Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

Novel design equations are proposed for the 3-dB microstrip branch-line coupler with a wide passband, utilizing multisectional branch lines. In addition, the proposed method makes it possible to reduce the internal impedance levels of branch-line couplers so they may be physically constructed by microstrip lines. Further, in terms of measured results, there is a wide bandwidth >70%. Synthesis of the 3-dB branch-line coupler is described in details as well. Good agreement between theoretical calculation and measurement validates the proposed method.

Design of Wide Passband Microstrip Branch-Line Couplers With Multiple Sections

With the rapid development of modern communication and radar technology, there is a need for the miniaturization, planarization, and modularization of microwave and millimeter-wave (mm-wave) systems, without losing excellent performance and reliability. The transmission line is the most basic component of microwave and mm-wave circuits and systems, and its characteristics-including loss, size, integration, cost, and weight-directly or indirectly affect the performance of the entire circuit and system. Commonly used transmission lines [1] include nonplanar transmission lines, such as a metal waveguide and coaxial line, and planar transmission lines, such as a microstrip, strip line, coplanar waveguide, and slot line.

Recent Progress in SISL Circuits and Systems: Review of Passive and Active Circuits Demonstrating SISL's Low Loss and Self-Packaging and Showcasing the Merits of Metallic, Shielded, Suspended Lines

We propose a new design methodology to broaden the bandwidth of a single-section 90° branch-line coupler (BLC) with arbitrary coupling level. The method used here to broaden the BLC bandwidth is to replace conventional uniform transmission lines that would never be feasible in many implementations with nonuniform lines governed by a truncated Fourier series. Based on how impedances are profiled, the fractional bandwidth of a single-section 90° 3-dB BLC is extended to 57%, and the realization of broadband BLCs with predefined coupling levels is also possible. Furthermore, higher order harmonics are suppressed by enforcing BLC $S$ -parameters to match the design requirements only at a given frequency range. A systematic design approach based on the even-odd mode analysis is first presented. Then, three examples of 3-, 6-, and 9-dB BLCs are demonstrated at a 3-GHz center frequency. The obtained theoretical response, supported by full-wave electromagnetic simulations and measurements, justifies the design concept.

Impedance-Varying Broadband 90° Branch-Line Coupler With Arbitrary Coupling Levels and Higher Order Harmonic Suppression

In this paper, a compact coupled-line trans-directional (TRD) coupler with wide continuous frequency tuning range and superior performance is presented. The proposed tunable TRD coupler is composed of three coupled lines, two shunt stubs, and three types of varactors. By providing suitable reverse bias voltages on these varactors, the operating frequency of the proposed TRD coupler can flexibly be adjusted as desired. Moreover, better impedance match and port isolation are maintained at all tuning center frequencies. A theoretical analysis using the even–odd mode theory is presented to clarify the influence of the design parameters on the minimum and maximum operating frequencies. It is exhibited that the proposed TRD coupler has approximately 150% frequency tuning range in ideal conditions. Due to the manufacturing limitation, a microstrip TRD coupler with a tunable frequency of 1.0–2.5 GHz (85.7%) is designed and fabricated. The measured results show that the proposed TRD coupler can be tuned from 1.0 to 2.5 GHz with more than 27 dB return loss and more than 35 dB isolation in the entire tuning range, agreeing well with the simulation results.

A Compact Trans-Directional Coupler With Wide Frequency Tuning Range and Superior Performance

Novel design equations and examples of the modified 3-dB microstrip tandem coupler are presented. In order to obtain a wide passband, couplers with a single pole/dual poles at the return loss are proposed. Compared to the conventional couplers such as Lange couplers and parallel coupled line couplers, high-impedance transmission lines and narrow coupling gaps are not required for the proposed microstrip coupler. In terms of measured results, there is a wide bandwidth of more than 70%. Moreover, good agreement between theoretical predication and measurement validates our proposed structure.

Ko-Cheng Hsu

Papers

Design of Wide Passband Microstrip Branch-Line Couplers With Multiple Sections

Design of the Modified Planar Tandem Couplers With a Wide Passband