| This paper focuses on the terahertz monopulse receiving system with low cost,miniaturization and high sensitivity.For the radar system,while there is a future demand for miniaturization and integration of the monopulse feed,based on the silicon micromachining process,the high-gain and small-size micro-lens antenna is applied as Cassegrain dual reflector system’s feed;a high integration,low profile,and low loss monopulse comparator network is designed.The main work and results are as follows:1.The monopulse comparator network based on gap waveguide technology is studied.Starting from the gap waveguide theory,the electromagnetic band gap and pass band range are calculated based on the dispersion mode method,and then the gap waveguide transmission line is used to complete the design of monopulse comparator network with four layers.Both reflection coefficients of the difference and sum channel are less than-15dB in the 285GHz-315 GHz frequency band,and the isolation between the difference channel and the sum channel is above 40dB.Since the four input signals are in the same plane,and the three output signals(sum signal,H-plane difference signal and E-plane difference signal)are also in the same plane,the signals between the four layers are coupled through slots,right-angle transitions,and ridge gap waveguides to standard waveguide probes without direct electrical contact,which can greatly reduce the requirements of processing tolerance and assembly accuracy in the later stage.From the point of view of performance and structure analysis,this structure is very suitable for realizing terahertz three-dimensional stacked circuit structure.2.The four micro-lens antenna feed of the Cassegrain monopulse system is studied.First the theory of the Cassegrain monopulse antenna is introduced,then a four micro-lens antenna feed is designed in the form of 2×2 pattern,with a center frequency at 300 GHz and a cell spacing of 3.6mm.Its size is 8mm×8mm.Then,in order to match the directional pattern of the feed,the Cassegrain antenna is designed.The main surface diameter is 65mm,and the sum beam and the difference beam have good rotational symmetry characteristics on the E plane and the H plane.The contradiction between the sum and the difference beams is between 0.7dB to 2.1dB while the gain of the sum beam is 40.5dB at central frequency.The unbalance of the difference beam is less than 0.5dB.The zero depth is bigger than 40dB with steep difference beam slope at the center frequency.A low profile,small angle measurement error,high tracking accuracy and sensitivity Cassegrain antenna is obtained.Moreover,the feed is near the vertex of the main surface,which causes little noise and is easy to integrate with subsequent circuits.3.A local oscillator multiplexer based on Fourier phase grating is studied to solve the problem of multiple THz frequency sources being expensive and difficult to synchronize.At first,according to the principle of Fraunhofer diffraction,the design principle and procedure of Fourier phase grating are given.Next,the reflecting Fourier phase grating of metal material is used to solve the problem of diffracted beam distortion caused by oblique incidence by phase compensation of the surface of the vertically incident Fourier phase grating.The designed one-dimensional 4 beams Fourier phase grating has a simulated diffraction efficiency of 85.7%and a reflection surface size of 4 mm×4 mm when the incident wave is obliquely incident at an angle of 25°.Then it is extended to the two-dimensional Fourier phase grating for 16 beams in the form of 4×4 array,and other complex two-dimensional Fourier phase gratings.Using the reflective Fourier phase grating to realize the space feeding of mixers can avoid the projection loss and the loss caused by the transmission line and is easy to process.The resulting LO signal array arrangement pattern is also more flexible and diverse. |
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