Volume 79, Issue 3-4

This paper presents a wideband reconfigurable coupler with tunable coupling ratios. It consists of two 3 dB quadrature couplers and two varactor-based continuously tunable reflection networks. The instantaneous bandwidth is enhanced by adding matching networks at all four ports. The proposed four port with reflection symmetry offers a return loss greater than 15 dB and an isolation greater than 20 dB through a fractional bandwidth of 23 % while exhibiting a very flat response. The coupling ratio can be tuned from −9 dB to 0.1 dB.

In this paper, a symmetric compact dual-band coupled-line coupler is proposed using microstrip transmission lines, circular resonators, and spiral lines for WiMAX applications. The proposed coupler provides two narrow operating bands, high coupling and isolation, and suitable return loss. The primary design consists of two parallel-coupled lines with a flat coupling over a wide frequency band. Then, the bandwidth, return loss, and isolation are optimized by adding circular resonators and spiral lines to achieve a compact size. In this design, the return loss is better than 30–35 dB in the bandwidth 3.4–5.79 GHz. Finally, this structure is fabricated using a Rogers-RT Duroid 5,880 substrate with a thickness of 20 mil, a loss tangent of 0.0009, a dielectric constant of 2.2, and an area of 18.8 × 14 mm 2 . The results of the measurements are in good agreement with those of the simulation.

This article presents a wideband wearable antenna with flexible substrate for Body Area Network application. The designed coplanar antenna has a return loss bandwidth of 3.5 GHz ranging from 5.15 GHz to 8.65 GHz with maximum return loss at 5.8 GHz (45.9 dB) and 7.4 GHz (31.4 dB). The average gain of the antenna is 4.069 dB. The obtained specific absorption rate of the antenna is below the FCC reference limit of 1.6 W/Kg per 1 g of tissue, making it suitable for biomedical application.

Two antenna arrays are designed for beam scanning in the azimuthal plane using the method of maximum power transfer efficiency (MMPTE). The first array consists of vertically polarized single-band bow-tie like dipole antennas operating at 3.5 GHz. It can be switched between directional and omnidirectional modes, achieving an omnidirectional/directional gain of 3.6/8.1 dBi. Based on the single-band array, a second vertically polarized dual-band dipole array is proposed by replacing the bow-tie arm with two nesting loops, which can achieve omnidirectional and directional radiations at 3.5 GHz and 4.9 GHz with an omnidirectional/directional gain of 1.7/7.5 dBi and 3.3/7.5 dBi respectively. The satisfactory dual-mode operations of the proposed arrays make them suitable for CPE applications.

As wireless communication continues to grow, reconfigurable antenna technologies have emerged as an optimal choice for multiband antennas. This study incorporates a 4 × 4 Artificial Magnetic Conductor (AMC) surface into a compact multiband frequency-reconfigurable antenna for diverse wireless applications. The antenna featured interconnected octagonal and rectangular patch slots in a radiating element with a defective ground structure. The antenna uses two-pin diodes to switch between four distinct working modes that produce dual wideband, triple-band, and quad-band responses. The AMC unit cell exhibits sextuple-band behavior at 2.5 GHz, 5 GHz, 6.5 GHz, 8.7 GHz, 10.5 GHz, and 11.4 GHz, with Double Negative material properties. The integrated antenna with dimension 50 × 50 × 10.2 mm 3 achieves an average gain enhancement of 3.29 dB across its four switching states, with a peak Front-to-Back Ratio (FBR) reaching 31.23 dB, a notable radiation efficiency of 87 % with an average back lobe gain reduction of 13.75 dB. The Specific Absorption Rate (SAR) reached a minimum of 0.0594 W/kg with an overall average reduction of 93.25 %. The antenna was tested in an anechoic chamber using a vector network analyzer, and the results matched the simulations. Ultimately, the antenna design offers a compact, low-profile configuration that is ideal for versatile wireless applications with multiple bands and modes.

In this paper, a type of reconfigurable filtering phase shifters (RFPSs) composed of stepped-impendence stub-loaded multimode resonators (SLMMR) is proposed. High frequency selectivity and wideband characteristics are realized in the presented work. Four transmission poles (TPs) are generated in the passband to exhibit a flat and wide passband. Meanwhile, the proposed SLMMR produces two controllable transmission zeros (TZs), which improves the frequency selectivity effectively. Meanwhile, radiofrequency switches are utilized to facilitate the transition between different phase shifts. Finally, the proposed RFPSs are designed and fabricated to verify the method. The measured results indicate that the designed RFPSs, which can be turned from 45° to 90° and from 135° to 180°, are capable of realizing more than 40 % FBW with a center frequency of 3.5 GHz.

In this paper, balanced tri- and quad-band bandpass filters (BPFs) with high selectivity and controllable center frequencies and bandwidths are proposed. In the tri-band BPF design, two differential-mode (DM) passbands are formed by utilizing a stub-loaded resonator (SLR) and a uniform impedance resonator (UIR). The coupling structure of the proposed BPF realizes the third DM passband. Moreover, the center frequencies and bandwidths of the three DM passbands can be controlled by the lengths of resonators and the gaps between the resonators. In order to improve the DM selectivity further, the source-load-coupled structure is introduced. In addition, common-mode (CM) suppression is achieved by using L-shaped balanced microstrip line to slotline transition structures, achieving the independence between CM responses and DM ones. Therefore, the design procedure can be simplified greatly. In order to validate the practicability, one balanced tri-band BPF operating at 2.5, 3.5 and 4.5 GHz is designed and fabricated. Moreover, by adding a short stub to the UIR located in the symmetrical plane, one flexible resonance frequency is generated, which is used to design the balanced quad-band BPF. By manufacturing and measurement, the measurement and simulation are in good agreement.

This paper presents a metasurface with three different useable configurations. The full metasurface consists of a PTFE enclosure having 12 compartments sandwiched between two layers of 2D periodic metallic patterned FR-4 substrates. The PTFE compartments can be kept empty or filled with deionized (DI) water. The first configuration is achieved when all the compartments are kept empty, the second configuration is achieved when alternate compartments are filled with DI water, and the third configuration has all the compartments filled with DI water. In the first configuration, the metasurface acts as a normal electromagnetic (EM) wave reflector, in the second configuration it acts as a dual-band spatial passband filter which allows EM waves within certain frequency bands to pass through and in the third configuration, it acts as a multiband EM wave absorber. The metasurface can operate within the S and C microwave bands. The thickness of the entire structure is only 13.04 mm, which corresponds to around λ 0 /3.7 ( λ 0 is the free space wavelength at the highest operating band). The transmission and absorption bands have good angular stabilities up to an incident angle of 60°.

In this paper, nano-silver and nano-silver coated tin solder joints with hot pressing bonding conditions of 250 °C, 2 min and 15 MPa were selected to study the shear strength of solder joints and their service reliability under hot cycling conditions. The main conclusions are as follows: The addition of nano-tin plays a dispersion strengthening role, which increases the shear strength of nano-silver solder joint from 40 MPa to 50 MPa. After thermal cycling, the main failure mode of the nano-silver-coated tin solder joints is ductile fracture. The main failure mode of the nano-silver solder joints is brittle fracture, firstly, the delamination appears at the interface, and then the crack passes through the outer side of the solder joints, showing cleavage fracture of the grain. The thermal fatigue life of the nano-silver solder joint is 145 cycles, and the thermal fatigue life of the nano-silver-coated tin solder joint is 175 cycles.