Author:
İsmail Oğuz Saylan
Year:
2019
Abstract:
Filters maintain their importance and necessity in electronic systems and filter demands are increased in recent years due to speed of emerging new technologies. One of the new technologies in communication system is 5G. With every new technology emerged in communication systems, existing frequency bands usage increases or new frequency band allocations are made. As a result of new frequency allocations, very close each other adjacent frequency bands are occurring. The filters are the essential part of communication systems to prevent transporting signal from interference. Different type of filters; low pass, high pass, bandpass or bandstop are used in communication systems. The bandpass filter can be used to pass signals in a specific frequency range and to attenuate signals out of this range. According to frequency band or application which filter will be used, filter technology can be chosen. Lumped element filters are not practical for compact designs and not reliable in high frequencies because the wavelength of the signal is much smaller than the physical dimensions of the circuit. Distributed element filter; can be used for high frequency applications with high dielectric constant, is low loss and easy to implement to transmission lines according to filter topology in communication systems. In this master thesis, a parallel coupled microstrip bandpass filter is designed, simulated, optimized and realized for 5G (n78band; 3400 MHz-3600 MHz) applications to prevent transporting signal from adjacent band interference. In the design and for filter realization, RO4350 (Rogers) with dielectric constant ε_r=3.48 is chosen as substrate material. In the filter design, 0.5 dB ripple in the passband Chebyshev low pass filter prototype is used. The 5th order parallel coupled microstrip bandpass filter is designed with 200 MHz bandwidth and central frequency 3.5 GHz. According to simulation results; the insertion loss s_21 is -3.49 dB, return loss s_11 is -16.94 dB at 3.5 GHz central frequency and -3 dB bandwidth is 199 MHz where upper and lower frequencies are 3617 MHz and 3418 MHz respectively. The stopband attenuation at “3.3 GHz” is -33.33 dB and at 3.8 GHz is -50.81 dB. The designed filter is realized and measured; the insertion loss s_21 is -3.23 dB, return loss s_11 is -27.84 dB at 3.5 GHz central frequency and -3 dB bandwidth is 233 MHz where upper and lower frequencies are 3617 MHz and 3418 MHz respectively. The stopband attenuation at 3.3 GHz is -22.45 dB and at 3.8 GHz is-41.99 dB. The realized filter measurement and the designed filter simulation have similar results in filter response. The designed filter is realized and as a result low insertion loss, low cost of realization and high attenuation characteristic is achieved. If there are not any limitations at the designed filter application area dimensions, this realized filter has the advantage for low cost solutions.