A Planar Substrate-Integrated Phased Array With an Over-One-Octave Bandwidth

A new wideband planar substrate-integrated phased array is presented in this article. The array element is based on an open slot excited by a coaxial probe. A T-shaped stripline with shorting pins is employed in each element to achieve a smooth mode conversion from quasi-coaxial to quasi-parallel plate waveguide (PPW) in a compact manner. In this case, the element supports a full quasi-TEM mode for transmission and radiation. In addition, the air-filled holes and metal pins are incorporated into the radiating and feeding structures to shift the undesirable resonance to a higher frequency. By combining these techniques, the impedance bandwidth can be extended to more than one octave. The radiation null caused by unexpected guided-wave mode during beam scanning along the H-plane is further analyzed in detail and removed from the desired frequency range by adjusting the corresponding element period and manipulating the guided-wave characteristics. A $10\times 12$ element phased-array prototype covering 8–18 GHz (76.9%) is fabricated and tested. Experimental results demonstrate that the proposed phased array achieves a beam scanning of ±60° in the E-, H-, and D-planes, with no radiation null occurring across the operating band.