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This communication presents a wideband circularly polarized (CP) 2 2 patch array using a sequential-phase feeding network. By combining three operating modes, both axial ratio (AR) and impedance bandwidths are enhanced and wider than those of previous published sequential-fed single-layer patch arrays. These three CP operating modes are tuned and matched by optimizing the truncated corners of patch elements and the sequential-phase feeding network. A prototype of the proposed patch array is built to validate the design experimentally. The measured -dB impedance bandwidth is 1.03 GHz (5.20-6.23 GHz), and the measured 3-dB AR bandwidth is 0.7 GHz (5.25-5.95 GHz), or 12.7% corresponding to the center frequency of 5.5 GHz. The measured peak gain is about 12 dBic and the gain variation is less than 3 dB within the AR bandwidth.

A substrate integrated waveguide (SIW)-fed circularly polarized (CP) antenna array with a broad bandwidth of axial ratio (AR) is presented for 60-GHz wireless personal area networks (WPAN) applications. The widened AR bandwidth of an antenna element is achieved by positioning a slot-coupled rotated strip above a slot cut onto the broadwall of an SIW. A 4 4 antenna array is designed and fabricated using low temperature cofired ceramic (LTCC) technology. A metal-topped via fence is introduced around the strip to reduce the mutual coupling between the elements of the array. The measured results show that the AR bandwidth is more than 7 GHz. A stable boresight gain is greater than 12.5 dBic across the desired bandwidth of 57-64 GHz.Index Terms-Antenna array, axial ratio, circular polarization, low temperature cofired ceramic, substrate integrated waveguide.

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of WLAN applications. A parametric study is implemented to investigate the characteristic of the proposed antenna. Two dominant parameters that determine the antenna's performance are discussed, and the simulated curves are given. The antenna not only has good impedance matching properties, but also the advantages of simple structure, small size, and low cost. All results demonstrate that the proposed antenna is of great use for WLAN applications. REFERENCES 1. J. Janapsatya, K.P. Esselle, and T.S. Bird, A dual-band and wideband planar inverted-F antenna for WLAN applications, Microwave Opt Technol Lett 50 (2008), 138-141. 2. D.-U. Sim and J.-Jck Choi, A compact wideband modified planar inverted F antenna (PIFA) for 2.4/5-GHz WLAN applications, IEEE Antennas Wirel Propag Lett 5 (2006), 391-394. 3. X.L. Bao and M.J. Ammann, Microstrip-fed dual-frequency annular-slot antenna loaded by split-ring-slot, IET Microwaves Antennas Propag 3 (2009), 757-764. 4. C.-M. Wu, Dual-band CPW-fed cross-slot monopole antenna forABSTRACT: This article present a development of low phase noise 14bit digitally controlled oscillator (DCO) based on ring oscillator with quadrature output in 0.18-lm CMOS technology. Proposed design use digital control and feed-forward technique to obtain wider output swing and stable quadrature output on even number of stages respectively. Designed DCO has tuning frequency range from 212 MHz to 1 GHz. Phase noise at 1-MHz frequency offset is À123.93 dBc/Hz, which is the lowest among the recently published result.

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