Low phase noise L-band oscillators based on novel general Chebyshev bandpass filters

Oscillators act as signal sources for wireless communication systems, radars, wireless charging, and other industrial applications, whose phase noises directly determine system performance. In this paper, two low-phase noise microwave oscillators based on novel microstrip second-order band-pass filters are presented. These filters are characterized by good frequency selectivity owing to two transmission zeros near to the passbands. As a result, relatively high group delay can be achieved at center frequencies, which is vital to the phase noise performance of the oscillators to be designed. Simultaneously, the bandwidths can be made narrow enough so that actual oscillating frequency is very close to the designed one. In addition, the introduction of stepped impedance makes these filters capable of harmonic suppression, which efficiently suppresses the harmonics in the output such as the second harmonic. These filters are compact and also of easy design. Finally, two microwave oscillators at 2.0 GHz are designed on these microstrip filters. As the measured results show, their output frequencies are 2.002 GHz. The phase noises are ?127.21 and ?127.03 dBc/Hz@100 kHz, respectively. The second harmonic suppressions are as great as 30.45 and 39.21 dBc, respectively.