Ming-Chun Tang

Compact UWB Antenna With Multiple Band-Notches for WiMAX and WLAN

In order to prevent interference problem due to existing nearby communication systems within the UWB operating frequency, a compact triple band-notch UWB antenna is presented in this communication. This antenna, designed for the rejection of interference with Worldwide Interoperability for Microwave Access (WiMAX), lower and upper wireless local area networks (WLANs) covering 3.3-3.6 GHz, 5.15-5.35 GHz and 5.725-5.825 GHz, provides three notched bands by only one structure with simple design. Based on simulation and measurement, it shows that the proposed antenna can guarantee a wide bandwidth from 3.03 to 11.4 GHz with triple unwanted band-notches successfully.

Wide-Angle Scanning Phased Array With Pattern Reconfigurable Elements

A novel phased array is presented to extend array scanning range by using pattern reconfigurable antenna elements and weighted thinned synthesis technology in this paper. The pattern reconfigurable microstrip Yagi antenna element is used as a basic element in array and it is capable of reconfiguring its patterns from broadside to quasi-endfire radiation by shifting states of the PIN diode switches integrated on parasitic strips. A weighted thinned linear array synthesis technique is analyzed and some interesting conclusions have been made. A linear array composed of eight pattern reconfigurable antenna elements is manufactured to demonstrate the excellent performance of the array. The active element pattern of each element is measured and pre-stored. Based on active element patterns and weighted thinned linear array synthesis technique, the pattern scanning performance of the novel array is synthesized. The results indicate that the array can scan its main beam from φ = -60° to φ = 60° in H-plane with gain fluctuation less than 3 dB while maintaining low side lobes, and the -3 dB beam width coverage is about from φ = -68° to φ = 68°. The performance is superior to the traditional phased array made of wide-beam elements.

Compact Hyper-Band Printed Slot Antenna With Stable Radiation Properties

A compact hyper-band ( >10:1 impedance bandwidth) printed antenna design is investigated numerically and experimentally. It is based on an elliptical-slot antenna augmented with a parasitic oval patch and driven with a specially engineered microstrip-line-fed elliptical tuning fork element. The parasitic and driven elements are adjusted along with the elliptical slot to create additional resonance modes; adjust the coupling strengths among all of the design components; facilitate the overlap of adjacent resonance modes; and fine tune the input impedance. The total size of the final optimized antenna is only 30 ×40 mm2. It exhibits a -10-dB impedance bandwidth from 2.26 to 22.18 GHz. Desirable radiation performance characteristics, including relatively stable and omni-directional radiation patterns, are obtained over this range. A prototype was fabricated and tested. The experimental results confirm the predicted input impedance bandwidth and radiation characteristics. While the hyper-band performance could be used for high fidelity short pulse applications, the antenna could also be used for multi-band operations from 3.1-10.6 GHz since it covers that entire ultra-wideband (UWB) spectral range.

A Study of Low-Profile, Broadside Radiation, Efficient, Electrically Small Antennas Based on Complementary Split Ring Resonators

The designs and performance characteristics of several electrically small antennas based on complementary split ring resonators (CSRRs) are reported. A coaxial-fed monopole is first integrated with a CSRR that is cut from a grounded finite copper disc. The presence of the electrically small CSRR element facilitates a nearly complete impedance match to the source, a nearly broadside radiation pattern, and a high radiation efficiency. The addition of a circular top-hat to the monopole then achieves an ultra-low profile (0.005λ0) design and an improved broadside pattern, while maintaining all other desirable features. Finally, to enrich their potential usefulness, two additional enhancements of these designs were accomplished. One is a further miniaturization that is achieved by introducing a more complex CSRR element, while maintaining a high, 82%, radiation efficiency. The second is a further enhancement of the directivity and front-to-back ratio through the introduction of a slot-modified parasitic disc, while maintaining the original impedance matching, low-profile and electrically small properties. These designs were consummated and their performance characteristics evaluated with the frequency domain ANSYS-ANSOFT High Frequency Structure Simulator (HFSS) and were confirmed independently using the time domain CST Microwave Studio (MWS) simulator. A prototype of the basic system was fabricated and tested; the agreement between the simulated and measured results validates the design principles.

Efficient, High Directivity, Large Front-to-Back-Ratio, Electrically Small, Near-Field-Resonant-Parasitic Antenna

Enhancements of the directivity and front-to-back ratio (FTBR) of a metamaterial-inspired electrically small, linearly polarized, coaxially-fed Egyptian axe dipole antenna are considered. They are accomplished with a particular augmentation of the original near-field-resonant-parasitic (NFRP) antenna with an additional NFRP element, a small disc conductor modified with two meanderline-shaped slots. The entire system is evaluated numerically with two independent computational electromagnetics simulators. The optimized results demonstrate an electrically small antenna (i.e., ka <; 1.0) with a reasonably low profile (i.e., height ~ λ/10) that improves the directivity from 1.77 to 6.32 dB, increases the FTBR from 0 to > 20 dB, and maintains large half-power beamwidths, while having a radiation efficiency over 80% with nearly complete matching to a 50 Ω source.

Planar Ultrawideband Antennas With Improved Realized Gain Performance

The design nuances and associated performance characteristics of two printed planar ultrawideband (UWB) antennas are reported. The designs achieve improved broadside-realized gains, particularly at the high-frequency side of the UWB band. An arc-shaped slot is etched into the radiating patch of a standard compact elliptically shaped UWB monopole antenna. The resulting parasitic element is engineered to produce its fundamental resonant mode in such a manner that a more compact overall design is realized and the broadside-realized gain in the upper UWB frequency range is improved while maintaining impedance matching without any significant changes to the original design parameters. In agreement with simulations, a 61.7% reduction in size from previous designs is demonstrated with more than a 6 dB increase in the realized gain near 10 GHz. To further improve its high-frequency characteristics, a multimode-resonator filter consisting of a single-wing element is combined with the slot-modified UWB antenna. The filter is first designed, fabricated, and measured to demonstrate that it produces the predicted appropriate transmission characteristics throughout the UWB band. The design integration of this compact filter is then presented and the resulting performance characteristics of the overall antenna system illustrate its advantages. The simulated and measured results are in good agreement. They indicate that the integrated design possesses sharp frequency cutoffs at both edges of the UWB passband, as well as strong upper stop-band attenuation. As a consequence, a 2.12 dB further increase of the broadside-realized gain values is demonstrated near 10 GHz.

Augmenting a Modified Egyptian Axe Dipole Antenna With Non-Foster Elements to Enlarge Its Directivity Bandwidth

Non-Foster elements are introduced to augment an Egyptian axe dipole (EAD) antenna-based system in order to expand its directivity bandwidth. The frequency-agile properties of the original antenna system are investigated near 300 MHz by linearly and discretely changing the values of its internal reactive element. The curve-fit reactance versus frequency curve is established. It is reproduced approximately by augmenting the antenna system with two non-Foster elements implemented internally in one of its near-field parasitic elements and with negative impedance convertor (NIC) designs. It is demonstrated that the resulting electrically small antenna system is capable of achieving excellent unidirectional radiation performance, including a broadside directivity in the range from 5.78 to 6.24 dB with more than a 20 dB front-to-back ratio (FTBR) over a 13% instantaneous fractional bandwidth. The corresponding half-power beamwidths in the E- and H-planes, respectively, are 78° and 138°; the radiation efficiency exceeds 65%.

Improved Performance of a Microstrip Phased Array Using Broadband and Ultra-Low-Loss Metamaterial Slabs

A novel broadband and ultra-low-loss electric metamaterial EM isolation slab is proposed to improve the performance of a microstrip array. The metamaterial slab is formed by periodically grounded edge-coupled split-ring resonators (PGE-SRRs). Outstanding improvements - including over -50 dB peak isolation, 15% fractional bandwidth (-10 dB isolation) and almost lossless operation - are obtained. The metamaterial slab is inserted halfway between the adjacent E-coupled elements in the microstrip array to suppress mutual coupling. A strong mutual-coupling suppression of -16.8 dB was exhibited experimentally in a two-element microstrip array with an element spacing of three-quarters of the operating wavelength. Theoretical and numerical studies were done to improve the performance of microstrip phased arrays using the proposed metamaterial slab. The analysis indicated that the scan blindness in an infinite phased array is well eliminated, the wide-angle impedance matching is remarkably improved, and the scanning range is extended from [-13°, 13°] to [-28°, 28°]. A 7×3 microstrip array was simulated to study the influence of the metamaterial slab on the arrays performance. The results indicated that the metamaterial slab can also enhance the radiation characteristics, extend the scanning range and suppressing grating lobes in microstrip phased arrays.

Design and Testing of Simple, Electrically Small, Low-Profile, Huygens Source Antennas With Broadside Radiation Performance

The efficacy of a simple, electrically small, low-profile, Huygens source antenna that radiates in its broadside direction is demonstrated numerically and experimentally. First, two types of electrically small, near-field resonant parasitic (NFRP) antennas are introduced and their individual radiation performance characteristics are discussed. The electric one is based on a modified Egyptian axe dipole NFRP element; the magnetic one is based on a capacitively loaded loop NFRP element. In both cases, the driven element is a simple coax-fed dipole antenna, and there is no ground plane. By organically combining these two elements, Huygens source antennas are obtained. A forward propagating demonstrator version was fabricated and tested. The experimental results are in good agreement with their analytical and simulated values. This low profile, ~0.05λ0, and electrically small, ka = 0.645, prototype yielded a peak realized gain of 2.03 dBi in the broadside direction with a front-to-back ratio of 16.92 dB. A backward radiating version is also obtained; its simulated current distribution behavior is compared with that of the forward version to illustrate the design principles.

Electrically Small, Broadside Radiating Huygens Source Antenna Augmented With Internal Non-Foster Elements to Increase Its Bandwidth

A broadside radiating, linearly polarized, electrically small Huygens source antenna system that has a large impedance bandwidth is reported. The bandwidth performance is facilitated by embedding non-Foster components into the near-field resonant parasitic elements of this metamaterial-inspired antenna. High-quality and stable radiation performance characteristics are achieved over the entire operational bandwidth. When the ideal non-Foster components are introduced, the simulated impedance bandwidth witnesses approximately a 17-fold enhancement over the passive case. Within this –10-dB bandwidth, its maximum realized gain, radiation efficiency, and front-to-back ratio (FTBR) are, respectively, 4.00 dB, 88%, and 26.95 dB. When the anticipated actual negative impedance convertor circuits are incorporated, the impedance bandwidth still sustains more than a 10-fold enhancement. The peak realized gain, radiation efficiency, and FTBR values are, respectively, 3.74 dB, 80%, and 28.01 dB, which are very comparable to the ideal values.