Chih-Lin Chang

A Rigorous Design Methodology for Compact Planar Branch-Line and Rat-Race Couplers With Asymmetrical T-Structures

In this paper, a rigorous design methodology is developed to design compact planar branch-line and rat-race couplers using asymmetrical T-structures. The quarter-wave transmission line, namely the basic element for realizing the coupler, can be replaced by the asymmetrical T-structure, which is composed of a low-impedance shunt stub and two series high-impedance lines with unequal electrical lengths. As compared with the use of the conventional symmetrical T-structure, employing the asymmetrical one to implement the coupler not only has the advantage of flexibly interleaving the shunt stubs to achieve a more compact circuit size, but also provides a wider return loss bandwidth. Based on the proposed designed methodology, the asymmetrical T-structure can be exactly synthesized and then applied to implement the compact planar couplers. The developed planar branch-line coupler occupies 12.2% of the conventional structure and has a 35.5% 10-dB return loss bandwidth. On the other hand, the rat-race coupler is miniaturized to a 5% circuit size and developed with a 29.5% 20-dB return loss bandwidth.

A Broadband Quadrature Power Splitter Using Metamaterial Transmission Line

A broadband quadrature power splitter (QPS) is developed using the metamaterial transmission line (MM TL). It consists of a Wilkinson power divider and two phase-adjusting TLs, namely a MM TL and a microstrip (MS). The slope of the phase-response curve of the MM TL is synthesized to be the same as that of the MS along with the 90deg phase increment at two design frequencies. Hence, the broadband quadrature phase difference over the desired frequency range can be obtained. In this letter, the QPS is developed at the center frequency of 2 GHz. Over the frequency range of 1.1-3.5 GHz, an amplitude imbalance of less than 0.9 dB and a phase error of less than plusmn5deg have been experimentally demonstrated.

Design of Low Phase-Noise Microwave Oscillator and Wideband VCO Based on Microstrip Combline Bandpass Filters

This paper presents a new low phase-noise microwave oscillator and wideband voltage-controlled oscillator (VCO) based on microstrip combline bandpass filters. For this type of oscillator, the passband filter is embedded into the feedback loop to treat as a frequency stabilization element. Instead of designing the oscillator at the group-delay-peak frequency of the filter to achieve a good phase-noise performance, in this paper, the peak frequency of the complex quality factor Qsc is adopted for oscillator design. To demonstrate the effectiveness of using Qsc-peak frequency, two filter-based oscillators are implemented at the Qsc-peak and group-delay-peak frequencies, respectively. The oscillator designed at the Qsc-peak frequency improves the phase-noise about 10 dB as compared with that realized at the group-delay-peak frequency. The developed oscillator with the three-pole combline filter is experimentally demonstrated at 2.05 GHz with -148.3-dBc/Hz phase noise at 1-MHz offset frequency. Moreover, by attaching a varactor on each resonator of the combline filter, the oscillator can be extended to a wideband VCO. The developed VCO has a frequency tuning range from 1.3 to 2.2813 GHz with a 54.8% bandwidth. Over this frequency range, all the phase noises measured at 1-MHz offset frequency are better than -117.19 dBc/Hz.

Design of Low Phase-Noise Oscillator and Voltage-Controlled Oscillator Using Microstrip Trisection Bandpass Filter

In this letter, a low phase-noise oscillator using a microsrtip trisection bandpass filter is designed, fabricated, and experimentally verified. The trisection filter is mainly treated as a frequency stabilization element, and then embedded into the feedback loop of the oscillator. As the oscillation frequency is designed at group delay peak of the filter near the passband edge, the phase noise of the oscillator can be significantly reduced. In addition, by attaching a varactor on one of the resonators of the trisection filter, the developed oscillator can be easily extended to a voltage-controlled oscillator (VCO). In this letter, the oscillation frequency of the oscillator is designed at 2.46 GHz, and the measured phase noise is -144.47 dBc/Hz at 1 MHz offset frequency. Moreover, the developed VCO has a frequency turning range from 2.497 to 2.537 GHz. Over this frequency range, the measured phase noise is from -127.47 to -138.17 dBc/Hz at 1 MHz offset frequency.

Improvement of Return Loss Bandwidth of Balanced Amplifier Using Metamaterial-Based Quadrature Power Splitters

A new balanced amplifier (BA) using metamaterial-based quadrature power splitters (QPSs) is presented in this letter. Instead of using conventional 90 couplers, the developed BA is implemented by two parallel amplifiers with broadband metamaterial-based QPSs at input and output ends. Since the QPSs can provide a broadband quadrature phase difference between two outputs, the input/output reflections from two amplifiers can be effectively cancelled over a wide bandwidth. The developed BA demonstrates the input/output return loss of better than 10 dB from 1.2 to 3.5 GHz with 97.9% relative bandwidth.

A New Monolithic Ka-Band Filter-Based Voltage-Controlled Oscillator Using 0.15

This letter presents a fully monolithic Ka-band filter-based voltage-controlled oscillator (VCO) with the 0.15 μm GaAs pseudomorphic high-electron-mobility transistor (pHEMT) as the active device. A three-pole combline bandpass filter is treated as a frequency stabilization element of the feedback oscillator to achieve a low phase-noise performance. The developed VCO has a frequency tuning range of 37.608-38.06 GHz, and in this frequency rage the calibrated output power is from 6.324 dBm to 10.46 dBm. The phase noise measured at 37.608 GHz is -112.31 dBc/Hz at 1 MHz offset frequency, and its corresponding figure-of-merit (FOM) is -182.7 dBc/Hz.

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A new circuit configuration of the image reject mixer (IRM) is developed with composite right/left-handed (CRLH) quadrature power splitter and IF hybrid. The CRHL components are employed to enhance the RF return loss bandwidth and miniaturize the circuit size of the IF hybrid. The IRM has been experimentally demonstrated to have a 104% RF return loss bandwidth and a 20 dB image rejection ratio with a 51% bandwidth at the lower sideband IF port.

m GaAs pHEMT Technology

This paper presents a miniaturized electronic beam-scanning phased-array antenna for ultra-high-frequency (UHF) radio-frequency identification (RFID) applications. The developed antenna consists of two dipole antennas and a beam-scanning network, which is composed by two reflection-type phase shifters and a power divider. To reduce the fabrication cost, the circuit sizes of the beam-scanning components are miniaturized using shunt-stub-based artificial transmission lines. The measured results of the developed phased-array antenna are in good agreement with the calculated results by the antenna array theory.

An Image Reject Mixer with Composite Right/Left-Handed Quadrature Power Splitter and IF Hybrid

In this paper, a compact X-band CPW branchline coupler is proposed using the glass integrated passive device (GIPD) technology. To reduce the circuit size and retain a similar return-loss bandwidth to that of conventional coupler, the asymmetrical CPW branch-type T-structures are employed to implement the proposed coupler. Each T-structure is realized by two sections of high-impedance lines with unequal lengths and a set of branch-type shunt stubs. The developed coupler has a 31.5 % 10-dB return loss bandwidth and only occupies a 17.79 % circuit size of the conventional one. The measured results of the developed branch-line coupler are in a good agreement with simulated results.

A miniaturized electronic beam-scanning phased-array antenna for radio-frequency identification (RFID) applications

In this paper, three filter-based microwave oscillators are developed using two-pole coupled-resonator filters with the electric, magnetic, and mixed coupling structures. The filter embedded in the feedback network plays an important role to improve the stability and selectivity performances of the oscillator. Besides, considering the effects of the insertion loss of the filter, the complex quality factor QSC is adopted for the oscillator design. The developed oscillator with the electric coupling filter is experimentally demonstrated at 2.0065 GHz with -140 dBc/Hz phase noise at 1 MHz offset frequency. On the other hand, the oscillators using the magnetic-and mixed- coupling filters operated at 1.987 GHz and 1.996 GHz have measured phase noises of -139.6 dBc/Hz and -136.81 dBc/Hz at 1 MHz offset frequency, respectively.