Yu-Shin Wang

A Decoupling Technique for Increasing the Port Isolation Between Two Strongly Coupled Antennas

A compact decoupling network for enhancing the port isolation between two closely spaced antennas is proposed in this paper. In the network, we first connect two transmission lines (TLs) individually to the input ports of two strongly coupled antennas. The length of the TLs is designed so that the trans-admittance between ports changes from a complex one at the antenna inputs to a pure imaginary one. A shunt reactive component is then attached in between the TL ends to cancel the resultant imaginary trans-admittance. Finally, a simple lumped-element circuit is added to each port for input impedance matching. The even-odd mode analysis is adopted to investigate the currents excited on the antennas for predicting the radiation pattern of the two-element antenna array. Two examples of printed antennas at 2.45 GHz are tackled by using the proposed decoupling structure. The measurement results agree quite well with the simulation ones. High antenna isolation and good input return loss are simultaneously achieved in both cases, which demonstrates the feasibility of the structure. The decoupled antenna array in each example radiates, as prediction, toward different but complementary directions when the input power is fed in turn to the two input ports. The array efficiency is estimated better than 75% in each example. This pattern diversity effect is helpful for reducing the channel correlation in a multiple-input multiple-output (MIMO) communication system.

Two PIFA-Related Miniaturized Dual-Band Antennas

There are two novel printed inverted-F antenna (PIFA) related dual-band antennas for 2.45 and 5.25 GHz wireless local area network (WLAN) applications introduced in this paper. One is designed by spiraling the tail of the PIFA and the other is by modifying the feed structure of the PIFA into a coupling configuration. An equivalent transmission line model is proposed to explain the dual-band operation of the spiraling PIFA. The measurement results show that the former antenna has a 10 dB return loss with bandwidth 140 MHz in the 2.45 GHz frequency band and bandwidth 756 MHz at 5.25 GHz, whereas the latter one has the bandwidth 240 MHz at 2.45 GHz and bandwidth 672 MHz at 5.25 GHz. In addition, omnidirectional radiation patterns are achieved at those operating frequency bands with average antenna gains near 0 dBi. The proposed antenna possesses the properties of good performance, compact size (about 50% of a typical PIFA), low profile, and low cost; hence, it is suitable for practical applications in a combo WLAN system

A Miniature Quadrifilar Helix Antenna for Global Positioning Satellite Reception

The design is described of a very compact quadrifilar helix antenna. A hollow ceramic rod is used as a dielectric load to reduce antenna size, which is only 2.7% of an air-loaded quadrifilar helix antenna. A simple equivalent circuit is established for the proposed quadrifilar helix antenna to demonstrate impedance characteristics. A self-phasing method for achieving circular polarization is also proposed. This method is convenient for tuning circular polarization. Additionally, a compact matching structure is designed to match the proposed antenna, which only utilizes short transmission-line sections and one capacitor. For experiments, the proposed antenna is designed at 1.575 GHz such that it can be utilized for global position system. Measurement and simulation results agree. A hemispherical pattern with a beamwidth of 150deg is measured. This circular-polarized pattern with a wide beamwidth is feasible for mobile applications.

A Short Open-End Slot Antenna With Equivalent Circuit Analysis

A novel configuration is described for a compact microstrip-line fed slot antenna which is shorter than one-eighth wavelength at the operating frequency. Antenna size is reduced by placing two matching capacitors at both sides of an electrically small open-end slot, through the use of a wideband antenna equivalent circuit model established by considering the physical geometry. With the proposed antenna configuration, a 2.45 GHz slot antenna is first designed using an open-end slot of size 9 mm by 1.5 mm that is originally resonant at 4.8 GHz in a conventional design. Experimental results correlate well with those of the full-wave simulation and the equivalent circuit calculation, which shows a bandwidth of 109 MHz and peak gain of 1.89 dBi. By using the same slot size, several slot antennas operating at even lower frequencies (1.9, 1.64, 1.57 GHz) are then designed and demonstrated. Nearly omni-directional radiation patterns with peak gains 0 dBi and radiation efficiencies larger than 45% are obtained. Given its simplicity and compactness, the proposed electrically small antenna is feasible for circuit integration and highly promising for wireless mobile devices.

Two nearby dual-band antennas with high port isolation

The structure of two dual-band nearby antennas with high port isolation is proposed. The decoupling and matching network consist of only reactive elements so that it does not dissipate the input power. For dual-band antenna, it is usually easier to have high isolation in high frequency band (5 GHz) due to its short wave length. Therefore, the decoupling design can be turned to improve low frequency band and not to influence the high frequency band as much as possible. Besides, the matching circuit is still required to match both low and high bands for maintaining good impedance matching. Measurement results demonstrate the good performance of the proposed configuration.

A Dual-Mode Millimeter-Wave Folded Microstrip Reflectarray Antenna

A dual-mode folded microstrip reflectarray antenna was developed and demonstrated in this paper. The proposed folded reflectarray antenna contains three parts: a planar main reflector, a planar subreflector, and printed feed antennas. The main reflector is used to produce twisted reradiated fields and to provide phase compensation for focusing. The subreflector parallel with the main reflector is made of a substrate printed with high-density metal grid lines, which is transparent to perpendicularly polarized fields, but would reflect the parallel ones. Three fixed-position patch antennas with polarization parallel to the grid lines are created for the radar mode, so that the radiation beam is switchable. Another patch with perpendicular polarization is designed for communication. A simple approach was proposed for simulating and designing the folded reflectarray. Measured results show good agreement with the calculated ones.

A Miniaturized Ground Edge Current Choke—Design, Measurement, and Applications

We propose a miniaturized microwave current choke for blocking the current flowing along the edge of a substrates ground plane. The proposed current choke is composed of a printed inductor and a printed capacitor, which possesses a size much smaller than a conventional quarter-wavelength current choke. By introducing the choke at one side of the ground plane, an effective electrical open circuit is performed for reflecting the ground edge current. The size of the proposed ground edge current choke (GECC) is as small as around 0.06 wavelength in free space. Two applications of the GECC are presented in this paper. The first is the radiation pattern regulation of a printed monopole antenna with long ground plane. The GECC in this application reflects the induced traveling-wave current along the ground plane edge and changes it to a standing-wave one, thus regulating the tilted radiation pattern due to the traveling-wave current to a broadside pattern. The other application is the decoupling of two nearby monopole antennas. By placing the proposed compact GECC in between the antennas, it is found that the isolation between the antenna ports can be enhanced from 8 dB to 32 dB. The experimental results agree well with the simulation, which demonstrate the feasibility of the proposed GECC.

A Compact Slot Antenna Utilizing a Right/Left-Handed Transmission Line Feed

A novel compact planar antenna utilizing cascaded right/left-handed transmission lines is proposed. The significance of layout planning with respect to radiation is investigated and discussed in this paper. Two segments of transmission lines of the same electrical length with opposite signs are cascaded to provide zero phase at the operation frequency. The closed-form formulas for the equivalent circuit of a transmission line are used for circuit design. Both antenna layout and radiation mechanism are discussed. For experimental demonstration, the proposed antenna operating at 2.45 GHz was implemented on an FR4 substrate. The topology using several patches has quite smaller size than the conventional patch antenna. Besides, a fairly omnidirectional radiation pattern was measured.

A novel small planar antenna utilizing cascaded right/left-handed transmission lines

In recent years, meta-material is very popular and widely applied to microwave circuits, including antennas. Antennas associated with left handed material are expected to provide superior characteristics, especially the miniaturized size. Amount of antennas employing CRLH structure were researched. Small planar antennas utilizing the ZOR mode were published in Sanada, A., et al (2004). The physical size of such antenna can be arbitrary regardless the operation frequency since it is specified by the value of the capacitances and inductances instead of the wavelength. Unlike employing CRLH or simply LH TL, a novel planar antenna utilizing cascaded right/left-handed transmission lines is proposed in this paper. A new concept of achieving resonance which is also regardless of the wavelength of the operation frequency is developed without using CRLH structure. The equivalent transmission line circuits are used to analysis and design the antenna.

A printed triple-band antenna for WiFi and WiMAX applications

In this paper, a tri-band antenna for wireless communication applications is presented. The antenna is composed of two different elements, that are an inverted-L monopole operating at 5.2 and 5.8 GHz and a coupled modified half-wavelength open-loop resonator operating at both 2.4 GHz and 3.5 GHz to cover the required bandwidth for IEEE 802.11a/b/g WLAN and IEEE 802.16e. The proposed antenna has the properties of good performance, small size, low profile, and low cost, which is thus suitable for practical applications in the multi-band wireless communication systems.