Cross Polarization Reduction of a Shorted Patch Antenna With Broadside Radiation Using a Pair of Open Ended Stubs
A novel design concept to reduce high H plane cross polarization of a shorted patch antenna (SPA) with broadside radiated patterns is presented by loading a pair of open ended stubs. Initially, the nonbroadside <inline formula> <tex math notation="LaTeX"\vert E_{\mathrm \theta \vert /tex math>/inline formula> component of the traditional SPA at TM<inline formula> <tex math notation="LaTeX"$_{\mathrm {1/2,2} /tex math>/inline formula> mode is demonstrated to be much larger than its broadside <inline formula> <tex math notation="LaTeX"\vert E_{\varphi \vert /tex math>/inline formula> component in H plane or <italic>yoz</italic> plane radiation patterns. In order to maintain its peak radiation in the normal direction, the far zone radiated fields of the antenna are theoretically studied and analyzed. The results demonstrate that the dual nodal lines of the TM<inline formula> <tex math notation="LaTeX"$_{\mathrm {1/2,2} /tex math>/inline formula> modal fields could be gradually moved far away from each other by increasing the stub length. As such, its <inline formula> <tex math notation="LaTeX"\vert E_{\varphi \vert /tex math>/inline formula> and <inline formula> <tex math notation="LaTeX"\vert E_{\theta \vert /tex math>/inline formula> components in H plane or <italic>yoz</italic> plane radiation patterns could be progressively strengthened and weakened, respectively. After that, by reallocating these dual nodal lines around the corners of the radiating patch, the nonbroadside radiated fields of TM<sub>1/2,2</sub> mode are successfully transformed into the broadside radiation, while keeping a low H plane cross polarization level. Additionally, the symmetric open ended stubs are folded so as to reduce the dimensions of the core radiator. In final, the proposed SPA is fabricated and measured. Simulated and measured results are found in good agreement with each other, and both of them illustrate that the antenna has satisfactorily acquired a normal radiation pattern at reshaped TM<sub>1/2,2</sub> mode. Most importantly, its high H plane cross polarization is dramatically reduced from 4.3 to 21.4 dB as compared to the traditional SPA at TM<sub>1/2,0</sub> mode.
IEEE Transactions on Antennas and Propagation