Reconfigurable and closely coupled frequency selective surfaces
The performance of a planar Frequency Selective Surface (FSS) cannot be changed or adapted once the manufacturing process has been completed. In practice, however, it would be advantageous to be able to do so, in order to increase flexibility of performance in multiband systems for example. This thesis examines a novel electromagnetict echniquet hat has beend eveloped,w hereby the frequencya nd/or the angular response of FSS's can be tuned in situ over a wide range of frequencies and/or steering angles. The technique employed is passive and relies upon the displacemento f closely separated( and therefore closely coupled) arrays with respect to each other. A global loading of the array results so that the reconfigurable FSS (RFSS) will produce a broadband and/or multibeam response without altering the individual array design. The experience and understanding gained during this work was subsequently used to produce FSS responses of extreme angular stability. In this case a static, double layer structure has been used to make use of the high coupling between the layers i.e. two FSS's printed on a single dielectric substrate to form a close coupled FSS (CCFSS). It was found that the coupling between the two layers was highly dependent on the relative displacement between arrays. This displacement is introduced statically during the manufacture of the FSS. The cases described use two identical layers. A further development of this concept makes use of complementary conducting and aperture elements giving rise to a complementary FSS (CFSS). The CFSS is also manufactured on a common dielectric and produces ultra stable resonant frequencies for both TE and TM oblique incidences. Theoretical verification of the measured results has been achieved, and the measured and predicted results agreed very closely. Modal analysis, using a novel coupled integral equation technique, has been used to predict the response of the RFSS and CFSS. The correlation between the predicted and measured transmission response of the RFSS was very good and it was discovered that operational stability of the bandwidths and band spacing ratios were significantly improved over conventional static FSS.