GB2157894A - Improvements in or relating to aerial systems - Google Patents

Abstract

With reference to Fig. 1, an aerial system comprises two secondary feeders 12, 13 fed from a primary feeder 17, through an impedance matching quarter- wavelength section 15 and a rotary contact 16. The rotary contact 16 is adjustable in position on a half- wavelength section 14 joining the ends of the secondary feeders 12, 13. <IMAGE>

Description

SPECIFICATION Improvements in or relating to aerial systems This invention relates to seriai systems.

It is already appreciated that the radiation characteristics an aerial system served by at least two feeders can be governed by the phase relationship between the feeders. If this phase relationship is to be accurately resolved, then the feeder length must be accurate. This gives rise to problems, especially where the phase relationship is required to change from time to time.

The present invention aims to provide means for readily and accurately adjusting the phase between a pair of feeders in an serial system. With such adjustment, cutting of feeder length accurately is no longer a critical factor.

According to the present invention, an aerial system comprises two secondary feeders which are fed by a primary feeder connected through an impedance matching section to a contact adjustable in position on a half-wavelength section joining the secondary feeders.

The impedance matching section may comprise a quarter-wavelength section.

The adjustment may be stepwise or smooth.

The half-wave and quarter-wavelength sections may be provided by printed circuit means.

The invention also comprises any novel subject matter or combination including subject matter herein disclosed, whether or not within the scope of or relating to the same invention recited in any of the claims of this application.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein Figure 1 illustrates an aerial system provided with a printed circuit arrangement giving step-wise adjustment and Figure 2 shows a mechanical arrangement giving smooth adjustment.

In Fig. 1, an aerial system comprises two secondary feeders 12, 1 3 fed by a primary feeder 1 7 connected to a transmitter or receiver. (Not shown). As explained hereinafter, the primary feeder 1 7 is connected via a quarter-wave impedance matching section 1 5 to a rotary contact 1 6 adjustable in position on a half-wavelength section 1 4 joining the ends of the secondary feeders 1 2, 1 3. The section 14 is of convoluted form, having a series of equi-angularly spaced inner and outer modes.

As used herein, the terms "fed" and "feeder" are to be construed as having equal application in both signal-receiving and signaltransmitting senses. It will be appreciated therefore, that reference to component 1 7 as a primary feeder does not mean that its function is limited to transmitting signals, as it may also be used to receive incoming signals.

A printed circuit board PCB provides connectors 10, 11 for connecting to the ends of the two secondary feeders 12, 13; the halfwavelength (at the design frequency) section 14, and the quarter-wavelength 1 5. The contact 1 6 comprises a twelve-position rotary contact arm or switch having a scale (not shown) and an arcuate-shaped contact head 16A. The arm of the rotary contact 1 6 is connected by a conductor 1 8 to one end of the impedance matching section 1 5 and, together with the conductor 18, forms a part of its quarter-wavelength.The other end of the section 1 5 is connected to the primary feeder 1 7. When rotated, the rotary contact 1 6 makes sequential contact at its head 1 6A with twelve inner nodes of the convoluted section 1 4. The head 1 6A functions in a make-beforebreak manner and provides a twenty-three step adjustment.

The rotary contact 1 6 does not have an indent mechanism. With the extra positions obtained when the contact head 1 6A is making with two fixed contacts, (i.e. a pair of inner nodes), instead of one, there are twentythree contact positions obtainable from the twelve way switch, giving the effect of continuous adjustment.

An adjustable capacitor 30 connects point X, (the connection between the conductor 1 8 and the section 15), to ground, so as to cancel out inductance of the rotary contact 16.

Section 1 5 catches the impedance of the primary feeder 1 7 to the impedance of the two secondary feeders 12, 13, which are in parallel.

In the modification illustrated by Fig. 2, an aerial system has two secondary feeders 22, 23 fed by a primary feeder 27 connected to a transmitter or receiver. (Not shown). The primary feeder 27 is connected via. an impedance matching quarter-wave section 25 to a rotary contact 26 adjustable in position on a half-wavelength section 24 which joins the ends A, B of the secondary feeders 22, 23.

The section 24 is of part-circular form.

The rotary contact 26 has a scale, (not shown), and a contact head 26A mounted on an arm. The end of the contact arm remote from the head 26A thereof is connected to, and is movable about, one end of the quarterwavelength section 25. The other end of the section 25 is connected to the primary feeder 27.

Section 25 matches the impedance of the primary feeder 27 to the impedance of the two secondary feeders 22, 23, which are in parallel.

The arrangement of Fig. 2 may, like that of Fig. 1, be provided by a printed circuit board.

The invention has application to a variety of aerial systems such as crossed Yagi system where polarisation can be adjusted, crossed horizontal dipoles both singly and stacked, to form turnstile arrays, and to stacked dipoles, both vertical and horizontal.

The invention enables optimum strength of signals to be obtained by chosing the appropriate polarisation, Conversley, interference signals can be phased out by adjustment of polarisation.

The arrangements described above and illustrated in Figs. 1 and 2 each provide 360 degrees of change of phase relationship between the secondary feeders 12/13 or 22/23 of the aerial systems. Individual feeder lengths thus have reduced importance as the required phase difference must be within the 360 degrees of coverage.

Calibration of the rotary contact 1 6 (or 26) is also on a 360 degree scale, and any variation in feeder lengths can be compensated for by simply locking the scale of the contact to the correct angular position thereof.

The half-wavelength sections 14, 24 are designed to have the same characteristic impedance as the associated secondary feeders.

The quarter-wavelength sections 15, 25 each have an impedance whereby each associated pair of secondary feeders are matched (in parallel) to the primary feeder. Typically, if each secondary feeder was of 52 ohms impedance, the matching section would be of 37 ohms.

Typically VHF systems would probably relate better to the arrangement illustrated in Fig. 1, while a UHF system would relate better to that illustrated by Fig. 2.

Two aerial systems, each according to the invention may be used, in back-to-back relationship, as a signal attenuator. Taking two systems as illustrated in Fig. 1 as an example, primary feeders 1 7 would then be connected to measuring instruments.

Claims (10)

1. An aerial system comprising two secondary feeders which are fed by a primary feeder, connected through an impedance matching section to a contact adjustable in position on a half-wavelength section joining the secondary feeders.

2. An aerial system as claimed in Claim 1, wherein the impedance matching section is a quarter-wavelength section.

3. An aerial system as claimed in Claim 1 or 2, having means whereby the adjustment is step-wise.

4. An aerial system as claimed in Claim 1 or 2, having means whereby the adjustment is smooth.

5. An aerial system as claimed in any one of Claims 2, 3 or 4, wherein the half-wavelength and quarter-wavelength sections are provided by printed circuit means.

6. An aerial as claimed in Claim 2 or Claim 5, wherein the half-wavelength section is shaped to provide a series of equi-angularly spaced inner nodes, the contact comprising a rotary arm which, on rotation of the arm, makes sequential contact with the inner nodes in a make-before-break manner.

7. An aerial system substantially as here it before described with reference to Fig. 1 of the accompanying drawings.

8. An aerial system substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

9. A feeder device for an aerial system, comprising a half-wavelength section whose ends are adapted for connection to two secondary feeders, a contact movable in respect to the half-wavelength section and connected to one end of a quarter-wavelength section whose other end is adapted to be connected to a primary feeder.

10. Any novel subject matter or combination including subject matter herein disclosed, whether or not within the scope of or relating to the same invention recited in any of the claims of this application.