In this study, a numerical method for designing efficient adiabatic devices with multiple structural parameter variations (NAMSP) is developed. This method can be applied to a wide range of devices based on adiabatic mode evolution structures. The numerical design complexity of multiple structural parameter variations will be greatly improved compared to the case of a single parameter variation. Therefore, an efficient domain decomposition scheme was originally introduced into the NAMSP method. The proposed method can help compute compact adiabatic guided-wave shapes for these adiabatic devices with multiple structural parameter variations. Adiabatic devices with multiple structural parameter variations are used to connect different complex waveguides, which are often difficult to design using analytical methods. The design involves tapering the width of the two or more core layers at one time; however, this change in the width typically affects the mode both vertically and horizontally. Our numerical method allows the shape of the width variation for each layer that facilitates compact adiabatic mode transformation to be obtained. The efficiency of the adiabatic device that was designed using the NAMSP method considerably exceeds that obtained using a linear-shaped device. Moreover, our designed adiabatic device enables an ultra-wide operating bandwidth (spans in the wavelength from 1050 nm to 4780 nm).

A novel miniaturized wideband bandpass filter (BPF) using capacitor-loaded microstrip coupled line is proposed. The capacitors are loaded in parallel and series to the coupled line, which makes the filter just require one one-eighth wavelength coupled line and achieve filtering response with multiple transmission poles (TPs) and transmission zeros (TZs). Compared with the state-of-the-art microstrip wideband BPFs, the proposed filter has the advantages of compact size and simple structure. A prototype centered at 1.47 GHz with the 3-dB fractional bandwidth of 86.5% is demonstrated, which exhibits the compact size of 0.003λ2 g (λg is the guided wavelength at the center frequency) and the minimum insertion loss of 0.37 dB.

A dual-patch antenna with filtering and decoupling properties is introduced. It excites the Quasi-TM01 and reverse TM02 modes of the dual patch by loading an open stub on the microstrip feed line, thus introducing radiation zeros at the upper and lower band edges to achieve effective filtering response. In addition, by combining a pair of vertical slots structures, the antenna provides decoupling effect in the radiation pattern of the same frequency two-element array. Because it has decoupling and filtering characteristics at the same time, it can realize decoupling between units at the same frequency band and adjacent frequency bands simultaneously. Compared with the existing design, thanks to its simple structure and symmetry, it can be more suitable for the layout of multiple antenna elements with additional advantage of enhanced bandwidth. The measured 10-dB impedance bandwidth for the two-element array in the same frequency band is 6.03% with the isolation higher than 14.8 dB, while the two-element array in adjacent frequency bands exhibits -10 dB impedance bandwidths of 6.35% and 7.08% with the isolation higher than 26.1 dB.

To address the limitation of insufficient effective decoupling bandwidth in existing dielectric resonator antennas (DRAs), this paper presents a DRA that achieves an effective decoupling bandwidth of 56.5% (3.68GHz-6.58GHz). This broadband effective decoupling is realized by combining the annular structure, stacked configuration, and multi-null generation. An annular dielectric structure is added above a 1×2 H-plane dielectric resonator antenna array with a center-to-center spacing of 0.45λ₀(λ₀ is wavelength in free space at the center frequency of the entire band). The annular dielectric structure is interconnected via non-metallized vias. The entire antenna array operates with four resonant points within the working band, corresponding to the TM₁₀, TM₁₁, and anti-phase TM₂₀ modes of the lower strip DR, as well as the TM₁₀ mode along the y-direction of the upper annular dielectric structure. Benefiting from the x-direction one and a half wavelengths strip of the upper annular dielectric structure, trough path cancellation generates two mutual coupling nulls at the lower frequency band. Simultaneously, the annular structure perturbs the E-field of the coupled elements, creating weak-field that realize port decoupling and rise two mutual coupling nulls. Furthermore, due to the stacked configuration, a mutual coupling null is introduced at higher frequencies. These five mutual coupling nulls realize isolation better than -22.6 dB in the entire band. The in-band envelope correlation coefficient (ECC) is below 0.006, and the peak efficiency reaches 96.7%.

In this paper, a dual-beam filtering patch antenna is proposed, wherein a symmetrical π-shaped metal vias-loaded dual-mode patch and a cross-shaped metal strip are utilized. The dual-mode patch resonator is realized through the loading of metal vias in the weak field region of mode TM21, which effectively moves mode TM01 closer to TM21. Using a cross-shaped metal strip to excite the dual-mode patch resonator not only provides a reflection zero and broadens the bandwidth, but also generates two radiation nulls through zero coupling, thus improving the frequency selectivity. Compared with reported dual-beam filtering patch antenna, the proposed design with the novel dual-mode patch resonator has a wide stopband, enhanced frequency selectivity, small size and a low profile. Measurements show that the antenna exhibits a 10-dB impedance matching bandwidth of 13% (3.23 GHz -3.69 GHz), with two radiation nulls at 3.15 GHz and 3.88 GHz and a measured 15 dB stopband of 2.14 f0.

This paper proposes a method to simultaneously suppress in-band and cross-band mutual coupling in MIMO patch antenna arrays. The proposed approach uses a short-circuited stub loaded half-wavelength strip resonator to couple patch antenna, achieving mutual coupling and radiation nulls. When the short-circuit stub loaded half-wavelength resonator operates in odd mode, it couples with the metal patch to form the radiation band and generate an upper radiation null. When the resonator operates in even mode, it generates a lower radiation null, enabling filtering characteristics that reduce cross-band mutual coupling. The loading of short-circuit stubs also adjusts the antenna's initial phase, and combined with the path superposition effect, mutual coupling null is generated, reducing in-band mutual coupling. Compared to the existing designs, the proposed approach is more compact, offers better isolation, and achieves both cross-band and in-band decoupling on a 2-D array. Additionally, it provides the extra benefit of reducing the Envelope Correlation Coefficient (ECC). To verify the effectiveness of the proposed method, an antenna array was fabricated and measured. The 10-dB impedance bandwidths for the antenna elements operating at 3.5 GHz and 3.8 GHz are 2.84% and 3.42%, respectively. The in-band isolation exceeds 31.3 dB, the cross-band isolation exceeds 30.8 dB, and the ECC within the operating band is less than 0.0005.