GB2135828A - A monopulse radar antenna - Google Patents
A monopulse radar antenna Download PDFInfo
- Publication number
- GB2135828A GB2135828A GB08305195A GB8305195A GB2135828A GB 2135828 A GB2135828 A GB 2135828A GB 08305195 A GB08305195 A GB 08305195A GB 8305195 A GB8305195 A GB 8305195A GB 2135828 A GB2135828 A GB 2135828A
- Authority
- GB
- United Kingdom
- Prior art keywords
- elements
- sum
- antenna
- difference
- signals received
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/42—Simultaneous measurement of distance and other co-ordinates
- G01S13/44—Monopulse radar, i.e. simultaneous lobing
- G01S13/4463—Monopulse radar, i.e. simultaneous lobing using phased arrays
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
- H01Q25/02—Antennas or antenna systems providing at least two radiating patterns providing sum and difference patterns
Landscapes
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
The antenna comprises an array of radiating elements 32 arranged in pairs symmetrically about the bore-sight axis 38. Each of four hybrid rings 40 form the sum and difference of the signals received by a symmetrically situated pair of elements 32 in an inner set of eight elements 32. The outputs of the hybrid rings are summed and applied to a sum output line 46a and a difference output line 46b. The signals received by the set of four elements 32 at each end of the array are summed separately and applied to a fifth hybrid ring 50. The outputs of the hybrid ring 50 and the output lines 46a, 46b are combined and fed to a sum port 34a and a difference port 34b. For generating a secondary surveillance control pattern, a directional coupler 66 divides power at a control port 67 in opposite phases between a central control element 64 and the divider 56 of the feed network. The main interrogation is effected by pulsing the sum port 34a; the coupler 66 routes this power only to the divider 56. <IMAGE>
Description
SPECIFICATION
A monopulse radar antenna
The present invention relates to a monopulse radar antenna and, more specifically, to the feed network used to feed signals to and from the radiating elements of the antenna.
The monopulse radar technique enables the bearing of a target to be determined accurately from a singie pulse of radar energy.ln principle, the technique can be used with a pair of radiating elements, by combining the signals received by the two elements to form the sum and the difference of the two signals.
The radiation pattern of the sum signal consists of a main lobe centred on the antenna boresight axis and flanked by side lobes falling off in intensity to either side of the main lobe. The radiation pattern of the difference signal has a null on the boresight axis flanked by two lobes of opposite phase. Again there are side lobes.
A comparison of the relative intensities of the sum and difference signals and a determination of the polarity of the difference signal enables the bearing of a target from the boresight axis to be determined uniquely.
When the monopulse technique is used in secondary surveillance radar, it is desirable that the side lobes be ignored. To this end, an additional pattern, known as the control pattern, is generated which is quasi-omni-directional and has an intensity intermediate that of the side lobes and the main lobes of the sum pattern which is used to transmit an interrogating signal. The control pattern in transmitting a control pulse before the main interrogating pulse, provides a reference intensity which enables signals arising from side lobes to be disregarded. The control pattern commonly has a narrow null on the boresight axis, corresponding to the main lobe of the sum pattern.
In order to achieve narrow enough main lobes in the sum and difference patterns, a monopulse antenna of the type formed by an array of antenna elements comprises substantially more than two elements and a feed network has to be employed to combine the signals from the elements appropriately to form both the sum signal and the difference signal. The object of the present invention is to provide an antenna with a simplifed feed network achieving the required combinations.
The present invention provides an antenna for a monopulse radar system comprising a radiating array extending to either side of the bore-sight axis of the monopulse radar pattern, the array comprising a plurality of first radiating elements on a first side of the bore-sight axis at respective spacings therefrom and a like plurality of second radiating elements on the second side of the bore-sight axis each at a like spacing therefrom as a respective corresponding first element, and the antenna further comprising a feed network with a plurality of first combining means each of which forms the sum and difference of the signals received by a respective one of a first set of first elements and by the corresponding second element, means for forming a first summation of signals received by a second set of first elements, means for forming a second summation of the signal received by the second elements corresponding to the second set of first elements, further combining means for forming the sum and difference of the first and second summations, and summation means for forming output summations of the sum signals and of the difference signals formed by the combining means, at sum and difference terminals of the antenna.
For convenience the antenna has been defined with reference to its properties when receiving.
However the antenna is a reciprocal device and may be used both to transmit and receive.
An embodiment of the invention will be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of a basic monopulse antenna array having two radiating elements,
Figure 2 indicates the form of the sum and difference patterns,
Figure 3 indicates the distribution of signals to be applied to an array of elements to generate the patterns of Figure 2,
Figure 4 is a schematic diagram of the radiating array and feed network of a known monopulse radar antenna,
Figure 5 is a schematic diagram of an antenna according to the invention,
Figure 6 is a schematic diagram of an antenna incorporating means for generating the control pattern, and
Figure 7 is a schematic diagram of an antenna according to the invention and incorporating the means of Figure 6 for generating the control pattern.
Referring to Figure 1, a simple monopulse radar antenna comprises two radiating elements 10a, 10b and a feed network 12 comprising a hybrid ring 12a.
The hybrid ring 12a is a transmission line 14 forming a circular path of circumferential length 3/2 X at the operating frequency. The ring has two feed ports 16a, 16b separated by 2 and A in respective directions around the transmission line.The feed ports 16a, 16b are coupled to respective radiating elements 10a, 10b. A sum port 16c is provided in the transmission line 14, midway along the section of line of length X between the feed ports 16a, 16b. A difference port 16d is provided one quarter of a wavelength along the section of line of length k between the feed ports 16a, 16b. When the elements 10a, 10b are receiving signals, the sum of the in-phase components of the signals received appears at the sum port 16c and the sum of the magnitudes of the out of phase components of the signals appears at the different port with a polarity according to whether the phase components of the signals appears at the different port with a polarity according to whether the phase of 1 0a lags the phase at 1 0b or vice versa.
Figure 2 shows the main lobes only of a sum pattern and a difference pattern suitable for use in a monopulse radar system as described above. The vertical axis represents the intensity of the pattern and the horizontal axis represents the bearing with respect to the bore-sight axis which is represented at the intersection of the two axes.
The far field pattern produced by an array of radiating elements is the Fourier Transform of the amplitude and phase distributions of the excitation currents across the aperture of the array. Figure 3 shows the form of distributions suitable for generating the patterns of Figure 2 from an array of a large number of elements. The vertical axis represents the amplitude of the excitation currents, with points above and below the horizontal axis having opposite phase, while the horizontal axis represents the position across the array of the elements to be excited. The bore-sight axis is at the intersection of the axes.
The distribution required to generated the sum pattern is symmetrical about the bore-sight axis and has a maximum at the axis. The distribution 24 which generates the difference pattern has two maxima of amplitude of opposite phase disposed symmetrically about the bore-sight axis.
Figure 4 shows schematically a known monopulse antenna 30 which comprises a line of eight radiating elements 32 which feed a sum signal to a sum port 34a and a difference signal to a difference port 34b through a feed network 36. The radiating elements 30 are disposed symmetrically about the bore-sight axis 38 of the antenna, so that, for every element 30 on one side of the bore-sight axis 38 there is a corresponding element on the other side, at the same spacing from the bore-sight axis 38. Each pair of corresponding elements 30 is connected to a respective one of four hybrid rings 40 by connectors 42, which may be waveguides or striplines for example. The elements 30 of each pair are connected to respective feed ports of the corresponding hybrid ring 40.
The sum ports of the hybrid rings 40 are connected to the sum port 34a of the feed network 36 through two-way power dividers 44. The connecting line from the sum port 34a to the hybrid rings 40 is bifurcated by respective dividers 44b,c. The four resulting lines are connected to the sum ports of respective hybrid rings. The difference port 34b is connected in like manner to the difference ports of the hybrid rings 40 through power dividers 45a, b, c.
The power dividers 44,46 do not divide power equally, but form weighted summations of the outputs of the hybrid rings 40 with weights according to the curves of Figure 3. The phase difference required by the difference pattern are provided by the hybrid rings, since the difference signal is formed by adding signals received by elements of one side of the array to out of phase signals received by the other side of the array. It will be clear that the principles of the antenna Figure 4 can be applied to an antenna with a larger number of radiating elements. An array of this type having N elements would require N/2 hybrid rings. Further, when N is large, a large number of power dividers are required.
Figure 5 shows an antenna according to the invention, having 16 radiating elements 32 but only five hybrid rings 40, 50. The radiating elements form an array which is symmetrical about the bore-sight axis 38. For every element 32 on the left hand side of the bore-sight axis 38 (as seen in figure 5) there is a corresponding element at the same spacing from the bore-sight axis on the right hand side of the axis.
The eight radiating elements 32 nearest to the bore-sight axis 38 are connected through a feed network 36' to a sum output line 46a and a difference output line 46b. The feed network 36' is similar to the feed network 36 of the antenna of Figure 4, except that the power dividing ratios of the power dividers incorporated differ, because the elements connected to the feed network 36' cover a portion only of the antenna aperture, whereas the elements of Figure 4 connected to the feed network 36 cover the whole aperture. Accordingly, the feed network 36' generates an excitation distribution according to a portion only of the curves of figure 3.
The eight remaining radiating elements 32 (the four elements at each end of the array) are connected to a feed network 48. Returning to Figure 3, it will be seen that the two distributions 22, 24 are substantially similar in amplitude near the edges of the array, but have opposite phase near the right hand end of the array (as seen in Figure 3). In order to generate the required distributions, the feed network 48 comprises power dividing networks common to the sum and difference signal paths to produce the common amplitude distribution, and a single hybrid ring 50 which produces the required phase relationship.
The four elements 32 atthe left hand end of the array of Figure 5 are connected to one feed port 50a of the hybrid ring 50 by a connecting line 52 which is bifurcated by a two way power divider 54a. The two branches of the bifurcated line 52 are bifurcated by two way power dividers 54b, 54c to produce four connecting lines which are connected to respective elements 32. The second feed port 50b is connected to the four elements 32 at the right hand end of the array in like manner by a connecting line 52' and three two-way power dividers 54'a, 54'b, 54'c.
The sum port of the hybrid ring 50 and the sum output line 46a of the feed network 36' are connected to the sum port 34a of the antenna by a final two-way power divider 56a. Similarly, the difference port of the hybrid ring 50 and the difference output line 46b of the feed network 36' are connected to the difference port 34b of the antenna by a final two-way power divider 56b.
Figures 6 and 7 show how a control element may be incorporated into an antenna according to the invention when side lobe suppression is required.
Figure 6 shows a known, simple antenna which comprises four radiating elements 62 and a control element 64 positioned on the bore-sight axis 38. A directional coupler 66 couples the control element 64 to the feed network of the rest of the array so that, when a control pulse is applied to a control port 67, the excitation current in the control element 64 is equal in amplitude to the sum of the currents in the rest of the array, but is opposite in phase. Accordingly, the desired control pattern is produced which is quasi-omni-directional but with a null along the bore-sight axis 38.
Figure 7 shows the antenna of Figure 5 to which has been added a central control element 64 on the bore-sight axis 38. The control element 64 is coupled to the sum port 34a by a directional coupler 66.
When a pulse is applied to the sum port 34a, the directional coupler passes all energy to the power divider 56a; none goes to the control element 64.
When a pulse is applied to the control port 67, power divides equally but with opposite phases (as described with reference to Figure 6) between the control element 64 and the power divider 56a.
The operation of the antenna of Figure 7 will now be described, when the antenna is receiving and transmitting. When receiving, the hybrid rings 40 form the sum and difference of the signals received by respective pairs of the eight central elements 32.
The four sum signals are combined by the power dividers to form a weighted sum, weighted in accordance with the curve 22 of Figure 3, on the sum output line 46a. Similarly, the result of a weighted summation of the difference signals from the hybrid rings, weight in accordance with the curve 24, is applied to the difference output line 46b.
The dividers 54a, b, c and the dividers 54'a, b, c form a weighted sum of the signals received by the four elements at the left hand end and the right hand end of the array respectively and apply the results to the hybrid ring 50. The sum of the two signals applied to the hybrid ring 50 is combined with the signal on the sum output line 46a by the divider 56a and the result is fed to the sum port 34a of the antenna which therefore receives the weighted sum of the signals received by all sixteen elements, the summations geing in accordance with the curve 22 of Figure 3.
The difference of the two signals applied to the hybrid ring 50 is combined with the signal on the difference output line 46b and fed to the difference port 34b. The difference port therefore receives the weighted sum of the signals received by all sixteen elements, with weights according to the curve 24 of
Figure 3, and with the signals of each side of the array being treated as having opposite phase, which treatment is a consequence, as described above, of taking the ouputs of the hybrid rings from their difference ports.
When the antenna is used to transmit the sum
pattern, a signal is applied to the sum port 34a which
is divided by the divider 56a and applied to the two feed networks 36', 48. The signal applied to the feed
network 36' is divided by the dividers 44a, b, c and applied to the sum ports of the hybrid rings 40 with weightings according to the curve 22. The hybrid
rings divide the signals at their sum ports and apply the results in phase to a corresponding pair of elements 32.
The signal applied to the feed network 48 is fed to the sum port of the hybrid ring 50 which divides the signal into two components of equal amplitude and
phase. The components are apportioned by the
divider networks 54, 54' between the four elements
at each end of the array. Accordingly the signal to the sum port is distributed amongst the antenna
elements with the distribution of the curve 22 of
Figure 3, and the sum pattern is transmitted.
When transmitting the control pattern, operation is esentially the same so far as the elements 32 are concerned, since the directional coupler splits power equally between the element 38 and the power divider 56a, in opposite phases.
The antenna system described above comprises hybrid rings coupling conductors of the feed network. Other hybrid couplers could be used instead of the rings, for example 3dB branch arm couplers.
Claims (9)
1. An antenna for a monopulse radar system comprising a radiating array extending to either side of the bore-sight axis of the monopulse radar pattern, the array comprising a plurality of first radiating elements on a first side of the bore-sight axis at respective spacings therefrom and a like plurality of second radiating elements on the second side of the bore-sight axis each at a like spacing therefrom as a respective, corresponding first element, and the antenna further comprising a feed networkwith a plurality of first combining means each of which forms the sum and difference of the signals received by a respective one of a first set of first elements and by the corresponding second element, means for forming a first summation of signals received by a second set of first elements, meansforforming a second summation ofthe signals received by the second elements corresponding to the second set of first elements, further combining means for forming a first summation of signals received by a second set of first elements, means for forming a second summation ofthe signals received by the second elements corresponding tothe second set of first elements, further combining means for forming the sum and difference fo the first and second summations, and summation means for forming output summations of the sum signals and of the difference signals formed by the combining means at sum and difference terminals of the antenna.
2. An antenna according to claim 1,further comprising a control element on the bore-sight axis operable to generate a control signal for side lobe suppression.
3. An antenna according to claim 2, further comprising directional coupling means coupling the control element to the sum terminal and a control terminal, the directional coupler being such that, when transmitting power applied to the sum terminal passes substantially exclusively to the said feed network whereas power applied to the control terminal divides with opposite phases between the feed network and the control element.
4. An antenna according to any of the above claims, in which each combining means comprises a hybrid coupler.
5. An antenna according to claim 4, in which the hybrid coupler is a hybrid ring.
6. An antenna according to any of the above claims, further comprising a plurality of power divider networks for performing the summations.
7. An antenna according to any of the above claims in which the summations are weighted summations.
8. An antenna according to any of the above claims, in which the first and second sets of first elements each comprise at least four radiating elements.
9. An antenna for a monopulse radar system substantially as described above with reference to
Figure 5 or figure 7 of the accompanying drawings
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08305195A GB2135828B (en) | 1983-02-24 | 1983-02-24 | A monopulse radar antenna |
| CA000433941A CA1200595A (en) | 1983-02-24 | 1983-08-04 | Monopulse radar antenna |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08305195A GB2135828B (en) | 1983-02-24 | 1983-02-24 | A monopulse radar antenna |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2135828A true GB2135828A (en) | 1984-09-05 |
| GB2135828B GB2135828B (en) | 1986-03-05 |
Family
ID=10538559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08305195A Expired GB2135828B (en) | 1983-02-24 | 1983-02-24 | A monopulse radar antenna |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1200595A (en) |
| GB (1) | GB2135828B (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0257884A2 (en) * | 1986-08-20 | 1988-03-02 | Plessey Overseas Limited | Radar transmitter-receiver isolation network |
| GB2202092A (en) * | 1986-12-22 | 1988-09-14 | Mitsubishi Electric Corp | Antenna device |
| EP0517352A1 (en) * | 1991-06-05 | 1992-12-09 | Siemens Plessey Electronic Systems Limited | A power distribution network for array antennas |
| EP0577520A1 (en) * | 1992-07-03 | 1994-01-05 | Thomson-Csf | Antenna for a secondary radar in S-mode |
| EP0619622A2 (en) * | 1993-04-09 | 1994-10-12 | Hughes Aircraft Company | Monopulse array system with airstripline multi-port network |
| WO1998001771A1 (en) * | 1996-07-05 | 1998-01-15 | Sperry Marine Inc. | A beam sharpened, low sidelobe antenna system |
| RU2506670C2 (en) * | 2012-05-11 | 2014-02-10 | Открытое акционерное общество "Научно-исследовательский институт приборостроения имени В.В. Тихомирова" | Phased antenna array |
| RU2538291C2 (en) * | 2012-12-27 | 2015-01-10 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Московский авиационный институт (национальный исследовательский университет)" | Method of reducing level of lateral radiation of antenna |
| RU2554521C2 (en) * | 2012-11-27 | 2015-06-27 | Открытое акционерное общество Центральное конструкторское бюро аппаратостроения | Distribution system for phase antenna array |
| EP1455412B1 (en) * | 2003-02-14 | 2020-09-16 | Alcatel Lucent | Angle diversity dual antenna system |
-
1983
- 1983-02-24 GB GB08305195A patent/GB2135828B/en not_active Expired
- 1983-08-04 CA CA000433941A patent/CA1200595A/en not_active Expired
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0257884A2 (en) * | 1986-08-20 | 1988-03-02 | Plessey Overseas Limited | Radar transmitter-receiver isolation network |
| EP0257884A3 (en) * | 1986-08-20 | 1990-03-14 | Plessey Overseas Limited | Radar transmitter-receiver isolation network |
| GB2202092A (en) * | 1986-12-22 | 1988-09-14 | Mitsubishi Electric Corp | Antenna device |
| US4827270A (en) * | 1986-12-22 | 1989-05-02 | Mitsubishi Denki Kabushiki Kaisha | Antenna device |
| GB2202092B (en) * | 1986-12-22 | 1991-06-05 | Mitsubishi Electric Corp | Antenna device |
| EP0517352A1 (en) * | 1991-06-05 | 1992-12-09 | Siemens Plessey Electronic Systems Limited | A power distribution network for array antennas |
| US5302953A (en) * | 1992-07-03 | 1994-04-12 | Thomson-Csf | Secondary radar antenna operating in S mode |
| FR2693317A1 (en) * | 1992-07-03 | 1994-01-07 | Thomson Csf | Secondary radar antenna operating in Mode S. |
| EP0577520A1 (en) * | 1992-07-03 | 1994-01-05 | Thomson-Csf | Antenna for a secondary radar in S-mode |
| EP0619622A2 (en) * | 1993-04-09 | 1994-10-12 | Hughes Aircraft Company | Monopulse array system with airstripline multi-port network |
| EP0619622A3 (en) * | 1993-04-09 | 1995-04-05 | Hughes Aircraft Co | Monopulse array system with airstripline multi-port network. |
| WO1998001771A1 (en) * | 1996-07-05 | 1998-01-15 | Sperry Marine Inc. | A beam sharpened, low sidelobe antenna system |
| EP1455412B1 (en) * | 2003-02-14 | 2020-09-16 | Alcatel Lucent | Angle diversity dual antenna system |
| RU2506670C2 (en) * | 2012-05-11 | 2014-02-10 | Открытое акционерное общество "Научно-исследовательский институт приборостроения имени В.В. Тихомирова" | Phased antenna array |
| RU2554521C2 (en) * | 2012-11-27 | 2015-06-27 | Открытое акционерное общество Центральное конструкторское бюро аппаратостроения | Distribution system for phase antenna array |
| RU2538291C2 (en) * | 2012-12-27 | 2015-01-10 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Московский авиационный институт (национальный исследовательский университет)" | Method of reducing level of lateral radiation of antenna |
Also Published As
| Publication number | Publication date |
|---|---|
| CA1200595A (en) | 1986-02-11 |
| GB2135828B (en) | 1986-03-05 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3295134A (en) | Antenna system for radiating directional patterns | |
| US5952965A (en) | Adaptive main beam nulling using array antenna auxiliary patterns | |
| US4032922A (en) | Multibeam adaptive array | |
| EP0028969B1 (en) | Omnidirectional side lobe sum and difference beam forming network for a multielement antenna array and method for determining the weights thereof | |
| US5532706A (en) | Antenna array of radiators with plural orthogonal ports | |
| US5128687A (en) | Shared aperture antenna for independently steered, multiple simultaneous beams | |
| US4451831A (en) | Circular array scanning network | |
| US3176297A (en) | Antenna systems | |
| US5041835A (en) | Electronic scanning type array antenna device | |
| US4673939A (en) | Test apparatus in a radar system | |
| EP0600715A2 (en) | Active transmit phased array antenna | |
| US4814775A (en) | Reconfigurable beam-forming network that provides in-phase power to each region | |
| EP0076213A2 (en) | Beam forming network for a multivibrator antenna array | |
| US3803624A (en) | Monopulse radar antenna array feed network | |
| US3940770A (en) | Cylindrical array antenna with radial line power divider | |
| EP0253465B1 (en) | Beam forming antenna system | |
| GB2135828A (en) | A monopulse radar antenna | |
| US5025493A (en) | Multi-element antenna system and array signal processing method | |
| US4692768A (en) | Feed device for a sweep beam array antenna | |
| US3568190A (en) | Full monopulse variable polarization feed bridge | |
| US5943011A (en) | Antenna array using simplified beam forming network | |
| US6169518B1 (en) | Dual beam monopulse antenna system | |
| US4213133A (en) | Linear antenna arrays | |
| US3729742A (en) | Simultaneous sum and difference pattern technique for circular array antennas | |
| US4503434A (en) | Lossless arbitrary output dual mode network |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19970224 |