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Tunable transmission lines have a high demand in the 5G wireless communication applications. In this brief, a novel transmission line is presented to control both electrical length and characteristic impedance individually, creating flexible functions. For the first function, the proposed transmission line can perform as a tunable phase shifter with 90° phase tuning range and a low insertion loss variation. For the second function, the proposed transmission line can tune the characteristic impedance from 23 Ω to 145 Ω with a fixed phase delay. The ABCD-matrix method is applied to derive the design equations. For the practical implementation, the varactor equivalent parasitic resistances are considered, and the even-odd mode is applied to re-optimize the proposed two tuning functions. To verify the design theory, an experimental prototype is simulated, fabricated, and measured. Both simulation and measurement results match well with the design theory. [ABSTRACT FROM AUTHOR]

In this paper, a 2-D beamforming phased array using a novel 2-D Nolen matrix network is presented. The Nolen matrix is a novel antenna feeding network composed of only couplers with dedicated coupling ratios and phase shifters. It does not require crossover and load termination compared to other networks based on Butler and Blass matrix. To be specific, the closed-form equations are derived first for uniplanar single $3 \times 3$ Nolen matrix, which is composed of three couplers and three phase delay lines. Most importantly, it is found that the proposed Nolen matrix can employ couplers with arbitrary phase differences to achieve relatively flexible progressive phase delays across the radiating elements, presenting a high degree of freedom on circuit topology and beamforming performance. Then, a 2-D antenna feeding network is designed by stacking and cascading six $3 \times 3$ Nolen matrices, and a 2-D patch antenna array is integrated with the proposed feeding network to generate nine radiation beams with unique directions on azimuth and elevation planes, realizing the 2-D beamforming function. To verify the proposed design concept, a prototype of 2-D beamforming phased array operating at 5.8 GHz is designed, fabricated, and measured, and the experimental results agree well with simulation and theoretical analysis. [ABSTRACT FROM AUTHOR]

In this letter, a novel planar branch line balun with transparent port impedance is presented. The balun is designed based on a symmetric four-port network with an open-ended transmission line stub in the middle of the branch at its unbalanced port side. From the even-odd mode analysis, the equivalent network is derived to be a short circuit under even-mode excitation, and the input impedance looking into the unbalanced port satisfies impedance matching under odd-mode excitation. Unlike previous designs, the equivalent cascaded impedance transformer in the proposed structure is independent to the system reference impedance in odd-mode excitation so that the termination at the unbalanced port is transparent to balanced ports. To prove the design concept, the closed-form equations are derived, and multiple prototypes with termination impedances 35, 50, and $75 ~\Omega $ are simulated, fabricated, and characterized. [ABSTRACT FROM AUTHOR]

In this paper, we design and implement a long-range and broadband aerial communication system using directional antennas (ACDA). The system integrates Wi-Fi devices with aerial networks to quickly establish a Wi-Fi infrastructure in the air, which provides real-time communication capability for disasters where a fixed communication infrastructure does not exist. ACDA utilizes unmanned aerial vehicle (UAV)-carried directional antennas to extend communication range, increase throughput, and reduce interference. A GPS-based control algorithm is designed and implemented to automatically reject wind disturbance and align the directions of antennas in accordance with UAV movement. A received signal strength indicator-based decentralized initial scan algorithm is also designed and implemented to quickly establish initial connection between the UAVs. Simulation studies verify the effectiveness of the heading control and initial scan algorithm. Field tests are also conducted to evaluate the performance of overall system in terms of throughput and delay with respect to the increase of communication range. The ACDA prototype system achieves 48 Mb/s throughput at a distance of 300 m and 2 Mb/s at 5000 m, and proves the promising usage of directional antennas for long-distance Wi-Fi aerial communication. Practical use of this on-demand communication system to aid emergency response is also demonstrated through a case study in a real disaster drill. [ABSTRACT FROM AUTHOR]

The 3-dB power divider is one of the most common three-port device in microwave systems, which equally splits the signal at its two output ports. In previous Wilkinson power divider design, the phase delay between the input and output ports is not considered into the design requirements. However, the zero-phase shifting power divider attracts great interest in modern microwave systems. In this letter, a 3-dB power divider with zero-phase delay is designed based on a zero-phase impedance transformer. Instead of metamaterial transmission line, a transmission line stub is added to connect the isolation resistor, and a capacitor is insert between the output ports and the end of main branch to cancel out the imaginary part of even–odd mode impedances. With this new design, it releases the layout restriction that the two branches route around to connect to lumped element resistor. Closed-form design equations are derived and a prototype device is then simulated and measured. The measurement results agree well with the simulation results. [ABSTRACT FROM AUTHOR]