Suthasinee Lamultree

BIDIRECTIONAL ULTRA-WIDEBAND ANTENNA USING RECTANGULAR RING FED BY STEPPED MONOPOLE

This paper presents an ultra-wideband rectangular ring fed by stepped monopole antenna. The initial parameters of rectangular ring are first considered to obtain the bidirectional pattern with the desired resonant frequency. Subsequently, the parameters of stepped monopole for enhancing impedance bandwidth are investigated. To study the impedance and radiation behaviors, the simulations of the proposed antenna have been carried out. It is found that this antenna offers a bidirectional beam with the impedance bandwidth (return loss lower than −10 dB) covered the frequency range from 3.1 to 10.6 GHz. At the desired direction along this frequency band, the gain of 2.33-5.21 dBi is achieved. Furthermore, the prototype antenna was fabricated and measured to verify the simulated results. Obviously, the simulation and measurement are reasonably in good agreement.

EQUIVALENT GRAPHICAL SOLUTIONS OF TERMINATED CONJUGATELY CHARACTERISTIC- IMPEDANCE TRANSMISSION LINES WITH NON- NEGATIVE AND CORRESPONDING NEGATIVE CHAR- ACTERISTIC RESISTANCES

EQUIVALENT GRAPHICAL SOLUTIONS OFTERMINATED CONJUGATELY CHARACTERISTIC-IMPEDANCE TRANSMISSION LINES WITH NON-NEGATIVE AND CORRESPONDING NEGATIVE CHAR-ACTERISTIC RESISTANCESD. Torrungrueng and S. LamultreeDepartment of Electrical and Electronic EngineeringFaculty of Engineering and TechnologyAsian UniversityChon Buri, 20250, ThailandAbstract—This paper presents the graphical solutions of conjugatelycharacteristic-impedance transmission lines (CCITLs) implemented byperiodically loaded lossless transmission lines (TLs), which can exhibitboth non-negative (NNCR) and negative characteristic resistances(NCR) with the corresponding propagation constants. The standardT-chart and the extended T-chart are employed to solve CCITLproblems with NNCR and NCR cases respectively, depending on theargument of CCITL characteristic impedances. The range of plottingof the standard T-chart and the extended T-chart is always insideor on the unit circle, and always outside or on the unit circle of thevoltage reflection coefficient plane, respectively. Two examples of finiteperiodicTLstructuresprovidingbothNNCRandNCRcasesaregiven.It is found that both T-charts provide the same input impedance ofthe corresponding CCITLs as expected, and the standard T-chart ismore familiar and easier to deal with.1. INTRODUCTIONOne class of transmission lines (TLs), called conjugately characteristic-impedance transmission lines (CCITLs), has been introduced recentlyin the literature [1–7]. By definition, a CCITL possesses conjugatecharacteristic impedances

FULL-WAVE INVESTIGATIONS OF A PROBE-EXCITED RECTANGULAR RING ANTENNA BY METHOD OF MOMENTS WITH RWG BASIS FUNCTIONS

Radiation pattern, impedance characteristics, and gain of a probe-excited rectangular ring antenna are investigated by the Method of Moments with the Rao-Wilton-Glisson (RWG-MoM) basis functions. The analysis is carried out for difierent lengths and positions of the probe as well as various lengths, widths and heights of the ring. In addition, the distribution of the surface current is also illustrated. Consequently, the suitable parameters are determined. It is obvious that the proposed antenna ofiers a bidirectional pattern with the impedance bandwith (jS11j < i10dB) of 17%. Along the direction of the ring aperture, the gain is 5.28dBi. Furthermore, the prototype antenna was fabricated and measured to verify the validity of the numerical calculation. It is found that the numerical and measured results are reasonably in good agreement.

On the characteristics of conjugately characteristic-impedance transmission lines with active characteristic impedance

This paper explores the possibility that the magnitude of the voltage reflection coefficient associated with conjugately characteristic-impedance transmission lines (CCITLs) can exceed unity and even approach infinity for some passive load terminations. It is found that CCITLs with active characteristic impedances play the key role in exhibiting this property. Although the magnitude of the voltage reflection coefficient exceeds unity, associated powers are still conserved.

Theory and experiment of an antenna using a probe excited rectangular ring

This paper presents the theory and experiment of the antenna using a probe excited rectangular ring radiating bidirectional pattern. The antenna structure is simple and easy to fabricate. Since it requires only one connector, it is low cost and suitable for mass production. The radiation pattern appears to be the bidirectional beam without any side lobe. The ring width and height is selected based on the dominant mode propagation. The ring length is optimized to achieve the optimum radiation pattern. The polarization is vertical linear polarization at the boresight direction. The impedance matching can be achieved by adjusting the probe length. The optimum parameters are used as the guideline for the antenna design. The antenna prototypes were fabricated to measure the radiation pattern. The experimental results agreed reasonably with the theoretical calculations. It is confirmed that this antenna can be applied for the mobile communication with long and narrow path service area.

Theory of Small Reflections for Conjugately Characteristic-Impedance Transmission Lines

In this letter, the standard theory of small reflections (TSR) is generalized for the case of multi-section transformers, composed of conjugately characteristic-impedance transmission lines (CCITLs) connected in cascade, with small discontinuities. Using the assumption of small reflections, the total voltage reflection coefficient looking into the input of the transformer can be approximated, resulting in the TSR for multi-section CCITL transformers with small discontinuities. Numerical results, some physical interpretations and potential applications of results will be discussed in this letter.

Design of UWB Bidirectional Rectangular Ring Antenna Fed by Stepped Monopole

An ultra-wideband rectangular ring antenna fed by stepped monopole is presented in this paper. The initial parameters of antenna design as well as the antenna revolutions for enhancing impedance bandwidth are shown. Simulations have been carried out to investigate the impedance and radiation behaviors. It is found that the antenna offers a bidirectional radiation pattern with the impedance bandwidth covered the frequency range from 3.1-10.6 GHz with the VSWR of less than 2:1.

Measurement of BCITL parameters

This paper presents a method to measure the characteristic impedances and propagation constant of bi-characteristic-impedance transmission lines (BCITLs). The derived expressions for determining the BCITL parameters via measurements are provided. An example of BCITLs is given for both passive (Re{Z₀ ^plusmn} ges 0) and active characteristic impedances (Re{Z₀ ^plusmn} < 0), where Z₀ ^plusmn are the characteristic impedances of BCITLs. Since Z₀ ^plusmn and gamma are independent of load impedance Z_L, Z_L can be varied appropriately to obtain the corresponding input impedances needed to solve for the unknown BCITL parameters. It is found that this method is successfully employed to determine these parameters.

Global Matching of Multi-section Transmission Lines Based on the CCITL Theory

This paper presents a method for global matching of multi-section transmission lines (MSTLs) based on the theory of conjugately characteristic-impedance transmission lines (CCITLs). To provide some physical insights, examples of two and three sections of MSTLs are given for both passive (Re{Z0 +} ges 0) and active characteristic impedances (Re{Z0 +} < 0), where Z0 + are the characteristic impedances of CCITLs. In addition, compared results of local and global matchings using both standard transmission line (STL) and CCITL theories are shown. It is found that the CCITL theory can be used to globally match MSTLs indeed without solving any optimization problems.

Parametric Study of a Bidirectional Antenna using a Probe Excited Rectangular Ring

The parametric study of a bidirectional antenna using a probe excited rectangular ring by using dyadic Green function approach is presented. The antenna characteristics depend on the probe length, ring width, ring height and ring length. The maximum elevation beam peak in E-plane is tilt a bit from z-axis as the reason of probe position is not symmetry between the upper and lower side of the ring. The radiation pattern in H-plane is inclined a bit, because the probe is not located at the center of the ring. In addition, the antenna was fabricated. The experiments were set up to verify the theoretical predictions. The ring width and ring height are selected based on the dominant mode propagation. The ring length is optimized to achieve the optimum radiation pattern. The antenna produces the linear polarization. Furthermore, it is found that the shorter ring length provide the higher level of cross-polarized field. The experimental results have the same trend with the theoretical predictions. However, the actual current distributions, mutual coupling, reflection at the edge are not taken into consideration; these are left for further study