This letter presents our design and experimental verification of a wideband dual-circular-polarized antenna operating in the W-band based on an optimized waveguide septum polarizer and a profiled smooth-wall horn. This antenna is capable of transmitting and receiving two orthogonal circular-polarized signals [left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP)] simultaneously to achieve full-duplex, hence, twofold spectrum efficiency for millimeter-wave (mmWave) wireless communications. The fabricated antenna shows 21% relative bandwidth from 76.8 to 94.7 GHz with axial ratio 20 dB for both LHCP and RHCP.

In this communication, a rectangular dielectric resonator antenna (DRA) is integrated with a backed cavity to enlarge the DRA side length by 1.8 times. The backed cavity also reduces the sensitivity of the DRA resonance to the DRA size, resulting in a relaxed fabrication tolerance. Based on the enlarged DRA design, a stacked DRA (sDRA) is proposed to improve the bandwidth from 8.7% to 15% and enhance the realized gain by an average of 1.5 dB. The proposed mechanisms are verified by fabricating a 4x4 sDRA array with an enlarged DRA side length of 1.8 mm (0.40λ), an improved bandwidth of 62.7-73.9 GHz (16.4%) and an enhanced measured gain of up to 17.2 dBi. The enlarged DRA dimension permits a higher DRA operating frequency without reducing the DRA size. The proposed millimeter-wave (mmW) sDRA array provides a wide bandwidth and high-gain solution for 67 GHz unlicensed band communications.

A novel ultrahigh frequency radio frequency identification reader antenna based on electromagnetic coupling between two open-ended microstrip (MS) meander lines for near-field applications is investigated in this paper. The corresponding currents flowing along the two MS meander lines are reversed in phase with approximately identical amplitudes. Meander-line units are introduced to achieve a uniform distribution of strong magnetic and electric fields. The performance of an antenna prototype comprised of six pairs of meander lines is analyzed. The proposed antenna simultaneously exhibits a uniform magnetic field distribution with a reading region of 480 mm × 200 mm × 20 mm and a uniform linear electric field distribution with a reading region of 480 mm × 420 mm × 300 mm. The proposed antenna exhibits a low far-field gain, and has a bandwidth from 914 to 929 MHz. Both simulated and measured results have shown a good performance of the antenna.

This paper presents and characterizes a novel antipodal linearly tapered slot antenna for generating the circularly polarized (CP) field. By introducing two symmetrical slots on the top and bottom layers of a rectangular WR-15 waveguide, we could obtain circular polarization with an axial ratio bandwidth of 34.1%. The waveguide was used to feed the proposed antenna with very wideband impedance matching. The antenna can achieve impedance bandwidth of 40% for S(1,1) <;-15 dB from 50 to 75 GHz. The simulation and measurement results show that the antenna can produce very good radiation patterns, with stable gain of 9.8 dBi ± 1.24 dBi, low back radiation, and narrow beamwidth over the operating frequency range. The working principle of this CP antenna is explained, using theoretical equations and explicit current distributions. The proposed antenna is easy to manufacture and is a compact candidate for high performance CP millimeter-wave antenna.

This paper presents and characterizes a novel high gain circularly polarized (CP) antenna array for 5G applications. The array element is an antipodal curvedly tapered slot antenna (ACTSA) generating circularly polarized field. The CP ACTSA fed by substrate integrated waveguide (SIW) is convenient to integrate with substrates. By introducing two sheet metals on the two sides of the rectangular Rogers 6002 substrate, an impedance bandwidth of 18.2%, a wide 3-dB axial ratio (AR) bandwidth of 16.9%, and stable gain of 8 ± 0.6 dBic over the operating band are achieved. By employing the proposed CP ACTSA as radiating elements, a 4 × 4 high-gain wideband antenna array is proposed for 5G E-band and W-band millimeter-wave applications. Fabrications are carried out using wire cutting electrical discharge machine and print circuit board process, which have advantages of low cost. The whole feeding network is realized by SIW with low insertion loss at millimeter-wave band. Benefiting from the wide impedance and AR bandwidth of the new antenna element, good impedance matching and AR characteristics can be achieved over the whole working frequency band from 81 to 95 GHz by this antenna array. Gain up to 18.5 ± 1.3 dBic is also obtained.

This letter presents our study on a compact and low-loss E-band bandpass filter (BPF) based on multilayer groove gap waveguide (GGW). Different from other reported planar GGW filters and vertically stacked substrate integrated waveguide (SIW) filters, the proposed filter realizes a cross-coupled quadruplet topology by introducing a pair of unique circular capacitive holes across layers, innovative ridges (capacitive iris), and conventional inductive irises on the same layer, which reduces the insertion loss (IL) while having a smaller size. By tuning the dimensions of the coupling structures and cavities, the filter is optimized to exhibit a superior performance in simulation. The designed filter is fabricated using CNC machining and verified in experiment. The measured results agree with the simulated ones quite well, showing an average IL of 0.45 dB and an 8% relative 3-dB bandwidth at a center frequency of 73.65 GHz. Therefore, the proposed multilayer GGW structure opens a new avenue in designing high-performance filters in millimeter-wave bands.