High Frequency SAW Research Articles

The use of saw oscillators to suppress fm noise in local oscillators for on‐board satellite applications

AbstractSAW oscillators can provide fundamental frequency operation to above 1·5 GHz, with stability and FM noise performance approaching that offered by bulk crystal oscillator technology. Their high fundamental frequency, small size and rugged construction gives SAW technology a unique capability at UHF and microwave frequencies.The low FM thermal noise floor associated with fundamental frequency operation can be combined with the stability and low close‐to‐carrier noise of multiplied bulk crystal oscillators by locking a high frequency SAW oscillator to a bulk crystal reference. SAW oscillator stability is compatible with conventional phase‐locked‐loop techniques and also with injection lock stabilization, and their own low close‐to‐carrier FM noise ensures that such locked sources exhibit minimum phase noise. Furthermore, locked oscillator phase noise is not significantly degraded when extreme operating conditions, such as those experienced in space applications, demand a reduced SAW device Q for reliable locking using either technique.Use of a PLL avoids any need for reference frequency multiplication, and provides additional design flexibility with respect to reference frequency selection and phase noise optimization. Injection locking offers design simplicity and uses fewer frequency control components, which can contribute additional noise in PLL sources.

Design of High-Frequency and Low-Loss SAW Filter Employing Multiple IDTs

This paper describes an accurate design method for the multi-IDTs type of SAW filters by equivalent circuit model analysis. Distances between IDTs are important design parameters to take account of mutual influence among all IDTs, especially in case of using single electrode transducers. Then, three-port admittance matrices of IDTs and two-port ones of SAW propagation paths are connected to compose a four-port admittance matrix. Iterative calculations of a four-port model are performed to determine numerous design parameters. Experimental results are in good agreement with calculation results. The experimental rejection level, however, is a little smaller than the calculated one because of electro-magnetic feed-through. Besides, the insertion loss is larger than the calculation in amount of two or three decibels.

Sputtered Al–Ti Electrodes for High Frequency and High Power SAW Devices

DC magnetron sputtering and Ti addition for Al electrodes are studied to achieve higher durability of SAW devices operating at high frequency and high power. Experiments on SAW resonators as a test medium show the following: the sputtering is better than conventional e-gun evaporation for both the reproducibility of film composition and for durability; 0.6 wt% to 0.9 wt% Ti addition to the sputtered Al films leads to durability for 3 times larger power than 0.7 wt% Cu addition to evaporated Al films, while less loss is experienced if resistivity is the same in each film.

Lift-off Process for the Fabrication of Thin Film Metal Lines with Small Line-Width

A repeatable process, based on a photoresist lift-off technique, has been developed to fabricate chains of about 2.6 micron wide thin film metal lines with 5.6 micronc entre-to-centre spacing. The photoresist stencil is formed with a single level resist, the surface of which is altered by a chemical treatment. In this report, we present the details of the process that appears adequate for the study of material structures and experimental devices with fine-line geometry and is potentially suitable for the fabrication of miniaturized devices, such as, high frequency SAW oscillators and LSI/VLSI circuits.

High Frequency Saw Filters Stretched Over Non-Overlapped Electrodes for Satellite Broadcast Receivers

We have developed a new UHF SAW filter for satellite broadcast receivers. The features are a high center frequency which suppresses image interference, sufficiently flat group delay for linear FM detection, and no necessity to adjust for tuning.

Application of (Pb, Nd)(Ti, Mn, In)O3 Piezoelectric Ceramics to High Frequency SAW Filters

High frequency (250∼650 MHz) SAW filters have been fabricated using (Pb, Nd)(Ti, Mn, In)O3 piezoelectric ceramics with a fine grain size less than 1 µm. These ceramics shows the lowest SAW propagation losses that have been reported for piezoelectric ceramics such as Pb(Ti, Zr)O3 ceramics. The fabricated filters shows a good bandpass response of about 20 dB insertion loss and 25 dB out-of-band rejection. This indicates that these ceramics have high potential for use as materials in high frequency SAW applications.