Abstract-A thin dipole antenna is a well-known antenna with linearly polarized wave operation. In this work, a wide-strip dipole antenna is proposed for circularly polarized wave operations. To obtain circularly polarized (CP) wave operations, there are two conditions to be satisfied. One is that the antenna must have two degenerated orthogonal modes with different resonant frequencies. The other is that the phase difference of two orthogonal modes is 90 degrees. To match the first condition, the slab width W is tuned to generate current distributions directed in two different directions. In addition, the second condition is matched by asymmetric feeding point by adjusting the overlapped square width C. The parametric study is completed by the Ansoft HFSS simulator. Simulated results reveal that the CP wave is mainly influenced by the slab width W . The influences of the parameters C and d on the performances of the proposed antenna are also investigated in this paper. Taking −8 dB as reference, there are two working bands for this proposed antenna and the measured center frequencies are 0.66 GHz and 2.04 GHz, respectively, and the corresponding bandwidths are 0.27 GHz (40%) and 1.78 GHz (87%), respectively. In addition, the measured center frequencies and bandwidths of the axial ratio are 1.94 GHz and 0.53 GHz (27%), respectively.Corresponding author: L.-P. Chi (cp531220@ms23.hinet.net). 70Chi et al.

Abstract-A coplanar-strip dipole antenna with two enhanced features is presented for broadband circular polarization (CP) operation. The first feature of the proposed antenna is the replacement of a conventional thin dipole by a wide strip, resulting in two degenerated orthogonal modes to make CP operation possible. The second one is the use of two coplanar strips instead of two non-coplanar ones, thereby giving rise to the advantages of easy implement, good impedance matching, and wide axial ratio (AR) bandwidth. Two examples are given, one for the lower band around 1.8 GHz and the other for the ultra-wideband (UWB). For the lower band, the measured −10 dB return loss (RL) bandwidth is 119% (0.74 to 2.93 GHz), and the measured 3 dB AR bandwidth is 50% (1.45 to 2.41 GHz). As for UWB, the measured RL is below −10 dB between 2.1 to 10.1 GHz, and the measured AR is below 5 dB between 4.1 to 7.75 GHz.

Moreover, we would like to note that the folded antenna has much smaller size than the unfolded antenna, in addition to the bandwidth improvement in the DCS band.An absolute gain including the return loss and radiation efficiency was measured. The measured radiation patterns for the proposed antenna at 1 and 2 GHz are presented in Figure 6. The radiation patterns of H, E1, and E2 planes were measured in the x-y, z-x, and y-z planes, respectively. In the x-y plane, the radiation pattern at 1 GHz had quite good omni-directional characteristics. The radiation pattern gets more directional in the high-order resonant 2 GHz band. For the GSM and DCS bands, maximum absolute antenna gains (G 0abs ) were Ϫ0.05 and Ϫ0.13 dBi, respectively. These radiation patterns show that the proposed antenna had a good radiation efficiency. CONCLUSIONA dual-band small chip antenna was designed to satisfy requirements for operation in the GSM and DCS bands. The impedance bandwidth and resonant frequency of each band was controlled by the intercoupling capacitance of the metallic structure. The intercoupling capacitance was created by folding a metallic structure. The resonant frequencies were nonuniformly shifted due to the intercoupling capacitance. This property was very useful in controlling the resonance frequencies and their corresponding bandwidths. The simulated and measured results show that the proposed antenna satisfies the requirements for both GSM and DCS bands simultaneously. This resonanceshift effect caused by the folding intercoupling capacitance can be usefully exploited in designing a multiband antenna with high-order resonance phenomena. printed monopole, Electron Lett 28 (1992), 1326 -1327. 4. M. Makimoto and S. Yanashita, Microwave resonator and filters for wireless communication, Springer Verlag, New York, 2000, pp. 84 -87. 5. C.A. Balanis, Antenna theory and analysis and design, Wiley, New York, 2005, pp. 177-217. ABSTRACT: Dielectric resonator-loaded circular microstrip patch antennas can be used as an alternative way to generate circular polarization. The dielectric resonator is placed on the edge of the circular microstrip patch antenna to result both strong coupling effect and two degenerated orthogonal modes. Then, we choose the feeding point, the placed position and size of DR, and the height of antenna as key tuning parameters; both wide circular polarization and impedance matching are achieved. Application is given for WLAN 2.4 GHz band. Both simulated and measured data are matched well. Measured results show that the center frequency is at 2.45 GHz. The impedance bandwidth is 19.2%. Besides, the axial ratio bandwidth is 3.7% (2.39 -2.48 GHz). The radiation patterns are broadside radiations and high antenna gain of 8.6 dBic is achieved.

A compact shorted rectangular‐ring slot antenna fed by a coplanar waveguide is presented for circular polarization operations. This proposed antenna has only 40 mm square size in the applications of WLAN 2.4 GHz band. It seems the most compact size while referenced to other shorted ring slot antennas in recent articles. The reduced size is over 30% will save much cost and antenna can apply to portable devices. Simulated and measured data are matched in the reflection coefficient, axial ratio (AR), radiation patterns, and gain. Its measured center frequency and impedance bandwidth are 2.38 GHz and 15.1%, respectively. Also, the frequency of minimum axial‐ratio and axial‐ratio bandwidth are 2.43 GHz and 4.1%, respectively. From the bandwidths of view, both impedance and AR bandwidths can cover the 2.4 GHz band's applications. The radiation patterns are broadside radiations. Forward radiation belongs to right hand circular polarization and backward one is left hand circular polarization, respectively. Also, antenna gain is about 3 dBic in the operating band of WLAN 2.4 GHz band. The antenna performances and compact size of the proposed antenna are easy to be applied in the consumer products. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2229–2232, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24524

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