Showing papers by "Shiban K. Koul published in 2015"

Reliability Analysis of Ku-Band 5-bit Phase Shifters Using MEMS SP4T and SPDT Switches

Abstract: This work presents a Ku-band microelectromechanical systems (MEMS) based 5-bit phase shifter using dc contact single-pole-four-throw (SP4T) and single-pole-double-throw switches. The design is implemented using a coplanar waveguide transmission line. Two individual 2-bit phase shifters and one 1-bit phase shifter are cascaded to develop the complete 5-bit phase shifter. The phase shifters are fabricated on 635- $\mu{\hbox{m}}$ alumina substrate using a surface micromachining process. The 5-bit phase shifter demonstrates an average insertion loss of 2.65 dB in the 13–18-GHz band with a return loss better than 22 dB and average phase error less than 0.68 $^{\circ}$ at 17 GHz. Total area of the fabricated 5-bit phase shifter is ${\hbox{4.7}}\times {\hbox{2.8}}\ {\hbox{mm}}^{2}$ . The reliability of the single-pole-single-throw and SP4T switches show more than 10 million cycles with an RF power of 0.1–2 W. Furthermore, reliability of the MEMS phase shifter is extensively investigated and presented with cold and hot switched conditions. To the best of our knowledge, this is the first reported MEMS 5-bit phase shifter in the literature that has undergone different reliability and qualification testing including 3-axis vibrations.

Bandwidth Enhancement of Three-Stage Doherty Power Amplifier Using Symmetric Devices

Abstract: This paper proposes a design scheme for extending the bandwidth of a three-stage Doherty power amplifier (DPA) based on symmetric devices for broadband applications. The proposed bandwidth enhancement scheme provides an optimized solution for the load combiner parameters while operating the auxiliary power amplifier (PA) at lower current values as compared to the main PA at saturation. The proposed scheme promises 30.3% fractional bandwidth in terms of efficiency enhancement up to 9.54-dB back-off. The proposed design methodology is validated with the design of a broadband three-stage DPA using three 10-W packaged GaN HEMT devices. Measurement results show more than 51.6% drain efficiency at 6-dB output power back-off (OPBO) over the entire frequency range from 700 to 950 MHz. At 9.54-dB OPBO, the drain efficiency is better than 50.2% over this 250-MHz band. The peak drain efficiency at saturation is better than 60.04% over the entire band of operation. Measurement with 5-MHz WCDMA modulated signal shows the average drain efficiency of about 57.6% at 33.97-dBm average output power at the center frequency of operation. The corresponding adjacent channel power ratio is better than ${-}{\hbox{45.6}}$ dBc after applying digital predistortion. The circuit is realized with microstrip technology, which can be easily fabricated using conventional printed circuit processes.

A Highly Linear CMOS Active Inductor and Its Application in Filters and Power Dividers

Abstract: A high linearity active inductor with a maximum measured Q of 70 and an input 1 dB compression point $({\rm P}_{{\rm in}, {1{\rm dB}}})$ of $+ 8$ dBm (associated with a 10% increase in inductance from its small signal value with higher input power) is presented in 180 nm CMOS. Applications of such an inductor in extending the ${\rm P}_{{\rm in},1 \ {\rm dB}}$ of a Wilkinson power divider and a fully integrated second order capacitively coupled bandpass filter for blocker tolerant receivers are also demonstrated. Up to an input power of ${+} 5$ dBm, the power divider is seen to have a measured insertion loss $({\rm S}_{21})$ of ${ dB. In each case, to the best of our knowledge, this work reports the highest measured ${\rm P}_{{\rm in},1{\rm dB}}$ .

10–25 GHz frequency reconfigurable MEMS 5-bit phase shifter using push–pull actuator based toggle mechanism

Abstract: This paper presents a frequency tunable 5-bit true-time-delay digital phase shifter using radio frequency microelectromechanical system (RF MEMS) technology. The phase shifter is based on the distributed MEMS transmission line (DMTL) concept utilizing a MEMS varactor. The main source of frequency tuning in this work is a bridge actuation mechanism followed by capacitance variation. Two stages of actuation mechanisms (push and pull) are used to achieve a 2:1 tuning ratio. Accurate control of the actuation voltage between the pull to push stages contributes differential phase shift over the band of interest. The functional behavior of the push–pull actuation over the phase shifter application is theoretically established, experimentally investigated and validated with simulation. The phase shifter is fabricated monolithically using a gold based surface micromachining process on an alumina substrate. The individual primary phase-bits (11.25°/22.5°/45°/90°/180°) that are the fundamental building blocks of the complete 5-bit phase shifter are designed, fabricated and experimentally characterized from 10–25 GHz for specific applications. Finally, the complete 5-bit phase shifter demonstrates an average phase error of 4.32°, 2.8°, 1° and 1.58°, an average insertion loss of 3.76, 4.1, 4.2 and 4.84 dB and an average return loss of 11.7, 12, 14 and 11.8 dB at 10, 12, 17.2 and 25 GHz, respectively. To the best of the authors' knowledge, this is the first reported band tunable stand alone 5-bit phase shifter in the literature which can work over the large spectrum for different applications. The total area of the 5-bit phase shifter is 15.6 mm2. Furthermore, the cold-switched reliability of the unit cell and the complete 5-bit MEMS phase shifter are extensively investigated and presented.

Ultra wide band balun/180° power divider using microstrip-slotline-microstrip transition

Abstract: A novel UWB (ultra wideband) BALUN/180° Power Divider utilizing the broadband characteristics of microstrip — slotline transition is reported. The measured operational frequency range of the BALUN on RO4003C substrate is 4GHz–45GHz, corresponding to a typical insertion loss of 4±1dB with an amplitude and phase imbalance of under ±1dB and ±7° respectively. Simulation and measurement of the design on LTCC substrates show reduced loss of around 3.5±1dB with amplitude and phase imbalance of under ±1dB and ±4° respectively, in addition to an increased operational frequency range of 8GHz–90GHz, and reduction in the physical dimensions to 3 mm × 8 mm. Simulations and initial measurement with sapphire substrate have shown the capability of the design to hold good up to 130 GHz.

Design scheme for broadband Doherty power amplifier using broadband load combiner

Abstract: This article proposes a design strategy for broadband Doherty power amplifier PA using broadband load combiner. The bandwidth of the Doherty PA based on the proposed combiner using packaged transistor is about 2.5 times the bandwidth of conventional Doherty PA using a quarter-wave transformer. An easy to implement analytical design methodology has been presented for the proposed load-combiner while describing the bandwidth enhancement strategy. The design methodology is validated with the design of a broadband Doherty PA based on CREE 10 W packaged GaN high electron mobility transistor devices using the proposed load combiner. Measurement results show more than 45% drain efficiency at 6 dB output power back-off OPBO over 400 MHz frequency range, centred around 1.95 GHz. The peak drain efficiency at saturation is better than 60% over this band of operation. At 6 dB OPBO, the maximum improvement of 18.5% in drain efficiency is achieved as compared to the balanced mode PA. Measurement with single carrier wideband code division multiple access modulated signal shows the average drain efficiency of more than 44% at 36.6 dBm average output power at center frequency of operation. The adjacent channel power ratio is better than -45 dBc after applying digital predistortion. The circuit is realized with microstrip technology, which can be easily fabricated using conventional printed circuit processes. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:655-674, 2015.

Modeling of LTCC-Ferrite Tunable Inductors and Development of an $\boldsymbol {L}$ -Band Phase Shifter

Abstract: This paper presents the modeling of a tunable inductor using a low-temperature co-fired ceramic (LTCC)-ferrite tape and subsequent development of a loaded transmission line phase shifter using these inductors. The inductors are initially realized in the form of circular disks fabricated from commercially available ferrite tape (ESL 40011) wound with a copper wire. A complete model of this inductor is obtained between 0.3 and 4 GHz and validated by measurements. The phase shifter comprises these inductors in shunt, thus minimizing the effect of low-field magnetic losses in $L$ -band. The magnetic material is operated below the resonance region in a partially magnetized state with the help of a bias current that configures the phase shifter electronically. The phase shifter exhibits an insertion loss of 2 ± 0.5 dB and a differential phase shift varying between 35° and 10° in the above band. Finally, to demonstrate the feasibility of integration with other RF components, a working prototype of the same phase shifter that is fully integrated in LTCC is also presented with measurements.

Multi-layer FSS for gain improvement of a wide-band stacked printed antenna

Abstract: In this paper, an attempt has been made to improve the gain of a wide-band antenna using two layers of frequency-selective surfaces. It is seen that using two layers it is possible to achieve flat transmission characteristics over a reasonable bandwidth. However with an actual antenna, the gain improvement has at present been achieved over only a small band. It is expected that with further optimization and possibly increasing the number of layers, wide-band gain enhancement can be achieved.

A novel fabrication process for MEMS spiral inductors realized on oxide islands

Abstract: In the present work, we report a novel fabrication process for spiral inductor structures. The inductors were fabricated on insulator-filled and planarized five micron-deep islands made on silicon substrate which involved bulk micromachining. For comparison purposes, similar types of inductors were made on plain oxidized silicon wafers. Simulation has been carried out using CST microwave studio in which geometric parameters such as line width, spacing between traces, number of turns, the depth of the island and the separation between the underpass and the top spirals, the separation of the ground plane from outer inductor arm were studied. The parameters were extracted from the measurements carried out on the fabricated inductors using the conventional $$\pi$$?-model in Agilent ADS and a good fit has been obtained. The characterization results showed that the quality factors of the structures fabricated on the insulator-filled islands outperform the devices fabricated on just silicon wafer surface.

Design of reconfigurable concurrent dual-band quarter-wave transformer with application of power combiner/divider

Abstract: This paper presents the analysis and design of reconfigurable concurrent dual-band quarter-wave transformer using two single pole single throw Micro-Electro-Mechanical Switches. The transformer will behave as concurrent dual-band quarter-wave transmission line at 800 MHz and 1800 MHz, when both the switches are OFF; whereas, when the two switches are ON, the same quarter-wave transformer will reconfigure for concurrent dual-band operation at 900 MHz and 2100 MHz. Thus, this dual-band transformer can effectively cover operation at four frequencies while operating simultaneously at two bands for carrier aggregation applications. For validation, this transformer is used to implement reconfigurable concurrent dual-band Wilkinson power divider/combiner at these frequencies.

A high efficiency inductor-less broadband fully integrated CMOS power amplifier

Abstract: This work presents the design and implementation of a novel broadband completely inductor-less 300 MHz–2.4 GHz power amplifier (PA) in 180 nm CMOS, primarily for applications in the ultrahigh frequency (UHF) industrial scientific and medical band. This is capable of delivering up to 15.6 dBm saturated output power with an associated peak power added efficiency of 31% in measurement. Although amplifiers with higher output power have been reported, this amplifier occupies only 0.086 mm2 and does not require any off chip component for its operation, even at the UHF band. It also achieves the highest power density among a similar class of PA's below 10 GHz. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:311–320, 2015.

Analytical treatment of microstrip monopole antenna with finite ground plane

Abstract: The effect of finite ground plane on resonant frequency of microstrip monopole antenna is studied Electric field corresponding to a microstrip monopole antenna follows an elliptic path between the monopole and the finite ground plane, and is analogous to TE c01 mode of an elliptic waveguide with PMC walls The authors have used this elliptic waveguide model to understand the effect of size of the finite ground plane on resonant frequency A prototype of microstrip monopole antenna resonating at 203 GHz on a substrate having e r = 43 is fabricated Good agreement between the theoretical and the measured results showed the validity of the proposed cavity model and the related analysis

Model extraction of micromachined planar inductors implemented on alumina substrate

Abstract: In this work, the high resistivity material property of Alumina substrate is made into use in order to minimize the substrate loss and thereby rendering of relatively high quality MEMS suspended inductors. The modified $$\pi $$?-model is used in order to account the skin effect as well as exploit the frequency-dependent losses in the devices. On-wafer-measurements were made prior to characterization and model extraction. The maximum quality factor achieved is about 37.2 with inductor value 3.98 nH at 1.28 GHz. This result is quite promising and could be further enhanced by increasing the metal thickness.

Injection locking in active antenna

Abstract: An oscillator type active antenna is designed using two-port microstrip antenna as feedback element for RF BJT amplifier. The injection locking of active antenna is demonstrated in time domain for first time. As per the reported literature active antenna circuit takes some time to lock at the frequency of injection signal. The locking time delay depends on injected power level and difference of active antenna free-running frequency and injected signal frequency. However it is observed experimentally for the first time that the dependency is weak, and only near the edge of the locking band does the locking delay rise sharply.

Frequency switchable active antenna

Abstract: This paper proposes a novel Active Antenna (AA) has capability of frequency switching. The passive antenna with rectangular slot and frequency splitter is used to design the proposed AA. Two separate networks are designed at two separate frequencies and integrated with three port rectangular slot antenna. PIN Diode switches are used to switch between two networks for achieving frequency switching. The proposed antenna can be used for WLAN applications.

Design of Dual-band Reconfigurable Substrate Integrated Waveguide Cavity-backed Slot Antenna Array

Abstract: In this paper, a dual-band reconfigurable substrate-integrated waveguide (SIW) cavity-backed slot antenna 1 × 8 linear array is presented with dual states. The proposed SIW antenna array combines the features of the conventional metalized cavity-backed patch arrays such as surface wave suppression, high efficiency with low-manufacturing cost. The basic element has been designed, fabricated and the performance has been verified in the outdoor antenna test range. Here, PIN diodes have been used as a switching device to achieve the reconfigurability with dual-band operation. A corporate feed network has been designed and integrated with the antenna to make it as a linear array.

Improved techniques for variable phase shifter design

Abstract: In this paper we firstly present the design and development of a compact analog phase shifter at 1.3GHz using varactor diode based reflective load and then we present an improved technique/ method applied into phase shifter designs which mitigates the problem of large insertion loss variation with control voltage, which is very vital requirement for the phase shifter acting as an actuator or control device in RF control applications. Although many designers had earlier minimized the insertion loss variation using shunt resistors with the reflective load, but it results in significant signal loss. The improved technique herein do away with the shunt resistor while significantly mitigating the problem and resulting in significant improvement. The full circuit was modeled, simulated and optimized in ADS / Momentum and finally fabricated/ implemented on microstrip. The design methodology, simulated and measured results are presented. The phase shifter is a vital control device used in several applications, one of such application is phase feedback control of the RF cavity voltage in RF particle accelerators which is essential so that the beam sees the constant and correct phase for proper acceleration.

Systematic Determination of Limits on Noise Figure and Distortion in Power Constrained Capacitive Desensitized CMOS LNAs

Abstract: A systematic and generic approach is proposed to determine the minimum noise figure (NF), minimum second- and third-order harmonic distortion (HD2, HD3), and maximum input third-order intercept point (IIP3), achievable in a class of power constrained common source inductively degenerated low noise amplifiers (LNAs) using capacitance desensitization with and without multiple gated transistors. This is verified in complementary metal oxide semiconductor (CMOS) 180 nm technology. A Volterra series method is adopted to obtain closed-form expressions for both second- and third-order non-linearity. For validation, this analysis is applied to a highly linear single band LNA at 1.8 GHz and a linear dual band LNA at 2.8/3.4 GHz and corresponding limits on IIP3 and NF are established. To the best of the authors’ knowledge for the first time, such quantitative limits for obtaining a simpler design trade-off have been presented to the LNA design community.