Research On W-band Limiter

The limiter is a protection device commonly used in the receiving front end,which can isolate or turn on the signal according to the power of the input signal.Unlike switches,limiters do not require an external bias to control the on/off of the signal,and it completely depends on the difference in input power to adjust its own state.Regarding the development of limiters,in the lower frequency bands of millimeter waves(such as the Ka band),the scheme of using PIN diodes to build limiting circuits has become more and more mature.With the development of wireless technology and the increasing shortage of spectrum resources,people’s demand for higher millimeter wave frequency bands is becoming more and more vigorous,and the receiver technology of the W-band is gradually improved.However,the protection methods for W-band receivers have always been defective,and there are risks such as insufficient reliability to protect the receiver with switches.Therefore,it makes sense to design a limiter that protects the W-band receiver.Based on other existing limiter schemes,a new limiter structure is proposed for the specificity of W-band in this thesis.A series of experiments are designed to verify the feasibility of the scheme.The core part of the scheme is that the coupler couples a portion of the energy to the detector,and the output of the detector acts as a bias to control the on/off of the switching diode.Experiments are designed to verify whether the detector can drive the switching diode directly,the relationship between the operating state of the switching diode and the corresponding bias,and the correspondence between the input power of the detector and the output level.The feasibility of the scheme is confirmed by experimental verification.The theoretical analysis of the W-band detector in the scheme is carried out after completing the scheme design.And the detector circuit form is determined to be diode series type according to the operating principle of the detector and the circuit specifics.The DC circuit,input matching and output filter are designed respectively by combining the previous detector diodes models,and finally the overall simulation of the detector is carried out to complete the circuit design and testing of this part.Third,the coupler and switch are further studied.The coupling flatness of the coupler is required for the consideration of the overall performance of the limiter.Combined with the coupler-related theory,the specific structure of the coupler is determined,and the design of the coupler is completed.The switch part is based on the previous experimental results and uses the existing switch structure in the laboratory.After each part is determined,the design of the overall layout and cavity of the limiting circuit is completed,and the design and debugging of the DC control circuit is also completed.Finally,after completing the processing,assembly and debugging of the W-band limiter,its performance is tested and analyzed.The experimental results show that the limiter operates at 87-92 GHz,and the threshold level at each frequency point is strongly correlated with the performance of the detector.Besides,the insertion loss in the operating frequency range is within 2dB.When the input power is 10.7dBm at 88 GHz,the spike leakage detection voltage 17.2mV.The isolation in the operating frequency band is greater than 25 dB,and the recovery time is 7.2ns.In addition,the W-band receiving front end was developed,and the related cavity filter and gold wire bonding compensation structure were designed for the problems of image frequency suppression and gold wire bonding.The receiver has an RF frequency of 94.5GHz,a gain of 23.8dB,a 1dB compression point of-23 dBm,a noise figure of 4.2dB,and image rejection of more than 40 dB.Finally,the practical application effect of the limiter in the receiving front end is experimentally tested.The results showed that the limiter had an insertion loss of 3dB,an isolation of 35 dB,a response time of approximately 55 ns,and a noise figure of 2.75dB at 94.5GHz.