Orthogonal frequency coded filters for use in ultra-wideband communication systems

Abstract

The use of ultra-short pulses, producing very wide bandwidths and low spectral power density, are the widely accepted approach for ultra-wideband (UWB) communication systems. This approach is simple and can be implemented with current digital signal processing technologies. However, surface acoustic wave (SAW) devices have the capability of producing complex signals with wide bandwidths and relatively high frequency operation. This approach, using SAW based correlators, eliminates many of the costly components that are needed in the IF block in the transmitter and receiver, and reduces many of the signal processing requirements. This work presents the development of SAW correlators using orthogonal frequency coding (OFC) for use in UWB spread spectrum communication systems. OFC and pseudonoise (PN) coding provide a means for UWB spreading of data. The use of OFC spectrally spreads a PN sequence beyond that of code division multiple access (CDMA) because of the increased bandwidth providing an improvement in processing gain. The transceiver approach is still very similar to that of a CDMA but provides greater code diversity. Experimental results of a SAW filter designed with OFC transducers are presented. The SAW correlation filter was designed using seven contiguous chip frequencies within the transducer. SAW correlators with a 29% fractional bandwidth were fabricated on lithium niobate (LiNbO3) having a center frequency of 250 MHz. A coupling-of-modes (COM) model is used to predict the SAW filter response experimentally and is compared to the measured data. Good correlation between the predicted COM responses and the measured device data is obtained. Discussion of the design, analysis, and measurements are presented. The experimental matched filter results are shown for the OFC device and are compared to the ideal correlation. The results demonstrate the OFC SAW device concept for UWB communication transceivers.

Initial Design and Quick Analysis of SAW Ultra–Wideband HFM Transducers

“…We carried out validation of the model using D. R. Due to the different reflections of the electrodes and coherent bulk conversion mode of up-chirp and downchirp transducers, experimental characteristics are slightly different [14]. Our model does not evaluate these effects, but we can see that the simulated characteristic form correlates well with the experimental data.…”

Effective Light Beam Modulation by Chirp IDT on a Suspended LiNbO3 Membrane for 3D Holographic Displays

“…Two wafers, 4" LiNbO 3 and silicon, were bonded together and then treated by chemical mechanical polishing (CMP) to reach to the desired thickness of the piezo membrane, which was processed by Nanoln (Jinan Jing zheng Electronics Co.) on customer demand (Figure 5a). A 128 • YX LiNbO 3 was chosen as the top piezoelectric membrane because it provides a Rayleigh wave, a high SAW propagation velocity, and a large electromechanical coupling factor [19][20][21]. A 1 µm thick photoresist (PR) layer was spin-coated and patterned for the slanted and chirp IDTs, followed by a 200 nm thick aluminum deposition via a thermal evaporator and lift-off by a microstriper (AZ400T) ( Figure 5b).…”

Ultra wide band dual orthogonal frequency coded SAW correlators using harmonic operation

“…Since the conductance is proportional to the chip frequency (f chip ), the beam width (W a ) and the number of chip wavelengths, it is necessary to adjust the chips in order to obtain a uniform conductance for each chip. The complete detailed development of the UWB OFC SAW is discussed in [5].…”

“…The initial design and performance of the UWB OFC correlator device has been demonstrated using a single inline dispersive transducer in conjunction with an unweighted transducer at a relatively low operational frequency of 250 MHz [5]. This frequency was chosen for proof-of-concept to demonstrate performance and due to ease of device fabrication using available conventional contact lithography techniques.…”