Output Amplitude Imbalance Research Articles

Analysis and design of ultra-wideband PRGW hybrid coupler using PEC/PMC waveguide model

In this paper, a new method to facilitate the design of Printed Ridge Gap Waveguide (PRGW) structures is introduced. One of the main difficulties in designing such structures is related to their simulation process which is really time and energy-consuming. Therefore, a suitable boundary condition is considered to bring about the primary structure without involving the bed of nails or mushroom unit cells. Using this technique, a wideband PRGW 3 dB hybrid double-box coupler is designed to serve in mm-wave frequencies at a center frequency of 30 GHz, which can be deployed for the next generation of mobile communication. The designed coupler provides a wide matching and isolation bandwidth with low output amplitude imbalance, which is unique in comparison with current couplers. The prototype of the proposed coupler is fabricated and measured where the simulation and measurement results show a good agreement indicating the strength of the proposed method in PRGW structure design as well. The measured results show the couplers achieve better than 10-dB return loss and isolation over the frequency range from 25 to 40 GHz (46% BW) with the power-split unbalance and phase error within ± 1 dB and ± 5°, respectively. In addition, square mushrooms are chosen here to satisfy the high impedance surface. Not only do they bring about larger stop bandwidth, but also their configuration facilitates the arrangement of them around the coupler. The proposed design has superb characteristics such as low profile, low loss, and easy integration with microwave circuits and systems that can be suitable for designing mm-wave beamforming networks.

Wideband 4 × 4 Butler Matrix in the Printed Ridge Gap Waveguide Technology for Millimeter-Wave Applications

A wideband printed ridge gap waveguide $4\times 4$ Butler matrix at 30 GHz is presented. The printed ridge gap technology is used as it has very low losses and supports the propagation of quasi-TEM mode. Each component of the Butler matrix has been designed and analyzed where a superior performance is achieved in terms of bandwidth and size. The designed components are combined to form the Butler matrix. The Butler matrix has a wideband performance where the return loss and isolation levels are higher than 10 dB in the frequency range from 26.9 to 33.3 GHz, the output amplitude imbalance is ±1.6 dB, and the phase error is ±10°. The measured radiation patterns are in a good agreement with the simulated ones, beam directions are at ±13° and ±36° at the center frequency. The gain is ranging from 10.2 to 11.35 dBi for excitation from port 1 and ranging from 8.4 to 10.2 dBi for excitation from port 2.

A Compact Wideband Millimeter-Wave Quadrature Hybrid Coupler Using Artificial Transmission Lines on a Glass Substrate

In this letter, a compact branch-line-based quadrature hybrid coupler using a line miniaturization technique for a 28-GHz application is presented. Coplanar waveguide-based artificial transmission lines are used in the miniaturization, and T-equivalent circuit models are exploited to elaborate on the optimization method. A multistage T-model is utilized to eliminate the need for lumped elements, improve bandwidth performance, and simplify the fabrication process. To validate the proposed approach, the designed quadrature hybrid coupler was fabricated on a glass substrate. The measured insertion loss and phase difference at 28 GHz were 3.86 dB, 3.94 dB, and 90.4°, respectively. The output amplitude imbalance was within a 1-dB range from 25.3 to 31.0 GHz, and the total device area, excluding the measurement pad, was $1.15\times0.98$ mm2.

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.

A Coupled Line-Based Coupler With Simultaneously Tunable Phase and Frequency

The tunability in phase characteristics becomes more and more important in the modern wireless communication system. However, the existing phase tunable coupler structures suffer from the narrow bandwidth and limited tunable range due to the much more complex design requirements. The further deterioration in performance occurs when additional tunability in operating frequency is considered. In this paper, a new simultaneously phase- and frequency- tunable coupler is proposed with the enhancement in both bandwidth and phase tunable range. Two tunable capacitors are loaded on the two terminals of a coupled line section to realize a novel tunable transmission line. This tunable element is introduced between two quarter-wavelength coupled line sections to implement the simultaneous tunability in both phase and operating frequency. For demonstration purpose, a highly flexible 3 dB coupler was designed, fabricated and measured. For a fixed operating frequency of 2.4 GHz, the coupler can provide a continuously tunable phase difference from 30° to 150° within a 10% bandwidth. For a standard phase difference of 90°, the operating frequency of the same coupler can be varied from 2.0 GHz to 2.75 GHz. Good performance in return loss, isolation, and output amplitude imbalance is achieved for all these states.

On the Design of <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math> </inline-formula>th-Order Polyphase All-Pass Filters

A structure for $n$ th-order polyphase all-pass filters (PAFs) is proposed that improves the tradeoff between output phase accuracy and filter loss. The filter also has a well-defined input impedance, which is independent of the phase accuracy and can generate the exact desired phase at $n$ distinct frequencies. The proposed structure along with its design approach is analyzed. The design procedure to design a second, third, and fourth-order PAFs is presented. It is shown that by increasing the order of the PAF structure, one can either improve the phase accuracy of the structure over the same bandwidth of interest or achieve the same phase accuracy over a wider bandwidth. Practical design considerations, including the effect of the parasitic capacitances, component tolerance, and inductor quality factors on the output amplitude imbalance and input impedance, are analyzed and discussed. As a proof-of-concept, experimental results are presented to show that the fourth-order structure is able to generate quadrature signals at four distinct frequencies.

Design of Compact High-Isolation Four-Way Power Combiners

In this paper, the design methods for four-way power combiners based on eight-port and nine-port mode networks are proposed. The eight-port mode network is fundamentally a two-stage binary four-way power combiner composed of three magic-Ts: two compact H-plane magic-Ts and one magic-T with coplanar arms. The two compact H-plane magic-Ts and the magic-T with coplanar arms function as the first and second stages, respectively. Thus, four-way coaxial-to-coaxial power combiners can be designed. A one-stage four-way power combiner based on a nine-port mode network is also proposed. Two matched coaxial ports and two matched rectangular ports are used to provide high isolation along the E-plane and the H-plane, respectively. The simulations agree well with the measured results. The designed four-way power combiners are superior in terms of their compact cross-sectional areas, a high degree of isolation, low insertion loss, low output-amplitude imbalance, and low phase imbalance, which make them well suited for solid-state power combination.

A Truly Balanced Q-Band CMOS Frequency Doubler Based on Hybrid Quadrature Coupler

In this letter, a truly balanced CMOS Q-band frequency doubler with an ultra-compact differential hybrid quadrature coupler is demonstrated using 90-nm CMOS technology. The doubler incorporates two Gilbert-cells fed by I/Q signals to compensate the time delay from transconductance stage and avoid output DC offset, providing truly balanced differential outputs. The doubler achieves a 3-dB bandwidth from 40 to 49 GHz with a minimum conversion loss of 1.6 dB at 44 GHz, while the output amplitude imbalance is measured to be less than 0.7dB. The measured I/Q mismatch of the quadrature coupler is less than 1° within 10 GHz bandwidth. The doubler chip consumes 9.6 mA from a 1.2-V supply, and the chip dimension is 0.7 × 0.9 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

An Amplitude-Balanced Current-Reused CMOS VCO Using Spontaneous Transconductance Match Technique

A 3.5 GHz, 0.18 mum CMOS current-reused voltage-controlled oscillator (VCO) with very high amplitude balance is presented. While the current-reused VCO can dramatically save dc power consumption, it has the drawback of output amplitude imbalance resulting from the asymmetric circuit structure. A spontaneous transconductance match (STM) technique is proposed to balance the transconductance of nMOS and pMOS transistors by the imbalance-induced voltage at the center-tapped point of the tank inductor. This transconductance match takes place spontaneously with the occurrence of signal imbalance such that imbalances can be instantly eliminated. The measured amplitude imbalance ratio is less than 0.7% over the entire tuning range of 2.93 to 3.62 GHz, significantly reduced from 3% of the VCO without STM. The power consumption is as low as 1.65 mW from a 1.5 V supply. The phase noise is -122 dBc/Hz at 1 MHz offset. A very high FOM of -195.7 dBc/Hz is achieved.

Experimental Investigation of New Ultra Wideband In-Phase and Quadrature-Phase Power Splitters

The design and realization of a new in-phase and quadrature-phase power splitters for ultra wideband (UWB) applications are described in this paper. The in-phase power splitter is first designed and then the quadrature-phase power splitter (QPS) is developed using the designed in-phase power splitter, a conventional microstrip transmission line (MS) TL, and a well-synthesized metamaterial (MM) TL. The phase response of the MM TL is synthesized to achieve the desired 90° phase difference over an UWB frequency range. Two splitters were designed, implemented for UWB operation and experimentally demonstrated. To examine the performances of the proposed splitters, even-odd mode analysis, numerical simulations and experimental measurements were carried out. The comparison between simulated and experimental results shows a good agreement. Results show that the proposed in-phase power splitter has good insertion loss with equal power split, acceptable return loss at all ports and satisfactory isolation performances within the whole UWB frequency range. The proposed QPS has an output amplitude imbalance of less than 2.4 dB and a phase error of less than +15° from 3.0–9.0 GHz (100% FBW).