A Shared-Aperture Antenna for (3.5, 28) GHz Terminals With End-Fire and Broadside Steerable Beams in Millimeter Wave Band

In this article, a concept of partial structure reuse is presented, and on this basis, a 3.5/28 GHz shared-aperture antenna supporting 2-D (endfire and broadside) steerable beams in the millimeter-wave (MMW) band is developed. The antenna consists of a 3.5 GHz planar inverted-F antenna (PIFA) and two 1
$\times $
6 28 GHz substrate-integrated DRA (SIDRA) beam-steerable arrays, in which partial structures of the PIFA are reused by the two MMW arrays. To improve the performance of PIFA, two narrow slots and one lumped capacitor are introduced to reduce its H-plane cross-polarization and enhance the operating bandwidth, respectively. To verify the design, antenna prototypes were fabricated and measured. Measured results show that the antenna can cover a dual-band of 3.28–3.67 (11.2%) and 26–29.7 (13.2%) for the endfire and 25.9–29.7 GHz (13.8%) for the broadside. The peak gains of 4.8 and 10 (endfire) and 10.8 dBi (broadside) are obtained by the MW element and two 1
$\times $
4 MMW arrays, respectively. Each of the MMW arrays can steer the beams from − 50° to + 50°, covering different parts of the space. The shared-aperture antenna has a compact size of 0.45
$\times $
0.3
$\times \,\,0.03\lambda _{01}^{3}$
(
$\lambda _{01}$
is the free-space wavelength at 3.5 GHz), making it suitable for terminal applications.