A simple decoupling method of using metallic vias to improve the isolation of millimeter-wave multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) elements is investigated. The vias are vertically added to the DRA elements, at appropriate positions. By means of the interaction with the electromagnetic fields, the vias can potentially affect the filed distributions and further reduce the coupled fields effectively. The isolation between the MIMO DRA elements can, therefore, be enhanced substantially. As the vias are placed inside the DRA elements, no extra footprint is needed, making the entire antenna system very simple and compact. Two typical examples, including an H-plane and an E-plane, coupled $1\times2$ MIMO DRA arrays, have been designed, fabricated, and measured to demonstrate the feasibility and universality of this method. The results show that by using the vias appropriately, the isolation of the H-plane coupled MIMO DRA array can be enhanced from ~15.2 to 34.2 dB, while that of the E-plane array can be improved from ~13.1 to 43 dB at 26 GHz.

A low-profile wideband circularly polarized (CP) crossed-dipole antenna that has both wide axial ratio (AR) beamwidth (ARBW) and half-power beamwidth (HPBW) is presented in this paper. The crossed dipoles are composed of four trapezoidal patch arms, and they are fed by a pair of vacant-quarter printed rings to generate CP radiation. Four identical parasitic elements that consist of a horizontal triangle patch and a vertical metallic plate are symmetrically intervened between the crossed dipoles and the ground plane. It has been found that the parasitic elements can effectively decrease the antenna profile, increase the operating bandwidth, and simultaneously enhance the ARBW as well as the HPBW. A prototype was fabricated and measured to verify the design. The measured results show that the prototype has a low profile of 0.1λ0, a –10-dB impedance bandwidth of 78.3% and a 3-dB AR bandwidth of 63.4%. Moreover, a 3 dB-ARBW of more than 120° and a HPBW of more than 110° are achieved simultaneously within a wide passband of 50.7%.

Total bandwidth of existing wireless communication technologies covers a wide frequency range of over one octave. But most existing power amplifier configurations cannot meet this requirement while at the same time maintaining a high efficiency. Therefore, a new structure that can achieve multioctave bandwidth is proposed in this paper together with the design methodology. The difficulty in realizing a bandwidth larger than one octave lies in the overlapping of fundamental and harmonic frequencies. Regarding this problem, the continuous class-F mode is extended to allow a resistive second harmonic impedance, rather than the pure reactive one. With the relaxed design requirements and overlapping design space of fundamental and second harmonic frequencies, harmonic tuning and fundamental frequency matching networks can be designed separately. More importantly, broadband matching for fundamental frequencies can be implemented simply by considering only three fundamental frequency points using the multiple frequencies matching method. To verify the validity of the proposed methodology, a multioctave power amplifier was designed, fabricated, and measured. Measured results verify a wide bandwidth of 128.5% from 0.5 to 2.3 GHz. Over this frequency range, drain efficiency was larger than 60% with output power greater than 39.2 dBm and large signal gain larger than 11.7 dB.

A low profile stacked dielectric resonator antenna (DRA) and a microstrip metasurface (MS) antenna are investigated and compared in this communication. It has been found that very similar radiation performance including resonant modes, reflection coefficients, boresight gains, and radiation patterns can be obtained between them, indicating that the dielectric superstrate of stacked DRA plays analogous role with MS in enhancing the antenna bandwidth and realized gain. Based on this observation, a broadband, low profile, and high gain filtering cylindrical stacked DRA is inspired by an MS-based filtering antenna. Four resonant modes including the higher order HEM _31δ mode and HEM _13δ mode are simultaneously excited in the DRA to provide a broad bandwidth of 61.4% and a peak gain of 11.4 dBi within passband, whereas a shorting via and two pairs of transverse stubs are introduced into the feeding microstrip line to generate radiation nulls in stopband and realize filtering function. Second harmonic suppression has been achieved without increasing the footprint of the antenna, and an out-of-band suppression of more than 23 dB is obtained within the wide stopband.

The coexistence of microwave and millimeter-wave technologies becomes the inexorable trend of future wireless communication systems. The corresponding components of the system are required to cover these two frequency bands simultaneously. However, it is difficult for the existing dual-band antenna configurations to achieve a frequency ratio larger than 3. In this paper, a novel topology is proposed to solve this problem. For the desired dual-band operation, a signal routing approach is proposed to guide the microwave/millimeter signals to the specific elements, respectively. The classical aperture coupling mechanism is deliberately utilized to block the millimeter-wave signal from feeding to the microwave antenna element and route the millimeter-wave signal into the millimeter-wave antenna element. Meanwhile, the substrate- integrated waveguide (SIW)-based millimeter-wave antenna element has the high-pass nature to reject the microwave signal. Therefore, the antenna elements for microwave and millimeter-wave bands can be designed separately with a high flexibility. First, a dual-band antenna was implemented to support 5.8 and 30 GHz simultaneously by integrating an annular-ring antenna element and an SIW slot antenna element. Furthermore, different radiation properties at the two bands can be easily realized owing to the high flexibility of the proposed approach. For validation, these two antennas were fabricated and measured.

A novel decoupling method is investigated for the multi-input multi-output (MIMO) microstrip patch antenna (MPA) array. This method makes use of the TM ₁₀ and TM ₀₂ modes, which are simultaneously excited in the rectangular MPA. It is found that by adjusting the frequencies of the two modes, their $E$ -fields coupled to the adjacent passive MPA can counteract each other to generate a specific null-field region. When the feeding position of the passive MPA is located in the null-field region, the MPA cannot be excited effectively, and hence an extremely low mutual coupling is obtained without requiring any extra decoupling structure. To validate the feasibility of this decoupling method, an E- and an H-plane-coupled $1\times 2$ MIMO MPA arrays are respectively simulated, fabricated, and measured. The isolation of the E-plane-coupled array is enhanced from ~11 to 57 dB, while that of the H-plane-coupled array is improved from ~18 to 51 dB.