Coax-fed Microstrip Research Articles

Metasurface-Based Cylindrical Lenses and Their Antenna Gain Enhancement

Electromagnetic metasurface lenses with the characteristic of being conformal to a cylindrical geometry are presented in this study. Based on the formulated principle of the cylindrical metasurface lens operating with transmission or reflection mode, the transmission or reflection phase gradient varying along the circumferential direction of a cylinder is implemented. A focused beam is observed at the objective focal point for each lens illuminated by a plane electromagnetic wave with transverse magnetic or transverse electric polarization. A coaxial-fed microstrip patch antenna element is used as a feeding of cylindrical metasurface lenses and positioned at their focal points, so as to evaluate their application in the enhancement of antenna gain along the boresight direction. By virtue of the focusing ability of presented lenses, effectively enhanced boresight gain from the cylindrical metasurface lens antennas are obtained, in comparison with the freestanding feeding antenna. The agreement between simulation and measurement validates the designs. Conformal integration or embedment of the electromagnetic lens into a certain platform skin with cylindrical characteristics is therefore potentially demonstrated, which implies an enhancement of boresight gain without obviously disturbing the local shape of the skin by apparent weight or drag.

New Insight and Design Strategy to Optimize Cross-Polarized Radiations of Microstrip Patch Over Full Bandwidth by Probe Current Control

A new design insight has been developed indicating possibilities of improved characteristics to be achieved in coax-fed microstrip antennas in terms of their polarization purity over the entire operating bandwidth. The investigation involves multiple configurations and variations of rectangular and circular patches to ensure conclusive inference. Their impedance profile including the probe parameters has been identified as the controlling factor to the cross-polarized (XP) profile over the band. Subsequently, a well-defined co-relation between the input and XP radiations has been established which leads to a theoretical model. Based on this understanding, an engineered feed with controlled reactance has been conjectured and proposed to achieve improved XP profile with increased polarization purity. This new finding and conjecture have been experimentally verified using multiple sets of prototypes operating in C-band. It confirms the predicted improvement in polarization purity over the entire bandwidth with a maximum of about 7 dB at the band-edge without imposing any change or degradation in other characteristics.

Frequency independent microstrip stacked antenna

The advancement of technological development in the microstrip antenna and its applications in diverse areas, have given rise to the need for a frequency agile and frequency independent microstrip antenna which could be used for the same range of frequencies without altering the system. Requirements of such nature could be met by log periodic antenna. However, in the present endeavour a frequency independent microstrip stacked antenna consisting of nine elements operating in the S-band (2.000–4.000GHz) has been proposed. The developed antenna has been experimentally tested over an achievable band of frequencies from 3.200 to 3.920GHz. The antenna performance has characteristics like E-plane radiation patterns. The 3dB beamwidth, radiated power and VSWR show very similar behaviour for the different frequencies of operation obtainable in the S-band. The coaxial-fed microstrip stacked antenna provides an operational bandwidth of approximately 23%, i.e. 3.200GHz to 3.920GHz. The VSWR for the entire operational band is around 2 whereas the gain for the antenna is found to vary from 4.00 to 8.36dB. The 3dB beamwidth has been found to fluctuate between 16.8° and 23.5°. The designed antenna can be well suited for the practical broadband applications.

Modelling of coaxial-fed microstrip patch antenna by finite difference time domain method

A direct three-dimensional finite-difference time-domain (FDTD) method is applied to coaxial-fed microstrip antennas. The model is shown to be an efficient and accurate tool for modelling coaxial-fed structures. The reflection coefficient can be determined from the simulated time-domain wave that is reflected down the coaxial line. Excellent agreement over a wide frequency range is shown in two cases between the measured and FDTD derived results.

Analysis of Coaxially Fed Microstrip Antennas of Arbitrary Shape with Thick Substrates

Arbitrarily shaped, coax-fed microstrip patch antennas with substrates that may be electrically thick are studied using a mixed-potential integral equation approach. Vector basis functions defined over triangular elements are used to approximate the current distribution on the conducting patch. Rigorous and simplified models of the probe-to-patch junction, compatible with the triangular element model of the microstrip patch, are implemented and their relative merits are discussed. Two models of the coaxial probe, differing in accuracy and complexity, are also implemented and their ranges of validity are examined. Input impedance data for several microstrip patch antennas of different shapes, computed using different coax feed models, are presented and compared with measured results.

End-correction network of a coaxial probe for microstrip patch antennas

A simple end-correction network for the constant current probe model of probe-fed microstrip patch antennas is derived. The parameters of the network are solved asymptotically and verified by the numerical solution of the integral equation formulation. Based on the analysis of a problem concerning a coaxial-fed microstrip patch, it is concluded that: (1) TEM (transverse electromagnetic) aperture field approximation can provide an accurate result to the input admittance, and there is no need to introduce a specific correction network for most applications; and (2) Constant current probe is valid only when both k/sub 1/h >

Analysis of arbitrarily shaped coax-fed microstrip antennas with thick substrates

Arbitrarily shaped, coax-fed microstrip patch antennas with thick substrates are studied using a mixed-potential integral equation approach. This incorporates a triangle-element model of the patch and a rigorous treatment of the probe-to-patch junction. Computed input impedance data are shown to agree well with measured results.

Erratum: Analysis of arbitrarily shaped coax-fed microstrip antennas with thick substrates

Erratum: Analysis of arbitrarily shaped coax-fed microstrip antennas with thick substrates

Correction to “Improved formulas for input impedance of coax-fed microstrip patch antennas”

In a recently published article by E. Lier [1] an approximation to the radiation conductance of a circular microstrip antenna was given. The presented formula was a three term Taylor expansion in inverse power of er. Unfortunately, the presented formula was incorrect in the last term. Because such a formula is useful for rapid calculations, the formula is corrected and a five term formula is presented here.

Improved formulas for input impedance of coax-fed microstrip patch antennas

The input impedances of rectangular and circular antennas have been improved by more accurate expressions for the input reactances and radiation conductances. The theory includes the effects of extended antenna patches due to fringe fields at the edge. Surface toughness of the dielectric substrate has also been accounted for. The measured and calculated curves for input impedances agree well.