Chi Hou Chan

Design of a 5.8-GHz rectenna incorporating a new patch antenna

This paper presents a rectifying antenna (rectenna) designed in a finite ground coplanar waveguide (FG-CPW) circuit. The new rectenna element is based on a new patch antenna and a new band-stop filter, in the form of compact CPW resonant cell (CCRC), located between the antenna and the rectifying diode. The novel coplanar patch antenna with about 9-dBi gain is proposed for the rectenna. The CCRC is adopted to suppress the second harmonic from radiation. With the use of this band-stop filter, a radio-frequency-to-direct-current (RF-to-dc) conversion efficiency of 68.5% using a 270-/spl Omega/ load resistor is obtained.

A novel microstrip ring hybrid incorporating a PBG cell

An experimental investigation of a novel compact microstrip 180/spl deg/ ring hybrid incorporating a one-dimensional (1-D) slow-wave structure, in the form of perforations on the ring itself, is presented. The size of the hybrid is reduced by 23% due to the slow-wave effect, and this size reduction technique has potential applications in MICs and MMICs. The measured insertion loss is comparable to that of a conventional microstrip hybrid.

60 GHz Plated Through Hole Printed Magneto-Electric Dipole Antenna

A wideband unidirectional antenna, which is composed of a planar electric dipole and a magnetic dipole formed by a vertically-oriented shorted patch antenna, is presented for millimeter wave applications. The antenna is realized by a plated through hole printed technique with the use of a microwave substrate and is excited by a T-shaped coupled strip feed. An impedance bandwidth of 33% (S11 ≤-15 dB) from 50 to 70 GHz is achieved. Stable radiation patterns with low cross polarizations and a stable antenna gain of ~7.5 dBi are achieved across the entire operating bandwidth. This single antenna element yields advantages of wideband, good directional radiation pattern and low fabrication cost.

Low-Loss Frequency-Agile Bandpass Filters With Controllable Bandwidth and Suppressed Second Harmonic

This paper presents a novel approach to design frequency-agile bandpass filters with constant absolute bandwidth and passband shape, as well as a suppressed second harmonic. A novel mixed electric and magnetic coupling scheme is proposed to control the coupling coefficient variation. Theoretical analysis indicates that it is able to achieve desired coupling coefficients between the proposed resonators at various frequencies so as to obtain constant absolute bandwidth. Moreover, this half-wavelength resonator has a Q higher than the quarter- and half-wavelength counterparts, thus resulting in low insertion loss. A filter of this type is designed to validate the proposed idea. To remove the spurious responses of the filter, a method is then introduced to suppress the second harmonic without degrading the passband performance. For demonstration, two frequency-agile filters with 60- and 80-MHz constant absolute bandwidth are implemented with the frequency tuning range from 680 to 1000 MHz. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

A Broadband Compact Microstrip Rat-Race Hybrid Using a Novel CPW Inverter

A new compact microstrip rat-race hybrid with an octave bandwidth employing a novel frequency-independent coplanar waveguide (CPW) phase inverter is reported in this paper. The 270deg branch of a conventional rat-race is replaced by a -90deg branch, which is realized by a 90deg microstrip line and the CPW phase inverter. A new microstrip-to-CPW transition is introduced for which a lumped-element model is devised to facilitate parameter optimization. The designed transition has an insertion loss less than 0.33 dB across the designed frequency band from 1.5 to 3.5 GHz. The footprint of the proposed design is reduced by 75% and shows almost 60% and 80% enhancements in the 0.5-dB mismatch bandwidth of amplitude and 10deg mismatch bandwidth of phase, respectively, when compared with the conventional implementation. The proposed hybrid can be fabricated using a conventional printed-circuit and plated thru-hole technologies

Wideband and High-Gain Composite Cavity-Backed Crossed Triangular Bowtie Dipoles for Circularly Polarized Radiation

A composite cavity-backed antenna excited by crossed triangular bowtie dipoles is proposed and investigated for circular polarization (CP) applications. It is fed by a novel balun, i.e., a transition from a microstrip line to double slot lines, providing symmetrical electric field distributions at the feeding port. Measurements of an optimized antenna prototype show that it can achieve an impedance bandwidth of over 57.6% for SWR ≤ 2, a 3-dB axial-ratio bandwidth of 39%, a broadside gain of 8-10.7 dBi, and symmetrical radiation patterns over the whole operating band. The operating principles of the proposed antenna are analyzed carefully and found quite different from crossed thin-wire dipoles with very weak coupling. Problems in the feeding balun, greatly deteriorating the CP performance at the resonance, are clearly addressed and solved. Detailed parametric studies are given in the final part of this paper.

Wideband Cavity-Backed Bowtie Antenna With Pattern Improvement

A wide-band unidirectional cavity-backed bowtie antenna with stable radiation patterns is proposed in this paper. It is differentially fed by a parallel strip line via a transition from a microstrip line. The corners of the conventional triangular bowtie dipole are rounded to achieve a larger impedance bandwidth. A circular ring, acting as a special reflector, is placed within the cavity, between the ground plane and the bowtie dipole, for stabilizing the broadside radiation patterns over the whole operating band. Numerical simulations and parametric studies are performed to verify the effectiveness of the ring reflector for radiation pattern improvement when it is electrically close to the bowtie dipole. The final design is fabricated and measured. Measured results indicate that the proposed antenna features an impedance bandwidth of 91.4% for SWR les 2, a 7.3-9.5 dBi broadside gain, a total size of 1.56 times 0.325lambda0 2 (lambda0 is the free-space wavelength at the center frequency) and stable radiation patterns over the whole band.

Small Antennas in Wireless Communications

The objective of this paper is to provide the context, physical insight, and perspective on antennas in wireless communications. Although it does not mean to be comprehensive, the four key technologies related to small antenna designs to be reviewed and discussed, including multiband planar inverted-F antennas, broadband folded patch antennas, compact differentially fed antennas, and miniature circularly polarized patch antennas, would cover a wide range of topical interests and practical applications. A brief overview of computer software for analyzing these antennas is also provided. Hopefully, this paper will be beneficial for the diverse engineering readership of the IEEE.

RF Tunable Bandstop Filters With Constant Bandwidth Based on a Doublet Configuration

This paper presents a novel approach to design RF tunable bandstop filters with constant absolute bandwidth. The filters are based on a doublet configuration which is attractive for high-order filter designs. In the doublet, two varactor-tuned resonators, arranged in a mirror-symmetrical manner, are coupled to a main transmission line. A novel coupling scheme is utilized between the resonators and the main line. Theoretical analysis indicates that, as the resonant frequency varies, the coupling coefficient within the fixed coupling region can be inherently changed to desirable values to meet the requirement of constant absolute bandwidth. Using the coupling scheme, constant absolute bandwidth can be obtained without extra circuits to control the coupling strengths. For demonstration, first-order and high-order filters are designed. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

Bandwidth enhancement technique for quarter-wave patch antennas

A novel technique that improves the performance of a conventional quarter-wave patch antenna is proposed. Two different geometries (U-slot and L-slit) are investigated experimentally. With the inclusion of a folded inner small patch, we achieve impedance bandwidths of 53% and 45% for the U-slot and L-slit, respectively, for a voltage standing wave ratio less than 2. Radiation patterns are stable across the whole operating frequency bands.