SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  N102-186 (Navy)
Title:  Wideband Low-loss Tunable Band-Pass Filter (BPF)
Research & Technical Areas:  Information Systems, Materials/Processes, Sensors, Electronics

Acquisition Program:  JPEO JTRS ACAT I
  Objective:  Develop wideband tunable BPF with unprecedented low insertion loss for small form-factor military transceivers designed to operate in the VHF and UHF bands.
  Description:  Some military SDR systems are specified to operate over an extremely large bandwidth (20MHz-2GHz+) while transmitting and receiving simultaneously on a shared antenna system. To accomplish this simultaneous operation without interference, these wideband SDR systems typically employ several filters in the signal chain after the power amplifier to prevent the transmitter from desensitizing or jamming the receiver. The losses of these filters and associated switches must be compensated for with additional power delivered by the power amplifier. For small form-factor SDR transceivers, this extra power (essentially all of which must be dissipated as wasted heat) has negative consequences for system reliability, cost, size, battery life and thermal dissipation. Small form-factor tunable filter technologies with potential to address this problem have been developed and commercialized, but these products are inadequate for many military SDR applications in their current state of evolution because they do not significantly improve the insertion loss characteristics as compared to those of the fixed-tuned BPF they would replace. Additionally, other promising technologies lack the power handling capability necessary for this application. This SBIR will focus on the definition and development of tunable BPF technologies that are broadband, low-loss, and centered around a small form-factor to maximize their utility for military SDR systems.

  PHASE I: Design a continuously tunable BPF from 20MHz – 1GHz with a 10 percent 3dB bandwidth and insertion loss of 1dB or less across the entire band. Demonstrate that the filter can be fabricated in a volume not exceeding 25 cubic centimeters and with power consumption not exceeding 500mW.
  PHASE II: Based on Phase I results, fabricate the prototype tunable BPF, characterize its performance over the design bandwidth and demonstrate that it meets proposed requirements for insertion loss, volume and power consumption.

  PHASE III: Phase III work would involve transitioning a successful prototype tunable BPF to manufacturing. PRIVATE SECTOR COMMERCIAL POTENTIAL/

  DUAL-USE APPLICATIONS: Successful development of wideband low-loss tunable BPF has the potential to benefit DoD and commercial market segments alike. DoD applications that could benefit from this technology include communications, navigation and electronic warfare systems. Commercial applications include wireless communications systems (handsets).

  References:   1. Manas Roy, Robert J. Ward, and J.A. Higgins, “SiC Varactor based Tunable Filters with Enhanced Linearity”, Silicon Monolithic Integrated Circuits in RF Systems, 2008. SiRF 2008. IEEE Topical Meeting, 23-25 Jan. 2008, page(s):163 – 166, Digital Object Identifier 10.1109/SMIC.2008.47. 2. Paratek Microwave URL (http://www.paratek.com/) 3. Agile RF URL (http://www.agilerf.com/) 4. Pole Zero URL (http://www.polezero.com/) 5. USPTO Patent Application 20090002915, Micro-electromechanical voltage tunable capacitor and filter devices.

Keywords:  Tunable band-pass filter; tunable filter; hopping filter; low-loss filter; co-site filter; electronically tunable filter.

Questions and Answers:
Q: The best way to handle this problem is with Tx signal cancellation then the Rx path. Since the Tx signal is "known" it will be convenient to null the exact signal that feeds back into the Rx path. A small, low loss tunable RF filter has been the holy grail for the industry for decades. Neither tunable BST (Barium Stontium Titanate) or Varactors (tunable capacitors) are going to solve this problem. In a handset application, RFIC integration is key. This should be done in an integrated front-end module with calibration capability built in.
Would this solution be appropriate for this project?
A: An integrated front-end RFIC module solution will require replacing more than the fixed BPFs (and switches) in our RF modules. Changing our entire RF module with RFICs will probably be appropriate to address the filter and switch losses but will require the additional associated control and software changes making this solution a major system upgrade instead of a simple technology inserted product improvement. The RFIC solution is beyond the scope of this SBIR.
Q: What are the desired RF power handling levels for the filter?
A: BPF should be able to handle 5W RF power.
Q: Is there any requirement for the noise figure of this filter?
A: Noise figure not specified at the filter level. At system level, the radio has to pass DD Form 1494 Stage 4 requirements.
Q: 1. Can a switchable BPF filter with discrete frequency bands be employed?
2. What frequency resolution is required?
3. What order filter is required?
4. Can the switching devices employed be cold-switched?
5. What is the required switching time?
6. What is the lifetime requirement of the switching devices?
A: 1. Can a switchable BPF filter with discrete frequency bands be employed?
Ans: Yes, as long as it can be demonstrated to meet size, reliability, power handling and insertion loss requirements.

2. What frequency resolution is required?
Ans: Not specified. Depends on RF measurement equipment accuracy.

3. What order filter is required?
Ans: Not specified.

4. Can the switching devices employed be cold-switched?
Ans: Yes, as long as it can be demonstrated to meet size, reliability, power handling and insertion loss requirements.

5. What is the required switching time?
Ans: Not specified. Dependent on design and filter specs.

6. What is the lifetime requirement of the switching devices?
Ans: Not specified. Comparable to products and components used in military, defense and aerospace industry.

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