Tản nhiệt của các ăng-ten PCB, có thể có hình dạng bất kỳ, tối ưu hóa để che băng thông UWB và thu nhỏ các ăng-ten. Hình dạng của nó có thể được hình bầu dục, hình chữ nhật, tam giác, hoặc một số việc kết hợp hoặc biến đổi, như thể hiện trong hình 7,22 (b) (d) [54-56]. | State-of-the-Art Solutions 255 Figure Multilayered roll monopole with broad bandwidth for impedance and omnidirectional radiation. Measurements in millimetres. Figure Monopoles printed onto a PCB a PCB antenna b microstrip-fed circular PCB antenna c CPW-fed slotted rectangular PCB antenna d microstrip-fed rectangular notched PCB antenna e CPW-fed elliptical slot antenna. The radiator of the PCB antenna which may be of any shape is optimized to cover the UWB bandwidth and to miniaturize the antenna. Its shape may be elliptical rectangular triangular or some combination or variation thereof as shown in Figure b - d 54-56 . 256 Antennas for UWB Applications Furthermore the radiator can be slotted for good impedance matching and size reduction as shown in Figure c 45 . The impedance matching can also be enhanced by notching the radiator as shown in Figure d 57 . The CPW-fed antenna is another important type of planar antenna as shown in Figure e 58 . This antenna is also known as the planar volcano-smoke slot antenna 59 . The printed PCB antenna is essentially an unbalanced antenna different from a balanced dipole and also a monopole with a large ground plane. The effect of the ground plane on the impedance and radiation performance of the PCB antenna is usually significant. The change in shape size and or orientation of the ground plane may affect the impedance and radiation performance of the PCB antenna 60 . This issue will be addressed in the case study in section . Besides the monopole-like printed PCB antenna the dipole antenna printed onto a PCB is also used in UWB devices as shown in Figure . Figure a shows the concept of printed dipole antenna on a PCB. Figure b is an implementation of the dipole antenna printed onto a PCB where a simple transition from an unbalanced-to-balanced feeding structure is formed by two microstrip lines which are etched on the opposite surfaces of the dielectric substrate. One of the
