Study On Strong Coupling Coherent Excited Double Whips Electrically Small Antenna

The theory of electrically small antennas was established by Wheeler, Chu and Harrington, etc. They figured out that the quality factor of the antennas increases quickly, while the bandwidth and the efficiency descend with the decrease of the dimension of the antennas, and they get the basic restrictions for electrically small antennas. CFA, EH are special electrically small antennas, which are composed by a few coherent excited strong coupled radiators. It is indicated by lots of papers that these antennas are not restricted by the theory of electrically small antennas. So we regard electrically small antennas that are restricted by the theory of Wheeler, Chu and Harrington as"conventional"electrically small antennas, and regard the theory as"conventional"theory of electrically small antennas. Meanwhile, we regard coherent excited strong coupled antennas like CFA, EH, as"unconventional"electrically small antennas.Compared with"conventional"electrically small antennas, CFA has the merits of small dimension and high efficiency, and so on. But its radial dimension is large, and its structure is complicated. So we establish the model of coherent excited strong coupled double whips in this paper to overcome these disadvantages, and we also analyze the model by the MOM. Further more, we design broad-band match network on the basis of the model by the real frequency method, and then we analyze the changes of VSWR and the transducer power gain.First, we introduce"conventional"theory of electrically small antennas, and analyze the efficiency of the whip through the"conventional"theory, and then we get the conclusion that"conventional"electrically small antennas can't get small dimension and high efficiency at the same time. Then we introduce CFA, and compare it with theλ/4 antenna.Second, we establish the model of coherent excited strong coupled double whips in this paper, and divide the model by the length of the model into four models: the model with the length of 1m, the model with the length of 1.5m, the model with the length of 3m, the model with the length of 5m. Then we calculate the characteristic of impendence of four models by the MOM, and also analyze the variation of mutual impendence by changing the radial distance and the portrait distance of two radiators. In addition, we take the model as an equivalent two-port network, and calculate the quality factor without match network, port VSWR without match network, the efficiency with lossless narrowband match network, the efficiency with narrowband match network whose quality factor is 100, the efficiency with narrowband match network whose quality factor is 400, and compare the results with whip antenna whose height and length are the same as the model, then we find that the model of coherent excited strong coupled double whips is better than the equivalent whip for every parameter.Finally, we introduce basic theory and rules of the real frequency method, and apply it into the design of broadband match network for the model of coherent excited strong coupled double whips. Further more, we compare the transducer power gain and VSWR between with and without broad-band match network, whose results provide useful reference for application of the model of coherent excited strong coupled double whips.