In wireless sensor networks, power consumption is the most important issue. That is wireless sensors are normally deployed into unattended places where power of sensors is hard to be charged. Indeed, the network lifetime of wireless sensor networks equipped with city power or deployed into attended place is much longer than those wireless sensors equipped with batteries. In general, wireless sensor nodes are connected together and become a network after deployed into certain places. With the certain range places that wireless senor nodes deployed into, finding the optimal clusters can increase the entire network lifetime. Also, adding the forwarding station extends the network lifetime. Therefore, this paper proposes the integration of both the forwarding station and optimal clusters in ad-hoc wireless sensor networks. Simulation results show that the entire network lifetime proposed is extended in this paper compared to both optimal cluster number selection and normal forwarding station.

A design for dual‐band circularly polarized (CP) antennas is presented. The antenna is composed of two concentric shorted annular slots, and each slot can generate CP radiation at its one wavelength resonant mode or one‐and‐a‐half wavelength resonant mode by varying the position of the shorted section. When the one wavelength mode of the outer slot and the one‐and‐a‐half wavelength mode of the inner slot are simultaneously excited with a microstrip line, the antenna has two CP operating frequencies with a large frequency ratio (FR). A small FR can also be achieved when the outer and inner annular slots are operated at the one‐and‐a‐half wavelength mode and one wavelength mode, respectively. For the proposed design, two examples with the FRs of 1.05 and 1.9 are designed and implemented. Details of the experimental results are shown. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2077–2080, 2013

A design for quad‐polarization‐agile antenna is described. A multiport crossed dipole that can provide dual orthogonal linear polarizations is used as the radiating element of the design. When the crossed dipole is fed with a tunable power divider, the two linear polarization radiations can be simultaneously excited with same amplitudes and difference phases. The resultant polarization modes include ±45° linear polarizations, right‐handed circular polarization, and left‐handed circular polarization. The overlapped operation bandwidth of the four polarization modes is about 49%, and the antenna operating in each polarization mode has almost the same radiation patterns. These patterns are also stable against frequency. Moreover, the occupied area of the polarization reconfigurable antenna is about 0.43λ0 × 0.43λ0.

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