A low-cost beam-steerable antenna operating at 28 GHz is presented for 5G mobile terminal applications. The proposed array has a sandwich-like stack structure, including ten patch elements, a ground plane with two rows of slots, and a long microstrip transmission feed line. The radiators and the transmission line are placed at the two sides of the ground plane, which provides great flexibility in designing the radiating pattern and the feed network. Switches are added on the transmission line to construct periodic distributed phase shifters for beam steering. 2-bit phase shifter with phases of 0°, 90°, 180°, 270° is formed without using phase delay lines. Continuous beam steering is achieved, and the steerable angle is 121° in the upper hemisphere. Two location configurations of the proposed array in 5G mobile terminals are analyzed and the angular coverage range is evaluated. The array can cover 38.8% of the hemispherical space with a gain threshold of 10 dBi.

A novel ultrawideband directive antenna for ground-penetrating radar (GPR) applications is presented in this letter. The antenna is designed for operation at frequencies below 500 MHz to allow for high-depth-resolution imaging of the deeply buried targets such as buried pipes and other deep underground man-made structures such as tunnels. The antenna is formed by a pair of coupled antennas inspired by an electrically narrow very low profile (ENVELOP) antenna with differential feeding to provide a directive pattern normal to the antenna ground over a wide bandwidth. An antenna operating in the range of 140-510 MHz is designed and fabricated using the printed circuit board (PCB) substrates. The antenna is designed and optimized for operation in the proximity of a half-space soil medium to achieve efficient coupling of power from the air to the ground. The measured reflection coefficient of the antenna near concrete and wet soil covered by sand and grass is shown to be better than -9.5 dB within the specified band. The simulated realized gain of the antenna in the presence of dry soil is better than 4.9 dBi within the range of 140-510 MHz. The antenna is low-profile with a total height of 153 mm and a lateral dimension of 600 mm x600 mm. The performance of the antenna for GPR applications is evaluated through a field measurement of a buried object in wet soil with high losses.

In this letter, a novel dual-polarized 1 × 4 patch array using proximity feed technique is presented. The proposed single-layer antenna consists of four square patch elements, two short-terminated parallel coupled microstrip lines, and a rat-race incorporated in the feed network. The patches are placed at the inner space between the two parallel microstrip feedlines. Horizontal and vertical polarizations of the patch array are excited by the even and odd modes of the two microstrip lines, respectively. The rat-race structure is used to provide in-phase and 180° out-of-phase feeds for the two modes. A prototype operating at 3.5 GHz is fabricated and measured. The measured overlapping bandwidth of the two ports is 81 MHz, also with port isolation higher than 40 dB. Owing to the symmetry of the structure and balanced excitations, the measured cross polarizations are all below −29 dB in E - and H -planes.

A novel wideband circularly polarized (CP) omnidirectional antenna operating at L-band is presented. The antenna operates based on excitation of a field distribution similar to circular waveguide TE21 mode over a wide bandwidth. It is shown that the circular TE21 mode generates a linearly polarized far-field electric field over the horizontal plane with its polarization tilt angle varying as a function of azimuth angle. It is also shown that the tilt angle varies by 90° for an azimuthal angle increase of 45°. To obtain circular polarization, two circular TE21 modes are excited such that one mode is spatially rotated by 45° with respect to the other mode. The phase difference between two modes is 90°. The modes are excited by an array of 16 monopole sectorial loop antennas to achieve a wide axial-ratio (AR) bandwidth. A right-handed CP antenna based on the proposed structure is fabricated and tested against simulation results. A feed network including Wilkinson power dividers and low-pass/high-pass phase shifters is also designed and fabricated to feed the antenna elements. The measurement results show 58% of 3-dB AR and 10-dB impedance bandwidth with the center frequency at 1.565 GHz. The total height of the antenna is 47 mm.

A state-of-the-art radar system suitable for terahertz (THz) sensing and imaging is presented. The system is composed of a bistatic superheterodyne transmitter–receiver (TX–RX) pair, designed and fabricated in a 65-nm CMOS process, driven by three coherent external sources and measured using a lock-in amplifier. The TX and RX chips each employ a wideband multiplier and amplifier chain to achieve a peak output radiated power of -2 dBm and a radar bandwidth of 25 GHz. A novel fully integrated dual-slot cavity backed antenna is designed based on characteristic mode analysis and coupled mode theory. The antenna achieves a 30 GHz wide gain, polarization and impedance bandwidth with front-side radiation and 18 dB polarization discrimination over the entire band. The three stage power amplifier (PA) is fed by a four-way slot-line-based balanced power divider. Miniaturization and symmetry enforcement are used to achieve 0.65 dB of insertion loss and less than 0.02^∘ of phase imbalance over an ultra-wide bandwidth of 50 GHz centered at 125 GHz. For the RX, a two-stage superheterodyne architecture is used to improve the noise figure (NF), which is measured to be 15 dB at its minimum. The system architecture enables the entire wide-band scattering data of all targets to be downconverted onto a single continuous wave (CW) signal, whose amplitude and phase are measured with very high sensitivity and accuracy using a lock-in amplifier. The measured range and velocity accuracy are 40 μm and 80 μm/s, respectively, which are shown to agree well with theoretical estimates. Finally, the system’s phase accuracy and long-term phase coherence are tested in a high-resolution inverse synthetic aperture radar (ISAR) experiment with several targets. The resulting images show a cross-range resolution that is at the theoretical diffraction limit (i.e., ≈λ/2). To the best of our knowledge, this article reports the first coherent imaging radar system above 200 GHz in CMOS.