sides of the passband) can be realized using
this method. The measured results are close to simulated ones.
