WO2021106003A1

WO2021106003A1 - Metal waveguide connected antenna array

Info

Publication number: WO2021106003A1
Application number: PCT/IL2020/051235
Authority: WO
Inventors: Eran Socher
Original assignee: Rfisee Ltd
Priority date: 2019-11-30
Filing date: 2020-11-30
Publication date: 2021-06-03

Abstract

The invention comprises a new method for production of a phased array working at millimeter-wave frequencies, wherein the individual antenna elements are connected to the transmitter and receiver silicon chip inputs/outputs through backshort transitions and a network of metal waveguides. Silicon transmitters and receivers for radars are available as off-the-shelf devices, and we introduce a novel method of connecting them with low loss and uniform gain and delay even for large area antenna arrays.

Description

Metal Waveguide Connected Antenna Array

Field of the Invention

The present invention relates generally to the field of radar design, and specifically to the design of phased arrays of transmit and receive radar elements.

Background of the Invention

A phased array antenna comprises multiple individual antennas or radiators, each of which may be operated in broadcast, receive, or both modes. These radiators can be operated using different phase shifts, which if chosen with care, allows the overall antenna pattern to be steered electronically, using interference and superposition. As will be appreciated such electronic steering is more flexible and requires less maintenance than the mechanical steering of an antenna.

To achieve high directivity, many radiators are used in the antenna field. Modem multi-function radar sets, on the other hand, use digital beamforming during the reception.

Advantages include high antenna gain, large side-lobe attenuation, milli- or microsecond changes in beam direction, and redundancy where the failure of some components does not result in a complete system failure.

Disadvantages of such systems include limited scanning range (e.g. up to a maximum of 120° in azimuth and elevation), deformation of the antenna pattern during beam steering, low frequency range, high costs, a requirement for exact antenna placement, and significant power losses in the conductive PCB elements generally used to connect one antenna to another.

The requirement for precision in antenna placement can be quantified in terms of the radar wavelength,

where δχ is the error in antenna position and λ is the wavelength of radiation. For example, a 4mm wavelength will require an accuracy in antenna placement of at least 0.4mm, with larger errors leading to deterioration in the radar quality (as would be seen by decreased resolution, larger lobes, etc). The antenna array control over the directivity of the beam, its shape and its overall power depend on the number of elements in the array. Array element spacing typically does not go below λ. Therefore, as larger arrays are desired, the distance to the edge of the array increases. At short wavelengths, which improve spatial resolution, this increased distance increases signal loss more significantly due to the higher signal frequency. This loss degrades the system signal-to-noise ratio and element uniformity.

It would thus satisfy a long felt need were a system introduced that allowed for reduced loss in transmit and receive arrays that cover a large total antenna aperture.

At the same time, covering a large total antenna aperture with a small number of antenna elements that each cover a large field of view (FoV) results in antenna array pattern with grating lobes, which create ambiguities in the direction of targets.

It is thus also necessary to design transmitter and receiver arrays in such a way to minimize and preferably eliminate such grating lobes in the overall transceiver array radar operation.

Summary of the Invention

The invention comprises a new method for production of a phased array, wherein the individual antenna elements are connected to the silicon semiconductor devices of the transmitters and receivers through a network of metal waveguides. This design has the advantages of low signal transmission and distribution loss even for an array of tens of cm in size; uniform interconnect loss and delay; and minimization of grating lobe effects when the number of antenna elements is low compared with the total antenna array aperture. Using metal waveguides for conducting transmitter signals to antennas and receive signals from antenna elements to the receivers also both lowers the losses in transmission, and enables lower amplitude and phase variability between array elements.

Using metal waveguides for signal transmission and distribution enables spacing the receive antennas across a large total aperture while integrating multiple receivers in integrated circuits not necessarily close to the antenna elements, thus increasing the system flexibility. Using metal waveguides for conducting the signal from integrated circuit transmitters to the transmitter antenna also enables flexibility in the position of transmitters in the integrated circuits and also implementing a dense 2D feed of the transmitter horn antennas. The foregoing embodiments of the invention have been described and illustrated in conjunction with systems and methods thereof, which are meant to be merely illustrative, and not limiting. Furthermore just as every particular reference may embody particular methods/systems, yet not require such, ultimately such teaching is meant for all expressions notwithstanding the use of particular embodiments.

Brief Description of the Drawings

Embodiments and features of the present invention are described herein in conjunction with the following drawings:

Fig. 1 shows an example of an embodiment of both transmitter and receiver metal waveguide network with 24 receive antennas showing the network of metal waveguides that connects the receiver inputs divided between 8 integrated circuits to a 5x5 (minus the center element) feed array of horn receive antennas, and 24 transmitter outputs divided between 8 integrated circuits connected through a network of metal waveguides to 2x12 ports of the transmit antenna, in a radar array.

Fig. 2 shows two horn antennas that form the transmit antenna, fed by 12 ports each.

Fig. 3 shows an example of the embodiment with a network of 4 metal waveguides of equal length that connect 4 receiver inputs within the same integrated circuit to 4 horn receive antennas that form part of the radar receiver array, and;

Fig. 4 shows an example of an embodiment with a transition between a microstrip line to a metal waveguide using a back-short.

In the following description, the term RF hereinafter refers to radio-frequency electromagnetic radiation, for instance signals having frequencies anywhere in the range from 10GHz to 1000GHz, or more specihcally in the mm- wavelength range 30-300GHZ. .

The term ‘PCB’ hereinafter refers to printed circuit board, for example those adapted for transmission of electrical signals in RF frequencies along ground planes.

The term ‘Tx’ hereinafter refers to transmit or transmission, e.g. RF Tx signals are RF signals to be transmitted

The term ‘Rx’ hereinafter refers to receive or receiptt, e.g. RF Rx signals are RF signals that have been received. The term ‘dense feeding’ hereinafter refers to an antenna having several ports, wherein the distance between ports is small compared to the wavelength being employed.

Detailed Description of Preferred Embodiments

The present invention will be understood from the following detailed description of preferred embodiments, which are meant to be descriptive and not limiting. For the sake of brevity, some well-known features, methods, systems, procedures, components, circuits, and so on, are not described in detail.

The invention consists of a novel implementation of phased array, wherein a PCB containing one or more silicon chips, each containing multiple outputs to transmitters and multiple inputs from receivers, for a radar system working at millimeter wave frequencies. The receivers are connected to an antenna array that covers an area larger than the wavelength by (for example) two orders of magnitude. The receiver antenna elements may take the form of horn antennas which are routed to the receiver input on the PCB using a network of metal waveguides. The metal waveguide is coupled to a microstrip line on the PCB using a back-short. The metal waveguides are designed to have low transmission loss and equal length so that both amplitude and phase variability between channels in the receive array are minimized. Since the 2D receive antenna array is larger than the wavelength by two orders of magnitude and only tens of elements are used, the distance between receive antenna elements is much larger than half wavelength and grating lobes are created when digital beamforming is performed on the multiple receive channel outputs.

The motivation for use of waveguides is, in part, due to the more efficient propagation of RF signals within waveguides than in microstrips. A second reason is to reduce the amount of RF noise sent into the environment, and a third to thereby also reduce crosstalk between channels.

Further advantages include uniform interconnect loss and delay; minimization of grating lobe effects when the number of antenna elements is low compared with the total antenna array aperture; and lower amplitude and phase variability between array elements;

The system is also more flexible, as the receive antennas may be placed across a large total aperture while integrating multiple receivers in integrated circuits not necessarily close to the antenna elements. Using metal waveguides for conducting the signal from integrated circuit transmitters to the transmitter antenna also enables flexibility in the position of transmitters in the integrated circuits.

Finally, a dense 2D feed of the transmitter horn antennas is made possible by this system.

An example of the metal waveguides is shown in Fig.l, for the network connecting receiver inputs to a 2D array of receive horn antenna array. That antenna array is sparse, with element pitch of 2.5l. Also, 24 metal waveguides (of which one is labeled 102) connect the transmitter outputs to the 2x12 feed array of a horn transmit antenna (see Fig. 2).

The transmitters are connected to horn antennas that are excited by a dense array of ports on a PCB using back-shorts. The array of ports is connected to the transmitter output ports distributed across the main PCB using a network of metal waveguides, coupled to microstrips on the two PCBs using backshorts.

Fig. 2 shows an example of PCB layers including two horn antennas 205, a magnetic choke 201 , microstrip inputs 202 to the horn antennas, PCB substrate (for example Isola Astra 77 of 0.005” thickness) 203, and feeding leaf 204. The horn antennas 205 together form the transmit antenna. Each of the two horns is driven by 12 microstrip inputs through metal waveguides and transitions to PCB.

Fig. 3 shows a closeup of a 4 waveguides (one of them being 301), connecting 4 receiver inputs within a single integrated circuits, which are being used to feed four receive horn antenna inputs by means of connections 302 (only one of which is labelled). The ground plane 303 is also visible.

Fig. 4 shows a milled element connecting a waveguide to a microstrip line, showing the feeding printed pin 401, milled edge 402, ground vias 403, metal back 404, microstrip line 405. mode chock vias 406, and waveguide 407.

Since dense feeding of the transmit horn antenna is used, which corresponds to half wavelength pitch, the transmitted beam does not contain grating lobes and can be physically steered by controlling the phase of each of the tens of transmitters. By ‘dense feeding’ we mean that the distance between ports is small compared to the wavelength being employed.

Since the aperture of the transmit horn antenna is smaller than the receive antenna array total aperture, the transmit beam is wider than the receive beam that is formed digitally and digital beam forming of received signals allows for RADAR imaging of reflectors within the transmit beam width. The receive and transmit beams are designed so that the receive array grating lobes are not illuminated by the transmit beam, which should be narrow enough as to suppress these grating lobes.

The waveguides of the invention may be produced using methods known in the art, for instance by means of CNC (computerised numerical control) machining; plastic molding and coating, lithography, and any other technique suitable for production of the generally rectangular cross-section conduits used in a waveguide system.

The foregoing description and illustrations of the embodiments of the invention has been presented for the purposes of illustration. It is not intended to be exhaustive or to limit the invention to the above description in any form.

Any term that has been defined above and used in the claims, should be interpreted according to this definition.

The reference numbers in the claims are not a part of the claims, but rather used for facilitating the reading thereof. These reference numbers should not be interpreted as limiting the claims in any form.

Claims

1. A phased array radar consisting of : a. one or more PCBs adapted to conduct electric signals and serve as a physical support for semiconductor devices; b. a set of transmit semiconductor devices adapted to generate RF Tx signals; c. one or more transmit antennas adapted to transmit said RF Tx signals connected to a corresponding set of microstrip lines on said PCBs using back-shorts; d. a set of transmit metal waveguides adapted to conduct said RF Tx signals from said transmit semiconductor devices to said transmit antennas; e. an array of receive antennas adapted to receive RF Rx signals connected to a corresponding set of microstrip lines on said PCBs using back-shorts; f. a set of receive semiconductor devices adapted to analyze said RF Rx signals; g. a set of receive metal waveguides adapted to conduct said RF Rx signals from said receive antennas to said receive semiconductor devices; wherein said array of receive antennas may be tens of cm in extent, while still maintaining low signal transmission and distribution loss, due to the efficiency of signal propagation in said metal waveguides.

2. The phased array radar of claim 1 further having uniform interconnect loss and delay, as well as minimization of grating lobe effects when the number of antenna elements is low compared with the total antenna array aperture, and lower amplitude and phase variability between array elements.

3. The phased array radar of claim 1 wherein the spacing of said receive antennas spans a large total aperture of tens of cm or more, while integrating multiple receivers in integrated circuits not necessarily close to the antenna elements, thus increasing the system flexibility.

4. The phased array radar of claim 1 wherein the position of transmitters in the integrated circuits can be varied.

5. The phased array radar of claim 1 implementing a dense 2D feed for said transmit antennas, wherein the distance between said antenna’s ports is small compared to the wavelength of said RF Tx and RF Rx signals.

6. The phased array radar of claim 1 wherein said metal waveguides are coupled to microstrip lines on said PCB using backshorts.

7. The phased array radar of claim 1 adapted for transmission and receipt of wavelengths in the range from 0.1mm to 5mm.

8. The phased array radar of claim 1 wherein two PCBs are used, a hrst PCB containing all said semiconductor devices and said metal transmit and receive waveguides, and a second PCB containing said antennas.

9. The phased array radar of claim 1 wherein said array of transmit antennas may be from one to tens of cm in extent.

10. The phased array radar of claim 1 wherein said waveguides are fabricated using techniques selected from the list consisting of: CNC machining of metal; plastic molding and coating fabrication; and lithography.

11. The phased array radar of claim 1 second reason is to reduce the amount of RF noise sent into the environment, and a third to thereby also reduce crosstalk between channels.

12. The phased array radar of claim 1 wherein said antennas may be placed across a total aperture orders of magnitude larger than the wavelength of said RF Tx and Rx signals.

13. The phased array radar of claim 1 wherein said receive and transmit seminconductor devices are not necessarily close to said receive and transmit antennas.

14. The phased array radar of claim 1 wherein said receive and transmit antennas are horn antennas.