The series-fed subarray still plays a critical role in a partially-corporate-fed array, which has advantages over the corporate feed one in terms of both beam steerability and freedom in array sizes. In this paper, two techniques are presented for the wideband design of series-fed waveguide slot arrays. Firstly, the overload technique is adopted to design standing-wave fed 1 × 4-element arrays of both coupling slots and radiating slots. The simulated bandwidths for |S 11 | < -15 dB are enhanced to 8.1% and 12.2%, respectively.Secondly, the open-cavities, namely decoupling structures above radiating slots, are introduced to suppress the mutual couplings among a 4 × 4-element array. Its bandwidth for |S 11 | < -15 dB is significantly improved from 5.1% to 11.3%. For demonstration, a 4 × 4-element array is designed in the X-band, and is fabricated by Direct Metal Laser Sintering technique. The measured bandwidths for |S 11 | < -12.5 dB and the antenna efficiency higher than 70% are as wide as 12.4% and 9.5%, respectively. The validity of those wideband design techniques is verified.

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