Study of High-order Overmoded Power Couplers for Multiple Sheet Electron Beam Devices

In this paper, two kinds of high-order overmoded power couplers for multiple sheet electron beam devices are presented. One kind of the couplers was based on coupling apertures, which was response for the mode conversion and power coupling. The other one consisted of a H-plane T-junction based mode converter and an overmoded Y-shaped coupler. To improve the performance, some other auxiliary structures, such as the matching steps, Bragg reflector, were introduced. Both of the two couplers could not only realize the beam wave convergence/separation but also the mode conversion from the fundamental mode to higher-order modes. As examples, two H-band (220-325 GHz) TE
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mode power couplers were manufactured by using nano-CNC machining and measured by using a vector network analyzer (VNA). For the first coupler, a 3-dB transmission bandwidth of ~56.3 GHz (222.2-278.5 GHz) was measured with a maximum transmission coefficient of -4.4 dB and a port reflection of ~-15.0 dB. For the second coupler, the measured transmission and reflection coefficients were respectively ~-2.0 dB and ~-10.0 dB in the frequency range of 250.0-294.0 GHz.