Search

A novel design concept to reduce the frequency ratio of a dual-band dual-circularly polarized (CP) microstrip patch antenna (MPA) is presented by using its reshaped TM10, TM01, and TM20 modes. First, the far-zone radiated fields of the traditional MPA are theoretically investigated. It demonstrates that the normal |Eθ| and |Eϕ| fields at xoz plane are orthogonally generated under its TM10 and TM01 modes, respectively. Unfortunately, its TM20 mode radiates the nonbroadside |Eθ| fields at xoz plane. Then, an open-ended stub is loaded around the edge of the radiator, aiming to reshape the TM20 mode as the broadside radiation. After that, the patch width is decreased with the loading of two shorting pins. The main target is to move the TM01 mode resonating between TM10 and TM20 modes. Finally, the proposed antenna is fabricated and tested. The results illustrate that its left-hand CP and right-hand CP radiation patterns are satisfactorily acquired at around 2.134 and 2.223 GHz, respectively, thus gaining a small frequency ratio of around 1.04. Meanwhile, the antenna holds the low-profile (0.02 free-space wavelength), small-backlobe, single-layer, single-fed, and single-radiator properties. [ABSTRACT FROM AUTHOR]

A novel design concept to reduce high H-plane cross-polarization of a shorted patch antenna (SPA) with broadside radiated patterns is presented by loading a pair of open-ended stubs. Initially, the nonbroadside $\vert E_{\mathrm {\theta }}\vert $ component of the traditional SPA at TM $_{\mathrm {1/2,2}}$ mode is demonstrated to be much larger than its broadside $\vert E_{\varphi }\vert $ component in H-plane or yoz plane radiation patterns. In order to maintain its peak radiation in the normal direction, the far-zone radiated fields of the antenna are theoretically studied and analyzed. The results demonstrate that the dual nodal lines of the TM $_{\mathrm {1/2,2}}$ modal fields could be gradually moved far away from each other by increasing the stub length. As such, its $\vert E_{\varphi }\vert $ and $\vert E_{\theta }\vert $ components in H-plane or yoz plane radiation patterns could be progressively strengthened and weakened, respectively. After that, by reallocating these dual nodal lines around the corners of the radiating patch, the nonbroadside radiated fields of TM1/2,2 mode are successfully transformed into the broadside radiation, while keeping a low H-plane cross-polarization level. Additionally, the symmetric open-ended stubs are folded so as to reduce the dimensions of the core radiator. In final, the proposed SPA is fabricated and measured. Simulated and measured results are found in good agreement with each other, and both of them illustrate that the antenna has satisfactorily acquired a normal radiation pattern at reshaped TM1/2,2 mode. Most importantly, its high H-plane cross-polarization is dramatically reduced from −4.3 to −21.4 dB as compared to the traditional SPA at TM1/2,0 mode. [ABSTRACT FROM AUTHOR]

In this paper, an offset reflector antenna with dual-beam and dual-polarization characteristics is developed to provide the angular diversity function for troposcatter communication system. The antenna system consists of a parabolic reflector and a dual-beam feed. For the dual-beam feed, two identical Ku-band feed elements are arranged side by side to generate two beams toward the reflector. The two beams are substantially nonoverlapping. The feed element is composed of a dielectric rod, a square waveguide, and an ortho-mode transducer. The dielectric rod is effective in reducing the beamwidth of the feed and providing more tapered illumination on the reflector in order to increase the antenna gain. Moreover, the developed antenna is able to produce two independent beams with the vertical and horizontal polarizations. The antenna was fabricated and tested with good agreement between the simulation and measurement results. The measured voltage standing wave ratios of the four feed ports are less than 1.5:1, and the beam separation angle is not more than 0.7° or about one time half-power beamwidth, and the antenna gain is higher than 45 dBi over the operating band from 14.5 to 15.35 GHz. [ABSTRACT FROM AUTHOR]

A novel broadband horizontally polarized (HP) omnidirectional antenna is proposed for meteor-burst communication system in VHF. The proposed antenna is composed of three bowtie dipoles, which are concentrically placed to form a loop antenna. The bowtie dipole is shorted at the terminal by folded elements in order to reduce antenna size. The bowtie dipoles are fed by a three-way power divider. A slotted line balun is employed to achieve broadband impedance matching and realize balanced-to-unbalanced transformation. The designed HP omnidirectional antenna exhibits a fractional bandwidth of 24.7% with VSWR < 2 ranging from 39 to 50 MHz. Uniform omnidirectional radiation patterns in the azimuth plane with HP have been obtained. The loop antenna provides a relatively low gain of no more than 1.5 dBi. Therefore, a two-element HP antenna array is developed to enhance its gain. In order to reduce longitudinal dimension of the array, the two loop antenna elements are placed in reverse and employ differential feeding method to realize in-phase current. Both the simulation and measured results are used to verify the design approach. [ABSTRACT FROM PUBLISHER]

ABSTRACT The wideband performance of a bowtie antenna with Γ-shaped strip feed and tuning stubs is presented. Besides two folded elements connecting the patches of the bowtie dipole for a compact dimension, the Γ-shaped strip feed structure and the four tuning stubs to effectively improve the impendence matching can be used for bandwidth enhancement. A wideband impedance characteristics of about 58.6% for VSWR ≤ 1.5 ranging from 1.58-2.89 GHz is obtained and the stable peak gain of around 9 dBi, unidirectional radiation patterns and low cross-polarization over the whole operating band are also achieved. It is very suitable for the recent wireless communication services for the indoor-base station such as 3G, WiFi, WiMax, Bluetooth, and LTE/2.5 applications, and so on. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2145-2149, 2013 [ABSTRACT FROM AUTHOR]

A novel miniaturized dual-band monopole antenna loaded with two types of loops is presented. The split loop is loaded at the center of the monopole for dual-band operation and the rectangular loop loaded at the top is for miniaturization. The novel miniaturization technique is used as a self resonant topology. The monopole below its resonant frequency is known to possess a capacitive reactance and the loop below its resonant frequency has an inductive reactance. So an inductive loop is used to match a below-resonant monopole for miniaturization. As an example of this principle, a miniaturized dual-band antenna prototype for WLAN applications is designed, fabricated, and tested. Measured results show that the antenna offers higher gains and better efficiencies than the unloaded monopole. The radiation patterns are seen to be unaffected by the presence of the top loaded loop. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1236-1239, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26784 [ABSTRACT FROM AUTHOR]