Compact Wideband Sequential-Phase Feed for Sequentially Rotated Antenna Arrays

This letter presents a compact wideband sequential-phase (SP) feed for use in sequentially rotated antenna arrays. The SP network is designed to match a 50-Ω coaxial line. The phase difference (out-of-phase) between the outer and inner conductors of the coaxial line is utilized as a 180° phase shifter; consequently, the desired phases at the outputs and a wideband operation are achieved. For a compact size, the SP feed is designed on two-layer substrates and employs two vacant-quarter printed rings that act as 90° phase delay lines. The SP design yielded a reflection coefficient (|S
₁₁
|) <; -15 dB and transmission coefficients (|S
₂₁
|, |S
₃₁
|, |S
₄₁
|, and |S
₅₁
|) of -6.4 ± 0.8 dB from 1 to 2 GHz (66.67%), whereas its output phases exhibited a progression of approximately 90° in the frequency range 1.4-1.8 GHz (25.0%). As an application, a planar 2 × 2 dipole array using the proposed SP feed has been designed, fabricated, and measured. The array with an overall size of 80 × 80 × 1 mm
³
resulted in a |S11| <; -10-dB bandwidth of 1.37-1.89 GHz (31.9%) and a 3-dB axial-ratio bandwidth of 1.49-1.85 GHz (21.56%).