X. L. Sun

Dual-Band Monopole Antenna With Frequency-Tunable Feature for WiMAX Applications

A planar dual-band monopole antenna with a frequency-tunable band is presented. The structure of the antenna radiator has a stem connecting to two branches that are used to generate two frequency bands at around 2.4 and 3.4 GHz for Worldwide Interoperability for Microwave Access (WiMAX) applications. The lower band covers the WiMAX frequency band of 2.3–2.4 GHz, while the higher band is frequency-tunable to the WiMAX frequency bands of 3.3–3.4, 3.4–3.6and 3.6–3.8 GHz. The frequency tunability is achieved by using the reverse-bias voltage across a varactor that is placed between the stem and one of the radiating branches of the radiator. In this study, the radiating branch responsible for the higher band is selected for tuning. A simple and novel biasing circuit, consisting of two radio frequency (RF) choke resistors and an L-shaped stub, is designed for biasing the varactor. Results show that the higher band can be continuously tuned in frequency, yet keeping the lower band unchanged. The reflection coefficient, radiation pattern, and efficiency of the antenna are studied using computer simulation and measurement.

CP metasurfaced antennas excited by LP sources

A metasurface which is considered as a polarizer for microwave antennas is proposed in this paper. Preliminary results have shown that circularly polarized (CP) radiation can be obtained from linearly polarized (LP) source antennas with the use of metasurface, antenna performance such as realized gain, efficiency and bandwidth are improved simultaneously. The metasurfaced antennas have a succinct non-resonant cavity in sub-wavelength (1/13 λ0) format.

A triple-band monopole antenna for WLAN and WiMAX applications

In this paper, a triple-band monopole antenna for WLAN and WiMAX wireless communication applications is presented. The antenna has a simple structure designed for 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX bands. The radiator is composed of just two branches and a short stub. The antenna is designed on a 40 × 40 × 0.8 mm3 substrate using computer simulation. For verification of simulation results, a prototype is fabricated and measured. Results show that the antenna can provide three impedance bandwidths, 2.35-2.58 GHz, 3.25-4 GHz and 4.95-5.9 GHz, for the WLAN and WiMAX applications. The simulated and measured radiation patterns, efficiencies and gains of the antenna are all presented.

A dual-band antenna for wireless USB dongle applications

In this paper, the design of a dual-band antenna for universal-serial-bus (USB) dongle applications in the 2.4-GHz wireless-local-area network (WLAN) and 3.5-GHz Worldwide Interoperability for Microwave Access (WiMAX) systems is presented. The antenna consists of two folded inverted-F radiating elements. One inverted- F element generates a 2.45-GHz band for the WLAN band (2.4-2.484 GHz), and both inverted-F elements together resonate at around 3.5 GHz to generate a wide frequency band for the WiMAX system (3.3-3.8 GHz). The antenna is designed on a 25×70 mm2 printed-circuit board (PCB), same size of an USB dongle PCB. For verification of simulation results, a prototype is fabricated and measured. Measured results show that the antenna has two impedance bandwidths, 2.39-2.5 GHz and 3.24-3.8 GHz, for the WLAN and WiMAX applications, respectively. The simulated and measured radiation patterns, efficiencies and gains of the antenna are all presented.

CPW-coupled-fed elliptical monopole antenna for UWB applications

In this paper, a coplanar-waveguide (CPW)-coupled-fed elliptical monopole antenna (CCFEMA) is presented for UWB applications. The antenna has a large bandwidth covering the frequency band from 2.8 GHz to 16.5 GHz with return loss larger than 10 dB and radiation pattern similar to that of a dipole antenna. With an appropriate modification of the radiation patches, a band-notched antenna based on the CCFEMA can also be designed to have a good band-notched performance for the band from 5.0 GHz to 6.0 GHz to avoid interfering with WLAN. The return loss, radiation pattern, peak gain, efficiency and band-notched characteristic of the antenna are studied using computer simulation. For verification, a prototyped antenna is also fabricated and then measured using the antenna measurement system, Satimo Starlab. The results show that the proposed antenna is a good candidate for UWB applications.

Metamaterial-line based feed-networks for wideband circularly polarized antennas

This paper presents a number of metamaterial-line based feed-networks for wideband circularly polarized (CP) antennas. These feed-networks were designed and fabricated using lumped-element integrated microstrip transmission-lines that were synthesized by using metamaterial transmission-line concept. Design examples for dual-fed, triple-fed and four-element CP antennas are demonstrated. Excellent performance and reduced substrate sizes were achieved.

A MIMO antenna for mobile applications

A multiband Multiple-Input Multiple-Output (MIMO) antenna for mobile phones applications in the next generation is proposed. The proposed MIMO antenna consists of two identical elements, each having three branches to generate two frequency bands, a wide higher and narrow lower frequency bands. Simulation results show that these two frequency bands can cover the lower band for Long-Term Evolution (LTE), the DCS1800, PCS1900 and UMTS-2100 bands, the Wibro Band, the 2.4-GHz band for the WLAN system and also the upper band for the WiMAX. By cutting a slit on the printed circuit board (PCB) serving the ground plane, a great enhancement of isolation between the two antenna elements can be achieved for the two frequency bands.

A small patch antenna using a single CRLH TL unit cell

This paper presents the design of a small patch antenna, which consists of one unit cell of composite right/left handed transmission line (CRLH TL). Due to the resonant frequency of the CRLH TL unit cell is determined not by the physical length but by the inductance and capacitance values loaded in the cell, the size of the patch antenna consisting CRLH TL unit cell can be reduced by tuning the LC values. The antenna is fed by a microstrip line. In order to improve the matching, a thinner microstrip line and two rectangular notches etched on the patch are used. The patch antenna including the feeding line is fabricated on a 3×3 cm2 substrate with εr of 3.5 and thickness of 1.5 mm. The size of the patch is reduced to 9 mm×12.9 mm, which is 0.18 λg×0.26 λg at the resonant frequency of 3.59 GHz, owing to the characteristic of the CRLH TL unit cell. The measured results exhibit a bandwidth of 24 MHz and conventional patch-like radiation pattern. The gain of -4.7 dBi and efficiency of 20% are achieved.

Simple dual-band notched design for CPW-coupled-fed elliptical UWB monopole antenna

This paper presents the results of a CPW-coupled-fed elliptical UWB monopole antenna (CCFEUMA) with a simple dual-band notched design for the WLAN Band. The antenna has a large bandwidth covering the frequency band from 2.5 to 14.6 GHz with the return loss larger than 10 dB. Two band notches at the lower (5.15-5.35 GHz) and higher (5.725-5.825 GHz) WLAN band are realized by cutting two half-elliptical arc-slots on the radiator. The return loss, radiation pattern, peak gain and efficiency of the antenna are studied using computer simulation and measurement.

A 5 th -order analog predistorter for NADC system

This paper presents the design of a 5th-order analog predistorter using the inband intermodulation (IM) signals for predistortion of base-station high power amplifiers (HPAs) for the North American Digital Cellular (NADC) system. The predistorter employs two mixers with same configuration to generate 3rd-order intermodulation (IM3) products and 5th-order intermodulation (IM5) products, to suppress the 3rd-and 5th-order intermodulation distortion products (IMDP3 and IMDP5) at the HPA output. The predistorter is implemented and tested using the pi/4-DQPSK signal of the NADC system at 2.2GHz in a practical 100W-HPA. The results show that, at the HPA output powers of 65.6, 56.2, 50 and 41.3 W, the predistorter can suppress the adjacent channel power ratio (ACPR) of the pi/4-DQPSK signal at ± 20 kHz from the center frequency by 15.16, 15.83, 16.17 and 15.17 dB, respectively.