High-gain printed monopole arrays with low-complexity corporate-feed network

Printed monopole antennas fed by microstrip lines can provide a wide bandwidth and can be employed as terminal antennas in RF circuits. In the same perspective, the authors propose a novel planar array in which N + 1 parasitic monopoles, properly placed in a linear array where only N directly-fed monopoles are used, allow a broadside radiation and a gain value close to that of a standard printed array composed of 2N + 1 directly-fed elements. To verify the validity of the proposed design, prototype arrays for the S and C bands, composed of five- and nine-monopoles, are simulated, fabricated and tested. In addition, it is demonstrated that a flat metal sheet placed at 0.25 λ0 from the array board can further increase the directivity of about 3 dB; as a result, the measured gain is ~10 dB for the five-monopole array and 14 dB for the nine-monopole array. Owing to their large fractional bandwidth (30%) and high gain, these monopole arrays may work as external antennas for high-data-rate point-to-point transmissions or for C-band radar sensors.