Compact Wideband Sequential-Phase Feed for ... - IEEE Xplore

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2016.2597970, IEEE Antennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT)
REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT)
REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < Middle layer

3

Top layer

Sub. 2

Sub. 1 Bottom layer

z x

y

SMA

(a)

W (a)

Wm

0

Ld

Ld

S-parameters (dB)

Sd -10

Wd

-20

Ri

-40 1.0

|S21| |S31|

|S41| |S51|

1.4 1.6 1.8 Frequency (GHz)

2.0

2.2

Wrm

Sd Wd La

Wt

y

Wd

x

x Top Middle z (b) (c) Fig. 5. Geometry of planar 2 × 2 dipole array fed by the proposed SP network: (a) cross-sectional view, (b) top and middle layers, and (c) bottom layer. z

(b) 90 0

Phase (degree)

Wd

y 1.2

Lf

Wt

|S11|

-30

Wg

Lt

Wrt

La

Wm

-90 -180 -270 -360 1.2

arg S21 arg S31 arg S41 arg S51 1.4

1.6 1.8 Frequency (GHz)

2.0

(c) Fig. 4. (a) Fabricated sample of the proposed SP network. Its measured (b) S-parameters and (c) transmission phases.

Fig. 6. Fabricated sample of the 2 × 2 dipole array.

(h1 = h2 = 0.508 mm, εr = 3.38 and tan δ = 0.0027). Two pairs of parallel dipoles were orthogonally placed at the four sides of a square contour. The two arms of the dipoles #1 and #2 were placed on the bottom and middle layers, whereas, the two arms of the dipoles #3 and #4 were placed on the top and bottom layers. The dipoles were fed by double-sided and balanced striplines. The array was optimized for a wide bandwidth in terms of the impedance matching and AR with the center frequency at around 1.6 GHz. For optimization, the design parameters for the feed structure of the array were slightly modified compared to those of the proposed SP network presented in the previous section. The optimized design parameters of the array are as follows: W = 80 mm, Ld = 34 mm, La = 13 mm, Sd = 37 mm, Lf = 15 mm, Wd = 3 mm, Wg = 20 mm, Lt = 25 mm, Ri = 6.5 mm, Wt = 2.4 mm, Wm = 1.1 mm, Wrt = 0.8 mm, Wrm = 0.3 mm, and h1 = h2 = 0.508 mm. The 2 × 2 dipole array was first characterized by the HFSS and then fabricated and tested. Fig. 6 shows the fabricated sample of the prototype that was realized on Rogers RO4003 sheets (copper thickness of 17 μm) via a standard wet-etching technology. The overall size of the fabricated array is 80 mm × 80 mm × 1.016 mm. Fig. 7(a) shows the comparison between the measured and simulated |S11| values for the planar 2 × 2 dipole array. The measured impedance bandwidth for |S11| < –10 dB is 1.37–1.89 GHz (31.9%), whereas, the simulated bandwidth is 1.35–1.90 GHz (33.85%). Fig. 7(b) shows the simulated and measured AR of the array, demonstrating a good agreement between the two. The measured 3-dB AR bandwidth

is 1.49–1.85 GHz (21.56%), whereas, the simulated 3-dB AR bandwidth is 1.49–1.84 GHz (21.02%). The radiation patterns of the fabricated prototype at 1.58 GHz and 1.76 GHz are shown in Fig. 8. Within the operational bandwidth, the patterns are rather symmetric in both the x–z and the y–z planes. The array radiates a bidirectional electromagnetic wave with similar gain values at the broadside (+z direction) and the backside (–z direction); i.e., the broadside has a right-hand circular polarization, while the backside has a left-hand circular polarization. A few ripples in the measured patterns could be attributed to the effects of the foam rack and the tapes behind the antenna in the measurement setup. Fig. 9 shows the comparison between the simulated and measured gains of the fabricated array. Both the measurement and simulation resulted in similar values for both the broadside and the backside gains across the 3-dB AR bandwidth. The measured broadside gain was 3.5–5.0 dBic, while the value at the backside was 3.6–4.5 dBic. In addition, the measurement resulted in a high antenna efficiency greater than 90% compared to the simulated value that was greater than 96% in the frequency range 1.5–1.9 GHz. Table I shows the performance comparison between the presented array and the previous sequential rotation 2 × 2 dipole arrays using traditional SP networks [5], [6]. All these arrays work at 1.6 GHz. Owing to the presence of the new SP feeding network, our design has yielded a significantly broader 3-dB AR bandwidth with a smaller size compared to prior designs. 3

1536-1225 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2016.2597970, IEEE Antennas and Wireless Propagation Letters

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT)