Fdtd Analysis Of The Circular Groove Waveguide Power Combiner

Circular groove guide is a new type of millimeter wave and sub-millimeter wave transmission line, which was firstly introduced by professor Yang Hong-sheng et al in Southeast University. In millimeter wave band and sub-millimeter wave band, it has characters of low loss, high power handling, low dispersion and single mode transmission medium. This gives an alternative to design the millimeter wave and sub-millimeter wave components. With the rapid development of millimeter wave solid device, millimeter wave circuit and system are bound to use solid device. But the disadvantage of solid device is low power, which becomes more and more intolerable. Millimeter wave power combining technique is one important method to overcome this disadvantage. The study on circular groove guide power combining technique is put forward in this situation. Circular groove guide is used as a resonate cavity, to combine millimeter wave power. In this paper, Finite-difference time-domain (FDTD) method is used to calculate the driving-point impedance of radial transmission-line structure in circular groove guide. Non-uniform grid and triangular grid are used to approximate the curvilinear metal boundary of circular groove guide. And perfectly matched layer (PML) is applied to the open boundary of circular groove guide. Fine-grid is used to calculate the field's value in the radial transmission-line in which we are interest. Discrete wave equation is used to update the tangential electric value on the boundary of coarse- and fine-grid. At last, the driving-point impedances of the radial transmission-line are obtained from the ratio of the Fourier transform of the voltage to the Fourier transform of the current. By changing the characters of the radial transmission-line, the input impedance figure related to the diameter, thickness and position of the radial transmission-line are gotten. Intuitional figures are helpful for the impedance matching in practice.