Fig. 1. Schematic diagram of omnidirectional conformal ring array based on tightly coupled antenna element. ( denates the amplitude excitation of the n-th port, r_a represents the distance from the centroid of the regular octagon to the center of the antenna element.)

Fig. 2. Structure diagram of tightly coupled long slot element: (a) traditional element and (b) element with short-circuit wall. (h denotes the height between the ground and long slot element.)

Fig. 3. Standing wave ratio of the planar element model after the use of short-circuit processing and resistive loading (f_l denotes the lowest operating frequency in the working band).

Fig. 4. Final tightly coupled long slot element model.

Fig. 5. Resistive frequency selective unit and its simulation results.

Fig. 6. Comparison of the standing wave ratio curves between the tightly coupled long slot element and a connected array element.

Fig. 7. Impact of different element numbers on the azimuth radiation pattern of the circular array. (φ is the azimuth angle, N is the antenna element number, f denotes the highest operating frequency, and a represents the radius of the circular array.)

Fig. 8. Tightly coupled antenna element structure for circular conformal array: (a) before improvement and (b) after improvement.

Fig. 9. Schematic diagram of the construction process of the omnidirectional circular conformal array.

Fig. 10. Actual antenna prototype of the omnidirectional conformal ring array.

Fig. 11. Measured active VSWR for each port of the omnidirectional conformal ring array.

Fig. 12. Measured and simulated gain patterns of the omnidirectional conformal ring array at some typical frequency points: (a) 2f_l , (b) 4f_l , and (c) 10f_l .