Series Arrangement Technique for Highly-Directive PCB Leaky-Wave Antennas With Application to RFID UHF Frequency Scanning Systems

The efficient series connection of planar leaky-wave antennas (LWA) to obtain directive frequency beam scanning, is proposed in this paper. Conditions for the proper performance are here derived, showing that the distance between antennas must be minimized while optimizing the phase shift introduced by the interconnection. Consequently, the methodology to design the transition is presented by an example using SMA connectors and a meander coaxial cable. Such series arrangement is useful to overcome the restricted directivity of planar LWAs in the UHF band due to limited PCB standard manufacturing sizes, while optimizing the radiation efficiency. The presented theory is validated with practical design examples of microstrip LWA arrays operating in the 900 MHz UHF band. Also, the frequency-beam scanning behaviour of the series-fed LWA array is analysed, demonstrating good performance when the proposed design conditions are satisfied, compared to a non-optimized design which can lead to destructive interference in the desired scanning directions.