2.1 UWB slot antennas for linear and circular polarizations

Three different types of broad multi-band linearly and circularly polarized slot antennas (rectangular-, circular-, and triangular-shaped slots) for millimeter wave wireless communication applications [27] are shown in Figures 2 and 3, respectively. Proposed antenna consists of a slot radiator on the top metal layer and coupled to a rectangular dielectric resonator above the slot. The conventional microstrip-line-feed is used for different shapes of slot antennas. Final designed antennas were fabricated, and their characteristics were measured as reflection coefficient. The bandwidth of |S11| < 10 dB was extended from 19.5 up to 75 GHz. This band covers wireless MM-wave applications and wireless networks, and the

WLAN, WPAN, and W-bands and most of 5th Generation mobile [28–32]. The average radiation efficiency and gain over the entire operating band are about 60% and 6 dBi, respectively [27]. Printed different shapes of slot antenna show small dimensions (Lg Wg) cut at different shapes of slots on larger conductor and are centered above the microstrip-feed line. The microstrip feed line is composed of a straight section of length Lf. To improve the antenna reflection coefficient response, a square stub slot is added with the side length S = 0.6 mm for further improvement in the antenna impedance matching as shown in Figure 2. The width of the tuning line is equal to that of the 50 Ω microstrip line (Wf = 0.56 mm). The optimized dimensions of the proposed antennas are shown in Table 1.

Figure 2(b). The ellipse slot major diameter is W = 4 mm, and different radius ratios were used including the design with a ratio equal to 1.35 as shown in Figure 4(b). The |S11| response shows that the optimal bandwidth at |S11| < 10 dB is obtained using a circular slot shape. The bandwidth extends from 21 to 80 GHz in this case, while for the case of the elliptical slot, the bandwidth starts from 28 GHz and has the same end at 80 GHz as shown in Figure 4(b). The triangular shape is the third slot shape used in this study, and it is compared to trapezoidal as an intermediate stage between a triangle and a rectangle slot as shown in Figure 2(c). Figure 4(c) shows that both of the stated shapes resonate at frequencies higher than the other

Wg Lg W Lr Lftc K Lt K2 d1 t 7 10 4 2.9 11.6 0.25 4.5 0.6 0.7 4.5 Lfr Lfc Wf S Lt C1 C2 K2 d1 t 8.6 8.5 0.56 0.6 4 0.7 0.7 0.6 0.7 4.5

Single-feed MPAs for CP are usually achieved by using traditional simple changes in the shape of the patch such as truncating corners, using nearly square or nearly circular patches, cutting a diagonal slot in the square or circular patches, protruding or inserting a pair of symmetric perturbation elements at the boundary of a circular patch [33–35]. However, this type produced narrow axial ratio (AR) bandwidth. The dual-fed and sequential array structure produced wider AR bandwidth, but this requires more complicated design and may occupy larger space. Slot antennas are expected to overcome the limited bandwidth problem as well as

Rectangular notches etched in the rectangular slot are used as a way to improve the 3 dB AR bandwidth as shown in Figure 5(a). The notch width C1 = C2 = 0.7 mm gives the best wideband AR. The comparison of AR between measured and simu-

In the proposed design, a square stub with dimension side K was added to the circular shaped slot to achieve the CP performance. The stub is added at a radial distance t from square stub. The locations of this stub set the AR bandwidth without degrading the antenna performance as shown in Figure 5(b). This figure shows that

the stub with notch at a distance t = 3 mm gives the best performance AR

Antenna |S11| response with different slot shapes (a) rectangular, (b) circular, and (c) triangular [27].

similar changes in the slot shape could be used to achieve CP.

previous shapes, as it starts from 29 GHz.

The optimized antennas (all dimensions in mm) [27].

DOI: http://dx.doi.org/10.5772/intechopen.88444

Passive Components for Ultra-Wide Band (UWB) Applications

Table 1.

2.1.2 Slot antennas for circularly polarized

lated is also shown in Figure 5(a).

Figure 4.

105
