Kam Man Shum

Novel 1-D microstrip PBG cells

Novel one-dimensional (1-D) microstrip photonic bandgap (PBG) cells are proposed. They are sections of microstrip line with special perforation patterns etched on the line itself. As examples, two types of PBG cell are investigated. Simulation and experiments show that the cell exhibits remarkable slow-wave and band-stop effects. An equivalent L-C circuit is used to model the PBG cell. Several cells connected in series form an excellent band-stop filter.

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.

Novel oscillator incorporating a compact microstrip resonant cell

A novel transistor oscillator incorporating a compact microstrip resonant cell (CMRC) as its terminating resonance is proposed. Adjusting the dimensions of the cell, it is possible that the fundamental frequency can be positively fed back and the second harmonic negatively fed back at the input port of the oscillator. The fundamental output is enhanced with the second harmonic being suppressed. The output power of the proposed CMRC oscillator is 14.7 dBm at 2.5 GHz with 27.1 dB rejection of the second harmonic, outperforming the conventional microstrip termination with a 40% size reduction.

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.

A Tunable Via-Patch Loaded PIFA With Size Reduction

A novel tunable planar inverted-F antenna (PIFA) is described. A via-patch is introduced under the main radiating element to create a capacitive coupling effect and lower the operating frequency. The antenna size is reduced by half when compared to the conventional PIFA. Incorporating with an L-shaped opening on the ground plane, the proposed via-patch loaded PIFA exhibits a 10-dB return-loss bandwidth of 8.91% for 2.4 GHz ISM band applications. In the proposed approach, the capacitive patch is connected to the ground through a via while a coaxial feed is directly connected to the radiating element. This is different from other capacitive-loading, size-reduction schemes in which the capacitive patch is connected to the coaxial feed, thus not able to provide frequency tuning. By simply replacing the via in our antenna with a screw and adjusting the height of the via-patch by turning the screw, a tuning range of 0.8 GHz from 2.5-3.3 GHz can be achieved. This makes the proposed PIFA a convenient tunable small antenna. Both simulation and measurement results are presented together with parametric studies on the via-patch and L-shaped opening ground plane

Low conversion-loss fourth subharmonic mixers incorporating CMRC for millimeter-wave applications

Low conversion-loss millimeter-wave fourth subharmonic (SH) mixer designs are proposed in this paper. A millimeter-wave (35 GHz) fourth SH mixer with four open/shorted stubs is designed and measured. The conversion loss is less than 15 dB within a 2.4-GHz bandwidth. The minimum loss is 11.5 dB at the center frequency. By replacing two of the shunt stubs with a dual-frequency in-line stub consisting of newly developed compact microstrip resonating cells (CMRCs), the performance of the SH mixer is improved significantly. At 35 GHz, the conversion loss of this new fourth SH mixer is as low as 6.1 dB with a 3-dB bandwidth of 6 GHz. The conversion loss in the whole Ka-band (26.5-40 GHz) is less than 16 dB. The proposed fourth SH mixer incorporating with CMRCs provides a low-cost high-performance solution for RF subsystem design.

A compact bandpass filter with two tuning transmission zeros using a CMRC resonator

This paper presents a new compact, low-insertion loss, sharp-rejection, and narrow-band microstrip bandpass filter (BPF) using a compact microstrip resonant cell (CMRC) as the resonator. Experimental results show that the filter only has 1.3- and 1.5-dB insertion losses when using the symmetrical and asymmetrical CMRC resonators, respectively. The effect of varying the length of the resonator to the notch frequencies of the filter has been studied. Furthermore, due to the CMRC characteristic, the size of this filter is only 0.1/spl lambda//sub g/ by 0.29/spl lambda//sub g/. Based on the same design methodology, a microstrip BPF with a coplanar-waveguide feed is also designed with an increased bandwidth. All the proposed filters have been verified by simulation and measurement with good agreement. These filters are attractive for hybrid microwave integrated circuit and monolithic-microwave integrated-circuit implementation.

Differentially Fed Planar Aperture Antenna With High Gain and Wide Bandwidth for Millimeter-Wave Application

This paper presents a novel planar aperture antenna with differential feeding. Compared with conventional high-gain aperture antennas, such as horn and reflector antennas, it maintains a high gain and wide bandwidth, but has a much lower profile with only one quarter-wavelength height. Since the height (λg/4) at millimeter-wave (mmWave) band is as low as the most of the commercially available laminates, planar aperture antennas with high gain and wide bandwidth can be realized at mmWave band using the proposed structure. A prototype working at 60 GHz band was designed and fabricated on a single layer laminate using standard printed circuit board (PCB) technology. A differential feeding network based on E-plane tee was also designed to feed the prototype for the measurement purposes. Experiment results show that the prototype achieves a -15-dB impedance bandwidth from 56.2 to 69.7 GHz (21.5%). The peak gain at broadside is 15.3 dBi at 60 GHz. The 3-dB gain bandwidth is from 54.0 to 67.5 GHz (22.2%). Within the operating bandwidth, the radiation pattern is stable with a low cross-polarization level below -24 dB, and is symmetrical about both the E- and H-planes.

Second-Generation RFID

Current ultra-high frequency air interface protocols help users get the true benefits of second-generation RFID standards. However, these technologies also have some security drawbacks and limitations.

Printed L-probe antenna on multi-layered PCB

A printed L-probe antenna fabricated on a multi-layered printed-circuit-board (PCB) with a very wide operating band is proposed. This antenna is a four-layered structure, consisting of a circuitry layer, ground layer, probe layer, and patch layer. The printed part of the L-probe provides extra degrees of freedom for tuning the antenna, achieving a wide operating frequency. A printed L-probe antenna centered at the frequency of 6.5 GHz was designed with a measured impedance bandwidth of 40% with constant radiation patterns across the operating band.