Miniaturized VHF Eletrical Tuning Receiver Front-End Research

Due to the vigorous development of the wireless communication industry in recent years,and in order to avoid the situation where electromagnetic waves in different frequency bands interfere with each other more and more severely,the existing various electronic systems put forward higher requirements for spectrum utilization and spectrum integration and multiplexing.Most of the VHF band wireless communication systems are used in aviation and marine communications.The frequency conversion technology has a very important role in its application range,and the development of the electric tuning filter technology can better enhance the system's communication capabilities under complex conditions.Modern communication systems are developing toward the trend of integration and miniaturization.Therefore,the miniaturized VHF band receiver has a high application value.This paper first introduces the main indicators of the receiver system,and analyzes and demonstrates the system scheme.Secondly,by analyzing the basic synthesis theory when designing filters and the coupling theory of lumped component band-pass filters,the tunable filters of series and parallel resonant circuit structures are simulated and analyzed.Finally,the two miniaturized VHF band filters with the center frequency is tunable and the bandwidth is tunable.The tuning filter is designed by changing the capacitance value of the varactor diode under voltage control.One is a miniaturized center frequency tunable filter whose center frequency is 180MHz to 290MHz and whose absolute bandwidth is kept unchanged at 20MHz.Another is a small-bandwidth tunable filter tuned with a center frequency of 235MHz and an absolute bandwidth of 25MHz to120MHz.It also perform physical tests of the two filters.Next,a preselected bandpass filter was designed using the high-low pass cascade structure.By testing,the bandpass filter with a center frequency of 231MHz,a 3dB bandwidth of 161MHz and the reflection coefficient better than-10dB can be obtained.Finally,by analyzing and clarifying the basic theories of low-noise amplifier design,a low-noise amplifier is designed using a monolithically integrated microwave circuit transistor.In this design,the broadband operation was realized by introducing negative feedback analysis,and the input and output ports of the circuit were matched with Smith chart.Finally,a low noise amplifier with in-band gain?21.3dB±0.4dB and noise figure NF?0.75dB was designed.Based on the above design method,this article developed two small VHF band front-ends with better performance.Combined with the test theory method of the receiver front-end system,the cascaded physical object designed in this paper is tested experimentally.Through the test experiment,the finished system gain is better than 15±0.5dB,and the NF?3dB,the VSWR is less than 2.0,and the P_out-1dB is more than 13dBm.Therefore,the design of the VHF band front-ends can meet the design requirements.