Mutual Coupling Effect in Unequally - Spaced Linear Antenna Array Performance

Unequally-spaced arrays can offer some advantages over equally-spaced arrays as follows: reducing the side-lobed level for the broadband array with an identical excitation coefficient. However, array design techniques do not take into account the mutual coupling effect among elements. In this article, the effect of mutual coupling on the array radiation pattern is investigated and discussed through studying the input impedance of the elements. Next, a technique for reducingmutual coupling based on radiation patterns of elements is presented. In this technique, the log-periodic dipole antenna with a frequency ranging from 900 MHz to 2500 MHz is selected as an array element. The results based on the FEKO magnetic field calculation program have shown that at 900 MHz, the proposed antenna array reaches a side-lobed level of -17.4 dB. At frequencies of 1500 MHz, 2000 MHz, 2500 MHz, the grating lobe levels of this antenna array are lower than 6.7 dB, 9.5 dBand 8.3 dB compared to those of the equally - spaced antenna array.