| Beam scanning antenna plays an important role in modern communication systems due to its high directionality and wide radiation range.The planar leaky wave antennas(LWAs)with frequency scanning characteristics have attracted extensive research in recent years due to the advantages of low profile,low cost,and simple feeding.However,there are still several problems in applying leaky wave antennas to wireless systems.Firstly,there is an open stopband(OSB)phenomenon near the broadside direction( = 0°)in the conventional leaky wave antenna,which leads to the inability to achieve continuous beam scanning from the backward to the forward;Secondly,the leaky wave antenna usually occupies a large frequency range to achieve a wide-angle beam scanning,resulting in a low scanning rate;Thirdly,it is hard to keep the stable gain of the antenna within the scanning range,which can cause problems such as decreased communication quality.The combination of the Composite Right/Left-Handed(CRLH)transmission lines and the leaky wave antenna can effectively overcome the shortcomings of conventional LWA.A balanced CRLH unit can transition continuously from the left-handed region to the right-handed region without the OSB and achieve a backward-to-forward beam-scanning.Based on this,in this article,a CRLH leaky wave antenna with high scanning rate and stable gain performance is proposed;and ulteriorly,a fixedfrequency beam-scanning leaky wave antenna is proposed.Both antennas have good development potential in the scarcity of spectrum resources.The main research contents of the paper are summarized as follows:1.A CRLH leaky wave antenna with high scanning rate and stable gain is designed.A method to improve the scanning rate of CRLH LWA is analyzed and obtained based on the basic equivalent circuit model of a composite right/left-handed structure.Then,a novel CRLH unit cell with high dispersion behavior is proposed,and the equivalent circuit model is extracted based on its physical structure.In addition,the consistent gain is achieved by adjusting the asymmetry of the unit cell to smooth the leakage constant.The measurement results show that the CRLH LWA composed of 16 cascaded units can achieve continuous scanning from-49° to +46° within operating band of 5.76-6.04GHz(relative bandwidth of 4.75%),with a high scanning rate of 20.The measured gain in the operating frequency band is 8.22-9.62 dBi,with a fluctuation of only 1.4dB.2.A fixed-frequency beam-scanning CRLH leaky wave antenna with a simple electrically controllable feeding network based on single-layer PCB technology is designed.By analyzing the electronic controlled scanning principle of the CRLH structure,a novel CRLH unit cell with adjustable element loading is designed and its equivalent circuit model is extracted.By loading varactors into the gaps and adjusting their capacitance,the phase constant of the unit cell can be regulated,thereby achieving beam scanning.The proposed antenna can achieve continuous beam scanning from-34° to+34° at 5.1GHz.The gain of the antenna is above 10.6dBi and the fluctuation is only 2.1dB. |
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