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D A Walker - One of the best experts on this subject based on the ideXlab platform.
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rich and cold diversity distribution and drivers of fungal communities in Patterned Ground ecosystems of the north american arctic
Molecular Ecology, 2014Co-Authors: Ina Timling, D A Walker, Chad Nusbaum, Niall Lennon, D L TaylorAbstract:Fungi are abundant and functionally important in the Arctic, yet comprehensive studies of their diversity in relation to geography and environment are not available. We sampled soils in paired plots along the North American Arctic Transect (NAAT), which spans all five bioclimatic subzones of the Arctic. Each pair of plots contrasted relatively bare, cryoturbated Patterned-Ground features (PGFs) and adjacent vegetated between Patterned-Ground features (bPGFs). Fungal communities were analysed via sequencing of 7834 ITS-LSU clones. We recorded 1834 OTUs – nearly half the fungal richness previously reported for the entire Arctic. These OTUs spanned eight phyla, 24 classes, 75 orders and 120 families, but were dominated by Ascomycota, with one-fifth belonging to lichens. Species richness did not decline with increasing latitude, although there was a decline in mycorrhizal taxa that was offset by an increase in lichen taxa. The dominant OTUs were widespread even beyond the Arctic, demonstrating no dispersal limitation. Yet fungal communities were distinct in each subzone and were correlated with soil pH, climate and vegetation. Communities in subzone E were distinct from the other subzones, but similar to those of the boreal forest. Fungal communities on disturbed PGFs differed significantly from those of paired stable areas in bPGFs. Indicator species for PGFs included lichens and saprotrophic fungi, while bPGFs were characterized by ectomycorrhizal and pathogenic fungi. Our results suggest that the Arctic does not host a unique mycoflora, while Arctic fungi are highly sensitive to climate and vegetation, with potential to migrate rapidly as global change unfolds.
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Patterned Ground facilitates shrub expansion in low arctic tundra
Environmental Research Letters, 2013Co-Authors: G V Frost, D A Walker, Howard E Epstein, G V Matyshak, Ksenia ErmokhinaAbstract:Recent expansion of tall shrubs in Low Arctic tundra is widely seen as a response to climate warming, but shrubification is not occurring as a simple function of regional climate trends. We show that establishment of tall alder (Alnus) is strongly facilitated by small, widely distributed cryogenic disturbances associated with Patterned-Ground landscapes. We identified expanding and newly established shrub stands at two northwest Siberian sites and observed that virtually all new shrubs occurred on bare microsites (‘circles’) that were disturbed by frost-heave. Frost-heave associated with circles is a widespread, annual phenomenon that maintains mosaics of mineral seedbeds with warm soils and few competitors that are immediately available to shrubs during favorable climatic periods. Circle facilitation of alder recruitment also plausibly explains the development of shrublands in which alders are regularly spaced. We conclude that alder abundance and extent have increased rapidly in the northwest Siberian Low Arctic since at least the mid-20th century, despite a lack of summer warming in recent decades. Our results are consistent with findings in the North American Arctic which emphasize that the responsiveness of Low Arctic landscapes to climate change is largely determined by the frequency and extent of disturbance processes that create mineral-rich seedbeds favorable for tall shrub recruitment. Northwest Siberia has high potential for continued expansion of tall shrubs and concomitant changes to ecosystem function, due to the widespread distribution of Patterned-Ground landscapes.
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soil nitrogen transformations associated with small Patterned Ground features along a north american arctic transect
Permafrost and Periglacial Processes, 2012Co-Authors: A M Kelley, Chienlu Ping, Howard E Epstein, D A WalkerAbstract:Small Patterned-Ground features (PGFs) in the Arctic have unique soil properties that vary with latitude and may greatly affect tundra biogeochemistry. Because nitrogen availability can strongly limit arctic vegetation growth, we examined how soil nitrogen transformations differ between PGFs and the surrounding inter-PGF tundra along an arctic latitudinal gradient. We collected soils at eight sites from the Alaskan Low Arctic to the Canadian High Arctic. The soils were incubated for 21days at 9 C and 15 C and analysed for changes in total inorganic nitrogen, nitrate and extractable organic nitrogen (EON). We found greater nitrogen immobilisation in the surrounding inter-PGF soils than in the PGF soils. Along the latitudinal gradient, differences in net nitrogen mineralisation and EON cycling between PGF and inter-PGF soils were strongly influenced by the presence of a pH boundary within the Low Arctic and the transition between the High and Low Arctic, with greater immobilisation in the nonacidic and Low Arctic sites, respectively. Incubation temperature affected EON flux but did not affect net nitrogen mineralisation or nitrification. These results show that spatial heterogeneity at several scales can influence soil nitrogen dynamics, and is therefore an important influence on arctic ecosystem function. Copyright © 2012 John Wiley & Sons, Ltd.
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vegetation of zonal Patterned Ground ecosystems along the north america arctic bioclimate gradient
Applied Vegetation Science, 2011Co-Authors: D A Walker, Patrick Kuss, Howard E Epstein, Anja N Kade, Corinne M Vonlanthen, M K Raynolds, Fred J A DanielsAbstract:Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small Patterned-Ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonal-Patterned-Ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-Ground complexes with the largest thermal differential between the Patterned-Ground features and the surrounding vegetation exhibited the clearest Patterned-Ground morphologies. Conclusions: Characterizing the composition and structure of small-scale plant communities growing on distinctive microhabitats within Patterned-Ground complexes was necessary to understand the biological and physical controls of vegetation on Patterned-Ground morphology. Coarser-scale vegetation units, referred to here as ‘zonal Patterned-Ground vegetation complexes’ (groups of Patterned-Ground plant communities within zonal landscapes), were useful for landscape and regional-level comparisons and for extrapolation of information collected at plot scales to larger regions. Vegetation maps of the representative landscapes in each subzone were needed for extrapolation. Different growth characteristics of plants growing in northern and southern parts of the gradient have an important effect in stabilizing highly frost-active soils. A conceptual diagram summarizes the interactions between vegetation and Patterned-Ground morphology along the Arctic climate gradient.
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a map analysis of Patterned Ground along a north american arctic transect
Journal of Geophysical Research, 2008Co-Authors: M K Raynolds, D A Walker, Corinne M Vonlanthen, Corinne A Munger, Anja N KadeAbstract:[1] Arctic Patterned-Ground features have been described individually, but never examined as parts of integrated landscape/ecosystems that vary along the Arctic climate gradient. Here we examine the complex interrelationships between Patterned Ground, climate, vegetation and soil along a north-south transect through all five bioclimate subzones of the North American Arctic. We mapped the vegetation, biomass, end-of-summer thaw depths, and snow cover on twenty 10 × 10-m grids. The vegetation maps illustrate the transition of vegetation types and patterns from north to south. Biomass maps showed lower biomass in the centers of Patterned-Ground features than in areas between features, and increasing biomass from north to south. Thaw-depth maps showed deeper thaw in the centers of features than between features, and shallow thaw on the north and south ends of the transect. Snow depth maps showed less snow on Patterned-Ground features subject to differential frost heave compared to areas between features which did not heave, and a north-south gradient of increasing snow depth. The maps also documented the change from small nonsorted polygons to larger nonsorted circles from north to south, and increasing pattern size with moisture. Principal components analysis revealed underlying relationships between Patterned-Ground landscapes and measured vegetation and environmental variables. Climate in combination with the vegetation was the most important factor affecting Patterned Ground on zonal sites, but soil moisture, texture and chemistry were also important.
Haruichi Kanaya - One of the best experts on this subject based on the ideXlab platform.
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bandwidth enhancement of 5g parallel coupled line band pass filter using Patterned Ground structure technique
International Journal of Integrated Engineering, 2020Co-Authors: Ummi Haziqah Morshidi, Dayang Azra Awang Mat, D N A Zaidel, Norhudah Seman, Melvin Philip Attan, M R M Sharip, Haruichi KanayaAbstract:This paper presents the design of parallel coupled line band pass filter with 10 GHz operating frequency that will be used in 5G applications. As 5G application requires big data usage and to cater the applications, the bandwidth of 5G devices need to be wider enough to support it. Thus, to improve the bandwidth performance of the designed filter, Patterned Ground structure (PGS) technique is implemented into it. The result shows that the bandwidth of the designed filter has been improved from 0.25 GHz to 4.98 GHz when PGS is implemented.
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60ghz band on chip marchand balun designed on flat and Patterned Ground shields for milimeter wave 0 18µm cmos technology
Asia-Pacific Microwave Conference, 2011Co-Authors: Dayang Azra Awang Mat, Rohana Sapawi, Ramesh K. Pokharel, Haruichi Kanaya, Keiji YoshidaAbstract:Milimeter-wave Marchand Balun designed on flat Ground and Patterned Ground shields are presented in this paper. Each of the baluns is designed on top metal (M6) in 0.18µm CMOS technology. In order to achieve sufficient coupling, the balun is stacked on the second highest metal (M5) connected using inter-metal vias. These balun have three port, differential ended port (on top metal) and single ended port (on second highest metal). Patterned Ground shield is designed on the Ground metal to reduce dielectric substrate loss with strips shield length (SL)=strips shield space(SS)=5µm. The sizes of both designs are 235µm × 340µm including pads. It shows that Balun-1 (with flat Ground) gave |S 11 | better than −15dB at 58.02GHz, with |S 21 | and |S 31 | at differential ports, 4.722dB and 5.671dB respectively, while Balun-2 (with pattern Ground shields) resulted |S 11 | better than −20dB, with |S 21 |, and |S 31 | of 2.969dB and 4.144dB significantly.
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60 ghz band low loss on chip band pass filter with Patterned Ground shields for millimeter wave cmos soc
International Microwave Symposium, 2011Co-Authors: Ramesh K. Pokharel, Ruibing Dong, A B A Dayang, Haruichi Kanaya, Keiji YoshidaAbstract:This paper presents a design of an improved on-chip open loop resonator band pass filter (OLR-BPF) for 60 GHz millimeter-wave applications in 0.18 µm CMOS technology. The proposed on-chip BPF employs the folded open loop structure on Patterned Ground shields. The adoption of a folded structure for the OLR-BPF and utilization of two transmissions zero permits a compact size and high selectivity for the BPF. In addition, the Patterned Ground shields obviously slowed down the guided waves, which enables a further reduction of the physical length of the resonator and finally an improvement of the insertion loss of the BPF. By comparison between the electromagnetic (EM) simulations and measurement results, the proposed BPF has the center frequency of 59 GHz, insertion loss 2.77 dB, band width 14 GHz, return loss is less than 27.5 dB, and chip size 910×650 µm2 (including bonding pads).
M K Raynolds - One of the best experts on this subject based on the ideXlab platform.
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vegetation of zonal Patterned Ground ecosystems along the north america arctic bioclimate gradient
Applied Vegetation Science, 2011Co-Authors: D A Walker, Patrick Kuss, Howard E Epstein, Anja N Kade, Corinne M Vonlanthen, M K Raynolds, Fred J A DanielsAbstract:Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small Patterned-Ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonal-Patterned-Ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-Ground complexes with the largest thermal differential between the Patterned-Ground features and the surrounding vegetation exhibited the clearest Patterned-Ground morphologies. Conclusions: Characterizing the composition and structure of small-scale plant communities growing on distinctive microhabitats within Patterned-Ground complexes was necessary to understand the biological and physical controls of vegetation on Patterned-Ground morphology. Coarser-scale vegetation units, referred to here as ‘zonal Patterned-Ground vegetation complexes’ (groups of Patterned-Ground plant communities within zonal landscapes), were useful for landscape and regional-level comparisons and for extrapolation of information collected at plot scales to larger regions. Vegetation maps of the representative landscapes in each subzone were needed for extrapolation. Different growth characteristics of plants growing in northern and southern parts of the gradient have an important effect in stabilizing highly frost-active soils. A conceptual diagram summarizes the interactions between vegetation and Patterned-Ground morphology along the Arctic climate gradient.
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a map analysis of Patterned Ground along a north american arctic transect
Journal of Geophysical Research, 2008Co-Authors: M K Raynolds, D A Walker, Corinne M Vonlanthen, Corinne A Munger, Anja N KadeAbstract:[1] Arctic Patterned-Ground features have been described individually, but never examined as parts of integrated landscape/ecosystems that vary along the Arctic climate gradient. Here we examine the complex interrelationships between Patterned Ground, climate, vegetation and soil along a north-south transect through all five bioclimate subzones of the North American Arctic. We mapped the vegetation, biomass, end-of-summer thaw depths, and snow cover on twenty 10 × 10-m grids. The vegetation maps illustrate the transition of vegetation types and patterns from north to south. Biomass maps showed lower biomass in the centers of Patterned-Ground features than in areas between features, and increasing biomass from north to south. Thaw-depth maps showed deeper thaw in the centers of features than between features, and shallow thaw on the north and south ends of the transect. Snow depth maps showed less snow on Patterned-Ground features subject to differential frost heave compared to areas between features which did not heave, and a north-south gradient of increasing snow depth. The maps also documented the change from small nonsorted polygons to larger nonsorted circles from north to south, and increasing pattern size with moisture. Principal components analysis revealed underlying relationships between Patterned-Ground landscapes and measured vegetation and environmental variables. Climate in combination with the vegetation was the most important factor affecting Patterned Ground on zonal sites, but soil moisture, texture and chemistry were also important.
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arctic Patterned Ground ecosystems a synthesis of field studies and models along a north american arctic transect
Journal of Geophysical Research, 2008Co-Authors: D A Walker, William B Krantz, Howard E Epstein, V E Romanovsky, Chienlu Ping, G J Michaelson, R P Daanen, Yuri Shur, Rorik Peterson, M K RaynoldsAbstract:Arctic landscapes have visually striking patterns of small polygons, circles, and hummocks. The linkages between the geophysical and biological components of these systems and their responses to climate changes are not well understood. The "Biocomplexity of Patterned Ground Ecosystems" project examined Patterned-Ground features (PGFs) in all five Arctic bioclimate subzones along an 1800-km trans-Arctic temperature gradient in northern Alaska and northwestern Canada. This paper provides an overview of the transect to illustrate the trends in climate, PGFs, vegetation, n-factors, soils, active-layer depth, and frost heave along the climate gradient. We emphasize the thermal effects of the vegetation and snow on the heat and water fluxes within Patterned-Ground systems. Four new modeling approaches build on the theme that vegetation controls microscale soil temperature differences between the centers and margins of the PGFs, and these in turn drive the movement of water, affect the formation of aggradation ice, promote differential soil heave, and regulate a host of system propel-ties that affect the ability of plants to colonize the centers of these features. We conclude with an examination of the possible effects of a climate wan-ning on Patterned-Ground ecosystems.
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phytomass patterns across a temperature gradient of the north american arctic tundra
Journal of Geophysical Research, 2008Co-Authors: Howard E Epstein, D A Walker, M K Raynolds, Gensuo Jia, A M KelleyAbstract:[1] Only a few studies to date have collectively examined the vegetation biomass and production of arctic tundra ecosystems and their relationships to broadly ranging climate variables. An additional complicating factor for studying vegetation of arctic tundra is the high spatial variability associated with small Patterned-Ground features, resulting from intense freeze-thaw processes. In this study, we sampled and analyzed the aboveGround plant biomass components of Patterned-Ground ecosystems in the Arctic of northern Alaska and Canada along an 1800-km north-south gradient that spans approximately 11°C of mean July temperatures. Vegetation biomass was analyzed as functions of the summer warmth index (SWI–sum of mean monthly temperatures > 0°C). The total absolute biomass (g m−2) and biomass of shrubs increased monotonically with SWI, however, biomass of nonvascular species (mosses and lichens), were a parabolic function of SWI, with greatest values at the ends of the gradient. The components of plant biomass on Patterned-Ground features (i.e., on nonsorted circles or within small polygons) were constrained to a greater degree with colder climate than undisturbed tundra, likely due to the effect of frost heave disturbances on the vegetation. There were also clear differences in the relative abundances of vascular versus nonvascular plants on and off Patterned-Ground features along the SWI gradient. The spatial patterns of biomass differ among plant functional groups and suggest that plant community responses to temperature, and land-surface processes that produce Patterned-Ground features, are quite complex.
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Patterned Ground plant communities along a bioclimate gradient in the high arctic canada
Phytocoenologia, 2008Co-Authors: Corinne M Vonlanthen, D A Walker, Anja N Kade, M K Raynolds, Fred J A Daniels, Hans Patrick Kuss, N V MatveyevaAbstract:Non-sorted circles, non-sorted polygons, and earth hummocks are common Ground-surface features ill arctic regions. The), are caused by a variety of physical processes that Occur in permafrost regions including contraction cracking and frost heave. Here we describe the vegetation of Patterned-Ground forms on zonal sites at three location!: along an N-S transect through the High Arctic of Canada. We made 75 releves on Patterned-Ground features (circles, polygons, earth hummocks) and adjacent tundra (Interpolygon, intercircle, interhummock areas) and identified and classified the vegetation according to the Braun-Blanquet Method. Environmental factors were correlated with the vegetation data using a nonmetric multidimensional scaling ordination (NMDS). We identified eleven commnunities: (1) Puccinellia angustata-Papaver radicalum community in xeromesic non-sorted polygons of subzone A of the Circumpolar Arctic Vegetation Map; (2) Saxifraga-Parmelia omphalodes ssp. glacialis community in hydromesic interpolygon areas of subzone A; (3) Hypogymnia subobscura-Lecanora epibryon community In xeromesic non-sorted polygons of subzone B; (4) Orthotrichum speciosum-Salix arctica community In xeromesic interpolygon areas of subzone B; (5) Cochlearia groenlandica-Luzula nivalis community in hydromesic earth Mocks Of subzone B; (6) Salix arctica-Eriophorum angustifolium ssp. triste community in hygric earth hummocks of subzone 13; (7) Puccinellia angustata-Potentilla vahliana community in xeromesic non-sorted circles and bare patches of subzone Q (8) Dryas integrifolia-Carex rupestris community in xeromesic intercircle areas and vegetated patches of subzone C; (9) Braya glabella ssp. purpurascens-Dryas integrifolia community In hydromesic non-sorted circles of subzone Q (10) Dryas integrifolia-Carex aquatilis community in hydromesic intercircle areas of subzone C; and (11) Eriophorum angustifolium ssp. triste-Carex aquatilis community ill hygric intercircle areas of subzone C. The NMDS ordination displayed the vegetation types with respect to complex environmental gradients. The first axis of the ordination corresponds to a complex soil moisture gradient and the second axis corresponds to a complex geology/elevation/climate gradient. The tundra plots have a greater moss and graminoid cover than the adjacent frost-heave communities. In general, frost-heave features have greater thaw depths, more bare Ground, thinner organic horizons, and lower soil moisture than the surrounding tundra. The morphology of the investigated Patterned Ground forms changes along the climatic gradient, with non-sorted pollygons dominating in the northernmost sites and non-sorted circles dominating, in the southern sites.
Ummi Haziqah Morshidi - One of the best experts on this subject based on the ideXlab platform.
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bandwidth enhancement of 5g parallel coupled line band pass filter using Patterned Ground structure technique
International Journal of Integrated Engineering, 2020Co-Authors: Ummi Haziqah Morshidi, Dayang Azra Awang Mat, D N A Zaidel, Norhudah Seman, Melvin Philip Attan, M R M Sharip, Haruichi KanayaAbstract:This paper presents the design of parallel coupled line band pass filter with 10 GHz operating frequency that will be used in 5G applications. As 5G application requires big data usage and to cater the applications, the bandwidth of 5G devices need to be wider enough to support it. Thus, to improve the bandwidth performance of the designed filter, Patterned Ground structure (PGS) technique is implemented into it. The result shows that the bandwidth of the designed filter has been improved from 0.25 GHz to 4.98 GHz when PGS is implemented.
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Bandwidth Enhancement of 5G Parallel Coupled Line Band Pass Filter Using Patterned Ground Structure Technique
'Penerbit UTHM', 2020Co-Authors: D N A Zaidel, Dayang Azra Awang Mat, Ummi Haziqah Morshidi, Melvin Philip Attan, M R M Sharip, Kanaya Haruichi, Norhudah SemanAbstract:This paper presents the design of parallel coupled line band pass filter with 10 GHz operating frequency that will be used in 5G applications. As 5G application requires big data usage and to cater the applications, the bandwidth of 5G devices need to be wider enough to support it. Thus, to improve the bandwidth performance of the designed filter, Patterned Ground structure (PGS) technique is implemented into it. The result shows that the bandwidth of the designed filter has been improved from 0.25 GHz to 4.98 GHz when PGS is implemented
Roberto Gomezgarcia - One of the best experts on this subject based on the ideXlab platform.
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design of on chip millimeter wave bandpass filters using multilayer Patterned Ground element in 0 13 mu m bi cmos technology
IEEE Transactions on Microwave Theory and Techniques, 2019Co-Authors: Feng Sun, He Zhu, Xi Zhu, Yang Yang, Roberto GomezgarciaAbstract:A novel design methodology for transmission-zero (TZ) generation in on-chip millimeter-wave (mm-wave) bandpass filters (BPFs) based on the original concept of multilayer Patterned-Ground (MPG) element is presented in this article. Unlike most of prior-art techniques available in the technical literature, this method has two distinct features. First, it is inherently suitable for miniaturized BPF design since the MPG element can be implemented through the layers below the top-metal layer and, thus, without occupying any additional die/chip area. Second, it provides a simple but effective way to produce a TZ at the upper stopband without adversely affecting other BPF performance metrics. To fully understand the operational insight of the engineered approach, a simplified LC -equivalent behavioral circuit model for the MPG element is developed. Using this model, three second-order BPFs based on different circuit configurations are codesigned to further demonstrate the experimental feasibility of the technique. All the filter prototypes are fabricated in a standard 0.13- $\mu \text{m}$ bipolar complementary metal–oxide–semiconductor [(Bi)-CMOS] technology. The obtained on-wafer measurements show that all fabricated BPF chips have the capability to suppress the second-order harmonic by more than 30 dB, which indicates the effectiveness of the proposed integrated BPF design approach with the MPG element.
