Circularly polarised microstrip line leaky-wave antenna terminated with patch

A novel gain/bandwidth enhanced leaky-wave microstrip line antenna with circular polarisation (CP) is proposed. Different from common leaky-wave antennas with an open, short or resistive termination, this antenna consists of a leaky-wave rampart-line antenna terminated with a CP patch radiator. The energy from the feeding point is first radiated by the rampart-line antenna, while the remaining part is radiated through the CP patch element. As a result, the size of the leaky-wave part can be reduced. The resulting size of this antenna is only 1.6 x 1.6 lambda(2.4G)(lambda(2.4G)is free space wavelength at 2.4 GHz). Energy loss caused by the resistive termination is avoided, so that high efficiency is achieved - higher than 85% within the whole band. By introducing slight CP centre frequency difference between the patch and rampart antenna, two CP resonances were generated and the 3 dB axial ratio (AR) bandwidth is substantially broadened. Measured AR bandwidth is 9.9% (2.30-2.54 GHz). Its - 10 dB impedance bandwidth is 2.25 GHz to higher than 3 GHz, and peak gain is 13.2 dBic. The proposed antenna has a fully used radiation aperture, achieving a favourable performance, such as wide bandwidth, high gain, and a relatively stable (less tilted) boresight radiation.