Quadrature Coupler Research Articles

Broadband parallel‐coupled quadrature coupler with floating‐potential ground plane conductor

AbstractThe design of a parallel‐coupled directional coupler, which has a broadband performance, is presented. A floating‐potential ground plane conductor is used underneath the coupled region to relax the requirement for a narrow slot between the coupled lines and to improve the isolation and return loss performance of the device. The simulated and measured results show that the designed coupler exhibits a coupling of 3 ± 1 dB across the band 4–10.2 GHz, when the spacing between the coupled lines is 0.13 mm, which is easy to manufacture. This broadband coupling is accompanied by an isolation and return loss which are better than 15 dB across the band 3.1–10.6 GHz. The simulated and measured results show good phase stability and flat group delay across the ultra wideband. The designed device has a compact size with a dimension of 30 mm × 20 mm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2304–2307, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.23701

A 3-dB Quadrature Coupler Using Broadside-Coupled Coplanar Waveguides

A 3-dB quadrature coupler which combines the advantages of broadside-coupling and coplanar waveguide structure suitable for a single-layer printed circuit board (PCB) circuit design is proposed. Compared to the recently published broadside-coupled structures, the proposed coupler can easily be realized in a single-layer substrate by using PCB manufacturing processes to eliminate the effects of uncertain factors from a multi-layer substrate. With the operation bandwidth ranging from 2.1 to 2.7 GHz, the measured return loss and isolation are all better than 19dB, and the insertion losses and relative phase difference between the direct and coupled ports are at 3.2 plusmn 0.1 dB and 90 plusmn 0.6deg, respectively. The dimension of the coupler is 2.1 cm times 1.9 cm.

A Full-360$^{\circ}$ Reflection-Type Phase Shifter With Constant Insertion Loss

A new reflection-type phase shifter with a full 360deg relative phase shift range and constant insertion loss is presented. This feature is obtained by incorporating a new cascaded connection of varactors into the impedance-transforming quadrature coupler. The required reactance variation of a varactor can be reduced by controlling the impedance ratio of the quadrature coupler. The implemented phase shifter achieves a measured maximal relative phase shift of 407deg, an averaged insertion loss of 4.4 dB and return losses better than 19 dB at 2 GHz. The insertion-loss variation is within plusmn0.1 and plusmn0.2 dB over the 360deg and 407deg relative phase shift tuning range, respectively.

Vestigial dual-band quadrature branch line coupler with aligned phase and improved bandwidth response

Previous dual-band quadrature branch line couplers were either narrow band or had phases in the two bands that are not aligned. A vestigial dual-band quadrature branch line coupler is presented that is phase aligned and with one band that is broad, making it ideal for WLAN and other dual-band applications.

Broadband quadrature coupler with slotted ground plane

AbstractThe design of an edge‐coupled quadrature directional coupler, which has a broadband performance and relaxed coupled‐line spacing, is presented. A slotted ground plane is used underneath the coupled region in order to relax the requirement for a narrow slot between the coupled lines. The simulated and measured results show that the designed coupler exhibits a coupling of 3 ± 1 dB across the band 3.8 GHz to 9.8 GHz, when the spacing between the coupled lines is 0.12 mm. Without the slot in the ground plane, the spacing should be less than 0.001 mm to achieve the same value of coupling across that band. This broadband coupling is accompanied by an isolation and return loss in the order of 13 dB or better across the band 3–10 GHz. The designed device has a compact size with a dimension of 30 mm × 20 mm. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 328–331, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23080

Broadband fixed phase shifter for C‐band applications

AbstractThe design of a fixed phase shifter for C‐band applications is presented. The proposed device is composed of two parts: a quadrature 3‐dB directional coupler and the Wilkinson combiner. The quadrature coupler used in the proposed phase shifter is based on the edge‐coupled microstrip lines with a slotted ground plane to make the gap required between the coupled lines feasible. The simulated and measured results of the phase shifter show a 45° ± 5° fixed phase shift across the band 4–8 GHz with less than 1‐dB insertion loss and better than 12‐dB return loss at the centre of the C‐band. The designed device also shows a flat group delay, which enables its use in a narrow pulse transmission/reception and in the high data rate systems. The designed phase shifter has a compact size with dimensions of 30 mm × 30 mm. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 396–399, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23133

A New Planar Artificial Transmission Line and Its Applications to a Miniaturized Butler Matrix

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A miniaturized quadrature hybrid coupler, a rat-race coupler, and a 4 <formula><tex>$\times$</tex></formula> 4 Butler matrix based on a newly proposed planar artificial transmission line are presented in this paper for application in ultra-high-frequency (UHF) radio-frequency identification (RFID) systems. This planar artificial transmission line is composed of microstrip quasi-lumped elements and their discontinuities and is capable of synthesizing microstrip lines with various characteristic impedances and electrical lengths. At the center frequency of the UHF RFID system, the occupied sizes of the proposed quadrature hybrid and rat-race couplers are merely 27% and 9% of those of the conventional designs. The miniaturized couplers demonstrate well-behaved wideband responses with no spurious harmonics up to two octaves. The measured results reveal excellent agreement with the simulations. Additionally, a 4<formula formulatype="inline"><tex>$\,\times\,$</tex></formula>4 Butler matrix, which may occupy a large amount of circuit area in conventional designs, has been successfully miniaturized with the help of the proposed artificial transmission line. The circuit size of the Butler matrix is merely 21% of that of a conventional design. The experimental results show that the proposed Butler matrix features good phase control, nearly equal power splitting, and compact size and is therefore applicable to the reader modules in various RFID systems. </para>

A 5–6 GHz 1-V CMOS Direct-Conversion Receiver With an Integrated Quadrature Coupler

This paper describes a novel monolithic low voltage (1-V) CMOS RF front-end architecture with an integrated quadrature coupler (QC) and two subharmonic mixers for direct-down conversion. The LC-folded-cascode technique is adopted to achieve low-voltage operation while the subharmonic mixers in conjunction with the QC are used to eliminate LO self-mixing. In addition, the inherent bandpass characteristic of the LC tanks helps suppression of LO leakage at RF port. The circuit was fabricated in a standard 0.18-mum CMOS process for 5-6 GHz applications. At 5.4 GHz, the RF front-end exhibits a voltage gain of 26.2 dB and a noise figure of 5.2 dB while dissipating 45.5 mW from a 1.0-V supply. The achieved input-referred DC-offset due to LO self-mixing is below -110.7 dBm.

Design of a Reflection-Type Phase Shifter With Wide Relative Phase Shift and Constant Insertion Loss

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A reflection-type phase shifter with constant insertion loss over a wide relative phase-shift range is presented. This important feature is attributed to the salient integration of an impedance-transforming quadrature coupler with equalized series-resonated varactors. The impedance-transforming quadrature coupler is used to increase the maximal relative phase shift for a given varactor with a limited capacitance range. When the phase is tuned, the typical large insertion-loss variation of the phase shifter due to the varactor parasitic effect is minimized by shunting the series-resonated varactor with a resistor <formula formulatype="inline"><tex>$R_{p}$</tex></formula>. A set of closed-form equations for predicting the relative phase shift, insertion loss, and insertion-loss variation with respect to the quadrature coupler and varactor parameters is derived. Three phase shifters were implemented with a silicon varactor of a restricted capacitance range of <formula formulatype="inline"><tex>$C_{v,\min}=1.4$</tex> </formula> pF and <formula formulatype="inline"><tex>$C_{v,\max}= 8\ $</tex></formula> pF, wherein the parasitic resistance is close to 2 <formula formulatype="inline"><tex>$\Omega$</tex></formula>. The measured insertion-loss variation is 0.1 dB over the relative phase-shift tuning range of 237<formula formulatype="inline"><tex>$^{\circ}$</tex></formula> at 2 GHz and the return losses are better than 20 dB, excellently agreeing with the theoretical and simulated results. </para>

Design of ultra wideband 3DB quadrature microstrip/slot coupler

AbstractThis article presents the configuration and design method of a compact ultra wideband 3dB quadrature coupler employing a microstrip/slot technology. The proposed device uses two substrates with a common ground plane. It is formed by two identical multisection elliptical conducting strips, which are broadside coupled through a multisection elliptical slot in the ground plane. Results of simulation and measurements show that the coupler exhibits a coupling equal to 3 ± 1 dB for the band 2.3–12.3 GHz. The isolation and return loss are better than 23 dB across that band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2101–2103, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22674

Varactor-Tuned Dual-Band Quadrature Hybrid Coupler

A tunable dual-band quadrature hybrid coupler for mobile GSM bands (900 and 1800MHz) is proposed and characterized. The structure is composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and two pairs of open-ended stubs. Frequency tuning is achieved by modifying the electrical length of the open-ended stubs with varactor-diode capacitors. A dual-band tunability of 33% and 10% is obtained for the first and the second bands, respectively

A 3-dB Quadrature Coupler Suitable for PCB Circuit Design

A quadrature 3-dB coupler, which combines the advantages of a coplanar waveguide and microstrip line structure suitable for single-layer substrate printed circuit board (PCB) circuit design is proposed. As compared to the conventional Lange coupler, the proposed coupler with the advantages of increasing the coupled linewidths and coupling spacing without using extra bonding wires can solve the drawbacks of Lange coupler. In addition, the proposed structure can easily be realized in a single-layer substrate by PCB manufacturing processes to eliminate the effects and uncertain factors from a multilayer substrate. Good agreements between the simulation and measurement in the frequency range from 0.45 to 5 GHz can be seen. With the operation bandwidth ranging from 1.8 to 2.8 GHz, the measured results of the return loss are better than 18.2 dB and insertion losses of coupled and direct ports are approximately 3plusmn0.1 dB; the relative phase difference is approximately 89.8deg. The dimension of the circuit is 2.7 cm times1.6 cm times0.08 cm

A 90-nm CMOS Doherty Power Amplifier With Minimum AM-PM Distortion

A linear Doherty amplifier is presented. The design reduces AM-PM distortion by optimizing the device-size ratio of the carrier and peak amplifiers to cancel each other's phase variation. Consequently, this design achieves both good linearity and high backed-off efficiency associated with the Doherty technique, making it suitable for systems with large peak-to-average power ratio (WLAN, WiMAX, etc.). The fully integrated design has on-chip quadrature hybrid coupler, impedance transformer, and output matching networks. The experimental 90-nm CMOS prototype operating at 3.65 GHz achieves 12.5% power-added efficiency (PAE) at 6 dB back-off, while exceeding IEEE 802.11a -25 dB error vector magnitude (EVM) linearity requirement (using 1.55-V supply). A 28.9 dBm maximum Psat is achieved with 39% PAE (using 1.85-V supply). The active die area is 1.2 mm/sup 2/.

A new broadband monolithic passive differential coupler for K/ka-band applications

A new broadband monolithic passive quadrature differential coupler has been realized at millimeter-wave frequencies. The new coupler is implemented on a multidielectric layer structure to achieve a broadband performance from 15 to 45 GHz in a simple coplanar configuration. The coupler has been monolithically fabricated using the IBM SIGEHP (BICMOS 5HP) process. Measured return loss better than 20 dB, with an isolation of 15 dB, and adequate phase and amplitude mismatch have been achieved over 3 : 1 bandwidth centered at 30 GHz. This performance is especially important to the intended use with wideband double-balanced mixers and amplifiers. To shrink the overall coupler area, a slow-wave technique has been introduced, resulting in an overall size reduction of the coupler by almost 38%. The fabricated slow-wave differential coupler measured results show return loss better than 25 dB, isolation better than 15 dB, and phase and amplitude mismatch within plusmn5deg and plusmn1 dB, respectively

A monolithic 5.9-GHz CMOS I/Q direct-down converter utilizing a quadrature coupler and transformer-coupled subharmonic mixers

We report the first monolithic 5.9-GHz CMOS I/Q direct-down converter by using a quadrature coupler and transformer-coupled subharmonic mixers (SHMs). Consuming 3.5mW, each SHM achieves a voltage gain of 10.8dB, 7.9-dBm IIP3, and 54-dBm IIP2. The input-referred dc-offset due to local oscillator self-mixing is -80.9dBm.

A compact quadrature coupler based on coupled artificial transmission lines

A new compact quadrature hybrid based upon artificial transmission lines (ATLs) is presented. Miniaturization is achieved through reduced even- and odd-mode phase velocities which are achieved using capacitive loading with interdigital open-circuited stubs. A proof-of-concept microstrip implementation of the quadrature hybrid exhibits performance comparable to a conventional branch-line coupler while occupying only 14% of the area. The compact structure of the hybrid is useful for RF applications and is suitable for scaling to frequencies above 100GHz where the size of shielded-microstrip components must be limited to prevent excitation of high-order modes.

Micromachining approach in fabricating of THz waveguide components

In this paper, we describe our progress in micromachining of submillimeter waveguide structures such as a quadrature waveguide coupler which is a part of a THz balanced heterodyne receiver. We have set up and developed pilot testing of the micromachining process with required high quality of structure.

A highly-integrated Doherty amplifier for CDMA handset applications using an active phase splitter

A highly-integrated extended Doherty-type amplifier has been developed for code-division multiple access (CDMA) applications. In order to overcome the size limit of the Doherty amplifiers for reduced form-factor applications such as handsets, bulky input quadrature coupler and output /spl lambda//4-line transformers have been replaced with an active phase splitter and lumped-element networks, respectively. The active phase splitter provides inherent gain and isolation. All the components except for the output circuits have been integrated on a single chip with a size of 1.1 mm/spl times/1.4 mm. The measured data of the proposed Doherty amplifier showed better than -45 dBc adjacent channel power ratio (ACPR) over the entire power range, and 16% and 38% efficiencies at 16 and 28 dBm, respectively. The average current consumption calculated using urban compact disk game (CDG) usage profile was reduced from 76 mA (conventional class-AB amplifier) to 31 mA using our approach. This concept can be applied to a variety of wireless TX applications requiring small form factors and enhanced efficiencies.

A 700- to 2500-MHz microstrip balun using a Wilkinson divider and 3-dB quadrature couplers

A simple microstrip wideband balun with low insertion loss for high-power operation is proposed. The balun is fabricated using one Wilkinson divider and two 3-dB quadrature couplers. A Wilkinson divider with a three-section structure is used for power splitting. A 180° phase difference is obtained by using two quadrature couplers with a twisted-pair coaxial cable. Experimental measurements show that the fabricated balun has an amplitude imbalance of ±0.5 dB and a phase imbalance of ±3.4° with an insertion loss of −1.3 dB over frequencies ranging from 700 to 2500 MHz. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 333–335, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21162

Fine-tuning of the resonant frequency using a hybrid coupler and fixed components in SAW oscillators for gas detection

A method for fine-tuning of the resonant frequency of a typical delay line (DL) SAW oscillator by means of a procedure simple and widely used in microwave circuits is presented. It consists of a quadrature hybrid coupler in whose coupled ports, two identical terminations are placed. Each of them is composed of a set formed by a fixed capacitor C and a fixed inductor L in series. In this way no variable components are used. Therefore the phase can be adjusted for every sensor once the polymer film is deposited and measured. The output signal has the same amplitude than the input one and its phase is changed depending on the value of C and L. The oscillator designed in this way exhibits stable frequency response and operates with a wide range of coatings in measurements with volatile organic compounds (VOCs).