This paper furnishes a compact modified hourglass-shaped aperture-coupled antenna for radar applications. The effect of slots of various shapes and various slot lengths on the input impedance, radiation pattern, and gain of the antenna are analyzed. The proposed antenna, designed using a modified hourglass-shaped aperture, offers a gain of 8.214 dBi for an compact antenna with a dimension of 20.4 × 20.4 × 1.041 mm3 and an aperture area of 2.495 mm2. Implementation of this proposed modified hourglass-shaped aperture offers a high gain per unit radiating patch area of 40.26 dB/ $\lambda _g ^2$ and a high gain per unit aperture area of 1324.84 dB/ $\lambda _g ^2$ . The proposed aperture feeds a circular patch which radiates at its resonant frequency of 10.5 GHz. The proposed design is fabricated and the simulated results are verified experimentally. Equivalent circuit analysis is also done. A measured gain of 7.2 dBi is observed at 10.5 GHz. The physical area of the antenna is reduced without compromising the gain by judiciously choosing the shape of slot with more degree of freedom for impedance matching. The proposed antenna is well suited for the unit cell of phased array antennas for X-band missile radar applications.

This letter describes a low‐profile three‐way fan‐shaped power divider integrable with aperture‐coupled antenna arrays. Each unit element is designed with a circular cavity‐based eighth‐mode substrate integrated waveguide. For better impedance matching, tapered feedlines are used at the output side. This structure is well suited for aperture‐coupled antenna arrays with a ground plane between the two substrates. The low‐profile power divider offers a 1 dB insertion loss (excluding the ideal power division of 4.8 dB). Magnitude and phase imbalance between output ports is  dB and , respectively. The performance of the power divider is validated by using it as a feeding circuit for an aperture‐coupled array antenna with three circular patches. The antenna array resonates at 10.5 GHz and gives a gain of 4 dBi.