GB2251518A

GB2251518A - Local oscillator feed for monolithic array receiver system

Info

Publication number: GB2251518A
Application number: GB8509122A
Authority: GB
Inventors: William David Waddoup
Original assignee: Northern Telecom Europe Ltd; Standard Telephone and Cables PLC
Current assignee: STC PLC; Nortel Networks Optical Components Ltd
Priority date: 1985-04-09
Filing date: 1985-04-09
Publication date: 1992-07-08
Anticipated expiration: 2005-04-09
Also published as: GB2251518B; GB8509122D0

Abstract

A monolithic array receiver system has a dielectric lens 41 in the focal plane of which there is a monolithic array 40 of crossed dipole elements such that substantially parallel beams of radiation received from different directions are focussed onto unique elements of the array, and polarisation means to effect linear polarisation of the received beam signals whereby the polarisation vector is aligned with one arm of each of said crossed dipole elements. The other orthogonal arms of the crossed dipole array are illuminated by a source 42 of local oscillator signals positioned to one side of the principal axis of the lens and out of the field defined by the crossed dipole array, said source being arranged to direct the local oscillator signals in parallel beams across the path of the beam signals. Plane mirror 50 in the path of the received beam signals deflects the local oscillator beam signals onto the lens substantially co-incident with the received beam signals, said local oscillator beam signals being orthogonally polarised with respect to the received beam signals and said mirror being polarisation sensitive so as to be transparent to the received beam signals and reflective to the local oscillator beam signals. <IMAGE>

Description

LOCAL OSCILLATOR FEED FOR MONOLITHIC ARRAY RECEIVER SYSTEM This invention relates to a local oscillator feed arrangement for a monolithic array receiver system (MARS).

The basic monolithic array receiver system comprises a dielectric lens designed to focus substantially parallel beams of radiation from different directions onto unique crossed dipole elements formed in a monolithic array in the focal plane of the lens. One arm of each crossed dipole is used to receive linearly polarised target signals whose polarisation vector is aligned with the arm. The orthogonal arm is used to receive linearly polarised local oscillator (LO) signals which must be orthogonally polarised with respect to the target signal. Diodes placed between the orthogonal arms implement a heterodyning process, enabling i.f. signals to be available directly for further processing.

The present invention addresses the problem of providing efficient and uniform excitation of the LO arms of the crossed dipoles in the array without causing blockage.

According to the present invention there is provided a monolithic array receiver system having a dielectric lens in the focal plane of which there is a monolithic array of crossed dipole elements such that substantially parallel beams of radiation received from different directions are focussed onto unique elements of the array, and polarisation means to effect linear polarisation of the received beam signals whereby the polarisation vector is aligned with one arm of each of said crossed dipole elements, characterised in that the other orthogonal arms of the crossed dipole array are illuminated by a source of local oscillator signals positioned to one side of the principal axis of the lens and out of the field defined by the crossed dipole array, said source being arranged to direct the local oscillator signals in parallel beams across the path of the received beam signals, the system including plane mirror means in the path of the received beam signals to deflect the local oscillator signal beams onto the lens substantially co-incident with the received beam signals, said local oscillator beam signals being orthogonally polarised with respect to the received beam signals and said mirror means being polarisation sensitive so as to be transparent to the received beam signals and reflective to the local oscillator beam signals.

Embodiments'of the invention will now be described with reference to the accompanying drawings, in which: - Fig. 1 illustrates a monolithic array receiver system, Figs. 2a-2c illustrate the operation of the system shown in Fig. 1, Fig. 3 illustrates a single crossed dipole element in the array of Fig. 1, Fig. 4 illustrates the illumination of a monolithic array by a complementary array of local oscillator signal sources, Fig. 5 illustrates an arrangement for illuminating a monolithic array avoiding blocking of the array field, Fig. 6 illustrates an alternative arrangement to that of Fig. 5 using a phased array source, Fig. 7 illustrates another alternative arrangement to that of Fig. 5 using a cluster of sources with a beam shaping reflector, and Figs. 8 and 9 illustrate alternative local oscillator sources combined with a dielectric lens.

rrrne monolithic array receiver system shown in Fig. 1 comprises a dielectric lens 10 (illustrated in half cut-away form) having in its focal plane a dielectric substrate 11 carrying an orthogonal array of crossed dipole elements 12. The lens is dimensioned to focus parallel beams 13 of radiation (target signals) onto unique crossed dipole elements according to the angle of incidence of the beams with respect to the principal axis of the lens. Consider for a moment Figs.

2a-2c, wherein there is illustrated a simple 3-element array of crossed dipole elements RXl, RX2, RX3 in the focal plane of the dielectric lens 10. A parallel beam 13(2) on the principal axis of the lens is focussed onto the central element Rx2 (Fig. 2a). In Fig. 2b a beam 13(3) arriving at an angle.+to the principal axis is focussed onto element Rx3 whilst another beam. 13(1) (Fig. 2c) arriving at an angle - swill be focussed onto element Rxl of the array. Reverting now to Fig. 1, the crossed dipole elements of the array are also illuminated by a local oscillator signal 14 from a source 15 (unspecified). Each crossed dipole element has the form shown in Fig. 3. The two horizontal (dotted) arms 30 form the target signal receiving dipole of the element.

The two vertical arms 31 form the local oscillator receiving dipole of the element. The two dipoles are connected by diodes 32 to implement the heterodyning function. One arm of the LO dipole is split into two parallel sections, coupled by a capacitance, the two sections being connected as inputs to an i.f. amplifier.

Conveniently the diodes, capacitance and amplifier are fabricated as integrated components carried on the rear of the substrate 11. To provide the correct decoupling of the local oscillator and target signals the target signals are linearly polarised with the polarisation vector aligned with the dipole arms 30 whilst the L.O.

signal is orthogonally polarised with respect to the target signal.

Ignoring for the moment the problem of blockage, it is clear that an efficient way of illuminating the receiver array with local oscillator signal is to construct a complementary lens and substrate array, provided with single dipoles only, facing the receiver array as shown in Fig. 4, and energising the complementary array with the local oscillator signal.

For the sake of simplicity consider a mere 3-element crossed dipole receiver array 40 carried on the focal plane face of dielectric lens 41. An identical lens 42 carries on its focal plane face a 3-element array of single dipoles 43 whose arms are aligned with the L.O.

arms of the crossed dipole receiver array 40. The LoO.

signal is split 3 ways and fed to the 3 dipoles of array 43. By reciprocity, even though the two lenses are in each others near-field, the signals radiated from the dipoles of lens 42 are transferred efficiently and with minimal loss to the dipoles of lens 40. Thus the signal emanating from dipole L01 is focussed on crossed dipole Rx1i whilst the signal from dipole L02 is focussed on RX2 and so on. Obviously, in practice, many more dipoles would be employed, a typical array being, say, 16 x 16 or even larger.

However, it is -clear that the arrangement shown in Fig. 4 is completely impracticable in as much as the L.O. lens, being directly in the field of the receiver lens, blocks out practically all of the possible target signal. This problem is overcome in the present invention by placing the L.O. lens to one side of and displaced far enough from the principal axis of the receiver lens to be out of the field of the latter, and providing polarisation sensitive deflection means in the field of the receiver lens to direct the L.O. signal onto the receiver lens, as shown in Fig. 5.The local oscillator lens 42 is placed to radiate the linearly polarised L.O. signals across the path of the receiving lens and the polarisation sensitive mirror 50 is placed in said path at an angle to reflect the L.O. signal onto the receiver lens 41 in parallel with the polarised target signals which pass through the mirror. Control of the excitation of the individual L.O. elements (L01 * L03) enables an arbitrary prescribed taper of L.O. signal power to be applied across the crossed dipole receiver array.

As an alternative to the dipole array source of L.O. signals the system may use instead a phased array source as shown in Fig. 6. An array 60 of radiating elements is fed with L.O. signal via a beam forming network 61 to form a number of beams of L.O. signal corresponding to the beams provided by the lens array of Fig. 5. The beams from the phased array 60 are likewise polarised and redirected by the mirror 50 onto the receiving lens 41. Another alternative is to replace the L.O. lens 42 of Fig. 5 by a cluster of offset radiating L.O. elements 70 which are directed towards a beam shaping reflector 71. The shaped beams are then re-directed by the polarisation sensitive mirror 50 as before.

Other alternative sources of L.O. signal are shown in Figs. 8 and 9. In Fig. 8 there is depicted an array of open ended waveguides 80 coupled to a dielectric lens 81. The L.O. signal is fed to the waveguides via a power divider network 82 and the waveguides have tuning screws to enable them to be individually matched to the dielectric lens interface. Yet another possible source could be fabricated by replacing the discrete L.O.

elements in the focal plane of the lens by a continuous dielectric launcher 90 to provide L.O. signal distributed uniformly over the lens focal plane as shown in Fig. 9, and hence by reciprocity over the receiver lens. Such a launcher could be stepped to provide a match between the lens 91 and the waveguide feed 92.

In one embodiment of the invention a slight simultaneous intentional misalignment of the polarisation vectors of both the polarising mirror and LO radiating elements with respect to the polarisation vectors of the receiving elements would enable a small fraction of the LO power to be injected into the signal arms of the receiving elements. The reduction of LO power into the LO arms of the receiving element would however be minimal. These signals could then form the basis of an inter-channel stability calibration process, the absolute calibration having been determined once and for all by some other method.

Claims

CLAIMS:

1. A monolithic array receiver system having a dielectric lens in the focal plane of which there is a monolithic array of crossed dipole elements such that substantially parallel beams of radiation received from different directions are focussed onto unique elements of the array, and polarisation means to effect linear polarisation of the received beam signals whereby the polarisation vector is aligned with one arm of each of said crossed dipole elements, characterised in that the other orthogonal arms of the crossed dipole array are illuminated by a source of local oscillator signals positioned to one side of the principal axis of the lens and out of the field defined by the crossed dipole array, said source being arranged to direct the local oscillator signals in parallel beams across the path of the received beam signals, the system including plane mirror means in the path of the received beam signals to deflect the local oscillator signal beams onto the lens substanially co-incident with the received beam signals, said local oscillator beam signals being orthogonally polarised with respect to the received beam signals and said mirror means being polarisation sensitive so as to be transparent to the received beam signals and reflective to the local oscillator beam signals.

2. A receiver system according to claim 1 characterised in that the source of local oscillator beam signals comprises a second dielectric lens identical to the receiver array lens and having in its focal plane an array of dipole elements complementary to the receiver crossed dipole array, the source lens being oriented toward the mirror means so that local oscillator beam signals from each source dipole are directed to and focussed on the respective dipole element of said monolithic receiver array.

3. A receiver system according to claim 1 characterised in that the source of local oscillator beam signals comprises a phased array of transmitting elements fed with local oscillator signals via a beam forming network whereby individual beams of local~oscillator signal formed by the array are directed to respective crossed dipole elements of the receiver array via the mirror means.

4. A receiver system according to claim 1 characterised in that the source of local oscillator signals comprises an array of transmitting elements the signals from which are directed to a beam shaping reflector before being redirected via the mirror means onto the crossed dipole elements of the receiver array.

5. A receiver system according to claim 1 characterised in that the source of local oscillator signals comprises a second dielectric lens identical to the receiver array lens and having in its focal plan an array of waveguide radiating elements fed with local oscillator signals via a power dividing network.

6. A receiver system according to claim 1 characterised in that the source of local oscillator signals comprises a second dielectric lens identical to the receiver array lens and having in its focal plane a dielectric signal launching means fed with local oscillator signals via a waveguide coupled to the launcher, the launcher being formed so as to spread the input local oscillator signal over the focal plane of the second lens.

7. A receiver system accorlding to any preceding claim characterised in that the polarisation of the local oscillator beam signals is misaligned with respect to the crossed dipoles of the receiver array by a predetermined amount whereby a portion of the local oscillator signal is injected into the target signal receiving dipole of each element of the monolithic array to enable the interchannel stability of the array-to be calibrated.

8. A monolithic array receive system substantially as described with reference to Figs. 5-9 of the accompanying drawings.