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This paper proposes a compact dual-band printed quadrifilar helix antenna (QHA) operating at GPS-L1 (1575 ± 2 MHz) and L2 (1228 ± 2 MHz) bands. To generate the dual operating bands, two interconnected lines with unequal lengths are introduced as a radiating element. The closely allocated radiators resonate in quarter-wavelength mode, which significantly miniaturizes antenna's size. Four shunt capacitors are loaded near ports to manipulate the mutual coupling between each two radiators, so that satisfactory matching condition with minimum active reflection at two target bands can be obtained simultaneously. Then, a compact feeding network consisting of on-chip hybrid couplers is designed and connected to the QHA. Measured results show that the compact proposed antenna achieves peak gains of 1.5 dBic and 2.6 dBic at 1575 MHz and 1228 MHz, respectively. The axial ratios (ARs) at L1 and L2 bands are both below 2.5 dB, and the half-power-beamwidths (HPBWs) are as wide as 130 and 116 , respectively. As compared with reported works, the proposed antenna can achieve much more compact size (0.11 × 0.21 λ 0 2) and dual-band radiation at the same time.

In this paper, a three-dimensional (3-D) printed spherical antenna with bandwidth enhancement under the operation of TM 101 and TM 211 modes is presented. The antenna is started from a metallized spherical cavity with a rectangular feed waveguide. Then, some slots are suitably introduced on its sidewall. With the help of these introduced slots, two resonant modes (TM 101 and TM 211) can be excited simultaneously and merged with each other, resulting in a wideband radiation characteristic with two resonances. An antenna prototype operating at X and Ku bands is designed and implemented as proof of concept. The antenna is additively manufactured by incorporating polymer-based stereolithography and electroless copper plating techniques. Measured results show that the antenna not only owns a wide impedance bandwidth of 40.9% from 9.77 to 14.81 GHz, but also maintains stable radiation patterns over the operating band. Besides, the measured average gain is as high as 10.1 dBi. As the measured results are in good agreement with the simulated ones, a simple and effective design of 3-D printed wideband spherical antenna with high radiation performances is verified. INDEX TERMS Spherical antenna, 3-D printed, waveguide-fed, wideband antenna.

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