IEEE MTT-S 2008 International Microwave Symposium Technical Program

Session: TH4A	Ferrites and Ferroelectrics
Chair:	Spartak Gevorgian, Chalmers University
Co-Chair:	Steven Stitzer, Northrop Grumman ES
Abstract:	Microwave ferroelectric materials have voltage controllable permittivity that is primarily used in realizing tunable reactance. The first four papers in this session explore applications of ferroelectric-based tunable capacitors. The first paper presents integrated broadband tunable filters with one filter operating from 230 to 400 MHz with an instantaneous bandwidth of 10% or less. The second paper describes a tunable matching network operating from 1.5 to 2 GHz with an impedance matching ratio of 4. Suppression of harmonic generation in a ferroelectric-based tunable antenna is described in the third paper. A reduced size power divider is realized using tunable lumped capacitors to provide tunable optimum performance. The last two papers address current topics in ferrite technology. The first of these uses flexible composite ferrite-based material to miniaturize flexible RF tags. The last paper of the session addresses nonlinear characterization of ferrites.

TH4A-01	Broadband Tunable Filters Using High Q Passive Tunable ICs
1586	M. Nguyen, W. D. Yan, E. P. Horne, Paratek Microwave Inc., Columbia, United States
	This paper presents the performance of tunable bandpass filters using high Q, wide-tuning-range passive tunable ICs. These passive tunable ICs are fabricated using ParaScanTM, Paratek’s proprietary doped BST material. The tunable capacitors in these passive ICs have a tuning ratio of 4.15:1 and a Q factor over 100, from 100 MHz to 1 GHz. Two tunable filters using these passive tunable ICs were designed, fabricated, and tested. The two-pole tunable filter has a tuning range of 56% from 300 to 470 MHz, an insertion loss less than 2 dB over the entire tuning range, and an IIP3 of 52 dBm. The three-pole filter demonstrates a tuning range of 74% from 230 to 400 MHz, an insertion loss less than 2.5 dB. Control of the tunable filters is achieved through an on-board, high voltage ASIC and a microprocessor. The two-pole filter has been evaluated over temperature from -40oC to 85oC and minimal temperature drift was observed.

TH4A-02	A Ferroelectric-Based Impedance Tuner for Adaptive Matching Applications
1669	J. Fu, X. A. Zhu, J. D. Phillips, A. Mortazawi, University of Michigan, Ann Arbor, United States
	A general purpose impedance tuner is proposed for adaptive matching applications to compensate the impedance variations of devices such as antennas or power amplifiers. The impedance tuner, composed of a phase shifter and a variable transformer, is designed based on all-pass networks. Thin-film barium-strontium titanate (BST) parallel-plate capacitors fabricated on sapphire are used as the tuning elements. The impedance tuner is completed by mounting chip inductors and blocking capacitors on the same substrate. On-wafer measurement results show that, at 1.8 GHz, impedance transformation ratio of 4 can be achieved and the dissipation loss for all biasing voltages (0 to 18 V) is less than 5.5 dB.

TH4A-03	Suppression of Harmonic Radiation of Tunable Planar Inverted-F Antenna by Ferroelectric Varactor Loading
1514	Y. Zheng, A. Hristov, A. Giere, R. Jakoby, TU Darmstadt, Darmstadt, Germany
	Low-cost ferroelectric varactors based on Barium-Strontium-Titanate (BST) thick-film technology have been implemented in a tunable Planar Inverted-F Antenna (PIFA). A prototype is realized and measured. The harmonic radiation is evaluated in detail. It is shown that, considerable RF voltage detunes the varactor and stimulates harmonic radiation in the varactor-loaded PIFA. It is discussed how such radiation can be suppressed by choosing the varactor’s tuning behavior. The passive BST thick-film varactors are proven to have advantages in reducing the harmonic excitation. When compared to a reference design using a silicon diode, the prototype shows suppressions on the second harmonic radiation up to 35.7 dB at -10 dBm input power. Possible suppression by BST thin-film varactors which are featured of low tuning voltages is also discussed.

TH4A-04	A Novel Flexible Magnetic Composite Material for RFID, Wearable RF and Bio-monitoring Applications
1769	L. Yang¹, L. Martin², D. Staiculescu¹, C. Wong¹, M. M. Tentzeris¹, ¹Georgia Tech, Atlanta, United States, ²Motorola, Plantation, United States
	This paper introduces for the first time a novel flexible magnetic composite material for RFID and wearable RF antennas. The successful implementation of the flexible magnetic composite material will enable the significant miniaturization of RF passives and antennas in UHF frequency bands, especially for applications requiring conformal modules that can be easily finetuned. A conformal RFID tag working at 480MHz is then fabricated and the miniaturization concept proven.

TH4A-05	A Tunable and Reduced Size Power Divider Using Ferroelectric Thin-Film Varactors
1090	E. Lourandakis¹, M. Schmidt², A. Leidl², S. Seitz², R. Weigel¹, ¹University of Erlangen-Nuremberg, Erlangen, Germany, ²Epcos AG, Munich, Germany
	A new concept for a reduced size and tunable power divider is presented based on Barium-Strontium-Titanate (BST) varactors. The proposed topology operates like a conventional Wilkinson power divider while achieving size reduction and a frequency agile behaviour in the frequency range of 1.7GHz to 2.1 GHz. Tuning the operating frequency is achieved by substituting the quarter-wavelength transmission line segments with equivalent lowpass structures and using ferroelectric varactors as tuning elements. A prototype circuit was implemented and characterised showing good agreement between simulation results and measurements. The additional insertion loss in both output branches varied from 1.2 dB to 0.6 dB while maintaining a worst case amplitude- and phase difference of 0.5 dB and 9 degrees respectively for all operating cases. The isolation between the two output ports exceeded 25 dB over the whole tuning range.

TH4A-06	Intermodulation Distortion Evaluation of Ferrite Element by Two-tone Method
1034	T. Miura, L. E. Davis, The University of Manchester, Manchester, United Kingdom
	A method to evaluate the intermodulation distortion (IMD) of a ferrite element by the two-tone method is proposed in which a dual mode resonator enables an intense RF magnetic field to be applied to the ferrite. A test fixture operating at frequencies around 2 GHz was designed and assembled based on this concept and it was verified that IMD of ferrite could be measured using this test fixture. The evaluation of IMD in the below-resonance field region suggested that a circulator with a hemi-spheroid ferrite element could show 10 dB smaller IMD and 8 dB larger handling power than a disc ferrite. Although the improvement of the magnetic characteristics by shaping the disc to spheroid has been predicted, this report is the first that confirmed the shape optimization quantitatively. An important fact from this study is that whatever improvements might be made in the quality of ferrite materials, this shaping technique will always produce further reduction of IMD.

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