VEHICULAR MICROWAVE TRANSCEIVER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Applications 60/799,953, 60/799,955 and 60/799,954, all filed May 11, 2007, which are assigned to the assignee of the present invention, and which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to transceiver design, and specifically to the design of transceivers for vehicular radars operating at millimeter wavelengths.

BACKGROUND OF THE INVENTION Radar transceivers operating at millimeter wavelengths have been in use for some time on vehicles, where they are installed to provide such features as warnings of obstacles that may not be visible to a driver of the vehicle, and/or for autonomous cruise control (ACC). Because of their use in vehicles, the transceivers have to comply with a number of constraints, which taken together make it extremely difficult to implement a simple, efficient transceiver that is to be usable in a mass market environment.

Some of the constraints are inherent when operating with millimeter waves, which are typically transmitted in waveguides, microstrips, or by short wire bonds between components. The problems generated by the millimeter (mm) wavelengths include requirements for close tolerances for mm wave structures such as the waveguides, microstrip chip adhesion, and wire bonds. Failure to meet these requirements leads to unwanted reflections, cross-talk between adjacent components, and/or absorption in the transceiver, with consequent degradation of received or transmitted signals. Typical cross-talk in adjacent mm wave receivers can be of the order of 15 dB or more.

Other constraints arise from the need to use the transceiver in a vehicle. Vehicular use requires that the transceiver be mechanically and electrically robust, be able to operate as an all-weather system, be relatively simple to construct, and be relatively small. Use on a vehicle also requires that the transceiver is simple and cheap to test, and is also simple and cheap to maintain. The latter constraints are necessary in order to keep the cost of the transceiver to acceptable levels. The former constraints must be met so that the transceiver functions acceptably, and continues to so function,

in the vehicle.

To meet these constraints there is a need for a low-cost, improved system for vehicular radar.

SUMMARY OF THE INVENTION In an embodiment of the present invention, a millimeter (mm) wave transceiver comprises a transmitter and a separate receiver which use respective antennas to radiate and receive electromagnetic waves. The transceiver is typically mounted on a vehicle to detect objects in the vicinity of the vehicle. The antennas are substantially similar in construction, each antenna comprising a waveguide horn. The waveguide horn connects a first port with a second port larger in cross-sectional area than the first port. Typically, the two ports are rectangular and have a common dimension, so that the waveguide horn has a generally flat shape. A horn bend is coupled to the larger port, and is oriented so that electromagnetic waves exit, (in the case of the transmitter), and enter (in the case of the receiver), via a horn aperture in an antenna propagation direction different from the direction of the waves in the waveguide horn. Typically the two directions are approximately orthogonal. The horn bend is configured so that the antenna maintains the generally flat shape of the waveguide horn.

The configuration of the horn aperture and larger horn port causes the antenna radiation pattern to be relatively narrow in elevation, while the azimuth is relatively wide. Both properties are advantageous for transceivers used in vehicles. Furthermore, the generally flat shape of the antennas allows the transceiver to be constructed as a relatively flat package that may be mounted broadside on a vehicle, without protruding from the vehicle, while generating the required antenna radiation patterns. In some embodiments a microwave lens may be positioned at the horn aperture, and the curvature of the lens surfaces may be set to adjust the radiation pattern. Radiofrequency (RF) chokes may be formed in the surface of the transceiver where the lens contacts the transceiver, to reduce leakage of RF radiation at the junction of the lens with the transceiver. In a disclosed embodiment, wherein the horn aperture is rectangular, one or more conductive septa may be positioned in the aperture to suppress higher order modes of the RF radiation traversing the antenna.

The transmitter comprises a transmitter module having an RF amplifier and a

built-in-test (BIT) circuit for the module. The BIT circuit consists of a single diode and a modulator, both of which are mounted on a substrate of the module. The modulator is coupled to the DC power inlet of the amplifier, and is typically a switch which may be activated to toggle the DC power on and off. In normal operation of the transmitter, the modulator is not activated so the RF amplifier operates normally. To test the transmitter, the modulator is activated so that the transmitter outputs amplitude modulated (AM) RF power at a frequency fRp.

The transmitter BIT circuit comprises a coupling between the output of the amplifier and an output port of the transmitter. The coupling is connected to the single diode. During a test, the coupling diverts a portion of the AM RF power to the diode.

In response, the diode generates an AC signal at the frequency of the modulation, and a level of the AC signal is indicative of the AM RF power output by the transmitter.

Any DC components in the AC signal may be removed by a capacitor, or by using an analog-to-digital (AJO) converter to sample the signal. Using one diode to generate an AC signal with no DC component provides a simple, accurate, and low cost method for testing the transmitter.

The receiver comprises a mixer which is mounted on a substrate of the receiver. A local oscillator (LO) frequency γLO * ^{S set as 8} ^ N^ ¹ sub-harmonic of fjyr.

The mixer receives fLO ^m & generates the N^ ¹ harmonic of γLQ i- ^e - _> ^RF= which the mixer beats with an RF signal from the receiver input port. The receiver thus operates as a homodyne receiver so that the mixer outputs an intermediate frequency (IF) signal which is a baseband signal.

The receiver also comprises a BIT circuit. The receiver BIT circuit is mounted on the substrate and comprises an LO coupler, which is able to divert an LO portion of the LO frequency, and a non-linear device (NLD) which has three ports, one of which is coupled to the LO coupler. Typically the NLD device comprises a diode. The other ports of the NLD device are an NLD bias control port which receives a bias signal, and an NLD output port which outputs a test signal produced in the NLD in response to the LO portion and the bias signal. In normal operation of the receiver, the bias signal is set at a level so that the

NLD device is in a non-conductive state, so that no signal is diverted from the LO coupler to the NLD device.

To test the receiver, the bias signal toggles the NLD device between a non-conductive state and a conductive state at a modulation frequency fjyiOD-

Because of its non-linearity, the NLD acts as a frequency generator producing an N* ^α harmonic of the LO signal, i.e., a signal having a fundamental frequency of fj^p. The modulation frequency causes the NLD to output sidebands fjyr + fjy[OD ^{as a tes} * signal at its output port. The receiver BIT circuit comprises an injection coupler which receives the test signal and injects it into the receiver input port. The mixer beats the test signal with the fRp generated in the mixer, generating an IF signal having a frequency of fjviOD- The level of the IF signal provides a very good metric for evaluating correct operation of the complete RF -IF -baseband chain of the receiver. In addition, because of the few components used, and their type, the BIT circuit takes minimal space on the substrate, is low cost, and has a very low probability of failure.

There is therefore provided, according to an embodiment of the present invention an antenna, including: a waveguide horn including: a first horn port having a first cross-sectional area; a second horn port having an second cross-sectional area larger than the first cross-sectional area; and a conductive structure including a planar horn surface, the conductive structure connecting the first horn port and the second horn port so as to convey electromagnetic waves between the first horn port and the second horn port in a horn direction; and a horn aperture bend including: a first bend port coplanar with the planar horn surface; a second bend port congruent and in registration with the second horn port so as to convey the electromagnetic waves therebetween; and a bend surface, connecting the first bend port and the second bend port,, which is configured to convey the electromagnetic waves through the first bend port in an antenna propagation direction different from the horn direction.

The waveguide horn may include a receive waveguide horn, so that the electromagnetic waves are conveyed from the first horn port to the second horn port. Alternatively, the waveguide horn may include a transmit waveguide horn, so that the electromagnetic waves are conveyed from the second horn port to the first horn port.

Typically, at least one of the first horn port and the second horn port includes a rectangular cross-section.

In a disclosed embodiment the first horn port includes a first rectangular cross-section and the second horn port includes a second rectangular cross-section, and the first and the second rectangular cross-sections have a common dimension.

In a further disclosed embodiment dimensions of the second horn port are selected in response to an ellipticity of a cross-section of a radiation pattern of the electromagnetic waves.

The antenna may include one or more conductive septa disposed in the horn aperture bend so as to suppress a higher order mode of the electromagnetic waves.

Alternatively or additionally, the antenna may include a microwave lens disposed in proximity to the first bend port so as to generate a radiation pattern of the electromagnetic waves.

In one embodiment, the antenna propagation direction and the horn direction are orthogonal.

There is further provided, according to an embodiment of the present invention a transmitter, including: a substrate; a modulator which is mounted on the substrate and which is configured to receive and modulate a DC power supply so as to provide a modulated DC signal; a radiofrequency (RF) amplifier which is mounted on the substrate and which is configured to receive RF power and the modulated DC signal, and responsively thereto, to output amplitude modulated (AM) amplified RF power from an amplifier output; a transmitter output port which is mounted on the substrate and which is configured to receive the AM amplified RF power and transmit the AM amplified RF power therefrom; a coupling between the amplifier output and the transmitter output port which is coupled to divert a portion of the AM amplified RF power from the output; and no more than one detector mounted on the substrate and connected to the coupling so as to generate an alternating current (AC) signal, in response to the portion of the AM amplified RF power, that is indicative of a level of the AM amplified RF power.

The transmitter may include a capacitor connected to the no more than one detector which is configured to remove a DC component from the AC signal. Alternatively or additionally, the transmitter may include an analog-to-digital (AJO)

converter configured to generate successive samples of the AC signal and to remove a DC component from the AC signal by subtraction of the successive samples. Further alternatively or additionally, the transmitter may include a switch which toggles the DC power supply provided to the RF amplifier between an operative level and a non-operative level.

There is further provided, according to an embodiment of the present invention a receiver, including: a substrate; a receiver input port which is coupled to receive a radiofrequency (RF) signal; a mixer, mounted on the substrate, which is coupled to receive a local oscillator (LO) frequency, to receive the RF signal from the receiver input port, and to output an intermediate frequency (IF) signal; an LO coupler, mounted on the substrate, which is connected to divert an LO portion of the LO frequency; a non-linear device (NLD), mounted on the substrate, including: an NLD input port which is coupled to the LO coupler so as to receive the LO portion; an NLD bias control port which is coupled to receive a bias signal; and an NLD output port which is coupled to convey a test signal produced in the NLD in response to the LO portion and the bias signal; and an injection coupler which is coupled to receive the test signal from the NLD output port and to inject the test signal into the receiver input port.

The NLD device may include a diode.

In one embodiment the bias signal includes a modulation signal, and the NLD device is configured to generate the test signal in response to the modulation signal, and the IF signal and the modulation signal have a common frequency fjyiOD-

Typically, the RF signal has a frequency fjyr, and the test signal includes sidebands having frequencies fRp ± iyLOD-

In a disclosed embodiment the LO frequency comprises an N" ¹ sub-harmonic of an RF frequency of the RF signal, where N is an integer greater than 1, and the NLD is configured to generate an N™ harmonic of the LO frequency. The mixer may be configured to generate an N^ ¹ harmonic of the LO frequency.

There is further provided, according to an embodiment of the present invention, a method for producing an antenna, including:

providing a waveguide horn including: a first horn port having a first cross-sectional area; a second horn port having an second cross-sectional area larger than the first cross-sectional area; and a conductive structure including a planar horn surface, the conductive structure connecting the first horn port and the second horn port so as to convey electromagnetic waves between the first horn port and the second horn port in a horn direction; and providing a horn aperture bend including: a first bend port coplanar with the planar horn surface; a second bend port congruent and in registration with the second horn port so as to convey the electromagnetic waves therebetween; and a bend surface, connecting the first bend port and the second bend port, which is configured to convey the electromagnetic waves through the first bend port in an antenna exit direction different from the horn direction.

There is further provided, according to an embodiment of the present invention, a method for producing a transmitter, including: providing a substrate; mounting a modulator on the substrate; configuring the modulator to receive and modulate a DC power supply so as to provide a modulated DC signal; mounting a radiofrequency (RF) amplifier on the substrate; configuring the RF amplifier to receive RF power and the modulated DC signal, and responsively thereto, to output amplitude modulated (AM) amplified RF power from an amplifier output; mounting a transmitter output port on the substrate; configuring the transmitter output port to receive the AM amplified RF power and transmit the AM amplified RF power therefrom; connecting a coupling between the amplifier output and the transmitter output port, the coupling being arranged to divert a portion of the AM amplified RF power from the output; mounting no more than one detector on the substrate; and connecting the no more than one detector to the coupling so as to generate an alternating current (AC) signal, in response to the portion of the AM amplified RF

power, that is indicative of a level of the AM amplified RF power.

There is further provided, according to an embodiment of the present invention, a method for producing a receiver, including: providing a substrate; coupling a receiver input port to receive a radiofrequency (RF) signal; mounting a mixer on the substrate; coupling the mixer to receive a local oscillator (LO) frequency, to receive the RF signal from the receiver input port, and to output an intermediate frequency (IF) signal; mounting an LO coupler on the substrate; connecting the LO coupler to divert an LO portion of the LO frequency; mounting a non-linear device (NLD) on the substrate, the NLD including: an NLD input port which is coupled to the LO coupler so as to receive the LO portion; an NLD bias control port which is coupled to receive a bias signal; and an NLD output port which is coupled to convey a test signal produced in the NLD in response to the LO portion and the bias signal; and coupling an injection coupler to receive the test signal from the NLD output port and to inject the test signal into the receiver input port. The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings, a brief description of which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram illustrating use of a microwave transceiver, according to an embodiment of the present invention;

Fig. 2 is a schematic diagram illustrating overall structure of the microwave transceiver, according to an embodiment of the present invention;

Figs. 3A and 3B are schematic diagrams of radiation patterns of receive and transmit apertures of the transceiver, according to an embodiment of the present invention;

Figs. 4A and 4B are schematic cross-sections of a folded horn antenna, according to an embodiment of the present invention;

Figs. 5A and 5B are schematic cross-sections of a folded horn antenna,

according to an alternative embodiment of the present invention;

Fig. 6 is a schematic block diagram of circuitry, according to an embodiment of the present invention;

Fig. 7 is a schematic diagram of a transmitter built-in-test (BIT circuit, according to an embodiment of the present invention; and

Fig. 8 is a schematic diagram of a receiver BIT circuit, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to Fig. 1, which is a schematic diagram illustrating use of a microwave transceiver, according to an embodiment of the present invention. In an environment 20, a vehicle 22, herein assumed by way of example to comprise an automobile, is in motion on a road 24, and the automobile is assumed to be moving from left to right. For clarity, in the description herein objects are referred to a set of orthogonal x, y, z axes. Thus, road 24 is assumed to be in an xy plane, and vehicle 22 is assumed to move parallel to the x-axis. Vehicle 22 has an axis 23 parallel to the x-axis, in the direction of which the vehicle travels when the vehicle is being driven in a straight line. There are one or more generally similar microwave transceivers 26 mounted on the front of the vehicle. As described in more detail below, transceivers 26 are constructed as substantially flat packages, and are advantageously mounted broadside onto the normal direction of travel of vehicle 22, so that the transceivers are in a yz plane.

While the description herein is generally directed to detection of objects in front of a moving vehicle, the scope of the present invention is not limited to such a scenario. Thus, one or more transceivers 26 may be mounted on vehicle 22 so as to detect objects at the side of, and/or behind, the vehicle, and the vehicle may be stationary, and/or moving in a straight or curved path in a forward or reverse direction. Furthermore, the scope of the present invention is not limited to vehicular use, so that embodiments of the present invention may be used for detection of substantially any type of object in front of an entity whereon one or more transceivers 26 are mounted. For example, one or more transceivers 26 may be mounted on a security fence, for detection of an object and/or a person coming into the vicinity of the fence.

Typically, the microwaves used by transceivers 26 have millimeter

wavelengths corresponding to W-band, having a frequency of approximately 77 GHz. Herein, by way of example, it is assumed that there are two transceivers 26 mounted close to the front bumper of vehicle 22, relatively close to the ends of the bumper. As is explained below, transceivers 26 are oriented and configured to detect objects in front of vehicle 22, i.e., in Fig. 1 to the right of the vehicle, and a process of triangulation may be used on the combined output of the transceivers. The detection of objects is typically used for warnings of obstacles that may not be visible to a driver of vehicle 22, and/or for autonomous cruise control (ACC) of the vehicle. Transceivers 26 are under overall control of a processor 28 mounted in vehicle 22. Fig. 2 is a schematic diagram illustrating overall structure of transceiver 26, according to an embodiment of the present invention. Transceiver 26 has an outer casing 27 which is advantageously formed from two mating sections 29 and 31. Transceiver 26 comprises transceiver circuitry 48 mounted within casing 27, and the circuitry receives its operational power from vehicle 22 via a cable 30. Cable 30 is typically also used to transfer signals between the transceiver circuitry and vehicle processor 28. Circuitry 48 is described below. An outer surface 32 of casing 27 is weatherproof, and the overall shape of the outer surface is typically in the form of a flat box, having approximate dimensions 1 cm x 15 cm x 10 cm. Transceiver 26 is assumed to have edges parallel to the x, y, z axes. Typically, a front surface 34 of the transceiver, lying in a yz plane, is covered by a plastic cover, not shown in Fig. 2, that is transparent to mm microwaves. As is illustrated in Fig. 1, transceivers 26 are mounted on vehicle 22 so that the 1 cm edges are parallel to the x axis and to axis 23. From an aesthetic as well as a practical point of view, it is important that transceivers 26 are as compact as possible, so that each dimension of a given transceiver 26 should be as small as possible. In particular, from the same points of view, it is important that transceivers 26 are as shallow as possible, so that the depth of a given transceiver 26 should be as small as possible.

Transceiver 26 has three rectangular apertures 36A, 38A, 4OA in front surface 34, the apertures being used respectively as a first and a second receive aperture, and as a transmit aperture. Apertures 36A and 38A are also referred to herein as left and right receive apertures. Edges of the apertures are respectively parallel to the y and z axes, and have substantially similar dimensions 2.5 mm x 13 mm. The functioning of the apertures as ports via which mm waves travel is described in more detail with respect to Figs. 3 A and 3B below. Each aperture 36A, 38 A, 4OA is connected to

substantially similar respective folded horn antennas 42, 44, 46. Antennas 42 and 44 are herein also termed receive antennas, and antenna 46 is also herein termed a transmit antenna.

Receive antenna 42 comprises a waveguide horn 42A which connects to a horn aperture bend 42B by a port 33B; receive antenna 44 comprises a waveguide horn 44A which connects to a horn aperture bend 44B by a port 35B; and transmit antenna 46 comprises a waveguide horn 46A which connects to a horn aperture bend 46B by a port 37B. Horn aperture bend 42B has respective ports 36B and 36C; horn aperture bend 44B has respective ports 38B and 38C; and horn aperture bend 46B has respective ports 4OB and 4OC.

Waveguides 43, 45, 47 are coupled by respective ports 33 A, 35 A, and 37A to horns 42A, 44A, and 46A of antennas 42, 44, 46, the waveguides coupling the antennas to circuitry 48. The structure and operation of folded horn antennas 42, 44, 46, referred to herein generically as folded horn antenna 45, and their component elements and ports, are described below with respect to Figs. 4A and 4B.

Figs. 3A and 3B are schematic diagrams of the radiation patterns of receive apertures 36A and 38 A, and of transmit aperture 40A ₅ according to an embodiment of the present invention. In order for transceiver 26 to function efficiently, the radiation pattern of all three apertures is generally flat in a yz plane. In this case, objects that are not in the yz plane of vehicle 22 are not directly illuminated by radiation from transmit aperture 4OA. Even if they are illuminated, for instance by indirect illumination such as by reflection from a directly illuminated surface, the flat radiation pattern of receive apertures 36A and 38A ensures that the objects are weakly detected or are not detected at all by transceiver 26, so improving the signal to noise ratio of the transceiver.

Fig. 3A shows schematic cross-sections in an xy plane of the far-field radiation pattern of the transmit aperture and of the left and right receive apertures. The radiation patterns are shown referenced to front surface 34. By way of example, the radiation patterns of the three apertures are herein assumed to be substantially similar in shape. However, there is no requirement that the radiation patterns are similar in shape, and the shape of the patterns may be modified if required, as is described further below.

The radiation pattern of transmit aperture 4OA has a schematic cross-section

50 which is generally oval-shaped, having an axis of symmetry 52 parallel to the

x-axis and a nominal beamwidth between half-power points of approximately 50°, i.e., 25° on either side of axis 52. The axis of symmetry of the radiation pattern of an antenna is herein also termed the antenna propagation direction. The radiation pattern of left receive aperture 36A has a schematic cross-section 54, and the radiation pattern of right receive aperture 38A has a schematic cross-section 56. The antenna propagation directions of cross-sections 54 and 56 are offset with respect to axis 52 by approximately 15° on opposite sides of axis 52. In practice, the overall receive radiation pattern of transceiver 26 has an angular beamwidth of approximately 50°.

Fig. 3B shows schematic cross-sections in a yz plane of the far-field radiation pattern of the three apertures, superimposed on a nominal aperture diagram 62, corresponding to apertures 36 A, 38 A, and 4OA. By way of example the cross-sections are assumed to be measured in a yz plane at the half-power points of transmit radiation pattern cross-section 50, but it will be appreciated that the shape of the three cross-sections is generally similar for yz planes at other positions in relation to front surface 34. Each cross-section is approximately elliptical, having a major axis parallel to the y-axis. A cross-section 64 is for the transmit radiation pattern, and cross-sections 66 and 68 are respectively for the left and the right radiation patterns.

Inspection of Figs. 3A and 3B shows that the radiation pattern of each of the three apertures is generally flat, in a common xy plane 70, which corresponds to the plane of Fig. 3 A.

Transceiver 26 operates to find directions and distances of objects in front of the transceiver. Herein it is assumed that transceiver 26 radiates chirped radio-frequency (RF) radiation from transmit aperture 4OA to illuminate a region in front of the transceiver. Typically the chirped RF radiation varies in frequency from approximately 16 GHz to 77 GHz, but any other suitable range of frequencies may be used. Reflected RF radiation from objects in the region is received at receive apertures 36A and 38 A. By measuring the phase, amplitude, and frequency of the received radiation, and referencing these values with the radiation patterns of the transmit and receive apertures, the distance and the direction of the objects relative to the transceiver may be calculated. PCT application WO 03/104833 , which is assigned to the assignee of the present invention and which is incorporated herein by reference, describes the production of chirped RF radiation, and the detection of objects which are illuminated by the radiation.

Figs. 4A and 4B are schematic cross-sections of generic folded horn antenna

45, according to an embodiment of the present invention. The description hereinbelow of the functioning and operation of antenna 45 applies, mutatis mutandis, to the functioning and operation of antennas 42, 44, and 46.

Tables I and II below show corresponding elements, and their identifying numerals, of antennas 45, 42, 44, and 46. The elements are referred to in the following description.

Table I

Table II

Fig. 4 A is a side view taken at a plane 81 of symmetry of the antenna, and Fig.

4B is a top view taken at a plane 83 of antenna 45. Horn antenna 45 is connected to a rectangular waveguide 82, corresponding to waveguides 43, 45, and 47 of antennas 42, 44, and 46. For operation at W-band the waveguides typically have rectangular internal dimensions approximately equal to 2.5 mm width x 1.3 mm height. A typical

free-standing W-band waveguide has walls of approximately 1 mm, giving external rectangular dimensions for the waveguides of 4.5 mm width x 3.3 mm height. Embodiments of the present invention typically incorporate the waveguides and/or folded horns required for operation of transceivers 26 as an integral part of casing 2.7, the waveguides and the folded horns being formed by the mating of casing sections 29 and 31. PCT application WO 03/104833 describes a system wherein the casing of a transceiver is used both as a heat sink and as a waveguide. Such a system may be advantageously applied to forming transceivers 26, in which case the casing sections may be formed from magnesium molded alloys. Folded horn antenna 45 matches the impedance of the mm waves traveling in waveguide 82 with the impedance of the waves traveling in free space. Antenna 45 comprises a waveguide horn 84 which is connected to a horn aperture bend 86. Typically, waveguide horn 84 and horn aperture bend 86 are formed as a single structure, or alternatively as two sections which are arranged to mate together, as described above, to form the one horn antenna.

Waveguide horn 84 comprises a first port 86 and a second port 88. In the description herein, ports are considered to be openings in a structure via which electromagnetic waves may transmit. As appropriate for the purposes of clarity, in the figures ports are indicated by broken lines. As shown by Table I above, when operating as transmit folded horn antenna 46, first port 86 corresponds to port 37A (Fig. 2) which is an inlet port to the horn, and second port 88 is outlet port 37B of the horn. When operating as receive folded horn antennas 42, 44, first port 86 corresponds to ports 33 A, 35A which are outlet ports of the horn, and second port 88 corresponds to inlet ports 33B, 35B. First port 86 and second port 88 both comprise rectangular plane surfaces which are parallel to each other.

A conductive structure 85, cqrresponding to horn 84, which is in the form of a right prism having a base in the form of a symmetrical trapezoid, connects first port 86 with second port 88. Structure 85 is typically formed of four substantially plane surfaces. An upper trapezoid shaped surface 90 and a lower trapezoid shaped surface 92 are parallel to each other, and are separated by the width of waveguide 82, i.e., 2.5 mm. Two rectangular surfaces 94 and 96 are orthogonal to surfaces 90 and 92, and there is an angle θ, typically approximately equal to 60°, between surfaces 94 and 96. The exact value of angle θ is a function of the separation between first port 86 and second port 88.

A horn aperture bend 100 is a conductive structure formed of three connected planar surfaces comprising two surfaces 102 and 104, each in the form of a right triangle, and a planar bend surface 106 which is in the form of a rectangle. Triangular surfaces 102 and 104 are parallel to each other, and are orthogonal to bend surface 106. Horn aperture bend 100 forms two planar ports, a first bend port 110 and a second bend port 108, the two ports having rectangular shapes with substantially the same dimensions. As is shown in Fig. 4 A, the two ports have a common edge 112, and are also connected by surface 106. As shown by Table II above, when operating in transmit folded horn antenna 46, first bend port 110 and second bend port 108 respectively correspond to outlet port 4OB and inlet port 4OC. When operating in receive folded horn antennas 42, 44, first bend port 110 and second bend port 108 respectively correspond to inlet ports 36B, 38B and outlet ports 36C, 38C.

Second bend port 108 and second horn port 88 are substantially the same opening, so that the two ports are substantially congruent and are in registration with each other. Horn aperture bend 100 is configured so that first bend port 110 is substantially coplanar with upper trapezoid surface 90.

Horn bend aperture 100 is typically connected at first bend port 110 to a rectangular waveguide 114, which has the same internal dimensions as port 110, i.e., 2.5 mm x 13 mm. Typically, waveguide 114 has a length corresponding to the thickness of the conductive material above surface 90, herein assumed to be 1 mm. Waveguide 114 acts as a conduit for radiation transferring between port 110 and a surface port 116 of the waveguide, the surface port being in the same plane as surface 34. For transmit folded horn antenna 46, surface port 116 corresponds to aperture 4OA. For receive folded horn antennas 42, 44, surface port 116 corresponds to apertures 36A ₅ 38 A.

Referring back to Fig. 3 B, by configuring port 110 to be rectangular with a longer dimension of the rectangle parallel to the z axis, the radiation pattern cross-section from the port is a relatively flat ellipse having its major axis orthogonal to the z axis. The ellipticity of the radiation pattern cross-section is a function of the ratio of the lengths of the sides of port 110, so that the more the ratio differs from 1, the greater the ellipticity. In some embodiments of the present invention at least one of the rectangularly shaped ports 110 has a length ratio different from the other ports 110, so that the ellipticity of its radiation pattern cross-section is different from that of the other radiation pattern cross-sections. For example, port 110 of transmit antenna

46 may be configured to have a transmit radiation pattern cross-section that has an ellipticity smaller than the ellipticity of the receive radiation pattern cross-sections.

Referring to Fig. 3A, the direction of the axis of symmetry of the radiation pattern of the antenna is related to the angle between bend surface 106 and surface 34, since the bend surface acts in a first approximation as a plane mirror. Thus, if surfaces 102 and 104 are right isosceles triangles, bend surface 106 makes an angle of 45° with surface 34. In this case, corresponding to transmit aperture 4OA, axis of symmetry 52 is substantially orthogonal to surface 34. For receive aperture 36A surfaces 102 and 104 are configured so that bend surface 106 makes an angle of approximately 50° with surface 34. For receive aperture 38A surfaces 102 and 104 are configured so that bend surface 106 makes an angle of approximately 40° with surface 34. The angles of the bend surfaces offset the radiation patterns of the receive antennas compared with that of the transmit antenna, as is illustrated in Fig. 3 A.

Figs. 5 A and 5B are schematic cross-sections of a generic folded horn antenna 145, according to an alternative embodiment of the present invention. Apart from the differences described below, the operation of antenna 145 is generally similar to that of antenna 45 (Figs. 4A and 4B), and elements indicated by the same reference numerals in both antennas 45 and 145 are generally similar in construction and in operation. Antenna 145 comprises a plurality of generally similar conductive septa 150 which are mounted in waveguide 114, in horn aperture bend 100, and in a part of waveguide horn 84 near second port 88. Septa 150 are mounted to lie in an xy plane. The septa are spaced so as to suppress unwanted higher order modes of the electromagnetic radiation, which would normally be supported in waveguide 114 and bend 100 because of the dimensions of the waveguide and the bend. In some embodiments a microwave lens 152 is mounted in front of surface port 116. Typically, the lens has a generally plane first surface 154 which mates with surface 34, although surface 154 may be curved. The lens has a second surface 156 which is curved, and the curvature of surface 156, and of surface 154 if it is curved, may be formed so as to alter the radiation pattern for antenna 145. The curvatures may be arranged to be spherical or aspherical, and the curvatures may also be different in different planes. For example, lens 152 may be configured as a cylindrical lens, having a positive curvature for surface 156 in an xy plane, no curvature for surface 156 in a yz plane, and surface 154 may be plane. Advantageously, if surface 154 is plane, one or more radiofrequency half-wavelength chokes 158 are formed in the wall

of waveguide 114, the chokes acting to reduce leakage at the junction between surface 154 and surface 34. It will be understood that the elements of antenna 145 described above with reference to Figs 5A and 5B may be applied to receive antennas 42, 44 and/or transmit antenna 46. Fig. 6 is a schematic block diagram of circuitry 48, according to an embodiment of the present invention. Circuitry 48 is typically mounted on a substrate 200 of a printed circuit board (PCB). Circuitry 48 comprises a digital signal processor (DSP) 201, which controls the operation of circuitry 48 and which communicates with processor 28. Circuitry 48 comprises a transmitter module 222 which generates mm waves, at frequencies of the order of W-band, the mm waves being coupled to port 37A of transmitting antenna 46 via a mm wave microstrip-waveguide transition 234 and waveguide 47. In order to generate its mm waves, transmitter 222 receives a low frequency (LF) chirped reference signal, at frequencies of the order of 12 GHz, from a waveform generator 232, which in turn receives instructions for the characteristics of the chirped signal from DSP 201. The LF signal is received via a microstrip-microstrip transition 247, which acts as an LF inlet port to transmitter module 222.

Transmitter 222 comprises a x3 frequency multiplier 236, a first amplifier 238, a x2 frequency multiplier 240, and a second amplifier 242, connected in series. Components 236 and 238 are incorporated into a first integrated circuit (IC) component 237. Components 240 and 242 are incorporated into a second IC component 241. IC components 237 and 241 are in turn mounted on a dielectric substrate 223, forming the base of a chip-scale package. Transmitter module 222 also comprises a built-in-test (BIT) circuit 224, which is used to test the operation of the transmitter module. BIT circuit 224 is described in more detail below with reference to Fig. 7. Transmitter 222 is preferably implemented using microwave integrated circuit (MIC) technology.

Circuitry 48 also comprises a mm wave homodyne receiver module 244, which is constructed to receive two mm wave signals, so that receiver module 244 comprises two sub-receivers 245A and 245B. The two sub-receivers have common elements, as well as separate but substantially similar elements, the latter being distinguished as necessary with a suffix A or B. Separate elements are also referred to herein generically without the suffix. For example, sub-receivers 245A and 245B comprise similar mixers 270A and 270B, which are also referred to generically herein

as mixer 270.

Each receiver module 244 comprises a x3 frequency multiplier 264 and an amplifier 266. Typically, multiplier 264 and/or amplifier 266 are substantially similar in physical dimensions to multiplier 236 and amplifier 238, and are advantageously implemented as a single IC 265. Each multiplier 264 receives the LF signal from synthesizer 232 via a microstrip-microstrip transition 269, which acts as an LF inlet port to module 244, and which is implemented in substantially the same manner as microstrip-microstrip transition 247. In module 244 an amplified output from amplifier 266, having a fundamental frequency, is fed to mixers 270A and 270B, typically formed as IC components, via a coupling line 276 which supplies the two mixers.

Mixers 270A and 270B are coupled to receive mm wave signals, via respective mm wave microstrip-waveguide transitions 268A and 268B. Optionally there are RF front-end components 269A and 269B, comprising elements such as filters, between the transitions and the mixers. Transitions 268A and 268B act as mm wave input ports, and are typically implemented in substantially the same manner as microstrip-waveguide transition 234. Transition 268A couples to waveguide 43, which in turn couples to port 33A of horn antenna 42. Transition 268B couples to waveguide 45, which couples to port 35A of horn antenna 44. Each mixer 270 mixes its mm wave input with a harmonic, typically a second harmonic, of the fundamental frequency of amplifier 266 so generating a baseband signal. Thus each mixer 270 acts both as a mixer and as a harmonic generator, generating a local oscillator (LO) mm wave frequency that is equal to the transmitted RF frequency and that is used internally within the mixer. Although the description herein assumes generation of a second harmonic to form the LO frequency, it will be understood that substantially any other harmonic may be used. For example, if multiplier 264 is replaced by a x2 multiplier, a third harmonic generated in mixer 270 generates an LO equal to the transmitted RF frequency.

Because the fundamental frequency from amplifier 265 is a sub-harmonic of the LO mm wave frequency, unwanted radiation out of each transition 268 is virtually eliminated. Coupling line 276 is advantageously configured to act as a low-pass filter, passing the fundamental frequency but stopping passage of the second harmonic mm wave frequency, so that there is very high cross-talk isolation of at least 30 dB between mixers 270A and 270B.

Each mixer 270 thus operates as a homodyne mixer, generating substantially down-converted baseband frequencies. Each mixer 270 is coupled to a respective baseband receiver block 204, comprising a baseband amplifier 202, most preferably a low noise amplifier. Each amplified baseband signal is transferred via filters 180 and 184, and amplifiers 182 and 186, to respective 12-bit analog-to-digital converters (A/D) 196, which provides a digital signal corresponding to the received signal at respective mm wave input ports 268 A and 268B. Each amplifier 182 most preferably has an adjustable gain, the amplifier receiving a gain adjusting signal from DSP 201 so as to maintain an input signal level to the respective A/D 196. DSP 201 and/or processor 28 process the values from the A/Ds to determine positions and directions of objects in front of transceiver 26.

Sub-receivers 245A and 245B respectively comprise BIT circuits 272A and 272B. BIT circuit 272B is described in more detail below with reference to Fig. 8.

Fig. 7 is a schematic diagram of transmitter BIT circuit 224, according to an embodiment of the present invention. Circuit 224 comprises a coupler 312, which diverts a portion of the RF signal from the output of amplifier 234, before the signal is received at transition 234. The diverted signal is fed to a detector 302, which is typically a diode. The detected output from the detector is conveyed via a capacitor

306 and a signal conditioning and filtering circuit 308 to an A/D converter 310. BIT circuit 224 also comprises a DC power supply switch 304, typically implemented as one or more transistors, which may be switched by applying a signal on a line 314 to the switch. Advantageously, components 312, 302, 306 308, 310, and 304 are mounted on transmitter module 222.

In normal operation of module 222, switch 304 is closed, and the module operates as a multiplier and amplifier of the LF signal received via transition 247, as described above.

In order to test that module 222 is operating correctly, a modulation signal is provided, typically from DSP 201 to switch 304. The modulation signal, assumed by way of example to comprise a square wave having a frequency of 10 kHz, is configured to alternately switch module 222 between an operative and an non-operative state, while the LF signal is being received. Thus, switch 304 acts as a modulator of the amplified RF signal output by amplifier 242. Coupling 312 diverts a portion of the modulated output to detector 302, which in response generates a 10 kHz signal having a DC component. The DC component of the 10 kHz signal is removed

by capacitor 306, and the 10 kHz signal is further filtered in circuit 308, which is typically a narrow-band 10 kHz filter, to provide a 10 kHz signal to A/D converter 310.

Since the 10 kHz signal to converter 310 has no DC component, the signal is not affected by DC fluctuations in detector 302, and the signal to converter 310 thus forms an accurate measure of the difference between the RF power levels output by module 222 in its operative and inoperative states. Typically, the values calculated by converter 310 are provided to DSP 210, and/or processor 28, which use the values to evaluate if module 222 is operating correctly. BIT circuit 224 comprises only one detector, unlike prior art BIT systems which use two detectors, one as a reference. Furthermore, BIT circuit 224 only uses one A/D converter and a non-differential amplifier, unlike prior art systems which use either two A/D converters or a precision differential amplifier.

In some embodiments of the present invention, detector 302 is directly coupled to A/D converter so that neither capacitor 306 nor circuit 308 are present. In this case, the DC component of the signal from detector 302 is removed by subtracting values of successive samples produced at sampling times of the converter corresponding to the transmitter being operative and non-operative.

Fig. 8 is a schematic diagram of receiver BIT circuit 272B of sub-receiver 245B, according to an embodiment of the present invention. The description below applies also to circuit 272A, if suffixes B are replaced by suffixes A. Circuit 272B comprises an LO sampling coupler 362 which is able to divert a portion of the LO signal from the output of amplifier 266 to a first port 360 of a non-linear device (NLD) 352. NLD 352 typically comprises a diode, although any other suitable non-linear device, typically comprising a semiconductor, may be used. Hereinbelow NLD 352 is assumed to comprise a diode 354, and port 360 is assumed to be connected to a first side of the diode. A second port 356 of the NLD, connected to the second side of the diode, is connected to a signal injection coupler 350. Coupler 350 is able to inject a portion of the signal from port 356 into the connection between transition 268B and components 269B, and so into the front end of receiver 245B. A third port 358 of NLD 352 is connected to the first side of diode 354. Port 358 is used as a bias port for the diode.

In normal operation of sub-receiver 245B, as described above, the receiver generates an LO having a frequency that is a sub-multiple of the RF frequency at

which transceiver 26 operates. Herein the LO frequency is assumed to be given by equation (1):

fLO = ^ _, (D where fLo is the local oscillator frequency generated by generator 232 (Fig.

6),

γRJ? is the RF frequency transmitted by module 222, and N is an integer greater than or equal to 2.

To maintain sub-receiver 245B in normal operation, DSP 201 provides a DC value to bias port 358 that maintains diode 354 in a non-conductive state. In this state, sampling coupler 362 is substantially inoperative, so that no signal is diverted by the coupler, and so no signal is injected at coupler 350.

To activate BIT circuit 272B so that it tests sub-receiver 245B, DSP 201 provides a modulating signal to bias port 358 so that diode 354 switches between a conductive state and a non-conductive state, at a modulation frequency fjyiOD' which is typically of the order of 100 kHz. Typically, the modulating signal is a square wave that switches between a first level causing diode 354 to conduct and a second level preventing the diode from conducting. In its conducting state, an LO signal is diverted into the diode from sampling coupler 362. Since the diode is a non-linear device, it acts as a frequency generator producing, inter alia, an N^ ¹ harmonic of the LO signal, i.e., a signal having a fundamental frequency of f^p. In addition, the diode acts as a mixer generating sidebands of the fundamental frequency with the modulation frequency, the sidebands comprising frequencies f$ given by equation (2):

^f S = ^f RF ± fMOD (2)

Injection coupler 350 injects a signal having frequencies fg into the front end of receiver 245B.

Mixer 270B receives the injected signal, via components 269B. The mixer beats the injected signal with the N* ⁿ harmonic of the LO signal that the mixer produces, i.e., f^p, to produce an intermediate frequency (IF) signal having a

frequency of fJVTOD- ^ ^e ^ signal is fed via baseband receiver block 204 to AfD 196, which measures the level of the IF signal as a test output level. The value of the test output level provides a very good metric for correct operation of the complete RF-IF-baseband chain of receiver 245B. Typically, the test output level is provided to DSP 201 and/or processor 28, which evaluate the signal to test if receiver 245B is operating correctly.

BIT circuits such as circuit 272B may be configured, together with the receiver components they are to test, as a monolithic microwave integrated circuit (MMIC). Alternatively, the BIT circuit may use discrete components. The small number of components of the BIT circuit leads to reductions in cost and reductions in space allocation for the circuit. Furthermore the simplicity of the components used, such as the diode, greatly reduces the probability of failure of the BIT circuit.

It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.