W-band Broadband Direct Detection Receiver Front-end Research

With the rapid development of the electronic information technology, as well asimproved requirement for receiver front-end in such areas as remote sensing, securitycheck and navigation, its research has far-reaching practical meaning. The main twotypes of the receiver front-end are superheterodyne and direct detection. Because of theadvantages of direct detection, just like simpler structure, lower power consumption andhigher integration, it has been the direction of development in the future. Therefore, thisthesis is focused on the W-band receiver front-end.Since the low noise amplifier (LNA) is designed by using MMIC whose ports arecoplanar transmission, a W-band rectangular-to-coplanar waveguide (RW-to-CPW)transition is designed. At the same time, a waveguide bend structure is designed for theconvenience of test and use. And the ground of the CPW is extended into the waveguideto obtain a well matched transition. In order to demonstrate the feasibility of thetransition, a back-to-back (BTB) structure is used. Considering the design of amplifier, a5.8mm long air cavity and coplanar transmission is placed between the pair oftransitions. It is known that the reflection of a scalar network analyzer (SNA) affects themeasurement results. In order to solve this problem, this thesis makes an error analysisand an appropriate test method is proposed to reduce the influence. The return loss ismeasured by connecting a matching load to the output of the device under test (DUT)while the insertion loss is tested by adding an attenuator between the DUT and thedetector of SNA. The measurement results show that, for the BTB transition in thewhole W-band, reflection coefficient is better than-15.65dB and insertion loss is betterthan1.53dB. The insertion loss of single transition is estimated to be0.21dB.Similarity, considering that port of the monolithic LNA is coplanar line, a coplanartransmission line is used. And simultaneously connecting the conduction band orground of MMIC and that of the transmission line’s by two gold bond wire separately. AW-band LNA which could be modulated is successfully designed. Measurements showthat its gain is between13dB and25dB, with average gain about20dB. The rising timeand falling time of the modulation circuit is about200ns. Under the limitation of testing condition, a noise figure from4.1dB to6.1dB is achieved, in the range from94GHz-95GHz.Since the inaccuracies of the diode SPICE design, the simplified physical model ofdetection diode is established. Then a W-band broadband detector is developed andfabricated after parameters extracted. A coplanar transmission line is used, benefit formodulation with LNA. A smaller dimension can decrease the loss and improve thevoltage sensitivity. The voltage sensitivity of better than1mV/μW in the wholeW-band and better than2mV/μW in the band of75-101.5GHz are achieved. Thetangential sensitivity is better than-58dBm in whole band when the video bandwidth is100Hz.Finally, a receiver front-end is completed, which consists of the LNAs, the detectorin this thesis and homemade video amplifier. An evident response over35GHz band,sensitivity of0.47K and an integration time of2.5ms is achieved.