Kian Sen Ang

Analysis and design of miniaturized lumped-distributed impedance-transforming baluns

Conventional distributed baluns employ /spl lambda//2 transmission lines or /spl lambda//4 coupled lines. By adding only one or two lumped capacitors, the required coupled-line lengths of a new balun structure can be made as short as /spl lambda//24. Design curves for these miniaturized impedance-transforming baluns are derived using a systematic even- and odd-mode analysis technique. This approach also provides valuable insight into the tradeoffs between coupled-line lengths, number of capacitors, bandwidth, and impedance-transforming ratios. Experimental results of a single-capacitor balun with /spl lambda//9 coupled lines and a two-capacitor balun with /spl lambda//24 coupled lines will be presented. Both baluns achieved 0.5-dB amplitude balance and 5/spl deg/ phase balance, with over 10-dB return loss from 1.1 to 1.6 GHz.

A derivation of a class of 3-port baluns from symmetrical 4-port networks

This paper describes an approach in deriving the general conditions that need to be satisfied for a class of 3-port baluns. This is done by analyzing the behavior of a general symmetrical 4-port network when one of the ports is terminated with an arbitrary impedance. These conditions will be useful in devising new balun structures and in deriving exact design equations for such baluns. Examples will be presented for some known and new baluns in this class. These insights have also made the cascading of multisection baluns possible by specifying the overall requirements for the cascaded structures. Based on these results, a 3-section, Marchand-type, coupled-line balun has been designed and fabricated. Good agreements between simulation and measured results have been obtained, thereby verifying the validity of the design equations.

Multisection impedance-transforming coupled-line baluns

A new class of multisection impedance-transforming coupled-line baluns is presented in this paper. It is based on the quarter-wavelength coupled-line balun. By cascading several coupled and uncoupled-line sections, broad-band baluns with good amplitude and phase balance can be realized using simple microstrip coupled lines. The resulting circuit has a simple structure with minimal discontinuities that is highly suited for very high-frequency applications. Simple design equations and experimental verifications will be presented. Using microstrip coupled sections with even-mode impedance of 159 /spl Omega/, the fabricated balun achieved 0.5-dB amplitude balance over 30% bandwidth. With higher even-mode impedance, almost perfect amplitude balance was achieved over 100% bandwidth.

A broad-band quarter-wavelength impedance transformer with three reflection zeros within passband

A new impedance transformer employing a transmission line and a coupled-line section is presented in this paper. It is physically a quarter-wavelength long, but can achieve three reflection zeros within the passband. Therefore, broad bandwidths can be obtained for a wide range of impedance ratios. The location of the reflection zeros can be synthesized through the transmission line and coupled-line parameters. Design curves for the transformer synthesis have been obtained by solving the design equations directly. Using these results, a stripline impedance transformer has been implemented. This 50-110-/spl Omega/ impedance transformer achieved over 25-dB return loss from 0.6 to 1.6 GHz.

Analysis and design of coupled line impedance transformers

Impedance transformers employing coupled line sections that are less than quarter wavelengths are presented in this paper. Exact solutions relating the coupled line parameters and arbitrary impedance transformation ratios are derived. This is unlike previous coupled line transformers, which were designed based on electromagnetic simulations and provide only impedance transformation ratios of 1:4. Various design curves demonstrating a wide range of practical coupled line parameter values are presented and validated with experimental results. A 50 /spl Omega/ to 170 /spl Omega/ impedance transformer using /spl lambda//8 coupled line section achieved over 10 dB return loss from 0.5 to 0.9 GHz.

A wide-band monopulse comparator with complete nulling in all delta channels throughout sum channel bandwidth

A broad-band monopulse comparator with complete nulling in the three delta channels throughout the sum channel bandwidth is presented in this paper. It is based on a new broad-band 180/spl deg/ hybrid with amplitude and phase balances that are theoretically perfect and frequency independent. Using this 180/spl deg/ hybrid, a microstrip monopulse comparator was realized on a low-cost FR-4 board. The comparator was fully characterized by its eight-port S-parameters to generate the sum and delta channel frequency responses. Over 30-dB null depths was achieved in the three delta channels across the sum channel passband from 1.1 to 3.3 GHz.

A broadband quarter-wavelength impedance transformer using vertically installed planar coupler

A broadband quarter-wavelength impedance transformer using a vertically installed planar (VIP) coupler is presented. A wide range of impedance transformation ratios and bandwidths can be achieved using this design. A 50 Ω to 100 Ω impedance transformer covering 0.7 GHz to 2 GHz is designed and implemented using the VIP. The measured results agree well with the simulation results. The design curves generated are useful for the design of this type of impedance transformer.

Geometrical stability criteria for two-port networks in invariant immittance parameters representation

This paper has presented the formulation of geometrical stability criteria for linear two-port networks in immittance parameters representation. The formulation has been carried out in terms of a more convenient set of S-parameter conversion formulas. A general expression of geometrical stability parameter has been obtained which takes the same invariant form for all immittance (z, y, h, g) parameters. Such expression finds more convenience in certain circuit stabilization, equivalent circuit modeling, feedback analysis and three-port network extension. The formulation herein may be extended readily to other criteria involving alternative stability parameters.

Multisection Vialess Baluns with Coupled-Line Impedance Transformers

Multisection vialess baluns are proposed by cascading several lambda/4 edge-coupled lines. Without needing any via-hole or ground connection, these vialess baluns are simply implemented on microstrip structures. With the backside aperture, the even-mode impedance of coupled microstrip lines is raised beyond 280 Omega. Taking advantage of multisection coupled line approach, the eventual even-mode impedance can achieve as small as 2 Omega, thus satisfactorily meeting the requirements of lambda/4 coupled line baluns with open-circuited terminals. Three- and five-section vialess baluns are designed and the predicted performances are validated by experiment. In a wide frequency range (1.8-3.6 GHz), the measured amplitude imbalance is less than 0.4 dB and phase imbalance is within plusmn5deg

Impedance-transforming, coupled-line 180/spl deg/ hybrid rings with frequency independent characteristics

A new impedance-transforming, 180/spl deg/ hybrid-ring using coupled-lines is presented. Its amplitude and phase balances as well as isolation between diagonal ports are theoretically perfect and frequency independent. This was achieved without using physical phase inverters on uniplanar structures. Instead, the ideal phase inversion between coupled-line structures is exploited. Simple design equations will be derived and validated by experimental results.