Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
  • H01Q13/02—Waveguide horns
  • H01Q13/0275—Ridged horns
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/12—Supports; Mounting means
  • H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
  • H01Q1/24—Supports; Mounting means by structural association with other equipment or articles with receiving set
  • H01Q1/247—Supports; Mounting means by structural association with other equipment or articles with receiving set with frequency mixer, e.g. for direct satellite reception or Doppler radar
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/021—Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals
  • G01S7/022—Road traffic radar detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/03—Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
  • G01S7/032—Constructional details for solid-state radar subsystems

Definitions

• This invention relates to microwave radar detectors, and particularly to the construction of a horn antenna and mixer therefor.
• Horn antennas for both receiving or transmitting microwave energy are well known, and it is well known to make such horns of an electrically conductive material or of a non-conductive material that is •plated or coated in some way with an electrically conductive material.
• horn antennas that are specifically designed as receiving horns, of no matter what frequency, are required to be dimensioned and flared so as to achieve a concentration of low energy but discernable fields at one or more specific frequencies in the throat area of the horn.
• Detectors often by way of a mixing diode or diodes — are inserted or placed at the throat of the horn so as to receive the energy that is present by way of .those fields at the frequency or frequencies for which the horn has been designed.
• a highly sensitive horn is required. This is particularly so where the source of the radar or microwave frequency energy to be detected is at some considerable range from the detector; and in such instances, the physical placement of the mixing diode with respect to the throat of the horn is important.
• planar aberrations can be corrected by a lens placed in front of the horn, there is still the requirement that there must be a positive coupling at the correct frequency between the field collector — the ridge — of the horn and the detecting circuitry such as the mixing diode or diodes.
• the present invention overcomes these problems by providing a positive, physically dimensionaily stable coupling of the ridge of the horn to a feed strip for a mixing diode or pair of diodes mounted in association with a microstrip board; and the present invention also provides a horn antenna construction that is easy to mount using standard assembly line technology without the requirement for tuning or balancing the energy collection or detection at the throat of the horn.
• a horn antenna construction where a substantially rigid -and planar mounting board having upper and lower surfaces has a microstrip board mounted on the upper surface thereof, where the microstrip board has a mixing diode or diodes mounted in association therewith, and a feed strip for the diode or diodes, and having the feed strip located at or near a first edge of the microstrip board on the upper, exposed side thereof.
• a one-piece molded horn element is provided that has an open bottom, an upwardly flared top wall and a pair of side walls, and having a downwardly extending ridge formed on the underside of the top wall.
• the ridge extends rearwardly to the throat of the horn, and extends downwardly at least in the throat area to such an extent that when the molded horn element is secured to the upper side of the mounting board, the bottom edge of the ridge in the throat area is brought into physical and electrical contact with the feed strip; and moreover, the upper surface of the mounting board then forms the bottom wall of the horn.
• Provisions are also made according to the present invention for extremely good isolation among the high frequency input port from the horn, the local oscillator input frequency port from the local oscillator, and the intermediate (I.F.) output port, of the mixer which is mounted on the microstrip board.
• L.O. local oscillator
• PALMER United States Patent 3,530,482, issued September 22, 1970, teaches a partitioned horn having variable flare sidewalls. Means are provided to change the physical dimensions, and thus the energy sensitivity, in the throat of the horn.
• RISKO United States Patent 4,058,813, issued November 15, 1977, teaches a wave guide horn antenna that may be assembled from sheet metal, and which may have several different embodiments.
• the horn antenna that is taught in that patent is one which still requires a tuning screw in the throat of the horn, and is one where the precise physical dimensions of the horn and thus its energy frequency sensitivity are not predictable due to the manufacturing processes that are employed.
• Figure 1 is an isometric view, from beneath, of a pressure cast horn and associated shielding cavities, according to the present invention
• Figure 2 is a plan view of a mounting board having a microstrip board thereon, in keeping with the present invention
• Figure 3 is a plan view of the mounting board of Figure 2 having the pressure cast horn of Figure 1 mounted thereto;
• Figure 4 is a sectional view taken in the direction of arrows 4-4 in Figure 3;
• Figure 5 is a sectional view taken in the direction of arrows 5-5 in Figure 3;
• Figure 6 is a diagrammatic view of the mixer portion of the microstrip board and its relationship to the horn. DESCRIPTION OF THE PREFERRED EMBODIMENTS:
• the present invention provides a horn antenna construction which is particularly adapted for use in microwave detection circuits, such as radar detectors that operate in the X-band and K-band; that is, at 10.525 GHz and 24.150 GHz, respectively.
• Three principal structural members include a substantially rigid and planar mounting board, shown generally at 12 in Figure 2; a microstrip board 14 on the upper surface of the mounting board 12, also shown in Figure 2; and a one- piece molded horn element 16, indicated in ' Figure 1.
• the entire assembly is indicated at 10 in Figure 3, as viewed from above.
• the specifics of both the mounting board and the microstrip board are of no particular concern to the present invention, and are illustrated as exemplary only.
• there may be mounted on the mounting board 12 a tunable inductor 18, a microchip 20, a connecting post terminal 22, and various and assorted capacitors, resistors, coils, etc., shown generally at 24, 26 and 28.
• the details of the microstrip board 14 are irrelevant, except to say it has printed or mounted on it — using printed circuit and microstrip technology — circuit components that include certain reactive components for both a local oscillator and a low pass filter, and other circuitry for creating and handling signals at the L.O. and I.F. frequencies which are below the horn frequencies.
• a mixing diode or diodes mounted on the board at a point shown at 30, and having a conductive feed strip formed as part of the conductive circuit elements on the microstrip board, at 32.
• the feed strip 32 is located at or at least near the edge 34 of the microstrip board, on the upper, exposed surface thereof.
• the vertical placement of the ridge 46 — and its height in the throat area 47 is such that it will be brought into both physical and electrical contact with the feed strip 32 on the upper surface of the microstrip board 14.
• the upper surface of the mounting board 12 in the area generally designated at 50, will form the bottom wall of the horn 41, so that the horn is defined by that bottom wall, its side walls 44 and its top wall 42.
• a ground plane is created at least in the area 50 on the upper surface of the mounting board 12, by plating or coating the mounting board with a conductive material.
• a connection is made between the bottom surfaces of the side walls 44 and the conductive upper surface of the mounting board 12, and because at least the inside surfaces of the one piece molded horn element 16 are conductive, an effective ground at the intermediate frequency is assured for the mixing diode through the physical and electrical connection between the ridge 46 in the throat area 47 and the feed strip 32 for the mixing diode.
• the one piece molded horn element 16 it is most conveniently pressure cast from zinc or other appropriate metal; but it may be constructed from such non-conductive materials as an injection molded thermoplastic, which would then n be conductively coated at least on the inner surface.
• Other techniques such as laid-up epoxy and glass fibre construction may be used, particularly at lower frequencies, but dimensional stability is better assured when the element is either injection molded or more particularly when it is pressure cast of metal.
• the under surface of the mounting board 12 would normally carry a printed circuit, again formed in the usual manner and with conventional printed circuit techniques, and the circuit elements 24, 26, and 28 that are mounted on the upper surface of the mounting board 12 are electrically connected through the board to the circuit lines on the underside thereof.
• the elements on the microstrip board 14 are isolated from the ground plane on the upper surface of the mounting board 12 by virtue of the dielectric material of the microstrip board; and thus, local oscillators operating at microwave frequencies or intermediate frequencies thereof, may be mounted and shielded on the mounting board or the microstrip board.
• each of those cavities are defined by having vertically extending walls 56 and an upper wall or cover 58. If the ground plane or conductive coating on the upper surface of the mounting board 12 underlies the bottom edges of the vertically extending walls 56, then there may be mounted into the cavities 52 or 54 local oscillators, such as a first local oscillator mounted on the microstrip board 14 within the cavity 52, and a second local oscillator mounted on the mounting board 12 within the cavity 54, and they will be shielded.
• local oscillators such as a first local oscillator mounted on the microstrip board 14 within the cavity 52, and a second local oscillator mounted on the mounting board 12 within the cavity 54, and they will be shielded.
• the horn 41 (which is now said to be defined by a flat bottom surface 50, a pair of side walls 44 and an upper wall 42 that flares upwardly) has the configuration so defined, there may be some elevation distortion in respect of the microwave energy received and concentrated by the horn. This may be overcome for the most part by the placement of a lens — such as that indicated by ghost lines at 60 in Figure 4 — in front of the horn 41.
• any tuning that is .necessary may be accomplished by the presence of printed elements on the microstrip board 14, without the necessity of physically tuning the throat area 47.
• the mixing diode may be securely physically mounted in the
• microstrip board 14 and there is a positive coupling between the ridge 46 and the low energy microwave frequency field that exists on that ridge, with the feed strip 32 on the microstrip board 14.
• the horn provides an effective ground return at the intermediate frequency and it also provides a return for the local oscillator signal.
• the die in which it is cast is very easily constructed. This is because the horn, the ridge 46, the side walls 44, the side walls 56 of the cavities, the studs 38, and all other features, are formed on the underside or the "pull" side of the casting. Therefore, a single pull pressure casting is possible, making the provision of a cast zinc microwave horn very economical. It is even more economical when it is considered that, by virtue of the present invention, there is no necessity to provide a tuning post or other physical and physically movable structures in the throat area.
• the present horn antenna construction provides for a single pull pressure casting — or a very easily injection molded part having no side movement or re-entrant shapes or requirements — and having temperature stability and effective shielding of first and second local oscillators, the entire assembly may be very economically provided.
• FIG 6 another advantage of the horn construction of the present invention may be realized. That is, because of the physical mounting of the throat 47 of the horn and its ridge 46 with respect to the feed strip 32, the mixing diode may be physically and securely mounted to the microstrip board. This gives rise to the provision for microstrip printed circuit elements that are operable at microwave frequencies, and thereby very effective port isolation of a three port mixer is achieved. Assuming that the horn 41 is essentially dimensioned to operate at the X-band and K-band frequencies (10.525 GHz and 24.150 GHz, respectively) , a mixer can be provided as indicated in Figure 6 — which is set out as exemplary and is not intended to specifically relate to physical details and dimensions.
• the mixer is indicated generally at 62, and can be said to comprise three ports: the high frequency port is essentially defined by the feed strip 32; the local oscillator (L.O.) port is defined by the circuit strip 64; and the intermediate frequency output port is defined at the circuit strip 66. All of those elements, and the other elements shown in Figure 6 except the horn and the diodes, may be printed directly onto the microstrip board. As stated above, the horn having sidewalls 44 is mounted with respect to the feed strip 32 so that the ridge 46 at least overlies a portion of the feedstrip 32 and is in physical and electrical contact therewith.
• a circuit strip 68 is provided; and connection point 30 is defined, as being where a one- quarter wavelength stub 70 for the X-band, and a one- quarter wavelength stub 72 for the K-band, contact the circuit strip 68.
• a pair of mixing diodes 74 which are usually mounted on a mounting stratum in anti-parallel connection, is connected from the end of the feed strip 32 to the connection point 30.
• a pair of elements 76 and 78 are also provided on the microstrip board between the circuit strip 68 and the circuit strip 66; and the elements 76 and 78 function to provide a low pass filter as described hereafter.
• a further pair of matching stubs 80 and 82 are provided somewhere along the length of the feed strip 32, as described hereafter.
• One of the aims of the present invention is to provide means to convert as much of the high frequency energy that appears at the horn ridge 46 and is thereby transferred to the feed strip 32, to intermediate frequency energy at the circuit strip 66 for further signal handling (which is beyond the scope of the present invention), as is possible. There should be good isolation between the three ports for the mixer, which ports are defined at feed strip 32, and circuit strips 64 and 66.
• the one-quarter wavelength stubs 70 and 72 a virtual short circuit at the X-band and K- band frequencies at the connection point 30 is assured. Therefore, any X-band or K-band frequency energy appearing across the mixing diodes 74 will cause conduction excursions by one or the other of the diodes.
• the horn element 16 provides a good ground return for the local oscillator and I.F. frequencies that are present on the microstrip board 14.
• Any energy reflected back to the feed strip from the mixing diode 74 will be cancelled by an out of phase reflection from the matching stubs 80 or 82, when they are properly placed along the length of the feed strip 32.
• the local oscillator frequency may be in the order of 6.0 GHz (more or less), and that the I.F.
• the low pass filter elements 76 and 78 are therefore placed and dimensioned so as to provide a low pass filter of approximately 2.0 GHz. Therefore, there is good isolation of the I.F. signal on the circuit strip 66 from the L.O. port at 64 or the high frequency port at 32. Moreover, because of the virtual short circuit at the X-band and K-band frequencies at the connection point 30, there is further assurance that there will be no leakage of high frequency energy past the connection point 30 into either the L.O. port at circuit strip 64 or the I.F. output port at circuit strip 66.
• the throat between the ridge 46 and either sidewall 44 appears as a reactive impedance at the first L.O. frequency, so that there is no outward radiation of local oscillator frequency from the horn 41, and a return path is provided for the L.O. signal to ground.
• the physical dimensioning is such that there is no outward radiation of I.F. frequency signals from the horn 41, because the horn throat 47 acts as an effective ground at the I.F. frequency.
• the low pass filter that is provided by the circuit elements 76 and 78 provides for good local oscillator to intermediate frequency port isolation.
• Other specific details of the structure of the microstrip board 14 and the mounting board 12, and of the circuit elements mounted or printed on them, are not relevant to the present discussion; however, it is clear that according to the present invention a horn antenna construction can be provided that will work at given frequencies — such as the X-band or K- band frequencies — where the operating frequency is determined by the physical dimensioning of the horn, the ridge and the throat area.

Landscapes

• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Waveguide Aerials (AREA)
• Radar Systems Or Details Thereof (AREA)
• Support Of Aerials (AREA)
• Transceivers (AREA)
• Accessories For Mixers (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=4126893

Family Applications (1)

Country Status (5)

Cited By (3)

Families Citing this family (4)

Citations (5)

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• 1984
  • 1984-01-06 CA CA000444841A patent/CA1187602A/en not_active Expired
  • 1984-12-21 AU AU38377/85A patent/AU572953B2/en not_active Expired
  • 1984-12-21 EP EP19850900486 patent/EP0167582A1/en active Pending
  • 1984-12-21 JP JP60500431A patent/JPS61500944A/ja active Granted
  • 1984-12-21 WO PCT/GB1984/000448 patent/WO1985003170A1/en not_active Application Discontinuation

Patent Citations (5)

Non-Patent Citations (2)

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