Design And Implementation Of A Broadband Dualchannel RF Front-end

With the wide application of wireless communications, the demand for radio frequency spectrum resources is showing a rising trend on a worldwide scale. In order to use and manage the radio system better, we need to detect character of signal in term of frequency, power direction of arrival(DOA) and information that the signal carries. In the early 1990 s,American scientists firstly proposed the concept of Software Defined Radio(SDR). It is widely believed the SDR cover the frequency band of 0.8GHz-6GHz, which includes the most of frequency bands of daily communication application.Referring to the frequency band of SDR, this thesis proposed a dual-channel RF front-end that can be used for communication and monitoring system. The RF front-end has a receiving frequency range of 30MHz- 6GHz. The system adopts super-heterodyne structure, and will convert the RF signal which is within the range of receiving frequency band into an intermediate frequency signal,of which the center frequency is 160 MHz and the channel bandwidth is 40 MHz.Firstly, the thesis investigated the performance of existing monitoring equipment and products both domestically and overseas, and then proposed requirement of the RF front-end of this monitoring equipment. By comparing the performance of typical receiver structure, the program is determined using super-heterodyne receiver structure. According to current conditions of ADC and frequency synthesizer, primary three-step frequency conversion scheme was determined.Secondly, according to the primary conversion scheme, image frequency, spurious response and intermodulation interference and other factor was analyzed and requirements of filters and selection of devices was determined. After determining the chain design of RF circuit, gain, noise factor(NF) and other system specifications are simulated. After finishing the simulation, the design of the module circuit was conducted, and I mainly completed analysis and design of pre-selection filters and IF filters and mixer circuit. The thesis proposed a local oscillator(LO) leakage signal suppression circuit to solve the problem of deficiency of filter suppression to LO leakage signal.Finally, we conducted circuit function debugging and testing. And gain, NF, linearity and other system specification was tested and verified, and we put forward the improved scheme according to the present problems. Circuit functions achieved the expected requirements.