Series collinear antenna designs are well-known, and have a number of advantages, including ease of construction and associated affordability. Series collinear antennas consist of a number of alternate radiating elements and inter-element phasing sections which together provide a phased array antenna.
U.S. Pat. No. 6,909,403 discloses a series collinear antenna design which comprises a plurality of radiating elements and inter-element phasing sections, which are arranged alternately on a single-sided elongate substrate. When in use, the substrate is configured to be curved about a longitudinal axis which runs parallel to the arrangement of radiating elements. The inter-element phasing sections are arranged in meander line configurations which are adapted so that emissions from the radiating elements are in-phase over an intended range of frequencies.
This prior art series collinear antenna design has a number of advantages relative to its predecessors. For example, it has improved broadband characteristics when compared to series collinear antenna designs implemented in a flat configuration on a standard printed circuit board (PCB) substrate. The curved substrate increases capacitance, improving the performance of the inter-element phasing sections. The antenna may be fabricated on a flexible substrate, enabling cost-efficient manufacturing. The antenna can be constructed to exhibit low passive intermodulation (PIM) distortion.
However, the prior art antenna described above operates over only a single frequency band. Current wireless communications systems, including GSM, 3G and 4G/LTE cellular systems, employ a number of frequency bands, e.g. within an overall range of around 700 MHz to around 2700 MHz. Other bands of the radio spectrum, extending up to 300 GHz, have also been allocated by national regulators for current and future fixed and mobile wireless communication.
Multi-band communications may be accommodated by providing a corresponding plurality of separate antennas, each of which is designed to operate within a specified frequency band. However, the use of multiple separate antennas may be undesirable for a number of reasons, including cost, space constraints, complexity of wiring, reliability and visual impact.
There is, accordingly, a need for multiband antennas that are able to mitigate these disadvantages, while providing performance that is comparable to known single-band antennas. It is an object of the present invention to satisfy this need.