Omidirectional and directional antenna assembly

• US 5,714,937 A
• Filed: 02/23/1996
• Issued: 02/03/1998
• Est. Priority Date: 02/24/1995
• Status: Expired due to Term

• Current Assignee: NTP Incorporated
• Original Assignee: NTP Incorporated
• Inventors: Campana, Thomas J. Jr.
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US08/605,956
• Time in Patent Office: 711 Days
• Field of Search: 340/573, 343/741, 343/789, 343/833, 343/866, 343/912, 342/147, 342/417
• US Class Current: 340/573.1
• CPC Class Codes: G08B 21/0202 Child monitoring systems using a transmitter-receiver system carried by the parent and the child
• CPC Class Codes: G08B 21/0222 Message structure or message content, e.g. message protocol
• CPC Class Codes: G08B 21/0227 System arrangements with a plurality of child units
• CPC Class Codes: G08B 21/023 Power management, e.g. system sleep and wake up provisions
• CPC Class Codes: G08B 21/0247 System arrangements wherein the alarm criteria uses signal strength
• CPC Class Codes: G08B 21/0263 System arrangements wherein the object is to detect the direction in which child or item is located
• CPC Class Codes: H04B 17/23 Indication means, e.g. displays, alarms, audible means
• CPC Class Codes: H04B 17/27 for locating or positioning the transmitter
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence

Abstract

An antenna assembly providing selectable omnidirectional or directional reception of radio transmissions in a frequency band in accordance with the invention includes an electrically conductive reflector (432) defining a cavity (702) having a bottom (708), an opening (714) and a surface (704 and 706) extending from the bottom to the opening and an electrical output (763); an electrically conductive loop (431) coupled to ground and having an electrical outlet (766) for coupling to an RF amplifier (407), the loop being positioned between the bottom opening of the cavity; a RF switch (406) having an input (760) and first and second outputs (762 and 764), the RF switch having a first switching state electrically connecting the input to the first output and a second switching state electrically connecting the input to the second output, the first switch output being electrically coupled to ground and the second switch output being electrically coupled to the output of the electrically conductive loop; and wherein the first switching state provides the directional reception and the second switching state provides the omnidirectional reception of the radio transmissions.

Claims

1. An antenna assembly providing selectable omnidirectional or directional reception of radio transmissions in a frequency band comprising:

an electrically conductive reflector defining a cavity having a bottom, an opening, a surface extending from the bottom to the opening and an electrical output;

an electrically conductive loop electrically coupled to ground and having an electrical output for coupling to an RF amplifier, the loop being positioned between the bottom and the opening of the cavity; and

a RF switch having an input and first and second outputs, the RF switch having a first switching state electrically connecting the input to the first output and a second switching state electrically connecting the input to the second output, the first switch output being electrically coupled to ground and the second switch output being electrically coupled to the output of the electrically conductive loop; and

wherein

the first switching state provides the directional reception and the second switching state provides the omnidirectional reception of the radio transmissions.

2. An antenna assembly in accordance with claim 1 wherein:

a closest separation of the loop from the cavity is not greater than one-tenth of a wavelength of the frequency band of the radio transmissions.

3. An antenna assembly in accordance with claim 2 wherein:

a closest separation of the loop from the cavity ranges between 0.005 and 0.02 of a wavelength of the frequency band of the radio transmissions.

4. An antenna assembly in accordance with claim 3 wherein:

the directional antenna has a beam width producing a maximum signal response to the radio transmission between 10° and

30°

.

5. An antenna assembly in accordance with claim 4 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

6. An antenna assembly in accordance with claim 5 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

7. An antenna assembly in accordance with claim 3 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

8. An antenna assembly in accordance with claim 7 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

9. An antenna assembly in accordance with claim 3 wherein:

the frequency band is between 902 to 928 MHz; and

a closest separation of the loop from the cavity ranges between 0.1 and 0.2 inches;

the loop is rectangular in cross section when viewed into the opening; and

the directional antenna has a beam width producing a maximum signal reception of the radio transmissions between 30° and

10°

.

10. An antenna assembly in accordance with claim 9 wherein:

the reflector, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2.5 inches; and

the loop, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2 inches; and

the loop is centered symmetrically with respect to the bottom of the reflector.

11. An antenna assembly in accordance with claim 10 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator may be used for direction finding of the transmitter relative to the radio receiver.

12. An antenna assembly in accordance with claim 9 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator may be used for direction finding of the transmitter relative to the radio receiver.

13. An antenna assembly in accordance with claim 3 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator may be used for direction finding of the transmitter relative to the radio receiver.

14. An antenna assembly in accordance with claim 2 wherein:

the directional antenna has a beam width producing a maximum signal response to the radio transmission between 10° and

30°

.

15. An antenna assembly in accordance with claim 14 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

16. An antenna assembly in accordance with claim 15 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

17. An antenna assembly in accordance with claim 2 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

18. An antenna assembly in accordance with claim 17 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

19. An antenna assembly in accordance with claim 1 wherein:

the directional antenna has a beam width producing a maximum signal response to the radio transmission between 10° and

30°

.

20. An antenna assembly in accordance with claim 19 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

21. An antenna assembly in accordance with claim 20 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

22. An antenna assembly in accordance with claim 19 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator may be used for direction finding of the transmitter relative to the radio receiver.

23. An antenna assembly in accordance with claim 1 wherein:

the electrically conductive loop has a length between the output and the electrical coupling to ground greater than 0.2 of a wavelength of the frequency band;

the cavity comprises at least two parts divided by a fold line which is the bottom of the cavity with the fold line being parallel to a directional axis of the directional reception and being a vertex of an oblique angle with first and second parts of the at least two parts of the cavity being sides of the oblique angle with ends of the first and second parts spaced from the vertex defining the opening of the cavity.

24. An antenna assembly in accordance with claim 23 further comprising:

a circuit board having the RF amplifier mounted thereon with the electrical output of the electrically conductive loop coupled to the RF amplifier with the circuit board being located further from the electrically conductive loop than the vertex.

25. An antenna assembly in accordance with claim 24 wherein:

the frequency band is between 902 to 928 MHz; and

a closest separation of the loop from the cavity ranges between 0.1 and 0.2 inches;

the loop is rectangular in cross section when viewed into the opening; and

the directional antenna has a beam width producing a maximum signal reception of the radio transmissions between 30° and

10°

.

26. An antenna assembly in accordance with claim 25 wherein:

the reflector, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2.5 inches; and

the loop, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2 inches; and

the loop is centered symmetrically with respect to the bottom of the reflector.

27. An antenna assembly in accordance with claim 23 wherein:

the frequency band is between 902 to 928 MHz; and

a closest separation of the loop from the cavity ranges between 0.1 and 0.2 inches;

the loop is rectangular in cross section when viewed into the opening; and

the directional antenna has a beam width producing a maximum signal reception of the radio transmissions between 30° and

10°

.

28. An antenna assembly in accordance with claim 27 wherein:

the reflector, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2.5 inches; and

the loop, when viewed from the opening, is rectangular in cross section and has a width and a length across the width and length of the cross section which are less than 2 inches; and

the loop is centered symmetrically with respect to the bottom of the reflector.

29. An antenna assembly in accordance with claim 23 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator is used for direction finding of the transmitter relative to the radio receiver.

30. An antenna assembly in accordance with claim 1 further comprising:

a radio receiver containing the antenna assembly, the RF amplifier, a digital signal processor, coupled to the RF amplifier and a display, coupled to the digital signal processor, for displaying a received signal strength indicator, the digital signal processor controlling switching of the first and second switching states and being responsive to a command to operate the antenna assembly as either an omnidirectional antenna during which the digital signal processor compares the received signal strength indicator representing the radio transmissions to a numerical value representing a set range between a radio transmitter broadcasting the radio transmissions and the radio receiver and generates an alert when the comparison reveals that the radio transmissions are received from the radio transmitter outside the set range or a directional antenna during which the digital signal processor drives the display to display a relative magnitude of the received signal strength indicator so that the display of the magnitude of the received signal strength indicator may be used for direction finding of the transmitter relative to the radio receiver.