Multi-band conical and inverted conical printed quadrifilar helical antennas with compact feed networks

Comparison between radiation patterns of quadrifilar helical antennas with three shapes of cylindrical, conical and inverted conical is provided in this paper. Multi-folded printed lines are used as the arms of quadrifilar helical antennas and the heights of them with their supports are fixed at 35 cm to make a valid comparison. These antennas have multiple resonance frequencies and they can be used for multiband applications. Radiation patterns of the three shapes are compared at three resonance frequencies, 435 MHz, 620 MHz and 755 MHz. It is indicated that the conical antenna has a wider beam-width and the inverted conical antenna has higher gain at broadside. In addition, three compact feed networks based on miniaturized single layer Wilkinson power dividers for three frequency bands of the antennas are designed and their parameters are reported. Furthermore, the conical antenna and the feed networks are fabricated and simulation results are validated by the measurement results.