Quadrifilar helix antenna with mechanically tunable compact geometry

We have studied a quadrifilar helix antenna(QHA) which was cut into three parts. By introducing a gap between the lower two parts of the QHA, we can adjust the resonant frequency because of a distributed reactance has been introduced around the gap. When the overlapped part is long, the resonant frequency will become lower than when the overlapped part is short. So we can vary the resonant frequency mechanically by varying the length of the overlapped part. Simulated and measured results were used to demonstrate that the resonant frequency was changed form 1.5GHz to 1.62GHz. If we increase the width of the gap, the resonant frequency will change more obviously.