Research On Test System Of Solid Dielectric Materials For Complex Permittivity In The K&Ka Band

Solid dielectric materials have been widely used in national defence and civil domain, especially in many kinds of microwave devices and systems. With the fast development of communication system with millimeter wave and radar navigation, it becomes more important to do research in solid dielectric materials measuring. This paper mainly does improvement task to the old microwave complex permittivity measuring system of dielectric sticks which has been build many years ago in our staff room base on the National standard “Test method for complex permittivity of solid dielectric materials at microwave frequency –Perturbation method”. The frequency band has been expanded from the Ka band to K&Ka band which satisfied the client’s needs.Following is the main contents of this paper:1. Optimizing the dimensions of the 0n0 TM mode cavity to satisfy the broadband frequency, simultaneity extending the distances of the dominant modes and the interferential modes and the minimal frequency difference is 290 MHz.And the influence of the interferential modes towards the dominant modes is very small.2. After designing the coupler structure, some interferential modes has been eliminated through the coupling structure of coaxial transmission line to the rectangular waveguide.3. Through milling several slots on the bottom of the cavity and loading of the absorbing materials, the interferential modes can be eliminated additionally. We can see from the test result: the insertion loss of the interferential modes which near the dominant modes is lower than the dominant modes by 3.9~19dB.4. Developing the automated measuring program using VC++ base on MFC which is developed by Microsoft encapsulated the windows API functions. And using the SICL interface functions to communicating with the vector network analyzer. With the measuring program the following functions can be achieved: automated searching and identifying modes, automated calculating the test points of dielectric stick, initializing the start position, stepping and resetting to zero point of the dielectric stick. This can reduce the human work markedly and achieving the automated measuring.5. After Building the measuring system the author did the modulation work of the cavity and the mechanical transmission part. It is consist of the 0n0 TM cavity, vector network analyzer, the mechanical platform which sustains the cavity, stepping motor and it’s drive, stepping motor controller and so on.After modulating the measuring system works well, and the measuring results and the measuring error satisfy the needs.