Shaojun Fang

Single-Fed Broadband Circularly Polarized Stacked Patch Antenna With Horizontally Meandered Strip for Universal UHF RFID Applications

In this paper, a horizontally meandered strip (HMS) feed technique is proposed to achieve good impedance matching and symmetrical broadside radiation patterns for a single-fed broadband circularly polarized stacked patch antenna, which is suitable for universal ultrahigh frequency (UHF) RF identification (RFID) applications. The antenna is composed of two corner truncated patches and an HMS, all of which are printed on the upper side of the FR4 substrates. One end of the HMS is connected to the main patch by a probe, while the other end is connected to an SMA connector. Simulation results are compared with the measurements, and a good agreement is obtained. The measurements show that the antenna has an impedance bandwidth (VSWR <; 1.5) of about 25.8% (758-983 MHz), a 3-dB axial ratio (AR) bandwidth of about 13.5% (838-959 MHz), and a gain level of about 8.6 dBic or larger within the 3-dB AR bandwidth. Therefore, the proposed antenna can be a good candidate for universal UHF RFID readers operating at the UHF band of 840-955 MHz. In addition, a parametric study and a design guideline of the proposed antenna are presented to provide the engineers with information for designing, modifying, and optimizing such an antenna. At last, the proposed antenna is validated in RFID system applications.

Analysis of asymmetric coplanar waveguide with conductor backing

This paper presents an analysis of the asymmetric conductor-backed coplanar waveguide by means of conformal mapping techniques. The effective permittivity, characteristic impedance, and electric-field strength are given. The field patterns are also plotted.

Broadband Circularly Polarized Microstrip Antenna with Coplanar Parasitic Ring Slot Patch for L-Band Satellite System Application

A novel capacitive-coupled probe-fed circularly polarized (CP) microstrip antenna with coplanar parasitic ring slot patch has been proposed for the International Maritime Satellite (INMARSAT) and the Global Positioning System (GPS) applications. The key feature of the design is employing capacitive-coupled four-probe feeds to increase impedance bandwidth and adopting coplanar parasitic ring slot patch to enhance CP bandwidth. The feed network is compact and neat using only T-junction power dividers and phase shifters with shunted short-circuited microstrip stubs for lightning protection. The characteristics of the proposed antenna have been studied by simulation and experiment. The final antenna can produce a S11 <; -14 dB impedance bandwidth of nearly 27%, a 3-dB axial-ratio bandwidth of nearly 16%, and a gain of higher than 8 dB in the whole maritime satellite communication work band.

An Inmarsat BGAN Terminal Patch Antenna Array With Unequal Input Impedance Elements and Conductor-Backed ACPW Series-Feed Network

A novel 2 × 2 sequentially rotated patch antenna array with unequal input impedance elements and a conductor-backed asymmetric coplanar waveguide (ACPW) series-feed network is proposed. The corner truncated patch element is fed by a three-dimensional meander strip, which can easily control the input impedance and has slight effects on the radiation performance. Compared to microstrip-line feed networks, the radiation loss of the proposed feed network is lower. Furthermore, the maximum characteristic impedance of transmission lines in the proposed feed network is 91.2 Ohm. As a result, it can be easily realized with printed circuit board (PCB) techniques. The measured results show that the proposed antenna array has an impedance bandwidth (VSWR <; 1.5) of about 40.5% (1244-1876 MHz), a 3-dB axial ratio (AR) bandwidth of about 25.6% (1412-1826 MHz), and a gain-level larger than 11.6 dBi across the broadband global area network (BGAN) operating bands. Therefore, the proposed antenna array can be a good candidate for Inmarsat BGAN portable terminal applications.

Novel Coupled Line 180

This paper presents a novel coupled line 180° hybrid with non-interspersed input/output ports. With the combination of a weak coupling parallel coupled line and strong coupling trans-directional coupler, a non-interspersed input/output ports coupled line 180 ° hybrid is obtained by using printed circuit board fabrication process, and reduced substrate area is achieved. The proposed hybrid owns the features of reducing the complexity of dc biasing for the next-stage active circuits. Moreover, it requires no bond wires, via-holes, or multilayer structures. The formula of the proposed hybrid is derived, and the characteristics of the hybrid are analyzed. Two prototypes are designed to verify the concept. One is arranged with the two couplers perpendicular to each other, and the other is constructed with the two couplers arranged in a line. The measured results are in good agreement with the simulated ones.

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A novel rat-race coupler with wide adjustable range of power-dividing ratio and uncrossed input/output ports is presented by using coupling adjustable trans-directional (TRD) coupled lines, parallel coupled lines and a 180◦ phase shifting line. Wide adjustable range of power-dividing ratios is accomplished by varying the coupling of the TRD coupled lines. Moreover, with the combination of the TRD coupled lines and parallel coupled lines, the input and output ports of the rat-race coupler are uncrossed. The structure of the proposed rat-race coupler is analyzed, and the design equations are derived. As an example to validate the feature of the proposed rat-race coupler, a prototype operating at 1.6 GHz is devised, fabricated and measured. The measured results show that the designed coupler has a wide adjustable range (−7 ∼ 15 dB) of power dividing ratio with a controlled voltage range of 3.3 to 13.5 V.

Hybrid With Non-Interspersed Input and Output Ports

In this paper, a compact coupled-line trans-directional (TRD) coupler with wide continuous frequency tuning range and superior performance is presented. The proposed tunable TRD coupler is composed of three coupled lines, two shunt stubs, and three types of varactors. By providing suitable reverse bias voltages on these varactors, the operating frequency of the proposed TRD coupler can flexibly be adjusted as desired. Moreover, better impedance match and port isolation are maintained at all tuning center frequencies. A theoretical analysis using the even–odd mode theory is presented to clarify the influence of the design parameters on the minimum and maximum operating frequencies. It is exhibited that the proposed TRD coupler has approximately 150% frequency tuning range in ideal conditions. Due to the manufacturing limitation, a microstrip TRD coupler with a tunable frequency of 1.0–2.5 GHz (85.7%) is designed and fabricated. The measured results show that the proposed TRD coupler can be tuned from 1.0 to 2.5 GHz with more than 27 dB return loss and more than 35 dB isolation in the entire tuning range, agreeing well with the simulation results.

COUPLED LINE RAT-RACE COUPLER WITH WIDE ADJUSTABLE POWER DIVIDING RATIO AND UNCROSSED INPUT/OUTPUT PORTS

A single-fed circularly polarized (CP) Radio Frequency Identification (RFID) reader antenna with a simple structure has been proposed for worldwide Ultra-High Frequency (UHF) band applications. The purpose of the antenna was to provide a low-cost and easy-fabricated solution with wide bandwidth and high performance. The proposed antenna is composed of a corner-truncated square driven patch with a stacked square parasitic patch and a microstrip match stub suspended above the ground plane. Good impedance matching and good CP radiation characteristics have been obtained. Experimental results of a fabricated prototype with the center operating frequency at 900MHz showed that the antenna has the desirable performance with a gain level of about 9 dBi, VSWR of lower than 1.5 and axial ratio of less than 3 dB within the frequency range of 840 ~ 960 MHz.

A Compact Trans-Directional Coupler With Wide Frequency Tuning Range and Superior Performance

A miniaturized circularly polarized (CP) patch antenna is proposed for ultra high frequency (UHF) radio frequency identification (RFID) reader applications. The antenna is composed of a vertical ground, a U-shaped strip, and a square patch with truncated corners. A novel U-shaped strip feed structure is proposed for good impedance matching. Broadband CP operation is achieved by using a thick air-layer substrate (about 0.08λ 0) and selecting an optimal size of the truncated corners. The antenna has an impedance bandwidth (S 11 < -20 dB) of about 141 MHz (861-1002 MHz or 15.1%), a 3-dB axial ratio (AR) bandwidth of about 30 MHz (899-929 MHz or 3.3%), and a gain level of about 7.2 dBi or larger within the 3dB AR bandwidth. The dimension of the antenna is 13 cm x 13 cm x 2.8 cm. The small size and high gain make this element suitable for portable UHF RFID reader applications.

Low-cost single-fed circularly polarized stacked patch antenna for UHF RFID reader applications

Coupled line trans-directional coupler with balanced output ports power distribution and consistent 90° phase difference is proposed in the paper, which is consisted of parallel coupled line and four capacitors. The parallel coupled line can be divided in to four coupled lines with equal electrical length, and the capacitors are shunted on the edge of each coupled line. By using the novel distribution of the capacitors, the bandwidth for amplitude (AP) < 1 dB and 90° ± 5° output port phase differences (PD) is improved. A simulation comparison is made between the proposed TRD coupler and the traditional TRD coupler. An improvement of 19.6 % and 28.5 % are obtained by the proposed TRD coupler under the criterion of AP < 1 dB and PD = 90° ± 5°. To verify the proposed structure, a prototype is fabricated and measured. The measured results show that the proposed coupler has good return loss, ideal isolation, balanced output ports power distribution and consistent 90° phase difference.