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A compact coplanar waveguide (CPW)-fed multi-band monopole antenna loaded with spiral ring resonators is presented. The proposed antenna consists of two spiral ring strips which are printed on the different sides of the substrate and connected through a via-hole. The size of the miniaturised antenna is only about 27.5 × 20 × 1 mm 3. The proposed antenna can excite multi-resonant modes close to the 2.5/3.5/5.5 GHz bands to meet the specifications of the worldwide interoperability for microwave access (WiMAX) system. By introducing the spiral ring structure, very good radiation pattern characteristics can be obtained. With a figure-of-eight pattern in the E-plane and omnidirectional pattern in the H-plane, measured peak gains are about 2.0/2.23/2.58 dBi at the 2.5/3.5/5.5 GHz operating bands, respectively.

A wideband conical-beam circularly polarized (CP) microstrip antenna for an electrically large platform is investigated. The antenna structure simply consists of a center-fed patch and eight shorting vias each of which is surrounded by a modified elliptical-ring slot. The θ-polarization of the proposed antenna is provided by the shorting vias and the coaxial probe, while the φ-polarization is generated by the modified elliptical-ring slots. Moreover, the amplitudes of the two orthogonal polarizations can be controlled separately and are less sensitive to the size of the metal platform. By employing the even and odd modes of the elliptical-ring slot, the proposed antenna exhibits a wide impedance bandwidth. A prototype of the antenna is fabricated and mounted on three ground planes, which function as electrically large metal platforms, with the radii of λ 0 , 2λ 0 , and 10λ 0 . The measured results show that the wideband CP antenna with these three ground planes have the 10-dB impedance bandwidths of 19.4%, 19.5% and 19.9%, and the corresponding 3-dB axial ratio (AR) bandwidths of 25.3%, 25.6%, and 24.8%, respectively. A detailed analysis on the radiation characteristics is also carried out for small to extremely large ground plane extensions.

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Abstract-A center-feed dual-band dual-polarized circular microstrip antenna employing the curved slots on the ground is proposed. The proposed antenna radiates ϕ-polarization by introducing 10 units of curved slots symmetrically on the ground and θ-polarization by the coaxial probe at the center. The measured results show that the proposed antenna provides two resonant bands, TM 01 and TM 02 modes, covering the frequency bands of the WLAN (2.4-2.484 GHz) with an omnidirectional right-handed circular polarized (RHCP) radiation pattern and the WiMAX (3.3-3.6 GHz) with an omnidirectional horizontal polarized radiation pattern, respectively. In addition, the effects of the unit number of the curved slots and the width of the slots on the frequency ratio of these two resonant frequencies are studied. Furthermore, for the low profile of 0.056λ 0 and good omnidirectional characteristic, the antenna is suitable for the modern multi-band wireless communication systems.

A miniaturized dual-frequency dual-polarization microstrip patch antenna with high isolation between receiving and transmitting ports (operating at 2.1 GHz for receiving and at 2.5 GHz for transmitting) is presented in this paper. The proposed antenna consists of a modified rectangular radiating patch, two 50 Ω microstrip feed lines, and two EBG filters. Two coupling microstrip lines are employed to excite two orthogonal fundamental modes (TM10and TM01). The high isolation is achieved by embedding two novel EBG filters underneath two feed lines to reject the incoming signal from the opposite line. Multilayer configuration, miniaturized EBG filters, and modified rectangular radiation patch contribute to size reduction. The total size is 0.67λ × 0.67λ × 0.03λ , only quarter of the multilayer rectangular radiation patch antenna (1.33λ × 1.33λ × 0.03λ) using common EBG filters with the same performance. Measured results on the reflection coefficients, isolations, and gains for the two frequencies are provided, which agree well with the numerical simulations. Also, measured isolations and radiation patterns at both two resonant frequencies are compared with the antenna without filters. The results show that the proposed method improves isolation by more than 20 dB with little influence on the radiation patterns.

Abstract-This paper presents a compact microstrip-fed slot antenna with triple-frequency operation. The proposed antenna structure consists of a cross-shaped microstrip feed line and multiple openended slots on the ground plane. By properly selecting shapes and dimensions of these embedded slots, the triple-resonance situations at 2.4/3.5/5.8 GHz are obtained. Meanwhile, the cross-shaped feedline with shorting pin makes a joint benefit to adjust the matching condition and impedance bandwidth. The numerical and experimental results exhibit the designed antenna operates over triple frequency ranges and covers numbers of useful frequency bands for present wireless communication systems. In addition, acceptable radiation characteristics are obtained over the operating bands.