This paper presents a novel distributed choking technique, the spiral choke, for scattering suppression in dual-band antenna arrays. The working principle and the scattering suppression capability of the choke are analyzed. The spiral chokes are implemented as low-band radiators in a co-located 4G and 5G dual-band array to suppress cross-band scattering while broadening the bandwidth of the choked element. The experimental results demonstrate that the cross-band scattering in the array is largely eliminated, and the realized dual-band array has very stable radiation performance in both well-matched bands.

A compact ultra-wideband (UWB) slot antenna with band-notched characteristics is proposed. A stepped slot is adopted as a radiator to realize UWB impedance matching and reduce the antenna size. By slitting an open-ended quarter-wavelength split slot on the back of the feed and a short-ended half-wavelength split-ring slot near the stepped slot, a second-order notched band of 5.15-5.85 GHz is achieved. Compared with the traditional band-notched antenna, the selectivity of the notched band is greatly improved and size of the antenna is reduced at the same time. The volume of the antenna is only 22 mm×8.5 mm×0.8 mm. Besides, the bandwidth can be easily controlled by adjusting the lengths of the two slots respectively. Good agreement is achieved between simulated and measured results, which show that the proposed antenna has nice impedance matching and radiation pattern characteristics.

A compact wideband four-way filtering PD is presented. The structure of the proposed device includes a pair of looped coupled-line structures to provide the needed power division to four output ports. Moreover, a pair of short-ended coupled-line stubs is used to introduce multiple transmission poles and transmission zeros for a sharp cut-off of the passband and high upper-stopband rejection. A detailed design procedure is shown to determine the initial design parameters. A prototype is designed, simulated and measured experimentally. The measured results show 56.5% bandwidth centered at 1.5 GHz with more than 15 dB upper-stopband rejection up to 4.15 GHz, more than 13 dB in-band isolation, and 15 dB return loss at all output ports.

A compact ultra-wideband (UWB) bandpass filter using dual-stub-loaded resonators (DSLR) is presented. The DSLR is analyzed by using the odd- and even- mode method. Four resonant modes can be tuned by the DSLR in 3.1 GHz - 10.6 GHz, and a pair of transmission zeros can be generated at the lower and upper stopband when the DSLR is applied to a UWB filter. Therefore a UWB bandpass filter is realized with good skirt selectivity, harmonic suppression, as well as compact size. Finally the proposed filter is simulated and fabricated. The measured results are in good agreement with the predicted one, demonstrating this structure is feasible in practical use.