Dual-Polarized (CP, LP, and Slant), Series-Fed, Monopulse Planar Array Antenna

A single-layered, series-fed monopulse planar array antenna system is presented, which reduces the complexity of corporate-fed monopulse antennas in terms of multilayered structures and number of 180° ring hybrid couplers as monopulse comparator circuit. The proposed antenna exploits only two 3-dB/180° hybrid couplers that results in reduced insertion loss of 3 dB. The proposed X-band monopulse antenna system exhibits the sum (Σ) patterns with dual (linear, circular, and slant) polarization, difference (Δ) patterns with dual linear polarization, bi-difference patterns with dual (slant and circular) polarization. The prototype of the proposed antenna system has been fabricated using 0.762-mm-thick Rogers 4350B substrate (ɛ r =3.66 and tan δ =0.0031). The theoretical and experimental results confirm that -10-dB impedance bandwidth (or VSWR <1.92) is recorded to be 190 MHz (9.56-9.75 GHz) for sum ports and 460 MHz (9.94-10.4 GHz) for difference ports with maximum null depth over -33 dB. The proposed antenna system presents a peak sum gain of 10.57 dBi, 3-dB axial-ratio (AR) bandwidth greater than 160 MHz, and root-mean-square-error (RMSE) less than 9° for both xo_z -plane and yoz-plane in the field-of-view (FOV) of 40° [- 20° + 20°] for all polarizations. To the best of our knowledge, this is first series-fed planar array antenna reported so far for dual-axis monopulse direction finding applications while offering all types of polarizations with reduced number of 180° ring hybrid couplers as monopulse comparator without compromising the radiation performance and electrical size.