GB2192490A

GB2192490A - Notch-fed dipole

Info

Publication number: GB2192490A
Application number: GB08616576A
Authority: GB
Inventors: Edmund Wergiliusz Woloszczuk
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1986-07-08
Filing date: 1986-07-08
Publication date: 1988-01-13
Also published as: GB8616576D0; EP0252648A1

Description

1 GB 2 192 490 A 1 SPECIFICATION intended transmission wavelength deep and

is narrow compared to its depth. The width of slot 10 Adipole can be varied in orderto alterthe input impedence of the dipole.

This invention relates to dipoles. 70 Arms 11 and 12, each approximately 1/4 of an Throughoutthis specification lengths of intended transmission wavelength long, areformed components expressed in terms of wavelengths are from conductive body 9 on either side of the slot 10.

their electrical lengths, physical lengths will The profile of arms 11 and 12 can be varied provided generally be slightly shorter. the top edge and the edges defining the slot 10 A notch fed dipole is generally of the form shown 75 remain straight and the two arms are symmetrical in figure 1. about an axis running along the centre of the slot 10.

The radiating part of the dipole consists of two The profile of arms 11 and 12 could be altered tothat arms 1 and 2. In orderto give efficient transmission shown bythe pairs of dotted lines 13,14or 15for of electro-magnetic energy, the length of each of the example.

arms 1 and 2 is approximately equal to 1/4 80 A grounded conductive reflector 16 is placed atthe wavelength of the intended transmitting frequency. level of the bottom of the slot 10.

The arms 1 and 2 are separated by a slot 3 cutfrom Similarlyto a conventional dipole the signal to be the body4 of the dipole. Slot 3 is approximately 1/4 transmitted is fed to the slot, by a co-axial cable 17, of a wavelength deep and narrow relative to its the control conductor 18 and outer conductor 19 depth. A reflector, formed by a grounded conductive 85 being connected to opposite sides of the slot 10, and plane 5, is located approximately a quarter of a as before a dipole resonance is set up. The position wavelength from dipole arms 1 and 2. at which the co-axial cable is connected can bevaried In operation a signal to be transmitted is applied up and down the slot. It is preferred to connect it across slot3. This is done using a co-axial cable 6, approximately half way up the slot, because this connecting the signal carrying central conductor 7 to 90 forms a balun, the exact position can be adjusted in one side of the slot 3 and the outer conductor8 tothe orderto optimise the dipoles characteristics.

other. This signal will set up a resonance on dipole The dipole arms 11 and 12 could be made a arms 1 and 2. multiple of 1/4 of an intended transmission Although the transmission will be most efficient at wavelength long, this would however alterthe the specific frequencyfor which the dipole was 95 impedence. ltwas decided for simplicity and designed it will be acceptably efficientfor a small compactness to use arms only 1/4 of an intended range of frequencies above and belowthis. transmission wavelength long.

A problem has been found in making such Although the profile of the arms can be widely conventional dipoles with a low input impedence varied it does affect the bandwidth, generallythe (50fl) and a wide bandwidth. 100 smallerthe arm area the narrowerthe bandwidth.

The present invention was made while attempting

Claims

to produce a dipole overcoming these problems. CLAIMS

This invention provides a dipole comprising two arms separated by a slot, the two arms being 1. This invention provides a dipole comprising electrically linked by a conductive path around the 105 two arms separated by a slot, the two arms being slot, each arm being X/4 long and the slot being X/2 electrically linked by a conductive path around the deep, where X is a wavelength of radiation thatthe slot, each arm being X/4 long and the slot being X/2 dipole is designed to receive ortransmit. deep, where X is a wavelength of radiation thatthe Two dipoles of this type can be arranged dipole is designed to receive ortransmit.

perpendicu la rto one another to form a cross-dipole, 110
2. A dipole as claimed in claim land additionally such an arrangement can be used to produce a comprising a feed arranged to apply a signal circularly polarised radiation or sensitivity pattern. between the two sides of the slot.

This structure provides a dipole with larger
3. A dipole as claimed in claim 2 and wherein bandwidth than normal and a 50fl input impedence. said feed is arranged to apply a signal approximately An input impedence of 5011 is desirable because it 115 half way up the slot.

is the same impedence as a co-axial cable and so
4. A dipole substantially as claimed in any gives very good impedence matching. preceding claim and wherein the two arms are Conveniently the dipole is fed with a signal to be rectangular.

radiated by a co-axial cable, the centre and outer of
5. A dipole as claimed in any preceding claim and the cable being attached to the opposite sides of the 120 wherein a reflector is placed atthe level of the slot at the same distance from the bottom of the slot. bottom of the slot.

A reflector of a known type, for example a
6. A dipole substantially as illustrated in figure 2 conductive metal sheet, maybe used to give the of the accompanying drawing and substantially as dipole a unindirectionai radiation pattern. Forthe described with reference thereto.

best resultsthis reflector should be placed atthe level of the bottom of the slot.

One wayof performing the invention will now be described with reference to figure 2. Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd, 11187, D8991685.

In figure 2 a conductive body 9 is shown, with a slot Published byThe Patent Office, 25 Southampton Buildings, London, WC2A lAY, 10 cutfrom it. The slot 10 is approximately 1/2 of an from which copies may be obtained.