Shyh-Jong Chung

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.

Design of a Planar Ultrawideband Antenna With a New Band-Notch Structure

A novel planar ultrawideband (UWB) antenna with band-notched function. The antenna consists of a radiation patch that has an arc-shaped edge and a partially modified ground plane. The antenna that makes it different from the traditional monopole antenna is the modification in the shape of ground plane, including two bevel slots on the upper edge and two semicircle slots on the bottom edge of the ground plane. These slots improve the input impedance bandwidth and the high frequency radiation performance. With this design, the return loss is lower than 10 dB in 3.1-10.6 GHz frequency range and the radiation pattern is highly similar to the monopole antenna. By embedding a pair of T-shaped stubs inside an elliptical slot cut in the radiation patch, a notch around 5.5 GHz WLAN band is obtained. The average gain is lower than -18 dBi in the stopband, while the patterns and the gains at frequencies other than in the stopband are similar to that of the antenna without the band-notched function.

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

Bandpass filter of serial configuration with two finite transmission zeros using LTCC technology

This study proposes a second-order bandpass filter of serial configuration. The filter schema incorporates a grounding capacitor, connecting the two conventional parallel LC resonators with the ground, to provide two finite transmission zeros. The impedance matrix and graphical solutions describe proposed filters operation principle. To demonstrate the proposed filter schema, two bandpass filters, with center frequencies of 2.44 and 4.8 GHz, were designed and implemented using low-temperature co-fired ceramic multilayer technology. The measured results were found to agree well with the simulation results. The 2.44-GHz fabricated bandpass filter was found to possess low in-band insertion loss and high out-band suppression, making it suitable in wireless local area networks, Bluetooth, and RF home links.

Synthesis and Design of a New Printed Filtering Antenna

Synthesis and design of a new printed filtering antenna is presented in this communication. For the requirements of efficient integration and simple fabrication, the co-design approach for the integration of filter and antenna is introduced. The printed inverted-L antenna and the parallel coupled microstrip line sections are used for example to illustrate the synthesis of a bandpass filtering antenna. The equivalent circuit model for the inverted-L antenna, which is mainly a series RLC circuit, is first established. The values of the corresponding circuit components are then extracted by comparing with the full-wave simulation results. The inverted-L antenna here performs not only a radiator but also the last resonator of the bandpass filter. A design procedure is given, which clearly indicates the steps from the filter specifications to the implementation. As an example, a 2.45 GHz third-order Chebyshev bandpass filter with 0.1 dB equal-ripple response is tackled. Without suffering more circuit area, the proposed structure provides good design accuracy and filter skirt selectivity as compared to the filter simple cascade with antenna and a bandpass filter of the same order. The measured results, including the return loss, total radiated power, and radiation gain versus frequency, agree well with the designed ones.

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 Filtering Microstrip Antenna Array

A new filtering microstrip antenna array is presented. The antenna elements, together with the very compact feeding network, function as a third-order bandpass filter. The feeding network, which consists of one power divider and two baluns, provides the first two stages, and the microstrip antenna elements provide the last stage in the filter design. The equivalent lumped circuit model is analyzed, and the detail synthesis procedure is presented. A third-order filtering 2 × 2 microstrip antenna array is designed at a center frequency of 5 GHz with 3% fractional bandwidth and Chebyshev 0.3-dB equal-ripple broadside antenna gain response. The results from circuit model, full-wave simulation, and measurements agree well. Compared to the conventional patch antenna array, the proposed filtering microstrip antenna array successfully suppresses the unwanted signals in out-of-band, preserves good selectivity at band edges, and retains the flatness of the passband broadside antenna gain response.

A Compact Filtering Microstrip Antenna With Quasi-Elliptic Broadside Antenna Gain Response

Design, fabrication, and measurement of a compact filtering microstrip antenna with second-order quasi-elliptic broadside antenna gain response are presented. A U-shape radiating patch is excited by a T-shape resonator through an inset coupling structure. The U-shape patch acts as a radiator as well as the last stage of the filter, and the inset coupling structure can be treated as the admittance inverter in filter design. The design procedure follows the circuit approach-synthesis of bandpass filters. The broadside gain of the filtering antenna has two poles in passband and two broadside radiation nulls (zeros) at the band edges for improving selectivity. Compared to the conventional inset-fed microstrip antenna, with a little extra circuit area, the proposed filtering antenna has a flatter passband response, better frequency skirt selectivity, and almost twice wider bandwidth. The measurement result shows a good agreement with the simulations.

A novel bi-directional amplifier with applications in active Van Atta retrodirective arrays

A novel two-port bi-directional amplifier, which may simultaneously amplify the waves coming from both ports, is proposed and demonstrated in this paper. Using this amplifier, a two-element active Van Atta retrodirective array is implemented and compared to a four-element passive array. The bi-directional amplifier is constructed by two identical one-port reflection-type amplifiers and a 3-dB 90/spl deg/ hybrid. The reflection-type amplifier is designed using an FET with a single-power-supply configuration. A quarter-wavelength microstrip radial stub is connected to the devices source terminal to narrow down the negative-resistance frequency range so as to avoid oscillation at undesired frequencies. The fabricated bi-directional amplifier provides the transmission gain over the frequency band from 5.76 to 6.88 GHz, with a peak value of 9.1 dB at 6.04 GHz. Printed Yagi antennas with four directors are adopted to build both the active and passive Van Atta arrays. The 3-dB back-scattering beamwidth of the active array is measured as wide as 74/spl deg/. Finally, it is observed from the measurements that, although only half of the antenna elements are used, the active Van Atta array produces a back-scattering field level 4.5 dB, on average, higher than the passive one does. This verifies the performance of the bi-directional amplifier.

A retrodirective microstrip antenna array

A Van Atta retrodirective reflector was designed and developed, using an aperture-coupled microstrip antenna array. This reflector possesses the advantage of reflecting high fields to the source point over a wide range of incidence angles and, owing to the low cost and conformability of the structure, is suitable for applications in intelligent vehicle highway systems (IVHS). An approximate theory associated with the reradiation and scattering principles of the reflector is presented for the purpose of understanding and designing the reflector. The utility of the retrodirective reflector was demonstrated by comparison with a plate reflector and a microstrip antenna array without a feed structure. Finally, a reflector with switches in the middle of the microstrip feed lines was investigated for possible applications in communications and remote identification.