Research And Design Of L-band DMB Transmitter Frequency Conversion Module

L-band signal interference is less,and the antenna size of L-band DMB transmitting system is small,which is conducive to the coordination of engineering implementation and the surrounding environment.Therefore,in practical engineering applications,there is a need to use L-band DMB transmission system in small areas such as schools.Based on the above application requirements,this paper studies the design of a miniaturized and low-cost converter module circuit that can convert the output signal of the existing III-band DMB transmitter to L-band.Firstly,according to the characteristics of the output signal of the III-band DMB transmitter,the paper determines the overall scheme of the up-conversion system and divides the system into two parts: active circuit and passive circuit.The active circuit includes a local oscillator source module,a mixing module,an amplifier module,and an active auxiliary function circuit.The ADF4351 is used to design the local oscillator module,and the ADL5350 is used to design the mixing module.The ADL5541 design amplifier module with a fixed gain of 15 dB is used.The active accessory function circuit includes a power control circuit and an MCU circuit.Passive circuit includes III-band bandpass filter and L-band bandpass filter.The filter is designed by insertion loss method and simulated on ADS platform.The simulation results show that the center frequency is 215 MHz,the passband bandwidth is32 MHz,the insertion loss is 0.35 dB at the center frequency,and the return loss in the passband is more than 20 dB.Rogers4350B dielectric material is used to simulate on ADS platform.The L-band bandpass filter layout is designed.The simulation results show that the center frequency is 1472 MHz,the bandwidth is 58 MHz,the insertion loss at the center frequency is 1.02 dB,and the return loss in the passband is more than 20 dB.Finally,the L-band frequency conversion module is fabricated and tested.The test results show that:(1)the size of active circuit and bandpass filter in III-band is87mm×85mm,and the phase noise of local oscillator module is-78.93dBc/Hz@1kHz and-83.06dBc/Hz@10kHz.(2)In passive circuits,the size of L-band bandpass filter is63mm×29mm,the center frequency is 1465.7MHz,the insertion loss at the center frequency is 2.84 dB,the bandwidth is 42 MHz,and the echo loss in the passband is more than 18.3dB.All the active and passive circuits designed are connected to the III-band DMB transmitter,and the output signal power is-15.1dBm.The L-band frequency conversion module is applied to DMB system.Wire test and wireless test are carried out respectively.The input frequency point is 221.568 MHz and the output frequency point is 1471.792 MHz.The test results show that the L-band frequency conversion module can be successfully used in DMB system.