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We present a new multiresonator loaded band-rejected planar monopole antenna for ultrawideband applications. The proposed microstrip-fed antenna is composed of a flared metal plate, a truncated ground plane, and two pairs of folded strips. By applying the resonance nature of the folded strips and the associated cross coupling effects, the proposed antenna demonstrates bandstop-filter-like response with bandwidth controllability at the targeted rejection band. To illustrate the antenna operating mechanism more clearly, an equivalent circuit model consisting of RLC lumped resonators and J-inverters is discussed and extracted. The antenna input admittance calculated with the help of the equivalent circuit model agrees reasonably well with the simulated one obtained by the full-wave simulator. The design concept and the simulated and experimental results including the return losses, radiation patterns, and gain responses versus frequencies are carefully investigated throughout the paper. A parametric study in terms of the bandwidth tunability of the proposed design at the notched band is performed. The effects of the finite size ground plane are studied in this paper as well. Index Terms--Equivalent circuits, monopole antennas, resonators, ultrawideband (UWB) antennas.

We propose a slotted bow-tie antenna with pattern reconfigurability. The antenna consists of a coplanar waveguide (CPW) input, a pair of reconfigurable CPW.to-slotline transitions, a pair of Vivaldi-shaped radiating tapered slots, and four PIN diodes for reconfigurability. With suitable arrangement of the bias network, the proposed antenna demonstrates reconfigurable radiation patterns in the frequency range from 3.5 to 6.5 GHz in three states: a broadside radiation with fairly omnidirectional pattern and two end-fire radiations whose mainbeams are directed to exactly opposite directions. The proposed antenna is investigated comprehensively with the help of the radiation patterns in the two principal cuts and also the antenna gain responses versus frequencies. The simulation and measurement results reveal fairly good agreement and hence sustain the reconfigurability of the proposed design. Index Terms--Coplanar waveguides, PIN diodes, reconfigurable antennas, slotline transitions, wideband antennas.

A miniaturized quadrature hybrid coupler, a rat-race coupler, and a 4 x 4 Butler matrix based on a newly proposed planar artificial transmission line are presented in this paper for application in ultra-high-frequency (UHF) radio-frequency identification (RFID) systems. This planar artificial transmission line is composed of microstrip quasi-lumped elements and their discontinuities and is capable of synthesizing microstrip lines with various characteristic impedances and electrical lengths. At the center frequency of the UHF RFID system, the occupied sizes of the proposed quadrature hybrid and rat-race couplers are merely 27% and 9% of those of the conventional designs. The miniaturized couplers demonstrate well-behaved wideband responses with no spurious harmonics up to two octaves. The measured results reveal excellent agreement with the simulations. Additionally, a 4 x 4 Butler matrix, which may occupy a large amount of circuit area in conventional designs, has been successfully miniaturized with the help of the proposed artificial transmission line. The circuit size of the Butler matrix is merely 21% of that of a conventional design. The experimental results show that the proposed Butler matrix features good phase control, nearly equal power splitting, and compact size and is therefore applicable to the reader modules in various RFID systems. Index Terms--Artificial transmission line, directional coupler, harmonic suppression, quasi-lumped elements, radio-frequency identification (RFID).

We propose a new printed dipole antenna for ultra high frequency (UHF) radio frequency identification (RFID) systems in North America. The antenna consists of a microstrip-to-coplanar stripline transition, a meandered driven dipole, a closely-coupled parasitic element, and a folded finite-size ground plane. The antenna geometry, design concept, simulated and measured results are carefully discussed throughout the paper. The experimental results demonstrate that the proposed antenna features a compact size, wide impedance bandwidth, moderate gain, and excellent front-to-back ratio. This antenna is well suitable for the applications in RFID handheld readers. Index Terms--Dipole antenna, printed circuits, radio-frequency identification, ultra high frequency.

We propose a new band-notched folded strip monopole antenna for ultrawideband applications. This antenna is composed of a forked-shape radiator and a 50 [OMEGA] microstrip line. To achieve band-rejected filtering property at the WLAN bands, the forked-shape strips are folded back and result in a pair of coupled lines on the radiator. The length and gap width of the coupled lines primarily determine the notched frequency of the antenna. Based on the band-notched resonance, an equivalent circuit model is proposed for the antenna and the calculated antenna input admittance agrees with the full-wave simulation data. With the help of the dimensionless normalized antenna transfer function, the radiation characteristics are investigated thoroughly. The transmission responses of a transceiving antenna system and their corresponding transient analysis are discussed at the end of this paper. Index Terms--Antenna transient analysis, equivalent circuits, monopole antennas, uitrawideband (UWB) antennas.

In this paper, we present a new coplanar waveguide-fed tapered ring slot antenna for ultrawideband (UWB) applications. This antenna consists of a 50 [ohm] coplanar waveguide feeding line, wideband coplanar waveguide-to-slotline transition, and a pair of curved radiating slots. The impedance bandwidth with VSWR< 2 is from 3.1 GHz to more than 12 GHz. The actual operating bandwidth is, however, limited by the distortion of radiation patterns. Such pattern distortion can be attributed to the antenna mode transition and is investigated in this paper with the help of the radiation patterns in the traditional sense as well as a dimensionless normalized antenna transfer function. By suitably allocating such mode-transition phenomenon to the notched band in a UWB radio, we demonstrate that antennas with desirable radiation characteristics in both UWB low and high bands can be readily achieved. The system responses of a transceiving antenna system in free space are addressed as well. Index Terms--Antenna radiation patterns, coplanar waveguide, slot antennas, ultrawideband (UWB) antennas.

In this paper a planar antenna is studied for ultrawide-band (UWB) applications. This antenna consists of a wide-band tapered-slot feeding structure, curved radiators and a parasitic element. It is a modification of the conventional dual exponential tapered slot antenna and can be viewed as a printed dipole antenna with tapered slot feed. The design guideline is introduced, and the antenna parameters including return loss, radiation patterns and gain are investigated. To demonstrate the applicability of the proposed antenna to UWB applications, the transfer functions of a transmitting-receiving system with a pair of identical antennas are measured. Transient waveforms as the transmitting-receiving system being excited by a simulated pulse are discussed at the end of this paper. Index Terms--Dipole antennas, slot fed antennas, ultrawide-band antennas.

A novel planar tapered-slot-fed annular slot antenna is proposed in this paper. The antenna utilizes a unique tapered-slot feeding structure and simultaneously possesses ultrawide bandwidth, almost uniform radiation patterns, and low profile. It is, hence, adequate for ultrawide-band (UWB) applications. By means of a normalized antenna transfer function, both frequency domain and time domain characteristics of the antenna are carefully investigated. Two measures, the uniformity related to the radiation patterns and the fidelity associated with the transient behaviors, are used to quantitatively describe the performance of an antenna over such an ultrawide bandwidth. Effects of varying the antenna's geometric parameters on the performance are then investigated. Finally, the influence of minimizing the antenna dimension is discussed at the end of the paper. Index Terms--Antenna radiation patterns, antenna transient analysis, slot antennas, ultrawide-band (UWB) antennas.