The Design Of 332MHz Helical Filter

A filter can separate signs,balance amplitude and phase character in using frequency range,also can restrain disturbing effectively.It's very important to sensitivity and selectivity of a communication navigation device.It is used in electronic equipments of communication,navigation and measurement,etc.A helical filter is widely used in frequency from 10 MHz to 1200 MHz because of little dimension and large power.A LC filter is widely used in frequency from 1kHz to 100 MHz.When frequency is over 100 MHz,the distributing parameter influence is severity,the loss becomes bigger and the quality factor becomes lower.The theory of a LC filter is the base of other filters.A helical filter is used in frequency from 10 MHz to 1200 MHz,Q-unload is about 1000,which can overcome the shortcomings of a LC filter.The application frequency ranges of a LC filter and a helical filter are recommended.According to this,designers can choose a correct filter.In this thesis,the theory of a LC filter is introduced.The design methods of network synthesis and its excellence are explained.The design methods of a LC low-pass filter,high-pass filter and band-pass filter are summarized.The advantages and shortcomings in different frequency range are compared.The coupling resonator circuit is used in a narrowband band-pass filter,which applies to a filter with quality factor of 10 or more than 10.The principles of capacitance coupling resonance circuit and inductance coupling resonance circuit are introduced,and the reasons for the phenomenon of less coupling,over coupling and critical coupling are analyzed.The response curve of less coupling,over coupling and critical coupling are showed.The component value critical coupling is listed,and the debug methods of coupling between resonators are introduced.These methods are also applicable to a helical filter.The principles of a resonator and a helical resonator are expatiated.The coupling matrix network synthesis is presented.The design method of a helical resonator is also summarized.The helical resonator model is built with HFSS simulation software.The factors effecting the character of a filter are analyzed.The eigenfrequency of single resonator is simulated by eigenmode solution type,while the character of the whole filter is simulated by driven modal solution type.The parameters are adjusted basing on simulation results,and the structure parameters are confirmed.The filter is debugged by a network analyzer,we get the ideal waveform.The debugging method is summarized.The filter with 332 MHz center frequency,3dB insertion loss,3dB bandwidth no less than 10 MHz,20dB bandwidth no more than 17.5MHz,2.5 dB inequality,VSWR(standing wave ratio)no more than 2 and 50? input and output impedance is designed.If it is realized by a LC filter,the component is too small to realize.If it is realized by a microwave filter,the dimension is too big.So,it is realized by a helical filter.The dimension of this filter is only 64mm(length)3 16 mm(width)3 26 mm(height).