A novel untilted edge-slotted waveguide antenna array with very low cross-polarization is presented, in which the radiating element is composed of an untilted narrow-wall slot and a pair of shaped irises that flank the slot in the waveguide. An array with 16 proposed elements for X-band application is designed and measured. The experimental results show that the antenna has an excellent cross-polarization level of < −40 dB and over 7% bandwidth of VSWR ≤ 1.5. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 91–93, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20556