Shared-Aperture Dual-Band Antenna for X and Ku Bands

A compact shared-aperture dual-band antenna is introduced. The antenna features a central modified circular patch for X-band operation (9.87-10.43 GHz) and four symmetrically arranged arc-shaped elements working as planar inverted-F antennas in Ku-band (14.68-15.31 GHz). The modified circular patch is probe-fed, while the arc-shaped elements are excited through a compact ring-shaped series-parallel sequential phase feeding network to ensure a circular polarization with less than 2.1 dB axial ratio across the operational bandwidth in Ku-band. The fabricated prototype demonstrates a performance aligned with the simulations across both bands, achieving an impedance bandwidth of 5.5% in X-band and an overlapping impedance and axial ratio bandwidth of 4.2% in Ku-band. A measured isolation exceeding 20 dB is achieved between the two bands. The measured realized gains, which agree with simulations, range from 6.5 to 7.1 dBi in X-band and 6.8 to 7.8 dBic in Ku-band. The frequency ratio is set during design by modifying the physical dimensions, particularly the length, of the arc-shaped elements, offering a degree of flexible tuning during the design phase.