Design and characterization of antennas for wireless communications systems

In this PhD thesis the author has dealt with the design and characterization of novel antenna layouts for modern communication systems. Specific attention has been devoted to cost-effective and compact solutions; also, some of the proposed antenna layouts have been designed facing with severe integration constraints. A novel slot-coupling feeding technique for dual-polarized patch antennas is presented in Chapter I. A square patch is fed through a square ring slot excited by two non-overlapping feed lines printed on the same side of a single-layer substrate. This technique was used to implement a wideband dual-polarized 2x1 microstrip stacked patch array working in the GSM band (1710 – 1910 MHz), UMTS band (1920 - 2170 MHz), ISM band (2400 - 2484 MHz) and UMTS 3G expansion band (2500 - 2690 MHz) or, alternatively, WIMAX™ band (2300 – 2700 MHz), with a resulting 45% percentage bandwidth. Moreover a circularly polarized 2x2 microstrip array, where each array element is fed through two microstrip lines which are excited 90° out-of-phase, has been realized for the WiMAX (3300 - 3800 MHz) band, resulting in excellent Axial Ratio performance. In Chapter II, a compact dual-band Planar Inverted-F Antenna (PIFA) working in both the DVB-T (Digital Video Broadcasting-Terrestrial) and the WLAN (Wireless Local Area Network) IEEE 802.11b,g frequency bands is presented. It has been designed to be integrated in a monitor-equipped device, exhibiting reduced electrical size with respect to similar PIFA solutions, also in a L-shape configuration. In the context of compact wideband antenna design, Chapter III presents a numerical analysis of a novel wideband two-arm Archimedean spiral antenna whose arms are made of vertical metallic strips. An advantage of this spiral is that the input impedance and polarization purity can be effectively controlled by varying the strip width and turn thickness. Also, when the antenna is embedded in a dielectric block, miniaturization is more effective than in conventional planar Archimedean spirals. In Chapter IV, two configurations of slot antennas suitable for integration into a class of commercial large photovoltaic (PV) panels are presented. The basic idea is to exploit the room available between adjacent PV cells, also taking advantage of the presence of the cover glass layer that gives a valuable miniaturization effect. As test cases, two antenna designs are presented for stand-alone communication systems operating in the GSM/UMTS (1710-2170 MHz) and WIMAX (3300-3800 MHz) frequency bands. Finally, a top-loaded vertical monopole antenna was designed to be integrated in a wireless sensor of a car park monitoring system operating at 433MHz, and it is described in Chapter V. The final design came out from a careful analysis of the effects on the antenna input impedance of nearby elements (photovoltaic cells, battery, sensor cover, ultrasonic transducer). A performance comparison between the proposed vertically polarized antenna and a commercial ceramic antenna has been carried out, showing an average increase of the received power level at the reader of about 2.2dB, when measurements are performed on a distance range of 10-60m between the sensor and the reader antenna of the car park monitoring system.