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A novel UWB balun with complete ground based on vertically mounted planar structure is presented. Two mutually perpendicular planes comprise the proposed balun. The vertical configuration of double-sided parallel-strip line ensures complete ground in the horizontal plane and the cascading of seven-section quarter-wavelength transformers facilitates UWB functionality. For verification, a prototype balun is designed, fabricated and measured. The simulation and measurement agree well, exhibiting a bandwidth from 0 up to 8 GHz with good return loss, flat insertion losses and high stability of 180°p hase difference.

For the first time, a novel bandwidth-tunable filtering balun based on compact 3D configuration is presented. The overall design is basically composed of a two-layer horizontal feeding plane, a three-layer vertically mounted plane, and the transmission-line circuits disposed on both. Implementing the ring resonator in vertical double-sided parallel-strip line, the complete horizontal ground and frequencyindependent phase difference are subtly combined. Connecting the shunt varactor diodes with the inserted vertical ground, the desirable filtering property and flexible bandwidth tunability are splendidly fulfilled. A prototype balun centred at 1.53 GHz is fabricated. The measured operating bandwidth is dynamically tuned from 0.87 to 1.23 GHz with a return loss <−10 dB, forcefully validating the design concept.

A novel three-dimensional high-isolated dual-band balun is proposed for the first time. A horizontal feeding plane, a vertically mounted plane, and four grounded resistors constitute the entire structure. By introducing the double-sided parallel-strip line with an inserted conductor plane to the middle of the vertical plane, the output matching and isolation, frequency-independent phase difference, and complete ground in the bottom layer of the horizontal plane are perfectly integrated in this novel balun. To prove this conception, a practical balun operating at 1.3/2.5 GHz is designed. As expected, remarkable consistency between the simulation and measurement is obtained.

In this paper, a circularly polarized filtering antenna with high out-of-band radiation rejection level is proposed. The entire design consists of a patch and a filtering feeding network, which are connected by metallic pins. First, a highselectivity filtering power divider is constructed utilizing