MULTIBEAM ANTENNA, WHICH CAN PROVIDE DIFFERENT BEAM POSITIONS ACCORDING TO THE ANGULAR SECTOR OF INTEREST

Abstract: Multibeam antenna, which has a high switching capability with high RF power levels, consisting of three sub arrays (5, 6, 7) which suitably spaced, assure angular coverage in the azimuth hemispace from 0<o> to 180<o>. A single beam forming network (2, 3) provides each sub-array with the correct field amplitude and phase distribution. Switching is performed electronically.

Description: "MULTIBEAM ANTENNA, WHICH CAN PROVIDE DIFFERENT BEAM POSITIONS ' ACCORDING TO THE ANGULAR SECTOR OF INTEREST" This invention concerns a multibeam antenna which has a high switching capability with high RF power levels. It belonges to the field of electronically switched beam antennas. The invention may find, application in the field of electronic defence systems fay tackling single or multiple threats arriving from different directions. The antenna can provide pseudo adaptability to the radar cross section, as it is made up of three sub arrays, each of which includes eight elementary equispaced radiators which assure angular coverage of the azimuth emispace from 0° to 180° , fed by a single beamshaping network which provides the correct field amplitude and phase distribution. The emispace is therefore divided into-thr=e angular sectors, each of which a sub array is associated. Switching between these angular sectors and within each sector is electronic. Each sub array, as mentioned above, shapes three beams which take different angular positions on the azimuth plane through the same feed network. The selection of these beams is electronic upon designation by the system which assesses relevant direction of arrival. One of the previous solutions was to utilize arrays fed by £ Rothman lenses or by Butler matrixes. An other solution , was provided by a series of di¬ rectional antennas, one for each beam to shape, fed by a n way switch (as many ways as the number of beams) or by tran¬ smitters. These solutions have a number of drawbacks, among which: - proliferation of the number of transmitters, with consequen¬ tial cost and dimensions 'increase; - low- switching speed, for the switching network, due tα the high RF levels at stake. The antenna, which is the subject of this invention, consists of three sub arrays (5), (6), (7) which suitably spaced, can assure angular coverage in the 0° : 180° azimuth emispace. (In a specular manner. three more sub arrays fed by a se¬ parate transmitter, can assure angle coverage in the other 180° : 360° azimuth emispace). The three sub arrays are fed by a single beamforming network which provides for the correct field amplitude & phase distribution to each subarray. The emispace is thus divided into three angle sectors, to each one of which a sub array is associated. Switching between these angular sectors is performed electro- nically and within each sector; the relevant sub array forms three beams which take different angle directions on the azimuth plane through the same feed network. Selection of these beams is in turn electronic, upon indi¬ cation from the designating system, i.e. the system which de- scerns the threat or threats direction of arrival. The beam- switching and farming network consists of solid state com¬ ponents to obtain the high switching speeds (100-150 nsec) which are required to satisfy the tasks set on the system. The gain of each beam, required to established the necessary effective radiated power,, is achieved by providing the array with a directivity also in the vertical plane. This can be achieved by using as an element of the array a sectorial horn radiator, over the aperture of which a phase correcting dielectric lens is placed, which enhances radiation efficiency. A most interesting characteristic of this indi¬ cating system is that of 'directing the beam to the desired direction in negligible times. This is achieved through: - high switching times with high total RF power radiated; - high effective radiated power associated to each single beam; — azimuth coverage over the whole round angle using- two radiating systems, each having a 0° to 180° coverage sector; — capability to adapt to the number of beams of the designa¬ ting system. This gives the antenna system the capability to tackle mul¬ tiple threats. The transmitting antenna is made up of two specular subassem- blies each covering a 180° sector. It may be installed, in its preferred configuration, on board a^ ship (Figure 1). The invention will now be described with reference to one of its forms presently preferred and provided as an illustration, but not limited to such form, with reference to figures and diagrams attached. Figure 1: Schematic representation of the system fitted on board a ship. Figure 2: Functional schematic of the antenna, consisting - Transmitter (1) - Power divider (2) - Delay line phase shifter (3) where 3a and 3c are beam se¬ lectors and 3b are the delay lines - Sub array selector (4) - Three sub arrays (5) (6) (7) - Pilot circuit (8) Figure 3: Block diagram of the antenna system where: (4) switching network (sub 'array selector); (3) delay line phase shifter; (2) power splitter; (5) (6) (7) sub arrays; Figure 4r Power splitter (noted as (2) in Figure 3). Here num¬ bers 1 to 8 indicate the RF signal outputs and IN is the input signal. Figure 5: Delay line phase shifter, indicated as a whole with numbers (2) (3) (4) in Figure 3. Figure 6: Pii t circuit, where d stands for the desired direc¬ tion, 3a, -; and 4 are the signals which enable each relevant block 3a, 3c and 4. (Figure 2) to deliver RF power in the de¬ sired directiσn. Figure 7: Detail of one of the sub arrays where X, Y, Z are the reference system; (5a) is the radiating element; (9) is the dielectric lens for field phase correction over the varying element; (10) is the polarization converter. Figure 8: Correspondence between the three sub arrays angular coverage and the designating system's angular coverage. With reference to the figures, the antenna systems operation will be described: the input RF signal (1) is split by the power divider (2) into eight parts, which are sent to the de- lay line phase shifter (3). The delay live phase shifter (3) provides the correct phase illumination to sub array (5) or (6) or (7) to radiate the RF signal in the desired direction. Such phase shifter consists of delay lines (36) either coaxial or triplate to assure stability in the radiation direction over the whole range of frequencies of operation. The switching network (selector) (4) which follows the phase shifter (3) switches the predetermined distribution onto one of the three sub arrays (5), (6), (7) which are geometrically set to achieve the coverage required (0° : 180°). The commands to the delay line phase shifter (3) and to the switching network (sub array selector) (4) are provided in parallel to the pilot circuit (8) as a function of the desired position of the beam. This pilot circuit can select the output signals, corre¬ sponding to theinput signal, required to drive the beam se¬ lectors 3a & 3c and the sub array selector (4) and then to deliver RF power in the desired direction. The insertion loss of the phase shifting splitting & switching network is δ dB so that the antenna gain, inclusive of losses, is 18 dB. For each subassy, nine beam positions are achieved. The centre subarray (Figure 3) covers the angular sector from 67.5° to 112.5°, while the two sub arrays (5), (7), cover each0°:67.5° and 112.5°:180°. This gain distribution may be exploited to make the antenna system pseudoadaptive to ship R.C.S. for a more effective electronic defence (ECM) of the same. The uniqueners of this antenna system consists essentially in: - the use of the array principle to switch large RF powers rapidly over different angular directions (100 : 150 nsec); - the adaptation to the designating system through the use of a single transmitter associated to a single feed network which manages three subarrays to cover the angular emispace. This adaptation provides the antenna system also with a pseudoadapting capability to the ship radar cross section, as in the angular sector where this is larger, there is a larger array gain and therefore .higher effective radiated power, known in leterature as ERP.

Claims: CLAIMS 1. Multibeam antenna which can provide different beam posi¬ tions, where these positions are acquired in very short times, with high RF power, characterized by including ar- power splitter (2), a delay line phase shifter (3) a sub array selector (4) and three sub arrays (5), (6), (7). 2. Multibeam antenna, as per claim 1, characterized by fur¬ thermore including a pilot circuit (6) which has the task of commanding the delay line phase shifter (3) and the sub array (4) to deliver the RF power in the desired direction. 3. Multibeam antenna, as per claims above, inclusive also of three sub arrays fed by a single splitting, phasing and switching network which provide different angle coverage. 4. Multibeam antenna, as per previous descriptions, drawings and claims above, in its wholeness and single components.

Inventors: RUSSO PASQUALE, SCARPETTA ROSARIO, RUSSO, PASQUALE, SCARPETTA, ROSARIO
Applicants: SELENIA IND ELETTRONICHE, SELENIA, INDUSTRIE ELETTRONICHE ASSOCIATE
Application year: 1985
Main classification: H01Q3
IPC codes: H01Q3