Lap K. Yeung

A compact second-order LTCC bandpass filter with two finite transmission zeros

A novel implementation and associated design formula for a compact low-temperature cofired ceramics (LTCC) lumped-element second-order bandpass filter are proposed in this paper. The filter schematic that provides two finite transmission zeros is well known. It is shown in the paper that the filter schematic is built on a pair of conventional inductive coupled resonator tanks with a feedback capacitor between input and output. While revealing its working mechanism both graphically and mathematically, a simple design procedure for such a compact filter is also given. The proposed filter has been implemented in a six-layer ceramic substrate using LTCC technology, showing promising application potentials in miniaturized mobile terminals and Bluetooth RF front-ends. The measured results agree very well with the full-wave electromagnetic designed responses.

An LTCC balanced-to-unbalanced extracted-pole bandpass filter with complex load

In this paper, the fundamental characteristics of a novel third-order RF balanced-to-unbalanced filter, namely, a balun filter, for integrated RF module applications are presented. This center-tapped transformer-based new device works concurrently as a balun, an extracted-pole bandpass filter, and a matching network. As coupled resonant tanks are employed to perform the balun type of operation, traditional coupled-resonator filter theory can thus be used to design and analyze such a new device. Moreover, an extracted-pole technique is used not only for creating a transmission zero, but also provides a capability to match the filter with a complex load. In addition to providing a simple design procedure for the device, its working mechanism is also revealed mathematically. Specifically, return-loss sensitivity with respect to each resonator admittance and complex load matching capability are discussed in details. This balun filter has been implemented in a multilayered low-temperature co-fired ceramic substrate, demonstrating its promising potentials in miniaturized RF front-end modules. Experimental measurements are also presented to validate the theory and computer simulations.

A Dual-Band Coupled-Line Balun Filter

In this paper, a new type of device called dual-band coupled-line bandpass balun filter is presented. Based on the traditional coupled-line filter theory and Marchand balun configuration, a new device with both filter-type, as well as balun-type characteristics is proposed. The new device utilizes -type transmission-line stepped-impedance resonators to achieve a dual-band operation. Besides providing a simple design procedure for the device, its working mechanism is also revealed mathematically. A prototype balun filter operating at 2.4 and 5.8 GHz has been realized using traditional printed circuit board technology to validate the proposed concept and theory, showing promising application potentials for future multiband RF wireless transceiver modules. Experimental measurements show good agreement with analytical and computer simulations.

A Compact Dual-Band 90° Coupler With Coupled-Line Sections

A new dual-band 90° coupler using coupled transmission lines is proposed in this paper. As the coupler consists of only three quarter-wave coupled-line sections, it occupies less circuit area as compared to other existing dual-band branch-line couplers. A desired dual-band operation can be achieved by proper design of the coupling level for those coupled-line sections. Moreover, the couplers configuration contains a degree of freedom so that its design is “customizable,” allowing itself to be conveniently realized on a variety of circuit and substrate technologies. As a result, it is suitable for use in many practical applications.

A Coupled Resonator Decoupling Network for Two-Element Compact Antenna Arrays in Mobile Terminals

A new concept for decoupling two coupled antenna elements in a broad band using a coupled resonator decoupling network (CRDN) is proposed for the first time. A synthesis and design theory of a CRDN is presented. Based on the admittance parameters of a given antenna array, a set of required rational functions and, consequently, the coupling matrix for a second-order decoupling network is obtained analytically. To prove the concept, two prototypes using microstrip resonators are designed and experimentally studied. Measurement results have demonstrated that an isolation improvement of more than 10 dB can be achieved within more than 15% bandwidth in both examples. The benefits of using a CRDN for different levels of isolation in a MIMO terminal are investigated through experiments and simulations. The results have shown that, as compared to the existing decoupling scheme using a lumped element, the proposed CRDN scheme can significantly increase the radiation efficiency, reduce the correlation, improve the channel capacity, and above all enhance the throughput of a MIMO terminal. The technique is general and can be applied to both symmetric and asymmetric arrays.

Mode-Based Beamforming Arrays for Miniaturized Platforms

In this paper, a new and practical mode-based array concept is proposed. The key principle of this mode-based approach is the use of orthogonal radiation modes existing in highly coupled arrays as individual information channels so as to avoid mutual coupling and correlation. Consequently, mode-based arrays can be very compact in size but without suffering undesired effects such as impedance mismatch or pattern distortion. While providing a general theoretical discussion for this mode-based approach, a practical application example, namely, a compact electronically scanning array module is developed. With a suitable signal combining algorithm, the module is capable of forming and full 360deg scanning of a high-gain radiation pattern in the azimuth plane. An experimental prototype has been fabricated on a traditional printed circuit board to validate the practicability of the proposed concept. Measurement results obtained are in good agreement with theoretical simulations, showing promising potential of mode-based array modules for modern miniaturized wireless devices.

Generalized Partial Element Equivalent Circuit (PEEC) Modeling With Radiation Effect

In this paper, a new frequency-domain formulation of the partial element equivalent circuit (PEEC) model incorporating the concept of generalized complex partial inductance and pure real capacitance is introduced for modeling of 3-D structures, to which the radiation effect is not negligible. Unlike conventional PEEC-based models, the proposed formulation accounts for the radiation effect by introducing physically meaningful complex-valued inductors and pure real-valued capacitors. In essence, the imaginary part of such an inductor represents a frequency-dependent radiation resistance. Having introduced the complex inductance, there is no inversion of the complex matrix of coefficients of potential, which is not physically meaningful and inevitably creates negative resistance. It is proven in this paper that the imaginary part of the generalized complex inductance for a short dipole exactly reflects the radiation resistance of the dipole. Several numerical examples are given to validate the proposed theory. The results obtained are in good agreement with those from commercial full-wave EM solvers, showing the potential of this technique for analyzing and designing high-frequency and high-speed electronic devices.

An integrated RF balanced-filter with enhanced rejection characteristics

In this paper, a new and simple 2.4-GHz third-order integrated RF balanced-filter for LTCC-based applications is proposed. This device is derived from the basic center-tapped transformer circuit and works as a balun as well as a bandpass filter at the same time. According to the center-tapped transformer representation, three coupled resonant tanks are used to perform the balun-type operation. Thus, with only minor modifications, a balun having specific bandpass filtering characteristics can be designed by the use of traditional coupled-resonator filter theory. In our case, a third-order Chebyshev filtering balun is designed and implemented. Furthermore, a transmission zero at 1.9-GHz is introduced to its transmission response by means of the extracted-pole technique. Experimental measurements show good agreement with computer simulations.

PEEC Modeling of Radiation Problems for Microstrip Structures

In this work, an accurate radiation model for the partial element equivalent circuit (PEEC) technique is introduced for modeling of microstrip structures. By making use of the concept of generalized complex inductance proposed recently for the free-space case, an accurate decomposition of the radiation resistance for a small dipole on microstrip substrate is derived for the first time using PEEC. Using the semi-analytical Greens functions for microstrip substrates, the imaginary part of this complex inductance can be shown to represent a frequency-dependent resistance containing contributions from spatial radiations (spherical and lateral) and surface waves (cylindrical). Hence, depending on how the structure of interest is divided into meshes, an equivalent circuit network of “distributed” radiation resistances can be obtained. Two numerical examples have been carried out to validate the model. Results obtained are in good agreement with those from commercial full-wave electromagnetic (EM) solvers, showing the potential of the proposed model for representing high-speed/high-frequency microstrip structures and antennas in the network realm.

A Dual-Band Balun Using Broadside-Coupled Coplanar Striplines

In this paper, a dual-band balun is presented. Based on the traditional Marchand balun configuration, this device utilizes a pair of lambda4 coupled-line sections and a single lambda4 open-circuit stub to achieve a dual-band balun-type function. An experimental prototype, operating at both 2.4- and 5.8-GHz bands, has been realized on a traditional printed circuit board using the broadside-coupled asymmetric coplanar stripline technique. Experimental measurements show good agreement with full-wave computer simulations, showing good potentials for dual-band/multiband RF front-end modules.