Wing Shing Chan

Broadband Phase Shifter Using Loaded Transmission Line

This letter presents a novel loaded transmission line, which has a constant phase shift over a wide bandwidth, referenced to a uniform transmission line. Compared with the conventional coupled line phase shifter, the configuration shows good performance with simplicity in both design and fabrication. The optimal design parameters for different phase shift values up to 120° are also presented to allow for a quick design process. To verify the configuration, a 90° phase shifter using a T shaped open stub loaded transmission line is designed, fabricated and measured. Excellent performance is achieved with small insertion loss and phase deviation over a bandwidth of 82%.

New linearization method using interstage second harmonic enhancement

Efficient use of the frequency spectrum necessitates the use of modulation formats such as /spl pi//4-DQPSK, which requires linear amplification to minimize spectral regrowth. A new linearization technique is presented that allows a more efficient operation of these linear amplifiers by combining both the advantage of the transparent nature of feed-forward linearization with the efficiency of feedback linearization. The method of convolution is used to analyze the amplifier characteristics and to determine how linearization can be achieved. This method is verified experimentally and proves that by careful use of the second harmonic component, a new method of linearization has been realized.

Computational Optimization Algorithms for Antennas and RF/Microwave Circuit Designs: An Overview

This paper provides an overview of optimization algorithms for antennas and radio frequency (RF)/microwave circuit designs. The significance of wireless communication to our daily lives and industrial engineering will first be discussed. Antennas and circuits used in wireless communication will then be introduced followed by a discussion on the need for optimization. After that, this paper will focus on three widely used optimization algorithms for antennas and RF/microwave circuit design. A survey of the optimization of antennas and microwave devices available in the literature will be presented and will include the use of other optimization algorithms. For illustration purposes two optimization examples with measurement results will be given.

Dual-Band Rectangular Patch Hybrid Coupler

This paper presents, for the first time, the design of a rectangular patch hybrid coupler that can operate at two arbitrary frequency bands with the same quadrature phase relation between the two outputs. The design procedure of the hybrid coupler is presented. For demonstration, a dual-band rectangular patch hybrid coupler is designed to operate in the 2.4- and 5-GHz bands corresponding to the IEEE 802.11 a/b/g bands. The measured result shows 9.3% and 18.2% bandwidth for the lower and upper frequency bands.

Reconfigurable RF Quadrature Patch Hybrid Coupler

A highly reconfigurable radio frequency patch hybrid coupler with a simple topology is presented for the first time. Due to the introduction of lumped equivalent circuit and flexibility of varactor loaded patterned ground plane, the complex reconfigurability in port arrangement and coupling coefficient can be implemented. Varying the capacitance across different planes allows the electronic switching between different operating modes of the patch hybrid coupler. When the auxiliary patch and patterned ground plane is placed closer to the two output ports, tunable coupling coefficient can also be implemented by changing the capacitance. This results in wide band reconfigurability for the coupling coefficient range. For demonstration purposes, a patch hybrid coupler operating at 2.4 GHz is designed and measured to validate the port reconfigurable concept. Also, a patch hybrid coupler with tunable coupling coefficient operating at 3.5 GHz is designed, fabricated, and measured. This circuit gives a reconfigurable coupling coefficient ranging from -4.2 to -10 dB while maintaining good performance.

A Bandwidth Improved Circular Polarized Slot Antenna Using a Slot Composed of Multiple Circular Sectors

A circular polarized (CP) slot antenna is designed with a slot composed of multiple circular sectors (MCS). The design has advantages of having a wide 3 dB axial ratio (AR) bandwidth of 57.4%, achieving a good AR smaller than 2 dB in most areas of the frequency range. The design of the antenna follows a multi-objective optimization procedure that applies computational power rather than human tuning. A comparison of the optimized antenna design with other wideband CP antennas in the literature shows that it has advantages of having a smaller physical size in the cross-sectional area than the antennas with multiple feeding structures and a wider operating bandwidth than all the compared antennas.

Size-Reduced Rectangular Patch Hybrid Coupler Using Patterned Ground Plane

This paper presents, for the first time, the design of a size-reduced rectangular patch hybrid coupler. Different types of compact rectangular patch hybrid couplers with different ground plane patterns are described. For demonstration, two compact rectangular patch hybrid couplers are designed to operate at 3.5 GHz. They are measured to have 30.1% and 33.3% bandwidth with 67.3% and 72.3% size reduction compared with the optimized one without patterned ground plane.

Novel Active Quasi-Circulator With Phase Compensation Technique

A novel active quasi-circulator using phase compensation technique for wideband isolation is proposed. It is formed by configuring three transistors with a complimenting phase shifter for equalization. It provides wideband frequency operation with sufficient return loss and isolation between ports without the need for passive filters. This compensation technique minimizes the circulators size compared with conventional ferrite circulators and is compatible with monolithic microwave integrated circuit technology. Experimental results show that the proposed quasi-circulator has insertion losses around 0 dB, return losses better than 10 dB at each ports and minimum isolation around 15 dB from 0.8 to 2.2 GHz. Good agreement is obtained between simulation and experimental results.

Design of Broadband Hybrid Coupler With Tight Coupling Using Jumping Gene Evolutionary Algorithm

This paper presents the design procedure for complex RF circuits using the Jumping Genes Evolutionary Algorithm (JGEA). Due to the complex and stringent requirements for industrial environments, it is not an easy task to obtain a good design in which irregular structures are always needed. In this paper, JGEA has, however, demonstrated its excellent ability in practical RF circuit design compared with other algorithms. For demonstration, it was used in the design of a slot-coupled 3-dB hybrid coupler operating in the popular Industrial, Scientific and Medical application frequency band with small amplitude imbalance, low cost, and small size.

Circular Sector Patch Hybrid Coupler With an Arbitrary Coupling Coefficient and Phase Difference

This paper presents, for the first time, a patch coupler configuration that can be designed with an arbitrary coupling coefficient and phase difference at the output ports. Four circular sector patches are combined to form the patch coupler resulting in ease of design and fabrication. To demonstrate and verify this, a patch quadrature coupler configuration is proposed to realize a wide range of coupling coefficients by adjusting the radii of each quadrant. To extend this concept of an arbitrary coupling coefficient for 180