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ABSTRACT: In this letter, the design and RF packaging of substrate integrated widely tunable filter is presented. The filter consists of two heavily loaded evanescent-mode cavities embedded into the substrate. The filter is actuated using two piezoelectric discs, which move thin, flexible membranes that form the top of the cavities. To demonstrate the wide tuning a filter is fabricated and measured to cover a very wide frequency range from 0.98 to 3.48 GHz (tuning ratio-3.55:1). The measured insertion loss is less than 3.57 dB for a 1.1% fractional bandwidth filter.
IEEE Microwave and Wireless Components Letters 09/2010; · 1.72 Impact Factor
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ABSTRACT: This paper presents a tunable bandpass filter with a reconfigurable filter order. The proposed filter consists of an array of tunable resonators with variable inter-resonator coupling structures between adjacent cavities. This allows the frequency selectivity of the filter to be adjusted for the given spectral environment without any geometrical modifications to the filter structure. To demonstrate the concept a 2 × 2 resonator array is fabricated using substrate integrated evanescent-mode cavity resonators at 3.2 GHz. Each resonator has an adjustable frequency response and can be tuned from 2.77 to 3.55 GHz. The filter has two separate signal paths, either through two or four resonators. The reconfigurable inter-resonator coupling is implemented with floating vias inside a coupling iris. The vias are connected using variable capacitors and can be included or excluded from the iris by adjusting the capacitance. This structure shows the potential for the inclusion of reconfigurable-order filters in future agile radio systems.
Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
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ABSTRACT: In this paper, the authors present a design technique that enables inter-resonator and external coupling control for high-quality-factor ( Q ) tunable bandpass filters. The design incorporates low- Q varactors as part of the inter-resonator and external coupling mechanisms without degrading the overall high Q of the original filter. Detailed design methodology and equations are presented to illustrate the concepts. A first-time demonstration of these concepts is presented for a widely tunable high- Q evanescent-mode cavity bandpass filter. The cavities are integrated in a low-loss substrate with commercially available piezoelectric actuators and solid-state varactors for frequency and bandwidth tuning. This technique allows for reduced bandwidth variation over large tuning ranges. As one example, a constant 25-MHz absolute-bandwidth filter in the 0.8-1.43-GHz tuning range with loss that is as low as 1.6 dB is presented as an example. The filter third-order intercept point is between 32.8 and 35.9 dBm over this tuning range. To further show the impact of the technique on high- Q filters, a filter Q that is as high as 750 is demonstrated in the range of 3-5.6 GHz, while using low- Q varactors (Q < 30 at 5 GHz for a 0.4-pF capacitance) to achieve more than 50% reduction in bandwidth variation over the tuning range.
IEEE Transactions on Microwave Theory and Techniques 01/2010; · 1.85 Impact Factor
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ABSTRACT: In the present work, a method for tracking the center frequency of a widely tunable evanescent-mode cavity filter in-situ is introduced. The goal is to be able to monitor the performance of a filter without disturbing the fields or degrading the quality. The proposed method is to monitor the resonant frequency of each resonator of the filter independently by inducing higher order differential modes. This method enables a continuous feedback loop to lock in the filter center frequency and shape. An example filter is fabricated to demonstrate the concept and tuned from 1.4 to 3 GHz while monitoring the differential mode at 4 to 6.5 GHz. The ability to independently monitor and control the individual resonators in-situ without disturbing the main mode is demonstrated and is a crucial step towards a robust fielded widely tunable filter.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: A switchless bank of three tunable bandpass filters is demonstrated which can be used as a triplexer over a large tuning range. Three high Q narrow-band evanescent-mode cavity filters are integrated in a single substrate using an input feed-line network to achieve multi-band operation. Using shorted feed-lines for magnetic field coupling allows the out of band impedance to be dominated by the reactance of the feed-lines. The feed-lines are then designed to have high out of band impedance over the tuning range. A three-way switchless filter bank is presented in the 1.7 GHz-3.4 GHz range maintaining less than 4 dB loss for 14 MHz-31 MHz 3-dB bandwidth over most of the tuning range. The filter bank is fabricated in one low-loss Rogers TMM3 substrate using standard PCB processing, and commercially available 0.5 mm thick piezoelectric actuators are used for the electrical tuning.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: In the present work, the authors present a design technique to create widely-tunable high Q narrow-band filters with bandwidth control by utilizing low Q varactors, while maintaining the high Q of the original filter. Detailed design methodology and equations are presented to illustrate the concept and a widely tunable high Q evanescent-mode cavity bandpass filter with controllable bandwidth is demonstrated as an example of this design technique. The filter is designed and fabricated in low-loss Rogers TMM3 substrate. A thin copper membrane is laminated on top of the substrate to allow frequency tuning, achieved using commercially available 0.38 mm thick piezoelectric actuators. The feed-lines with the impedance matching and the varactor based bandwidth control section are incorporated in parallel with the coupling iris on the back-side of the filter. A constant absolute bandwidth filter is also presented, which is tuned from 0.89 GHz to 1.47 GHz with constant 25 MHz (plusmn 0.2 MHz) 3-dB bandwidth and less than 3 dB insertion loss over the entire tuning range. The extracted filter Q is in the range of 250-350, even though low Q varactors (Q < 30@1 GHz) with capacitance in the 0.5 pF to 4 pF range are utilized for the bandwidth control.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: Randomly dispersed particles in a material can be forced to align due to the presence of an externally applied field. These self-aligning materials are examples through which order is obtained through structure created internally which alters the bulk properties of the material. One such material is a magnetically aligned anisotropic conductive adhesive which uses the alignment of ferromagnetic particles in order to create current flow in only one direction. This paper discusses microwave application of such a material. We demonstrate that the magnetically aligned Z -axis anisotropic conductive adhesive works at microwave frequencies interconnecting silicon substrates through 90 GHz. The Z -axis material is found to be a suitable replacement for solder bumping even at high frequencies of operation. The effect of material composition and the radio frequency design is discussed in this paper. Finally, the Z -axis anisotropic conductive adhesive is found to be a suitable cost-effective replacement for solder bumps at high frequencies.
IEEE Transactions on Microwave Theory and Techniques 01/2009; · 1.85 Impact Factor
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ABSTRACT: This paper reports the use of an evanescent-mode cavity resonator as a temperature sensor. The frequency loading is achieved by a capacitive post in the center of the cavity confining the electric field in a small volume. The resonant frequency of a loaded evanescent-mode cavity is related to the capacitance of the loading mechanism. As a sensing mechanism, a rectangular array of thermally actuated bilayered microcantilever beams on a silicon substrate has been fabricated using conventional microfabrication processes and placed inside the resonator. A temperature change causes the microcantilevers to deflect, changing the parasitic capacitance of the cavity and hence the resonant frequency of the resonator. Loaded microwave cavities have been fabricated using a layer by layer stereolithographic process and then metallized. The Si hosting the cantilevers is attached to the cavity. The resonant frequency of the sensor is monitored as a function of temperature and varies from 11.34 GHz at room temperature to 12 GHz at 90degC. At room temperature, the sensor has a temperature coefficient of frequency (TCF) of 0.029%/degC.
Sensors, 2007 IEEE; 12/2007
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ABSTRACT: A 10-GHz filter/receiver module is implemented in a novel 3-D integration technique suitable for RF and microwave circuits. The receiver designed and fabricated in a commercial 0.18-mum CMOS process is integrated with embedded passive components fabricated on a high-resistivity Si substrate using a recently developed self-aligned wafer-level integration technology. Integration with the filter is achieved through bonding a high-Q evanescent-mode cavity filter onto the silicon wafer using screen printable conductive epoxy. With adjustment of the input matching of the receiver integrated circuit by the embedded passives fabricated on the Si substrate, the return loss, conversion gain, and noise figure of the front-end receiver are improved. At RF frequency of 10.3 GHz and with an IF frequency of 50 MHz, the integrated front-end system achieves a conversion gain of 19 dB, and an overall noise figure of 10 dB. A fully integrated filter/receiver on an Si substrate that operates at microwave frequencies is demonstrated.
IEEE Transactions on Microwave Theory and Techniques 12/2007; · 1.85 Impact Factor
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ABSTRACT: In the present work, a widely tunable high-Q air filled evanescent cavity bandpass filter is created in an LTCC substrate. A low loss Rogers Duroid<sup>reg</sup> flexible substrate forms the top of the filter, acting as a membrane for a tunable parasitic capacitor that allows variable frequency loading. A commercially available piezoelectric actuator is mounted on the Duroid<sup>reg</sup> substrate for precise electrical tuning of the filter center frequency. The filter is tuned from 2.71 to 4.03 GHz, with insertion losses ranging from 1.3 to 2.4 dB across the range for a 2.5% bandwidth filter. Secondarily, an exceptionally narrow band filter is fabricated to show the potential for using the actuators to fine tune the response to compensate for fabrication tolerances. While most traditional machining techniques would not allow for such narrow band filtering, the high-Q and the sensitive tuning combine to allow for near channel selection for a front-end receiver. For further analysis, a widely tunable resonator is also created with a 100% tunable frequency range, from 2.3 to 4.6 GHz. The resonator analysis gives unloaded quality factors ranging from 360 to 700 with a maximum frequency loading of 89%. This technique shows a lot of promise for tunable RF filtering applications.
Microwave Symposium, 2007. IEEE/MTT-S International; 07/2007
