In this paper, a printed LPDA antenna fed by a MSL to DSPSL from backside is described.
General configuration of LPDA antennas is described by the scaling factor [tau] = [l.sub.n+1]/[l.sub.n] = [d.sub.n+1]/[d.sub.n] = [w.sub.n+1]/[w.sub.n], where [d.sub.n] is the distance between the nth element and the (n+1)th element and [l.sub.n] and [w.sub.n] are the length and width of the nth element, respectively.
To the best of our knowledge, only a few works dealing with printed LPDA antennas operating both in the C, X and Ku bands can be found in the open literature (see, e.g., ).
The LPDA array has been designed using CST Microwave Studio 2012, a general purpose software for the 3D electromagnetic simulation of microwave components, and the designed antenna has been manufactured with the mirror coaxial cable.
The proposed antenna is designed by a semi-empirical way like the design procedure of traditional LPDA. Firstly, the LPDA basic parameters are determined by operating frequency and gain.
Design of Euclidean LPDA has been very mature, and the key of which is the selection of some special parameters, including scaling factor [tau], spacing factor [sigma] and the number of dipoles N, that is,
This solution allows the obtaining of a log periodic antenna with a reduced size, operating only in the ranges 2.4-3.0 GHz and 5.2-5.8 GHz, instead of a complete printed LPDA array working between 2.4 and 5.8 GHz.
In our case, for the proposed printed LPDA feed, we require an average directivity of 9 dBi, and therefore, following Carrel , we set the log period, [tau] = [L.sub.n+1]/[L.sub.n], and the spacing factor, [sigma] = [S.sub.n]/4[L.sub.n], of both groups of dipoles to the values [tau] = 0.94 and [sigma] = 0.17.
The LPDA is located on the "opposite end" of the long dimension of the ground plane from the cylinder with the forward apex of the LPDA located 5 m from the aperture of the cylinder with the elements of the "rear" reflector dipole located approximately 2m from the end of the aluminum ground plane.
EM coupling measurements and modeling of this geometry (aluminum cylinder with slot being illuminated by the LPDA) without the presence of the aluminum ground plane has been addressed previously [3-8].
The LPDA  antenna is built by assembling 21dipoles for a frequency range between 1 GHz and 2 GHz.
This is probably due to an imperfect symmetry of the LPDA on the ground plane.