VSWR reduction for large millimeter-wave cassegrain radiotelescopes

Multiple reflections in large radiotelescopes used for astronomical spectroscopy cause characteristic modulations of the observed spectrum (baseline ripple). For a given mechanism, the magnitude of the effect depends primarily on the reflection coefficient, which for the most important paths is proportional to . Although ripple is thus generally negligible at mm-wavelengths, there are some instances where it may still be significant, and a recent experiment at the15 m James Clerk Maxwell Telescope was severely affected. We describe a technique which has proved effective in reducing the ripple to an acceptable level.The purpose of this research note is to draw this technique to the attention of the astronomical community. We calculate the reflection coefficient for a typical instrument and show that it can be greatly reduced over a very broad bandwidth by means of a tapered absorber in the centre of the secondary mirror. The graphical analysis of the tapered absorber also demonstrates that the scattering cones and circular absorbers widely used in radioastronomy donot in fact reduce the reflection coefficient significantly.     

Design of a stripline kicker for tune measurement in CSNS RCS

For CSNS RCS tune measurement, tune value is measured by exciting the bunch with a strip-line kicker fed with white noise and using a FFT algorithm. This article simulates the strip-line kicker in RCS and the efficiency of the kicker is discussed in a Matlab environment. The parameters of the kicker with an arc electrode structure such as a VSWR, wake impedance, and thermal state are analyzed based on the advantages of this design.     

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE₀₁ circular waveguide mode into the TE₁₀ rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.     

定向耦合法测量非标准接口元件驻波系数

 利用网络分析仪,根据需要在设定的频率范围进行扫频测量,网络分析仪的端口1输出的微波信号经过微波传输转换器进入与待测非标准元件匹配连接的连接段（如波导）;网络分析仪的端口2连接定向耦合器,用于监测传输段内的反射微波信号。首先,在非标准接口端面连接短路面,通过网络分析仪测量反射信号在设定频点的相对幅度值;然后去掉短路面,在非标准接口端面连接待测元件,再次测量反射信号在特定频点的相对幅度值;最后根据本文推导的公式得出驻波系数。该方法的测量误差与定向耦合器的方向性（方向性系数越大越好）和待测元件驻波系数有关。将该方法运用在非标准接口匹配负载驻波系数的测量中,定向耦合器方向性系数取为40 dB,测得其驻波系数小于1.2,误差小于20%。该方法简便可行,可以用于测量常用的非标准接口元件尤其是非标准低驻波系数元件的驻波系数。     

Design of a capacitive main power coupler for RF superconducting accelerators

An updated main coupler has been designed for the superconducting accelerator of Free Electron Laser (FEL) project under construction in Peking University. A capacitive structure is chosen for the main coupler. Numerical investigation using CST Microwave Studio demonstrates the cold window part. The other nonstandard structures such as holding rods and antenna are also optimized. The coupler uses a 95% purity Al2O3 ceramic cold window. The VSWR (Vottage Standing Wave Ratio) is 1.02 at 1.3 GHz and the frequency bandwidth is 45 MHz with VSWR<1.1. The electric field intensity is 8.5×10m-2 kV/mm around the window with 20 kW Continuous Wave (CW) transmitted power. The Qext is designed variable from 5×106 to 1×107.     

S-Band 3dB定向耦合器的优化设计及应用

3dB定向耦合器在组成微波器件中有着广泛的应用, 在我们的实验室中最常用到的带有3dB向耦合器的微波器件是移相器、衰减器和能量倍增器等, 3dB定向耦合器的性能参数对上述器件的性能起着决定性的作用. 在对原有S-band 3dB定向耦合器模拟研究的基础上, 通过对不同组数据的分析比较, 提出了此结构的优化设计方案. 重新设计后的3dB定向耦合器不仅简化了加工工艺, 而且驻波比、不平衡度、隔离度都达到了更好的效果. 将新设计的定向耦合器应用到移相器中, 通过对新老移相器的模拟和测试结果的比较可以看到移相器的各项指标均比原来有所提高, 而这也是以往移相器所无法达到的新指标. 对新加工的移相器试验件的测试数据表明, 实验测试和模拟计算的一致性很好.