In this paper, antenna ultra wideband enhancement by non-uniform matching is proposed. The antenna consisted of a rectangular shaped radiator with two convex circled corners. Simulated results using CST Microwave Studio and measured results of a fabricated antenna concord well to prove that it can operate from about 3.5 GHz to 4.6 GHz and from 7.4 GHz to 12.7 GHz for Su(11) (dB) < 10 dB. In addition, a good impedance matching is noted in the IEEE radar engineering X band range since the return loss coefficient remains below 50 dB value at 9.5 GHz and can reach 45 dB at 11 GHz. A current density comparison at 11 GHz, supporting our argument, between a stepper corner and convex corner demonstrates that the current density can reach 52 A/m with a convex corner whereas it does not exceed 33 A/m for the antenna with a stepper corners. Radiation patterns at various frequencies and peak gains show clearly interesting features of such antennas.

The out band response of filters is of major importance because it mitigates interferences for adjacent applications. In this paper, a novel technique based on non uniform transmission lines (NUTLs) is used to suppress harmonics in the out band of a low pass microstrip filter. Explicit expressions describing accurately the behaviour of NUTLs are obtained from numerical resolution of Hill's equation. Practical measurements showed good agreement with simulation results.