Efficient front end and antenna implementation
A tightly integrated combined transmit and receive dual quadrifilar antenna is provided. The antenna comprises four helical transmit elements and four helical receive elements disposed about a common axis. A receiver front end includes an arrangement of two 90 degree hybrids which serve to effectively reject signals cross coupled from the transmit elements back into the receive elements, while still allowing the receiver to receive signals.
1. An antenna assembly comprising:
a set of four transmit antenna elements including a first transmit antenna element, a second transmit antenna element, a third transmit antenna element and a fourth transmit antenna element, wherein said set of four transmit elements are arranged in order about an axis and are equally spaced about said axis in azimuth angle;
a set of four receive antenna elements including a first receive antenna element, a second receive antenna element disposed adjacent said first receive element, a third receive antenna element disposed adjacent said second receive antenna element and a fourth receive antenna element disposed adjacent said third receive antenna element and said first receive antenna element, wherein said set of four receive antenna elements are arranged in order about said axis, equally spaced about said axis in azimuth angle;
a transmitter front end coupled to said set of four transmit elements;
a receiver front end coupled to said set of four receive elements.
2. The antenna assembly according to claim 1 wherein said transmitter front end is adapted to provide four signals to said set of four transmit antenna elements wherein, in proceeding from transmit antenna element to transmit antenna element azimuthally in a predetermined azimuth direction, each successive element receives a signal that has a phase that is advanced by 90 degrees relative to a signal applied to a preceding element.
3. The antenna assembly according to claim 2 wherein:
said receiver front end comprises a first 90 degree hybrid coupled to said first receive element and said second receive element and a second 90 degree hybrid coupled to said third receive element and said fourth receive element.
4. The antenna assembly according to claim 3 wherein said transmitter front end comprises a third 90 degree hybrid coupled to said first transmit element and said second transmit element and a fourth 90 degree hybrid coupled to said third transmit element and said fourth transmit element.
5. The antenna assembly according to claim 3 wherein:
said receiver front end further comprises a balun coupled to said first 90 degree hybrid and said second 90 degree hybrid.
6. The antenna assembly according to claim 5 further comprising:
a first low noise amplifier coupled between said first 90 degree hybrid and said balun;
a second low noise amplifier coupled between said second 90 degree hybrid and said balun.
7. The antenna assembly according to claim 3 wherein:
said receiver front end further comprises a differential input low noise amplifier coupled to said first 90 degree hybrid and said second 90 degree hybrid.
8. The antenna assembly according to claim 2 wherein said transmitter front end comprises a first 90 degree hybrid coupled to said first transmit element and said second transmit element and a second 90 degree hybrid coupled to said third transmit element and said fourth transmit element.
9. The antenna assembly according to claim 8 wherein:
said transmitter front end further comprises a balun coupled to said first 90 degree hybrid and said second 90 degree hybrid.
10. The antenna assembly according to claim 9 further comprising:
a first power amplifier coupled between said balun and said first 90 degree hybrid;
a second power amplifier coupled between said balun and said second 90 degree hybrid.
11. The antenna assembly according to claim 9 wherein:
said transmitter front end further comprises a differential output power amplifier coupled to said first 90 degree hybrid and said second 90 degree hybrid.
12. The antenna assembly according to claim 1 wherein each of said receive elements is equally spaced from two of said transmit elements.
13. The antenna assembly to claim 1 wherein said receive antenna elements and said transmit antenna elements are disposed on a common surface.
14. The antenna assembly according to claim 13 wherein said common surface is a cylindrical surface.
15. The antenna assembly according to claim 13 wherein said common surface is hemispherical.
16. The antenna assembly according to claim 13 wherein said common surface is frusto conical.
17. The antenna assembly according to claim 1 where said receive antenna elements are disposed on a first surface and said transmit antenna elements are disposed on a second surface that is coaxial with said first surface.
18. The antenna assembly according to claim 17 wherein said first surface is cylindrical and said second surface is cylindrical.
19. The antenna assembly according to claim 1 wherein said receive antenna elements and said transmit antenna elements are helical.
20. The antenna assembly according to claim 1 wherein a gain pattern of said set of four receive elements is substantially equal to a gain pattern of said set of four transmit elements.
21. The antenna assembly according to claim 1 wherein said receive elements are tuned to a first frequency and said transmit elements are tuned to a second frequency.