Chia Ching Lin

Metamaterial-Inspired Engineering of Antennas

A variety of antennas have been engineered with metamaterials (MTMs) and metamaterial-inspired constructs to improve their performance characteristics. Examples include electrically small, near-field resonant parasitic (NFRP) antennas that require no matching network and have high radiation efficiencies. Experimental verification of their predicted behaviors has been obtained. Recent developments with this NFRP electrically small paradigm will be reviewed. They include considerations of increased bandwidths, as well as multiband and multifunctional extensions.

Single, Dual and Tri-Band-Notched Ultrawideband (UWB) Antennas Using Capacitively Loaded Loop (CLL) Resonators

Two compact, printed, ultrawideband (UWB) monopole antennas with tri-band notched characteristics are reported. The notched filters are achieved by introducing printed, electrically small, capacitively-loaded loop (CLL) resonators. The directly driven elements consist of printed top-loaded CLL-based monopoles and 50 Ω microstrip feed lines. By adding three CLL elements close to the feed line, band-notch properties in the WiMAX (3.3-3.6GHz), lower WLAN (5.15-5.35GHz) and higher WLAN (5.725-5.825GHz) bands are achieved. Each antenna system is contained on a 27×34mm2 sheet of Rogers Duroid 5880 substrate. One is designed with three additional CLL elements; the other is achieved with only two. Comparisons between the simulation and measurement results show that these UWB antennas have broadband matched impedance values and stable radiation patterns for all radiating frequencies.

Multifunctional, Electrically Small, Planar Near-Field Resonant Parasitic Antennas

Planar analogs of previously reported electrically small, electric metamaterial-inspired, near-field resonant parasitic (NFRP) antennas are reported. As with the nonplanar designs, the driven and parasitic elements in each presented case are designed to achieve nearly complete matching of the entire system to a 50-Ω source without any matching network and to yield a high radiation efficiency. By introducing multiple NFRP elements, linearly polarized (LP) dual-band and circularly polarized (CP) planar NFRP antennas are realized. These low-profile designs are validated with experimental results.

Design and Experimental Verification of a 3D Magnetic EZ Antenna at 300 MHz

Several variations of a 300-MHz version of the electrically small coax-fed three-dimensional (3D) magnetic EZ antenna were designed and tested. The final version of this low-profile antenna had an electrical size that was ka ~ 0.437 at 300.96 MHz. Nearly complete matching to the 50-Omega source and high overall efficiency (nearly 100%) were achieved. The measured fractional bandwidth was approximately 1.66%. The numerically predicted and the measured results were in good agreement. Comparisons to similar-sized loop antennas that were matched to the source with both custom-made and commercially available, general purpose external matching networks confirm the performance enhancements achieved with this metamaterial-inspired, near-field resonant parasitic antenna.

Multi-Functional, Magnetically-Coupled, Electrically Small, Near-Field Resonant Parasitic Wire Antennas

Several electrically small antenna systems that utilize the magnetic couplings between a coaxially-fed semi-loop antenna and capacitively-loaded loop (CLL)-based near-field resonant parasitic (NFRP) elements are presented. Both one and two gap CLL elements are considered; their impact on the system performance, particularly their effects of the resonance frequencies and the corresponding Q values, is evaluated. By integrating multiple NFRP CLL elements with the coaxially-fed semi-circular loop antenna, electrically small multi-band systems are achieved. They can be designed for a broad range of frequencies by tuning the NFRP elements separately. Dual band designs are reported that achieve operation at the GPS LI (1.5754 GHz) and L2 (1.2276 GHz) frequencies. Their operational modes and performance characteristics are studied. These lead to additional electrically small antenna designs, which feature only one driven loop antenna and two NFRP CLL elements and which achieve circularly polarized (CP) operation. A CP antenna whose electrical size is ka = 0.495 at the GPS LI frequency is presented in detail. Its simulated bandwidth and beamwidth, for which the axial ratio (AR) is less than 3 dB, are, respectively, 7.8 MHz and 76°.

An efficient, low profile, electrically small, three-dimensional, very high frequency magnetic EZ antenna

A very high frequency version of the electrically small, coax-fed, three-dimensional magnetic EZ antenna was designed and tested. The fabricated antenna was formed by integrating a capacitively loaded loop element with a coaxially-fed, electrically small, semicircular loop antenna. This low profile antenna (height ∼ λ / 25 ) had an electrical size that was k a ∼ 0.46 at 105.2 MHz (where a is the radius of the minimum enclosing hemisphere). Nearly complete matching to the 50 Ω source and a high overall efficiency (nearly 95%) were achieved. The numerically predicted and the measured results were in good agreement.

Metamaterial-inspired magnetic-based UHF and VHF antennas

We have demonstrated that the magnetic-based, metamaterial-inspired electrically small antennas that incorporate a lumped element capacitor can to be scaled to lower frequencies without changing their accepted power performance. This occurs without the intervention of any external matching circuit. On the other hand, the overall efficiency decreases significantly because of conductive losses arising from increasing current densities in the copper structures. We are continuing our investigations to determine if other variations of these structures can mitigate some of the copper losses at the lower VHF frequencies.

Multi-band linear and circular polarized, electrically small, near field resonant parasitic antennas

We have developed a variety of electrically small, near-field resonant parasitic (NFRP) antennas. Several examples and their performance characteristics will be presented. These are based on capacitively-loaded loop (CLL) NRFPs with both electric and magnetic couplings to the driven element; both varieties will be compared and contrasted. Integrating multiple NFRP CLL elements with coaxially-fed electrically-small monopoles or semi-circular loop antennas, both single- and dual-band, linearly (LP) and circularly polarized (CP) antenna designs are achieved. The CP designs rely on two orthogonal equivalent magnetic dipoles tuned at slightly different resonance frequencies to achieve the requisite 90° phase shift between them at an intermediate frequency. Two driven monopoles are required for the electrically-coupled version; one driven semi-loop antenna is required for the magnetically-coupled version. However, only the electrically-coupled design has enough tuning parameters to lead to a dual-band, NFRP CLL-based CP antenna. This dual-band CP design will be discussed in our presentation.

Tri-band notched ultra-wideband antenna using capacitively loaded loops (CLLs)

Ultra-wideband (UWB) communication systems have become an attractive wireless topic since the Federal Communication Commission (FCC) first approved in 2002 the rules for the 3.1 −10.6 GHz unlicensed band for commercial UWB communications utilization [1]. The high demands on such a communications system have stimulated research into many UWB antenna designs. Nonetheless, antenna designs for UWB applications face many challenges including their impedance matching, radiation stability, compact size, low manufacturing cost and electromagnetic interference (EMI) problems. The EMI problems are quite serious for UWB systems since there are several other existing narrowband services which occupy frequency bands within the designated UWB bandwidth. These include world interoperability for microwave access (WiMAX) service from 3.3 to 3.6 GHz; wireless local area network (WLAN) services such as IEEE 802.11a in the USA (5.15 to 5.35 GHz, 5.725 to 5.825 GHz) and HIPERLAN/2 in Europe (5.15 to 5.35 GHz, 5.47 to 5.725 GHz); and satellite services near 8 GHz. To avoid the interference with these coexisting systems, a UWB antenna which has intrinsic filtering properties at such service frequencies is necessary to mitigate the potential interferences. It is highly desirable for them to be intrinsically handled rather than through an external band-stop filter device to minimize the footprint of the antenna system, the signal processing requirements, and the cost.

A compact planar near field resonant parasitic (NFRP) antenna for MIMO applications

A planar near field resonant parasitic (NFRP) antenna for multiple-input multiple-output (MIMO) applications in the WLAN 2.4/5.2/5.8 GHz frequency bands is presented. The NFRP antenna can create tri-band functions by incorporating three different parasitic elements. Nearly complete impedance matching to a 50Ω source is shown at the desired resonant frequencies. Additionally, NFRP antenna array configurations show good isolation between the radiating elements even with small spacing between them. Calculated envelope correlation values are less than 0.12 within the bands of interest. A detailed design methodology is described.