A Printed Dipole Antenna (PDA) has numerous advantages in terms of weight, size, aerodynamic drag, ease of fabrication, cost, etc. Yet it suffers from the inherent disadvantage of incompatibility with wideband operation. Both microstrip dipole and PDAs are of resonant type and hence present narrow bandwidth. PDAs are often used to replace Microstrip Dipole Antennas (MDA) since it offers somewhat better Return Loss (RL)/impedance bandwidth because of the presence of four radiating slots. However, maximum RL bandwidth reported is not sufficient for many present -day data applications like streaming video and real-time navigation, as also applications like medical imaging, broadband EMI measurement, etc. A simple design of PDA without flared arms and with shaped ground plane is presented here, using which –10 dB impedance bandwidth as high as 41% in L band and below is achieved. The shaped ground plane acts as an integrated balun. By flaring its arms, the same antenna provides –10dB impedance bandwidth as high as 51% in the same band frequency. Both antennas are designed to operate in L band and below so that these can be used in GSM and CDMA wireless applications. The measured results of both antennas show good agreement with the simulated results.

Unlike Microstrip Dipole Antenna (MDA), two arms of Printed Dipole Antenna (PDA) are printed on opposite surfaces of a dielectric sheet, known as the active and ground radials. But like Microstrip Dipole, PDA is also designed with narrow rectangular strips. The rectangular strip width is taken typically less than 0.05 0 (Bahl et al., 2001). With the decrease of width to length ratio, the transverse current component also decreases and so also the cross-polar component. But the geometries of rectangular microstrip patch and PDA are similar. So are their longitudinal current distributions in fundamental mode. However, as width to length ratio of PDA is taken very small compared to the microstrip rectangular patch antenna, antenna gain also becomes less.

PDA can be modeled having four radiating slots with two in each surface. Therefore, PDA provides better impedance bandwidth. The rectangular strip conductors may be flared in a triangular shape to increase the Return Loss (RL)/impedance bandwidth. This is known as double-sided bow-tie-antenna or flared PDA. The linear taper in the rectangular strip, described by the opening angle 0 , gives rise to gradual impedance transformation resulting in wider RL/impedance bandwidth. A dipole with rectangular strip (0 = 0) has been reported with –10 dB impedance bandwidth of 20% (Lin and Syh-Nan, 1998). They have also studied double-sided bow-tie-antenna with increased bandwidth of 40%. But a separate balun network has also been used between microstrip and parallel strip feed making feed structure more complicated. In comparison with the double-sided bow-tie antenna, a single-sided bow- tie-antenna (in a single-sided bow-tie antenna both arms are printed on the same surface of a dielectric) is also studied with RL bandwidth of 36% (Lin and Syh-Nan, 1997). This has proved the effectiveness of double-sided bow-tie antenna, i.e., PDA, compared to single-sided one for greater impedance bandwidth.

Electrical and Electronics Engineering Journal, Printed Dipole Antenna (PDA), Shaped ground plane; Broadband, Return Loss (RL)/Impedance bandwidth.