Both branch-line and rat-race couplers are easily realized using planar circuit technology as they employ only transmission lines without additional components. However, as the electrical lengths of the transmission line elements are either 90/spl deg/ or 270/spl deg/, such couplers consume a significant amount of circuit area. This paper shows the development of branch-line and rat-race couplers that use artificial transmission lines (ATLs) in place of conventional transmission lines resulting in significant size reduction. As the ATLs are constructed entirely from microstriplines, the couplers are easily fabricated using conventional printed-circuit processes. The design formulas developed for the ATLs are explicit. Full-wave simulation and experimental results were used to confirm the design approach for hybrids operating at 1.8 GHz. The frequency response of the proposed hybrids is similar to conventional hybrids.

/pdf/compact-planar-microstripline-branch-line-and-rat-race-4w9wmoer09.pdf

Compact planar microstripline branch-line and rat-race couplers

Composite right/left-handed (CRLH) substrate integrated waveguide (SIW) and half mode substrate integrated waveguide (HMSIW) leaky-wave structures for antenna applications are proposed and investigated. Their propagation properties and radiation characteristics are studied extensively. Their backfire-to-endfire beam-steering capabilities through frequency scanning are demonstrated and discussed. These metamaterial radiating structures are realized by etching interdigital slots on the waveguide surface and the ground. The slot behaves as a series capacitor as well as a radiator leading to a CRLH leaky-wave application. Four antennas are fabricated, measured, and analyzed, including two balanced CRLH SIW designs characterized by single-side or double-side radiation, and two unbalanced HMSIW designs characterized by different boundary conditions. Antenna parameters such as return loss, radiation patterns, gain, and efficiency are all provided. Measured results are consistent with the simulation. All these proposed antennas possess the advantages of low profile, low cost, and low weight, while they are also showing their own unique features, like high directivity, quasi-omnidirectional radiation, miniaturized size, continuous beam-steering capabilities covering both the backward and forward quadrants, etc., providing much design flexibility for the real applications.

Composite Right/Left-Handed Substrate Integrated Waveguide and Half Mode Substrate Integrated Waveguide Leaky-Wave Structures

Although microfluidics has shown exciting potential, its broad applications are significantly limited by drawbacks of the materials used to make them. In this work, we present a convenient strategy for fabricating whole-Teflon microfluidic chips with integrated valves that show outstanding inertness to various chemicals and extreme resistance against all solvents. Compared with other microfluidic materials [e.g., poly(dimethylsiloxane) (PDMS)] the whole-Teflon chip has a few more advantages, such as no absorption of small molecules, little adsorption of biomolecules onto channel walls, and no leaching of residue molecules from the material bulk into the solution in the channel. Various biological cells have been cultured in the whole-Teflon channel. Adherent cells can attach to the channel bottom, spread, and proliferate well in the channels (with similar proliferation rate to the cells in PDMS channels with the same dimensions). The moderately good gas permeability of the Teflon materials makes it suitable to culture cells inside the microchannels for a long time.

https://www.pnas.org/content/pnas/108/20/8162.full.pdf

Whole-Teflon microfluidic chips

Analysis and design techniques for designing a lumped-element 3-dB quadrature coupler with wide-band flat coupling are proposed for microwave integrated-circuit/monolithic-microwave integrated-circuit applications. The proposed design technique can produce a coupler with flat coupling over 50% fractional bandwidth, which is wider than the conventional lumped-element design methods. A prototype consisting of a capacitive coupled high-pass network is designed and fabricated to verify the design concept. Measurement and simulation results closely correspond to each other.

Design of a wide-band lumped-element 3-dB quadrature coupler

A super-compact substrate integrated waveguide (SIW) directional coupler is proposed and demonstrated. This coupler consists of a simple cross-over of two SIW sections with two inductive metallic posts in a square junction, showing a cruciform. Attractive features including compact size and planar form make this coupler structure easily integrable in microwave and millimeter-wave planar circuits, especially in beam-forming networks. A 3-dB coupler operating at 24GHz is designed using HFSS, fabricated and measured. Characteristics of 15dB isolation and 90deg phase shift between the output and coupled ports are achieved over 18% bandwidth. Design considerations and simulated as well as measured results are presented and discussed.

Super-Compact Substrate Integrated Waveguide Cruciform Directional Coupler

This paper describes a novel Wilkinson power divider operating at two arbitrary different frequencies. The proposed divider consists of two-section transmission lines and a series RLC circuit connected between two output ports. The circuit parameters for a dual-band operation are derived by the even/odd mode analysis. Equal power split, complete matching, and good isolation between two output ports are numerically demonstrated. Dual-band and broadband Wilkinson power dividers can be successfully designed. Finally, verification of this design method is also shown by electromagnetic simulations and experiments.

Dual-Band Wilkinson Power Dividers Using a Series RLC Circuit

This paper suggests a very compact waveguide directional coupler with a tight coupling of 3-dB or so, which is composed of two cross H-plane rectangular waveguides having two metallic posts in the square junction and an inductive window at each port The metallic posts are set symmetrically along a diagonal line of the cross region mainly to make for the directivity properties, and the inductive windows are arranged properly at each input/output port near the junction to realize a matched state Actually, several couplers are successfully designed based upon this concept Additionally, the design procedure is validated by em-simulations (HFSS) and experiments The present coupler is marked by a compact coplanar structure, four right-angled ports and ease of realizing 3-dB coupling

Cruciform directional couplers in H-plane rectangular waveguide

Downsizing of microstrip coupled-line 3 dB forward (codirectional) couplers are proposed. An enlargement of the difference of the effective phase velocities for the cou- pled-modes is accomplished by loading a coupled micrstrip with periodic shunt capacitive stubs, and consequently the length of the coupled line section is considerably reduced to 18% of a tra- ditional coupled line section. Furthermore, a flat coupling, or a broadband performance, is achieved by use of asymmetrically loaded coupled line section. Finally, the design results are con- firmed both experimentally and numerically.

http://ieeexplore.ieee.org/iel5/10171/32491/01516900.pdf

Size-reduction of coupled-microstrip 3 dB forward couplers by loading with periodic shunt capacitive stubs

In this paper, we first describe a general design procedure of a twofold symmetric directional coupler. Next, we design four types of lumped-element quadrature 3 dB hybrids and try to improve the bandwidth of the performance in accordance with the present procedure. As a result, we realize a flat coupling over a fractional bandwidth of about 26 percent. Experimental verification is described also.

A design of lumped-element 3 dB quadrature hybrids

This paper treats broadband branch-line couplers with arbitrary power split ratios utilizing microstrip series stubs as matching networks. Proposed series stubs are structurally integrated in input/output microstrip transmission lines. Based on the equivalent admittance approach, dual-band/wide-band characteristics with relative bandwidths of over 30 % can be obtained in the case of a coupler with a power split ratio of 1 to 5. Validity of this design procedure can be demonstrated by electromagnetic simulations and experiment.

http://ieeexplore.ieee.org/iel5/5606055/5614756/05616093.pdf

Isao Ohta

Papers

Dual-Band Wilkinson Power Dividers Using a Series RLC Circuit

Cruciform directional couplers in H-plane rectangular waveguide

Size-reduction of coupled-microstrip 3 dB forward couplers by loading with periodic shunt capacitive stubs

A design of lumped-element 3 dB quadrature hybrids

Broadband branch-line coupler with arbitrary power split ratio utilizing microstrip series stubs