Centre-fed dual band omnidirectional array antenna with electrical down tilt

A centre-fed dual band (3.5 GHz/5.8 GHz) omnidirectional microstrip array antenna for using in wimax applications is presented. Two distinct series fed back-to-back subarrays separated by a power divider are designated for these two bands. The proposed centre-fed structure reduces interference of two subarrays and provides a flexible progressive phase and so independent tilt angle control in dual bands. In addition, it is shown that compared to edge-fed dual band structure, the centre-fed structure makes the use of low permittivity substrates possible which are more appropriate for antenna radiation. The fabricated antenna can cover 3–3.7 GHz and 5.4–6.4 GHz frequency bands with S11 < −10 dB. It also shows about 10° down tilt in both frequency bands.