Improved Axial-Mode-Helical-Antenna Impedance Matching Utilizing Triangular Copper Strip for 2.4-GHz WLAN

Design of Internal Wire-Based Impedance Matching of Helical Antennas Using an Equivalent Thin-Wire Model

“…When a helix is internally matched by a vertically profiled metallic plate [7,11,12] wound around a PVC tube, an accurate model cannot be formulated easily. As opposed to this, when a helix is internally matched by a wire, an equivalent model is relatively easy to formulate, especially when the matching is made of the same wire as that in the helix.…”

“…Inherently, they are poorly matched to the standard 50 Ω transmission lines. However, they can be matched utilizing classical external matching networks (located beyond the antenna port) or utilizing metallic and dielectric features (internal) incorporated into the antenna structure [7,[9][10][11][12].…”

“…An alternative solution, an impedance transformer similar to a quarter-wave transformer, comprising the helix reflector and a metallic plate vertically attached to the beginning of the helical conductor, was presented in [7,11,12]. The characteristic impedance of this transformer should be smaller than the characteristic impedance of the transmission line formed by the beginning of the helical conductor and the reflector, as it transforms the helix input impedance (close to 150 Ω) to 50 Ω.…”

“…The characteristic impedance of this transformer should be smaller than the characteristic impedance of the transmission line formed by the beginning of the helical conductor and the reflector, as it transforms the helix input impedance (close to 150 Ω) to 50 Ω. Thus, the added metallic plate should decrease the characteristic impedance of the transmission line formed by the helical conductor and the reflector; namely, its per-unit-length (PUL) capacitance should be increased and hence the metallic plate should preferably be attached to the bottom of the helical conductor [7,12] (as close as needed to the helix reflector), as opposed to the solution presented in [11].…”

“…We recognize that one of the main challenges when designing an internal matching is its strong electromagnetic (EM) coupling with the antenna. The matching network must therefore be designed in the presence of the antenna by means of either relatively lengthy and expensive prototype tuning [11] or complex full-wave numerical analysis [12]. In addition, we formulate here a wire-based equivalent (simplified) model of the internally matched helix.…”