**4.5. Section I: The feed section**

Planar antennas and arrays have been used for micro-wave and millimeter-wave applications for decades, especially in mobile communications where system design requires low profile, lightweight, and high directivity. The two most used feeding methods are micro-strip line (MS) and coplanar waveguide (CPW), they both carried signal excellently in narrow-band and UWB antennas and devices. Many planar antenna arrays have been designed by using MS, however, until recently, only a few works so far have used CPW to feed the array. The CPW has gained increasing popularity in recent years, since it has several advantages over the MS, such as low radiation losses, less dispersion, easier integration with solid-state active devices, and the possibility of connecting series and shunt elements, and suitable for SMD-technology, also for SWB- antennas/devices CPW feeding provides better match and performs better than the MS line (Simons, 2001).

In search for the SWB radiator, both radiator and the feed must be super wide band. Since the SWB-signal first must able to pass through the feeding-line before reaching the antenna, obviously that the feed must be considered first in advance of other sections, we conduct the work with bottom-up approach, i.e., the feed is consider first, because if the feeding mechanism fail to be SWB, then there is no SWB radiator exists no matter how good the radiator will be. The coplanar waveguide is the first choice for feeding the signal to the radiator, because the CPW's effective dielectric is constant, (this property is a key feature in wide band matching the antenna), over a wider BW than micro-strip line, another advantage is, in contrast with MS line, one of the parameter pair ( WS, WG) can be varied in size and shape, whilst the other is correspondingly changes to keep the characteristic impedance stays unchanged, furthermore CPW is low-loss, and the signal width can be chosen width enough to support characteristic impedance from 30Ohm and higher (Simons, 2001, p.52),

The CPW would be a better choice for SWB-feeding because of it considered features, summarized as follows:

• **SWB behavior**: the effective dielectric constant is almost independent of frequency (Simon op cit.), this feature is a priori condition for SWB feeding and matching.

