Conventional Rat-race Coupler Research Articles

A Compact Rat-Race Coupler with Harmonic Suppression for GSM Applications: Design and Implementation Using Artificial Neural Network.

In this paper, a compact microstrip rat-race coupler at a 950 MHz operating frequency is designed, simulated, and fabricated. New branches are proposed in this design using high-/low- impedance open-ended resonators. In the conventional rat-race coupler, there are three long λ/4 branches and a 3λ/4 branch, and they occupy a very large area. In the presented designed, three compact branches are proposed for use instead of three λ/4 branches and an ultra-compact branch is suggested for use instead of the 3λ/4 branch. Additionally, an artificial neural network (ANN) approach is incorporated to improve the performance of the resonators using a radial basis function (RBF) network. The proposed compact structure has achieved a reduction of more than 82% compared with the size of the conventional coupler structures. Additionally, the proposed coupler can suppress the 2nd up to the 5th harmonic to improve the performance of the device.

RF Rectifiers With Wide Incident Angle of Incoming Waves Based on Rat-Race Couplers

This article presents a radio frequency (RF) rectifier with a wide incident angle of incoming waves, based on a rat-race coupler (RRC). Two identical sub-rectifiers replace the two load circuits of the conventional RRC. When compared with the previous Wilkinson power combiner (WPC)-based rectifier, the proposed topology advances with a smaller variation in power conversion efficiency (PCE) over the incident angle. In addition, it simplifies the matching network (MN) design and enables a lower input return loss due to the fully symmetric circuitry between 0° and 180°. Furthermore, it allows a higher design flexibility on the rectifier topology. For validation, we designed and fabricated two wide-angle rectifiers, one working at single band (2.45 GHz) and the other at dual band (0.9 and 2.4 GHz). The single-band rectifier achieved a 67.3% peak PCE and 7.9% efficiency variation within the 0°–360° incident angle range. For the dual-band rectifier, the peak PCE is 78.4% and 70.2%, while the variation is 4% and 8.8%, for 0.9 and 2.4 GHz, respectively. The PCE variation is the smallest among previous works.

Filtering rat‐race couplers with impedance transforming characteristics based on terminated coupled line structures

In this study, a series of rat-race couplers with bandpass filtering responses and impedance transforming characteristics are presented based on novel coupled-line structures. Firstly, a novel filtering rat-race coupler core circuit is proposed by introducing coupled-line structures into conventional rat-race coupler. Then, a series of rat-race couplers with enhanced filtering responses and stopband rejections are constructed by employing various types of impedance transformers. The even- and odd-mode methods are adopted to explain the operating mechanisms. Finally, a filtering rat-race coupler prototype with a fractional bandwidth of 35.2% is designed and measured. The measured results show high passband selectivity, good out-of-band rejection and isolation performances, which is attractive for practical application.

Wideband Printed Ridge Gap Rat-Race Coupler for Differential Feeding Antenna

In this paper, a wideband 3 dB hybrid 180° rat-race coupler is introduced in the printed ridge gap waveguide technology. It has simultaneous wide matching and isolation bandwidth with low output amplitude imbalance. It operates in the millimeter wave band from 25.8 to 34.2 GHz (27.96%) with 15 dB return loss and isolation, and ±0.5 dB output amplitude imbalance. The proposed design employing an open stub at the middle of the $3 \lambda /4$ branch line and quarter wavelength lines at all the ports of the coupler. The objective of the added open stub is to separate the output ports amplitudes around the -3 dB level by certain values depending on the required amplitude imbalance. The analytical derivation for the role of the added open stub is presented along with a parametric study on its effect on amplitude imbalance, matching, and isolation. This results in having two intersection points for the output ports instead of one of the conventional coupler and hence the amplitude imbalance bandwidth increases. The objective of the added quarter wavelength lines is to improve the matching and isolation bandwidths. First, the conventional rat-race coupler is presented and a bandwidth of 14.25% at 30 GHz is achieved. After that the rat-race with the added quarter wavelength lines is presented to illustrate the objective of the added quarter wavelength lines and a bandwidth of 19.44% is achieved. Finally, the rat-race with the quarter wavelength lines and the added stub is presented and a prototype is fabricated and measured. The s-parameters measurements are in a good agreement with the simulated ones.

Reply to “Comments on ‘A Theorem on Asymmetric Structure-Based Rat-Race Coupler”’

The theorem proposed in the original article ( IEEE Microw. Wireless Compon. Lett. , vol. 25, no. 3, pp. 145–147, Mar. 2015.) regarding the replacement of six quarter-wavelength lines of conventional rat-race coupler (RRC) using asymmetric two-port networks (TNs) is absolutely correct. This letter will further illustrate the concept of single-frequency equivalence of the conventional RRC using asymmetric TNs.

A Theorem on Asymmetric Structure Based Rat-Race Coupler

An asymmetric structure is in general never equivalent to a quarter-wavelength (symmetric) transmission line. However in this letter a theory has been derived, wherein each of the six quarter-wavelength transmission lines of a conventional rat-race coupler can be replaced by any arbitrary asymmetric structure connected in identical orientation. The theorem exploits the mirror-symmetry of a rat-race coupler, even when the asymmetric structure is used as its building block. It is also observed that every asymmetric structure has an equivalent frequency independent symmetric representation when used in a rat-race coupler. Asymmetric-T has been used as an example of the asymmetric-structure to demonstrate the accuracy of the theory and has been compared with that of the conventional and existing asymmetric-T based couplers.

A compact microstrip rat-race coupler constituted by nonuniform transmission lines

In this work, a step-by-step development of a compact microstrip rat-race coupler (RRC) has been presented and discussed. A high degree of miniaturization has been obtained by substituting six quarter-wavelength uniform atomic building blocks of a RRC by their nonuniform counterparts. The miniaturization procedure has been real- ized in three progressive steps: (i) the first layout solution of a miniatur- ized RRC has been acquired using an accurate mathematical model of a nonuniform transmission line (NUTL); (ii) the second layout solution has been obtained by a manual refinement and electro-magnetic (EM) fine-tuning of the NUTL geometry aimed at the utilization of the interior of the RRC in a highly efficient manner; (iii) the final layout, occupying only 8.5% estate area in comparison to a conventional RRC, is the result of the EM optimization. The experimental results confirm the theo- retical predictions, proving the vital usefulness of the approach. V C 2014

Photonic crystal based rat race coupler for optical applications

In this paper photonic crystal based rat race couplers having circular and/or elliptical rods are proposed which exploit the photonic band gap effect. 2D simulations of the proposed structures are also carried out using FDTD method. The effects of change of the shapes of rods, refractive index of wafer and wavelength of operation are also studied. It is observed that the performance of rat race coupler with all elliptical rods is similar to the conventional rat race coupler operating at microwave frequency. By changing the orientation of the elliptical rods in one of the proposed structures, inverse behaviour of that of conventional rat race coupler is observed. These structures can therefore find applications in power combiners/dividers at optical frequencies.

Miniaturized wide-band rat-race coupler

New designs of wide-band rat-race couplers are proposed. The wide-band operation is achieved with the use of the microstrip nonuniform transmission line sections for the branches of the conventional rat-race coupler. The design formulas are developed using ABCD matrix and the even- and odd-mode analysis. The theoretical analysis has been verified by measurements of the two manufactured wideband rat-race couplers, one operate within 0.85-1.92 GHz and other within 1.55-3.55 GHz frequency range with the equal nor- malized characteristic impedance functions. For both fabricated couplers, the isolation pa- rameter is better than 15 dB over a 77% relative bandwidth. Also, it is shown that the designed wide-band rat-race coupler can be realized in higher frequency bands with the fixed fractional bandwidth. V C 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 00:000- 000, 2012.

Compact substrate-integrated waveguide bandpass rat-race coupler and its microwave applications

A reduced size rat-race coupler incorporating a bandpass frequency response characteristic is presented and designed based on substrate-integrated waveguide (SIW) technology. By use of electric- and magnetic-coupling structures between adjacent SIW cavity resonators, a conventional rat-race coupler and a bandpass filter with a 200-MHz bandwidth at a centre frequency of 7.75 GHz can be integrated as one component resulting in miniaturisation. A design process based on the coupled-resonator network is introduced to synthesise such a bandpass coupler with desired bandwidth, return loss and coupling. A Butler matrix and a six-port junction with bandpass response are then developed based on the proposed rat-race coupler. They represent excellent candidates for miniaturised transceiver and direct conversion systems. The measured results are in good agreement with the simulated predictions.

Novel Compact Dual-Band Rat-Race Coupler Combining Fractal Geometry and CRLH TLs

A super compact fractal-shaped composite right/left handed (CRLH) rat-race coupler (RRC) is proposed for the first time by skillfully combining two circuit schematics of the RRC operating at two arbitrary frequencies. For dual-band (DB) purpose, novel circuit schematics of RRC are deducted, and close-form formula and design procedures are derived in detail. The CRLH transmission line (TL) consists of lumped elements for the left handed part and Koch-shaped microstrip lines (MLs) for the right handed part. Since conventional RRC exhibits two types of unique branches, the DB design often suffers a tedious process. By employing the CRLH TL, the realization of a DB RRC becomes much easier. Moreover, constructing the microstrip lines as Koch curves enables the compactness of the circuit. For verification, a coupler operating at 0.75 and 1.8 GHz is fabricated and measured. Consistent results between simulation and measurement have confirmed the design and shown that the RRC with an area of 10.2% of its conventional counterpart owns excellent in-band performances.

Size Miniaturized Rat-Race Coupler Using Open Complementary Split Ring Resonator

In this paper, a rat-race hybrid coupler based on an open complementary split ring resonator (OCSRR) is presented. By embedding the OCSRR in the microstrip transmission line, slow-wave effect is introduced to achieve size reduction. The proposed rat-race coupler size is 37% smaller than the conventional rat-race coupler. Besides, the proposed coupler provides better third harmonic suppression up to 35dB. The simulated results are compared with the measured data and good agreement is reported.

A novel tri‐band rat race coupler with T‐shape step impedance transformers

AbstractA novel tri‐band 3‐dB rat race coupler operating at two arbitrary frequencies and their mean frequency is presented through replacing quarter‐wavelength impedance transformers in a conventional rat race coupler by T‐shape step impedance transformers, which can be equivalent to quarter‐wavelength impedance transformers at the three frequencies. Closed‐form design equations are derived. For verification, a microstrip tri‐band 3‐dB rat race coupler operating at 1.5/3.5/5.5 GHz is fabricated, aimed to cover the 1.5 GHz GPS band, and the 3.5/5.5 GHz WiMAX bands. Simulated and measured results are in good agreement. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1240–1244, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25186

Miniaturized broadband microstrip fractal rat‐race coupler with shunt stubs

AbstractMiniaturized broadband microstrip rat‐race coupler is implemented by incorporating space filling fractal structure with microstrip shunt open stubs. The proposed design occupies just 18.5% of the conventional rat‐race coupler. Fractal structure is utilized to reduce the area occupied by the conventional rat‐race coupler and shunt stubs are incorporated to shrink the linear dimensions of fractal rat‐race coupler. Performance of the proposed rat‐race coupler is comparable with that of a conventional rat‐race coupler. Measurement results are compared with simulations to validate the design. This new type of rat‐race coupler operates over 33% bandwidth (1.1–1.5 GHz) with matchingand isolation values of better than 20 dB over most of the band. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 289–292, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24897

Microstrip rat‐race couplers with predetermined miniaturization and harmonic suppression

AbstractIn this letter, design of compact size rat‐race coupler (RRC), based on impedance‐controlled simple transmission line structure is proposed for predetermined harmonic suppression. The present approach has the advantage that within the fabrication limit of high‐impedance lines, a large number of harmonics are suppressed. Design guidelines are provided. Theoretical predictions are verified by implementing a prototype microstrip RRC, with upto twelfth harmonic of the operating frequency suppressed along with 75% size reduction compared with the conventional RRC. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 30–34, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24832

Design of dual-band rat-race couplers

New designs of dual-band rat-race couplers are proposed. The desired dual-band operations are realised by adding tapped open stubs to the branches of the conventional rat-race coupler. It is found that these stubs can be implemented in two different ways to satisfy the conditions for dual-band applications, which results in two types of designs. The two different designs can be separately used to achieve low and high ratios between two operating bands, therefore providing enhanced design flexibility. The design formulas are developed using ABCD matrix and the even-odd mode analysis. On the basis of the derived design equations, a type I rat-race coupler working at 1 GHz/3.5 GHz and a type II coupler working at 2 GHz/5 GHz are devised and fabricated on Rogers's RO3006 printed circuit boards. Measurement results prove the design concepts.

Compact slow-wave microstrip rat-race ring coupler

A compact slow-wave microstrip rat-race ring coupler is presented. The new structure effectively reduces the occupied area to 8% of the conventional rat-race ring coupler due to the slow-wave effect. The design is validated both by using the full-wave electromagnetic simulator and by measurement.

Miniaturized Rat Race Coupler With Suppression of Spurious Passband

A new hybrid ring coupler design is devised for circuit miniaturization based on the periodic stepped-impedance ring resonator structure. The circuit has an area of 21.5% of a conventional rat race coupler and no passband up to the sixth harmonic of the design frequency. The designs are validated by comparing measured four-port parameters with the simulated results

Compact rat-race hybrid coupler using meander space-filling curves

A new family of compact rat-race hybrid couplers is proposed. The novelty of the new structures stems from the idea of utilizing the vacant space inside the conventional rat-race coupler in increasing the rat-race ring path. The couplers have been designed to operate at 1.8 GHz. The size of the new structures is 70% less than conventional rat-race hybrid coupler at the same center frequency. The measurements are in good agreement with the designed values. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 606–609, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21421