U.S. Philips Corporation

John M Schofield

Robert Frederick Milsom

Robert J Murray

The difficulty of making Doppler shift velocity measurements in a chirp pulse echo ranging system is overcome by employing a pulse frequency compression filter, suitably a SAW compressor 45, having individual outputs 64, 65, 66, 67 respectively relating to adjacent contiguous frequency bands A, B, C, D, (FIG. 3) each having a bandwidth approximately equal to the chirp frequency swing. Signal detection and processing means 70 senses the occurrence of a compressed pulse on any of the outputs and measures the amplitudes of signals on all the outputs. A computer then computes the Doppler shift from the amplitude ratio of the sensed signals to adjacent frequency bands, determines the target velocity therefrom and uses the result also to correct the range measured by the counter 5.

Chirp pulse echo ranging apparatus

In a surface acoustic wave device including launching and receiving transducers (2, 3) and a reflective multistrip coupler (4), the inner boundaries of the input and output electrode arrays (5, 6) of the reflective coupler (4) are defined both electrically and acoustically by an electrically discontinuous strip (23) formed for example by isolated islands of metalization (24) in conjunction with corresponding adjacent portions of interconnecting conductors (16). This enables the effective apertures of the input and output arrays (5, 6) to be better matched to the transducers (2, 3). The arrangement can reduce the insertion loss in low-loss SAW devices (i.e. in which both ends of the transducers (2, 3) are coupled via corresponding reflective couplers (4)) and also in single symmetrical guided mode SAW devices in which the strip 23 can provide an effective inner guiding bus bar whose surface mass loading corresponds to that of the outer bus bars (9, 10).

Surface acoustic wave device

In a surface acoustic wave device which includes a relfective multistrip coupler (4, 4'), direct electrical breakthrough resulting from the adjacent location of the input and output transducers (2, 3) is reduced by including at least one forward multistrip coupler (24,25) in each path coupling the transducers (2,3) via the reflective couplers (4,4') so as to space the transducers (2,3) from one another. In a so-called low-loss device in which both ends of the transducers (2,3) are reflectively coupled, the arrangement enables the input/output track separation (23) of the reflective couplers to be reduced thereby significantly reducing the insertion loss of the device.

Surface-propagating acoustic wave device

An improvement to the reflective multistrip coupler of the surface acoustic wave device described in EPA No. 0098661 for overcoming the k-determined bandwidth limitation wherein, instead of being uniform, the electrode spacing is varied correspondingly along the input and output arrays of the coupler with the result that different frequency bands will be reflected by different groups of electrodes. At least two reflective couplers (24, 25) with complementary spacing variations are included in the path coupling the input and output transducers (2, 3) so that all frequencies in the overall passband have substantially the same overall time delay. Contiguous bands of frequencies f.sub.1, f.sub.2, f.sub.3, f.sub.4 may be reflected by individual related groups 26, 27, 28, 29 of uniformly spaced electrodes forming either a monotonic or a permutated sequence, or the spacing can be varied continuously and monotonically.

A low insertion loss surface acoustic wave filter in which withdrawal weighted launching and output transducers 20, 40 are acoustically coupled by two high efficiency reflective multistrip couplers 6, 6'. To reduce the insertion loss, the inner bus bars 21, 41 are reduced in width so as to reduce the dead space 12 in the coupler. This makes it impossible to form a reliable wire bond connection to the inner bus bars which are therefore connected via a conducting path across the propagation path at the ends of the transducers. Further reduction in the widths of the inner bus bars and consequent increase in resistive losses are offset by several connections to a further bus 23, 43 via groups 25 of dummy electrodes arranged at null points in the weighting pattern.

An acoustic surface wave device employing an input and an output transducer (2, 3) and a multistrip coupler (5). The input and output tracks (11, 12) are separated to avoid unwanted acoustic energy transfer. As a result, a significant loss can occur from the launching of acoustic energy from the interconnecting conductors of the msc. The interconnecting conductors (22, 32') of the multistrip coupler are spaced differently from the, or the equivalent, wide-aperture beam spacing of conductors (16, 17; 36', 37') in either track of the msc so as not to launch any acoustic surface or bulk waves within the frequency passband. In a forward transfer msc different spacings can alternate, and in a reflective msc the spacing can take the mean of the respective equivalent wide-aperture-beam spacings of the coupler electrodes. In a reflective msc, to overcome spurious responses due to acoustic reflection from one track to the other, especially when single guided mode transducers are employed, the connecting strips (32') are inclined to the perpendicular to the propagation direction.

Acoustic surface wave device

An acoustic surface wave device using an interdigital electrode array 2, 3 to launch and receive surface waves overcomes problems of diffraction by making the arrays approximately 3.lambda..sub.c wide between the outer boundaries of the bus bars. As a result, the arrays can each only propagate and transduce a single acoustic surface waveguide mode which is symmetrical about the axis of the array.

An acoustic surface wave device comprising a piezoelectric substrate provided with an input transducer (2), an output transducer (4) and a compact reflective multistrip coupler (6) in which the strips of each pair of comparatively widely spaced strips (7 or 8) in one array of mutually parallel strips are connected to respective strips of a pair of comparatively narrowly spaced strips (8 or 7) in the other array. The wide and narrow spacings alternate along each array. The improvement provides further electrodes 9 located in the relatively wide spaces in each array and electrically interconnected so as to effect a transfer of signal currents along each array and from one array to the other. The device improves efficiency, reduces insertion loss and improves the shape of the pass band.

Acoustic surface wave device including a reflective multistrip coupler

A surface acoustic wave device includes apodized interdigital electrode arrays 2,3 coupled by a multistrip coupler 5. In a device in which the apodization 8 comprises a main lobe flanked by a succession of minor lobes, the effects of diffraction relating to short electrode pair overlaps are reduced by dividing at least the far end of the array into two or more series connected array portions 21, 22. Difficulties arising from unbalanced electrode edge overlaps at transitions 20 between different members of electrode pairs connected in series are reduced by locating such transitions in the region of nulls in the apodization pattern.

SAW Device with special length-weighted interdigital electrode array

An acoustic surface wave device using apodized interdigital transducers 32, 33, of the kind disclosed in DE 28 54 072 in which the ungrounded bus-bar 44 is inclined towards the transducer axis and a velocity compensation section 36 is provided formed by grounded dummy electrodes 37 arranged parallel to the array electrodes. The improvement comprises locating a grounded bus-bar portion 38 adjacent the inwardly inclined bus-bar portion 44' so that the facing boundary edges are uniformly spaced in the axial direction, the inclination being such that either a minimum or a side-lobe of substantially reduced magnitude of the sin x/x response is directed axially.

A surface acoustic wave bandpass electrical filter has double electrode input and output transducers (IP and OP) whose combined amplitude-frequency response has a fundamental passband centered on a frequency f.sub.o and a corresponding third harmonic passband. An interposed multistrip coupler (MSA2) has strips (ST) with a mark-to-space ratio of one-to-one and a center-to-center spacing .lambda..sub.S2 /2 chosen such that f.sub.o /f.sub.S2 is in the range 0.80 to 1.14 but excluding substantially 1.0, whereby a stopband in the amplitude-frequency response of the coupler (MSA2) between 2f.sub.S2 and 4f.sub.S2 suppresses the amplitude-frequency response of the input and output transducers (IP and OP) over a range of frequencies including 3f.sub.o .+-.0.5f.sub.o.

Acoustic wave bandpass electrical filters

A surface acoustic wave bandpass electrical filter consists of input and output interdigital transducers (IP, OP) with an interposed track changing multistrip array (MSA). A conventional broadband array (MSA) is divided into three sub-groups of strips with respect to a center of symmetry (C) separated by different distances along the input track (T1) and the output track (T2) such that the amplitude-frequency response of the array (MSA) has a stopband centered on a predetermined frequency. If the input and output transducers (IP, OP) both have a double electrode configuration, electrode separation .lambda.o/4, providing a fundamental passband at a corresponding frequency f.sub.o and an equal amplitude passband at the third harmonic 3f.sub.o, then a separation difference of .lambda.o/6 between the sub-groups of the array (MSA) in the two tracks (T1, T2) can suppress the third harmonic passband in the filter output.

Growing community of inventors

Redhill, United Kingdom

John M Schofield