Broadband rectangular slot cut modified circular microstrip antenna

Broadband microstrip antenna is more commonly realized by cutting the slot at an appropriate position inside the patch which is fabricated on lower dielectric constant thicker substrate. In this paper, a new 270⁰ sectoral microstrip antenna is proposed. The 270⁰ sectoral patch, derived from conventional circular microstrip antenna, has an additional mode below the resonance frequency of fundamental mode of the equivalent circular patch. The variations of sectoral patch, namely, 300⁰, 320⁰ and 340⁰ sectoral microstrip antenna are also discussed. By studying the surface current distributions at first two modes of sectoral patch, a formulation in resonant length / patch radius, is proposed. The frequencies calculated using them closely agrees with the simulated results. Further a rectangular slot cut 270⁰ sectoral microstrip antenna is proposed. An analysis to study the effects of slot in sectoral patch is presented. The rectangular slot reduces the resonance frequency of second order mode of 270⁰ sectoral patch and along with its fundamental mode, yields broadband response. The measured and simulated BW of nearly 450 MHz at center frequency of around 1000 MHz is obtained. The proposed broadband antenna shows broadside radiation pattern with gain of more than 6 dBi over the operating bandwidth.