Sonasang, S., and อังควิศิษฐพันธ์ น. “Directivity Enhancement of Microstrip Parallel Coupled Lines Techniques”. Journal of Engineering Technology Access (JETA) (Online), vol. 1, no. 1, June 2021, pp. 12-31, https://ph02.tci-thaijo.org/index.php/JETA/article/view/244237.