Zero tilt omnidirectional collinear array antenna with coplanar feed

An innovative approach to the design of a centre-fed omnidirectional collinear array for use in the 900 MHz band is presented. The coplanar printed circuit realisation using a combination of the CPW and coplanar strips is shown to be very effective in eliminating beam tilt with change in frequency. Both measured and simulated results confirm less than 1.5° of beam tilt in the omnidirectional pattern with an azimuth ripple of approximately +/-0.7 dB, over an impedance bandwidth of greater than 10%.