GB2228833A - Directional antenna - Google Patents

Abstract

A directional antenna 2, e.g. for reception of TV signals broadcast by satellite, is movably mounted on a support structure which also supports circuitry 6 for converting the antenna signal into a lower-frequency signal for supply to a transmission line or cable, the circuitry further comprising circuit means responsive to the lower-frequency signal for detecting when the antenna is correctly positioned and for operating an indicator 20 in proximity to the antenna in dependence upon such detection. <IMAGE>

Description

IIdPROVEMENTS IN AND RELATING TO ANTENNAS This invention relates to antennas, and particularly but not exclusively to antennas for receiving microwave signals broadcast by satellites.

It is becoming increasingly important to be able to supply antennas which can be both purchased and set-up inexpensively.

According to one aspect of the invention there is provided a device for mounting in proximity to an antenna, the deice comprising an indicator and circuit means for operating the indicator in dependence on whether or not the antenna is directed toward a signal source. Preferably, the indicator is a simple on/off device, such as a light emitting diode, in order to reduce costs and to render it easier for someone orientating the antenna to deduce that it is correctly positioned.

According to another aspect of the invention, an indicator which is arranged to be operated in dependence upon whether or not an antenna is directed toward a signal source is mounted on the same structure as that supporting the antenna, and is preferably fixed with respect to the antenna. The antenna is preferably mounted on the SU52G'-t structure in such a way that it can be re-orientated with respect to the structure to facilitate the aiming of the antenna toward the signal source.

According to a further aspect of the invention, there is provided circuitry in proximity to an antenna and preferably mounted on the same support structure as the antenna, the circuitry be operable to convert a signal output from the antenna to a lower frequency signal for transmission along an antenna lead at reduced loss, the circuitry further comprising circuit means for driving an indicator in dependence upon whether or not the antenna is directed toward a signal source, the indicator also being mounted in proximity to the antenna and preferably on the same support structure as the antenna. Preferably the circuit means is responsive to the down-converted lower frequency signal for determining whether or not the antenna is directed toward the signal source.The lower frequency signal mass in fact be an intermediate frequency signal which is delivered to apparatus at the other end of the antenna lead for converting the signal into a still lower frequency and demodulating and decoding the signal. The signal may then be supplied, e.g. to a television.

The arrangement described in the preceding paragraph has the advantage that the circuit positioned in proximity to the antenna can act both to down-convert the frequency of the antenna signal and thereby reduce the signal losses in the antenna lead, and also to drive the indicator.

Preferably some or all of the above aspects of the invention are combined.

An arrangement embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a flat array antenna in accordance with the invention; Figures 2(a) and 2(b) are side elevations cf dish antenna in accordance with the invention; and Figure 3 is a block diagram of the circuitry of an indicator for the antenna of the preceding drawings.

Preferring to Figure 1, a directional antenna 2 comprises a panel 4 which is of generally rectangular or square shape and which includes an array of microwave horns, dipoles or slots interconnected by transmission lines or waveguides, with the common output connected to circuitry indicated at 6. The panel 4 is supported by a bracket 8 carried by a support post 10, which is in turn supported by a base 12. The base 12 is fixedly mounted to a rigid structure, for example, the wall of a house, by fixing means such as bolts 14. The support structure formed by elements 8, 10 and 12 is such that the panel can be pivoted about a horizontal axis 16 and about a vertical axis 18, and thus can be re-orientated to a desired position.The circuitry 6 is fixedly mounted with respect to the panel 4, and is connected to an indicator 20 in the form of a light emitting diode, which is also mounted on the bracket 8 and is thus fixed with respect to the antenna 4. The indicator 20 is visible to an observer while he is repositioning the antenna.

The invention is also applicable to dish antenna, such as the prime focus dish shown in Figure 2(a) and the offset dish shown in Figure 2(by, in which figures the dishes are indicated by reference no. 22, and the circuitry and indicators by the same reference nos. 6 and 20 as used in Figure 1.

With reference to Figure 3, the circuitry 6 includes means (not shown) for converting the antenna signal of about 12 GHz into an intermediate frequency of about 1 GHz. This is supplied to the circuit means 30 in Figure 3, at an input terminal 32. The signal passes to an output terminal 34, which is coupled to a transmission line or cable (not shown) leading to signal utilization apparatus at a remote position.

The intermediate frequency signal is tapped by coupling means 36, which may be a resistor, waveguide, inductance, etc. The tapped signal is delivered to one input of a mixer 38. The other input of the mixer 38 is supplied by voltage controlled oscillator 40, which is driven by a ramp signal generator 42 so that the frequency supplied to the other input of the mixer sweeps across a band of about 1 GHz to 1.5 GHz.

The output of the mixer is fed through an amplifier 44 and a band pass filter 46 having its centre frequency set at about 18 NRz to a detector 50. As the output of the voltage controlled oscillator 40 sweeps through an intermediate frequency associated with a specific channel frequency, and assuming that the antenna is correctly oriented, the output of the detector will rise and then fall back to ambient noise level. The output of the detector is fed through a differentiator 56 to a comparator 58 which provides an output at terminal 60 only if its input level exceeds the ambient noise level. In an alternative embodiment, the items 38, 40, 42 and 56 are omitted, and items 44, 46 and 50 are tuned to a desired channel which therefore causes an output to be generated at terminal 60. The signal output terminal 60 is used to drive the indicator 20. Accordingly, if the indicator 20 is illuminated, the operator knows that the antenna is picking up a signal.

Claims (7)

CLAIMS:

1. A directional antenna structure comprising an antennas support means for supporting the antenna, circuitry in proximity to the antenna for converting an output signal from the antenna into a lowerfrequency signal and an indicator also in proximity to the antenna for providing an indication of whether or not the antenna is correctly oriented, the circuitry including circuit means for driving said indicator.

2. A structure as claimed in claim 1, the circuit means being responsive to the lower-frequency signal for detecting when the antenna is correctly oriented.

3. A structure as claimed in claim 1 or 2, wherein the indicator is an on/off device.

4. A structure as claimed in any preceding claim, wherein the circuitry and the indicator are also mounted on said support means.

5. A structure as claImed in claim 4, when the circuitry and indicator are ir. a fixed position with respect to the antenna.

6. A structure as claimed in any preceding claim, when the support means supports the antenna in such a manner that the antenna can be re-oriented.

7. A directional antenna substantially as herein described with reference to Figure 3 with any one of Figures 1, 2(a) and 2(b) of the accompanying drawings.