Design And Research Of Multilayer Microwave Filter Based On LTCC Technology

The demand for performance and size of RF devices is increasing with the constant innovation of mobile communication technology.Microwave filters are widely used as a type of RF devices.It is of great significance to miniaturize them.The Low Temperature Cofired Ceramic technology can realize a multilayer circuit layout,which can effectively reduce the volume of the RF device.The basic design theory of microwave filters was analyzed,the circuit analysis method of the filter coupling matrix is introduced,the design process of a coupled resonant filter based on LTCC technology is described in detail,and summarized some laws in filter design process.The working principle of introducing transmission zeros through cross coupling is analyzed with phase shift,the idea of using transmission zeros to approach the passband to reduce the bandwidth of the passband is proposed,and two coupling resonance filters with transmission zero were designed.The first filter is an S-band fourth-order bandpass filter.The filter consists of four resonators which is composed of three layers of stacked coupling lines cascaded by weak coupling.The filter has a center frequency of 3.45GHz,a bandwidth of 300MHz,an insertion loss of less than 2.1dB in the passband and a stopband loss greater than 31dB.In order to introducing transmission zeros in the stopband,the cross-coupling between the resonators is strengthened by adding U-shaped strip line.The final size of the filter is 4.5×3.6×1.2mm~3.The second filter is a C-band fourth-order bandpass filter.The basic design idea of this filter is the same as the S-band filter,the difference is that the resonator consists of two layers of stacked coupling lines.The filter has a center frequency of 4.92GHz,a bandwidth of140MHz,an insertion loss of less than 2.9dB in the passband and a stopband loss greater than 42dB.The position of the transmission zero in the stop band is changed by adjusting the size and position of the U-shaped strip line,and passband bandwidth is reduced to140mhz by this method.The final size of the filter is 5.1×2.8×1.2mm~3.