The Research And Design Of A Tunable Band-pass Cavity-filter

The tunable bandpass cavity filter presented here is an essential part of the optical-frequency-comb system. The filter enjoys such merits: narrow bandwidth, low insert-loss in the passband, and high attenuation in the stopband, wide stopband and changeless bandwidth and filter characteristics. And besides, its structure is compact and easily to be manufactured. The introduced filter is used to modulate the optical vibration-frequency to microwave-frequency. To do so is because the value of the former is much higher than that of the later. Then the electrical devices can record the modulated frequency. Equipped with this tunable bandpass cavity filter, the optical-frequency-comb system, which has the optical-frequency standard, is offered a way to connect with the atom-clock microwave-frequency one. So it will contribute to design an optical-clock with higher precision than the atom-clock. During the course of the research, the focuses are put on the followings: On the base of the theories of the network design and coupling-cavity filters design, we study the processes from the lowpass filter prototypes to the tunable bandpass coupling-cavity filters, including the design method of the K/J inventor, network prototype circuits of the coupling-cavity bandpass filters, design formulas of the input/output rectangular coupling loop and the coupling hole between the cavities. About the tunable filters, we analyze the relation between the variable center frequency and the filter's parameters, and design formulas are presented. The emphases of the work are to design the filter, including simulation process with the help of the HFSS software, and the adjustment process. The first part is to obtain the exacter dimensions of the filter on the base of the former analysis. For unique characters of our filter, we adapt some special methods to simulate, such as the way to design the tunable capacitance patch. The second part is to adjust the filter. That means to adjust the position and area of the input/output coupling loop, as well as the compensation capacitance patch, in order to make the five cavities resonate on the same frequency, and remain the constant absolute bandwidth and filter characteristics. To measure the performances of the finished filter, and to analyze the reasons of dissatisfactory indexes.