IEEE802.11 Wireless Local Area Networks (WLANs) are becoming more and more pervasive due to their simple channel access mechanism, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), but this mechanism provides all nodes including Access Point and other Stations with the same channel access probability. This characteristic does not suit the infrastructure mode which has so many downlink flows to be transmitted at the Access Point that congestion at the Access Point is more likely to occur. To resolve this asymmetry traffic problem, we develop an Optimal Contention Window Adjustment method assuming the condition of erroneous channels over WLANs. This method can be easily implemented and is compatible with the original CSMA/CA mechanism. It holds the ratio of downlink and uplink flows and at the same time achieves the maximum saturation throughput in the WLANs. We use the Markov Chain analytical model to analyze its performance and validate it through the simulations.

In this paper, we propose a wideband four-way turnstile-junction waveguide divider/combiner in the Ka-band. The proposed divider/combiner has an insertion loss of less than 0.8 dB over the frequency range of 28–39.5 GHz. A power combiner amplifier using this circuit and four MMIC amplifiers has been demonstrated with 83% combining efficiency at 34.9 GHz. The measured results show that the turnstile-junction waveguide divider-combiner is a suitable element for developing a broadband millimeter-wave spatial power combiner amplifier.

In this letter, a novel 4-way X-band spatial power divider/combiner has been developed using a modified quasi-Yagi antenna transition. The divider has an insertion loss of less than 0.5 dB and a power balance of +/-0.8 dB over a bandwidth of 3.5 GHz in the X-band. A power combiner amplifier using this circuit and four MMIC amplifiers has been demonstrated with 84% combining efficiency. The obtained results show that the modified quasi-Yagi antenna is a suitable element to develop a broadband spatial power combiner.

In this letter, a broadband coupler is presented that makes use of a half mode substrate integrated waveguide (HMSIW) technique using a printed circuit board process. The coupler is realized by a parallel HMSIW line which couples energy by magnetic field. Compared with micro-strip coupler and conventional HMSIW coupler, it has lower loss and better Electromagnetic Compatibility owning to the closed field structure. Compared with SIW coupler, it has smaller size and lower cost owing to the half TE10 model. The coupler is simulated and measured at 8-12 GHz. Measured results show a good agreement with simulation.

In this paper, a novel eight-way Ka-band spatial power combining structure based on SIW/HMSIW is presented and studied. The power-combining structure is realized by transitions between HMSIW and parallel multiport planar microstrip lines. The power combiner is designed and fabricated in 33.5-35 GHz. The measured results show a good agreement with simulation and a combining efficiency of 72% is achieved at 34.3 GHz.