@article{lam_haridasan_feng_steer_kingon_maria_2012, title={Scaling Issues in Ferroelectric Barium Strontium Titanate Tunable Planar Capacitors}, volume={59}, ISSN={["1525-8955"]}, DOI={10.1109/tuffc.2012.2179}, abstractNote={We report on the geometric limits associated with tunability of interdigitated capacitors, specifically regarding the impact of a parasitic non-tunable component that necessarily accompanies a ferroelectric surface capacitor, and can dominate the voltage-dependent response as capacitor dimensions are reduced to achieve the small capacitance values required for impedance matching in the X band. We present a case study of simple gap capacitors prepared and characterized as a function of gap width (i.e., the distance between electrodes) and gap length (i.e., the edge-to-edge gap distance). Our series of measurements reveals that for gap widths in the micrometer range, as gap lengths are reduced to meet sub-picofarad capacitance values, the non-tunable parasitic elements limit the effective tunability. These experimental measurements are supported by a companion set of microwave models that clarify the existence of parallel parasitic elements.}, number={2}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Lam, Peter G. and Haridasan, Vrinda and Feng, Zhiping and Steer, Michael B. and Kingon, Angus I. and Maria, Jon-Paul}, year={2012}, month={Feb}, pages={198–204} }
 @article{haridasan_lam_feng_fathelbab_maria_kingon_steer_2011, title={Tunable ferroelectric microwave bandpass filters optimised for system-level integration}, volume={5}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2010.0461}, abstractNote={Tunable bandpass filters are critical components in emerging radio frequency front-ends. A system-aware design guideline and figure of merit (FOM) are developed for optimum system-level performance. The optimisation metric discussed here deviates from earlier guidelines as the filter bandwidth is allowed to vary in the tunable range, constrained only by the downstream system analogue to digital converter. The system-aware FOM uses worst-case filter design parameters and a tuning sensitivity term that captures the frequency tunability relative to material tunability. A 6.74-8.23-GHz tunable barium strontium titanate-based filter is presented as an example to illustrate the design methodology.}, number={10}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Haridasan, V. and Lam, P. G. and Feng, Z. and Fathelbab, W. M. and Maria, J-P. and Kingon, A. I. and Steer, M. B.}, year={2011}, month={Jul}, pages={1234–1241} }
 @article{feng_fathelbab_lam_haridasan_maria_kingon_steer_2009, title={Narrowband Barium Strontium Titanate (BST) Tunable Bandpass Filters at X-band}, ISBN={["978-1-4244-2803-8"]}, ISSN={["0149-645X"]}, DOI={10.1109/mwsym.2009.5165883}, abstractNote={A 3rd-order combline tunable filter with very narrow bandwidth at X-band is implemented utilizing ferroelectric Barium Strontium Titanate (BST) interdigitated varactors. The filter and its varactors are integrated on a ceramic substrate together with a simple resistive biasing circuit. Upon the application of a bias voltage ranging from 0 to 90 V the passband of the filter tuned from 8.127 to 9.973 GHz while maintaining a fractional bandwidth of approximately 4.8–5.9 %. Over the tuning band the passband insertion loss varied from 10.7 dB to 7.5 dB while the return loss was better than 15 dB. The tuning ratio is 23 %.}, journal={2009 IEEE/MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM, VOLS 1-3}, author={Feng, Zhiping and Fathelbab, Wael M. and Lam, Peter G. and Haridasan, Vrinda and Maria, Jon-Paul and Kingon, Angus I. and Steer, Michael B.}, year={2009}, pages={1061-+} }
 @article{lam_feng_haridasan_kingon_steer_maria_2009, title={The Impact of Metallization Thickness and Geometry for X-Band Tunable Microwave Filters}, volume={56}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2009.1122}, abstractNote={The impact of dc resistance on the performance of X-band filters with ferroelectric varactors was investigated. Two series of combline bandpass filters with specific geometries to isolate sources of conductor losses were designed and synthesized. Combining the changes in filter geometry with microwave measurements and planar filter solver (Sonnet software) simulations quantitatively identified the dependency of insertion loss on overall metallization thickness and local regions of thin metallization. The optimized 8-GHz bandpass filters exhibited insertion losses of 6.8 dB. These filters required 2.5 ¿m of metal thickness (or 3 effective skin depths) to achieve this loss. The trend of loss with thickness indicates diminishing return with additional metal. The integration scheme requires thin regions of metal in the immediate vicinity of the varactors. It is shown through experiment and simulation that short distances (i.e., 15 ¿m) of thin metallization can be tolerated provided that they are located in regions where the resonant microwave current is low.}, number={5}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Lam, Peter G. and Feng, Zhiping and Haridasan, Vrinda and Kingon, Angus I. and Steer, Michael B. and Maria, Jon-Paul}, year={2009}, month={May}, pages={906–911} }
 @inproceedings{feng_fathelbab_lam_haridasan_maria_kingon_steer, title={A 6.2-7.5 GHz tunable bandpass filter with integrated barium strontium titanate (BST) interdigitated varactors utilizing silver/copper metallization}, booktitle={Rws: 2009 ieee radio and wireless symposium}, author={Feng, Z. P. and Fathelbab, W. M. and Lam, P. G. and Haridasan, V. and Maria, J. and Kingon, A. I. and Steer, M. B.}, pages={607–610} }