Simple design of broadband circularly polarized two‐arm Archimedean spiral antenna

Abstract

This article presents a broadband circularly polarized two‐arm Archimedean spiral antenna with a novel simple feeding method. Contrary to the conventional spiral antenna excited by a vertically or horizontally balun, the presented design is directly fed by a coxial cable with a planar feeding section optimized to provide a broadband input impedance matching. An antenna prototype has been fabricated and measured to validate the concept. Measured results of reflection coefficient and axial ratio show a good performance over a frequency range from 1.0 to 3.5 GHz, equivalent to ~111.1%. Within this band, the antenna prototype exhibits bidirectional radiation with broadside gain values of better than 3.6 dBic.

Fully planar frequency independent square Archimedean spiral antenna with impedance transformer for ground penetrating radars

“…where c 0 is the speed of light in free space and ε r,eff is the effective relative dielectric constant of CPS 25 (FR4_epoxy ε r = 4.4), the effective relative dielectric constant is 2.23. In reality, the value of the distance S max is approximate twice the S max calculated from (11), that is, r max = r out = 2. S max .…”

“…3,4,[6][7][8][9][10] The vertical impedance transformer (balun) always has an essentially long length and contributes to the high profile antenna and causes problems in the assembly of the antenna. 11 Additionally, it makes the antenna structure nonplanar, complex, and large size, 12 conflicting with the requirements of the low-profile geometry which makes the entire antenna voluminous. This threedimensional feeding way is well investigated in the past.…”

“…The ordinary feeding structure for planar spiral antennas is located in the middle of the spiral and expanded into the third dimension 3,4,6‐10 . The vertical impedance transformer (balun) always has an essentially long length and contributes to the high profile antenna and causes problems in the assembly of the antenna 11 . Additionally, it makes the antenna structure nonplanar, complex, and large size, 12 conflicting with the requirements of the low‐profile geometry which makes the entire antenna voluminous.…”

“…The approach of using CPW to feed ultra‐wideband coplanar strips (CPS) rectangular spiral antenna is suggested in 24 where the CPS consists of a gradual lowering in the width of CPW ground planes without a required balun. Lately, in 11 a technique of using a transition section, which is incorporated into the spiral arms at the center, is proposed, consequently, the antenna is directly fed by a coaxial cable without the need of a balun. Another approach is used to feed an Archimedean spiral antenna with an integrated microstrip‐to‐coplanar stripline (CPS) balun 25 .…”