Filter And Balun Design Based On LTCC Process

With continuous development and progress of industrial technology,the design and development of high-performance,miniaturization and low-cost electronic components have being the main direction for the development of microwave RF components.Microwave filter is a key component in radio frequency communication systems.Its performance and size greatly influences system density and performance stability of the communication system.Therefore,the design of passive microwave devices with high performance,miniaturization,and low-cost is the key for the development of highly integrated and highly reliable electronic communication systems.Based on the advantages of LTCC technology in making passive microwave devices,this paper reported the design of four kinds of microwave devices.Among them,high pass filter,band pass filter,and Balun were practically fabricated and testing after the completion of design.The results of the designed devices are listed as follows:The size of the designed low-pass filter is 4.5mm×3.2mm×1.5mm.By designing a three-dimensional capacitive-inductive structure in an equivalent circuit model,an LCtype low-pass filter with a cutoff frequency of 1.45 GHz and an out-of-band loss greater than 30 dB were realized.The final realization of low-pass filter design with the passband insertion loss is less than 3.5dB,the passband VSWR(voltage standing wave ratio)is less than 1.4,and the out-of-band loss is greater than 35 dB.The high-pass filter has a design size of 3.2mm×1.6mm×1mm.The principle of the LC filter and the snake-shaped inductor structure were used to achieve high-pass filter with a cut-off frequency of 5.05 GHz and a high-pass insertion loss of less than 2dB for the passband(5.05GHz-10GHz).In the design of band-pass filter,the resonant structure of 4 UIR(Uniformity Impedance Resonator)was adopted to realize the band-pass filter with a central frequency of 625 MHz and a bandwidth of 50 MHz.And a new type of coupling structure is designed to enhance the coupling between the resonant levels,thereby reducing the insertion loss(S21)and pass-band fluctuations in the passband and enhancing out-of-band rejection.Finally achieved an external dimension of 5.0mm ×5.0mm × 1.5mm,insertion loss of less than 3.5dB,bandwidth of 50 MHz,greater than 40 d B out-of-band rejection at 70 MHz,in-band fluctuations of less than 1.0dB,VSWR less than 1.5,And there is no parasitic passband in 3GHz,the center frequency is the band pass filter of lower frequency of 625 MHz.The design of Balun adopted the Marchand Balun structure and used a stripline structure to design the overall stack structure to achieve the miniaturization design.The final Balun size is 3.2mm×1.6mm×1mm,the working frequency band is 1.6GHz-2.6GHz,the insertion loss in the frequency band is less than 0.63 dB,the phase imbalance is less than 5.5 degrees,and amplitude imbalance is less than 0.6dB.