Figure 8.30 Measured (dark line) and simulated (dotted line) SWR of the half-U-slot patch antenna with a shorting pin. Thin line and thin dotted line provide measured and simulated data, respectively, for the full-U-slot patch for a comparison ([8f], copyright C 2005 IEEE).

the dimensions of an example antenna with length L = 70 mm (0.21λ0), and width W = 42 mm (0.13λ0) (f0 = 0.9 GHz) are given along with the size of the half-size slot. The feed probe line (radius of 2 mm) and the shorting pin (radius of 4.65mm) support the patch in air and they are located at the non-radiating edge of the half-U-slot patch. The ground plane is a square with side of 1λ0. Measured and simulated SWR of the half-U-slot patch with shorting pin are shown in Figure 8.30, where for comparison, those of a full U-slot patch antenna are also provided. In the figure, thick line and thick dotted line, respectively, indicate measured and simulated VSWR of the half-U slot patch and thin line and thin dotted line. respectively, give those of the full U-slot patch.

A U-slot embedded on a rectangular patch is modified to achieve various functions such as wideband, multiband, and circular polarizations. Figure 8.31 shows representative ones: (a) double U-slots [9, 10], (b) a U-slot on a square patch with truncation [9], and

(c) an unequal arm U-slot patch [9, 11]. Parametric analysis of design for the U-slot rectangular patch antennas has been described in [12]. A U-slot can be applied to a triangular patch to achieve wideband operation [13].

8.1.2.1.1.2.2.2 Rectangular patch with square slot

Bandwidth can be enhanced by embedding slots/slits with various shapes on the surface of the patch antenna as has been shown in previous sections. Similar methods can be applied to achieve multiband operation.

A square patch with a square slot fed by a microstrip line is a typical design example for wideband operation [14]. The antenna geometry with dimensional parameters is illustrated in Figure 8.32, where two types of feeding are shown: (a) with a fork-like

Y

1.6 mm-FR4 substrate

70 mm

Figure 8.34 Geometry of antenna with a rotated square slot fed by microstrip line ([15], copyrightC 2005 IEEE).

When the square slot is rotated as shown in Figure 8.34, the bandwidth is further enhanced with proper selection of rotation angle α and length L of the feed line [15]. With a square slot size of 24.7 mm designed for operation at 4 GHz as shown in the figure, nearly 2.2 GHz impedance bandwidth for –10 dB VSWR is obtained when α = 45◦ and L = 31.5 mm, This wide bandwidth is about four times that of the corresponding conventional microstrip line-fed wide-slot patch antenna.

8.1.2.1.2 Multiband and wideband 8.1.2.1.2.1 Multiband antenna

Recent small wireless equipment requires small antennas with not only compact structure, but also multifunctional operation in nature. Late-model mobile phones have evolved from telephone devices toward information terminals dealing with multimedia information, involving audio, video as both still and dynamic media, data, radio, digital TV, and internet access. All of this, in addition to telephone voice, requires antennas that are small, compact, built-in, low cost, yet able to provide high-performance facilities to deal with high-data-rate information, and handle multiband communications.

Types of antennas for these applications are necessarily small, compact planar types, generally represented by various printed patch antennas and modified PIFA (Planar Inverted-F Antenna) combined with variously shaped wire elements or printed strips, stubs, slots, and so forth. Antennas are designed to be installed not only in mobile terminals, but also in various small wireless equipment and apparatuses, on which wireless systems are installed, including small portable terminals, personal computers including standard, laptop, and tablet types, USB cards and dongles, and TVs.