US3482252A - Dual-mode conical horn antenna - Google Patents
Dual-mode conical horn antenna Download PDFInfo
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- US3482252A US3482252A US597600A US3482252DA US3482252A US 3482252 A US3482252 A US 3482252A US 597600 A US597600 A US 597600A US 3482252D A US3482252D A US 3482252DA US 3482252 A US3482252 A US 3482252A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/02—Waveguide horns
- H01Q13/025—Multimode horn antennas; Horns using higher mode of propagation
Definitions
- This invention pertains to antennas and, more particularly, to dual-mode conical horn antennas.
- aperture phase dispersion a term used to describe the difference in relative phase between the TE and TM modes at the horn opening.
- the radial components of the electric field for the two modes be 180 degrees out of phase at the edge, i.e., at the boundary walls of the antenna.
- mode conversion from the TE mode to the TM mode may be effected by a simple step transition between guide sections of a first and second predetermined diameter.
- the length of the guide section of said second predetermined diameter, identified by Potter as the phasing section is selected to account for the relative phase lengths of the horn for the two propagating modes in the horn. Since overall antenna specifications usually determine the antenna aperture diameter, cone angle, and diameter of the phasing section, the length of the horn section is therefore determined, and, thus, so is the relative phase shift between the two propagating modes.
- the effect of aperture phase dispersion is mitigated by the use of a horn antenna of a predetermined configuration. More particularly, a dual-mode conical horn is utilized which is characterized by a double flare. One section of the horn, i.e., the frustrum of a cone, has a predetermined half angle to give the correct aperture dimensions, and another section, i.e., a second frustrum of a cone, has a half angle selected to yield the correct relative phase.
- the dispersive phasing section relied upon in the prior art, is relegated to a vernier or trimming function, required only to compensate for small errors in design and construction. The necessity for a lengthy and highly dispersive phasing section is therefore eliminated with a corresponding improvement in antenna performance.
- FIG. 1 is an illustrative diagram of a prior art dualmode conical horn antenna
- FIG. 2 is an illustrative diagram of a dual-mode conical horn antenna which embodies the principles of this lnvention.
- FIG. 3 is a graphical presentation of the difi'erential phase shift of a particular waveguide configuration.
- FIG. 1 is included to represent a typical prior art dual-mode conical horn antenna.
- Source 11 of FIG. 1 excites in hollow waveguide section 12, of circular cross section, energy which propagates in the TE (dominant) wave mode.
- the diameter A of section 12 is selected, in a manner well known to those skilled in the art, so that the guide is cut off for modes other than the TE
- the combined TE -TM wave mode mixture propagates in horn section 15, e.g., a hollow frustrum of a cone, and is radiated into the atmosphere at aperture 16.
- design specifications comprise the horn aperture diameter, indicated as C in FIG. 1, the half angle flare 0 of the conical horn, and the relative power in the two propagating modes, the specifications being determined on the basis of overall antenna requirements.
- diameter B of guide section 14 it should be made sufficiently large so that the TM mode is well above cutoff, but not so large that the required input waveguide 12, itself, becomes overmoded.
- aperture phase dispersion a term used to describe the difference in relative phase between the TE and TM modes at the horn aperture 16. Proper phasing of these two modes at the horn aperture is therefore the dominant problem in constructing an efficient dual-mode conical horn antenna.
- the length of the horn section 15 is also determined and so, therefore, is the relative phase shift between the two modes. Quite often, the error in relative phase between the two modes at the aperture is so large that it becomes necessary to use a long and therefore highly dispersive phasing section 14.
- a phasing section 14 of length L was required which had phase dispersion by itself, over a ten percent frequency band, equal to approximately 25 degrees. Coupled with the intrinsic phase dispersion of the horn 15, which may, by itself, be of the same order of magnitude, the total aperture phase dispersion would be approximately 50 degrees.
- the effect of such a large phase dispersion, especially in a reflector feed system, is to decrease the circular symmetry of the radiation pattern and also to cause a decrease in the antenna gain with a concomitant increase in unwanted sidelobe levels.
- FIG. 2 This deleterious effect of prior art antennas may be eliminated in accordance with the principles of this invention by using a horn antenna of the type illustrated in FIG. 2.
- the antenna of FIG. 2 is characterized by a horn with a double flare, one section 1512, to yield the correct aperture dimensions (diameter and angle) and another section 15a, Whose angle is selected to yield the correct relative phase at the aperture 16.
- the phasing section 14, is thus relegated to a trimming function used only to compensate for small errors in design and construction.
- source 11 of FIG. 2 excites in waveguide section 12 a propagating wave in the TE mode.
- the step discontinuity 13 which forms a conductive boundary between guide sections 12 and 14, converts a portion of the incident propagating energy into the TM mode.
- the combined wave modes, TE and TM propagate in horn sections 15a and 15b and are radiated into the atmosphere at aperture 16.
- the horn of the antenna comprises two frustrums, 15a and 15b, each having a predetermined half angle 6 and 0 respectively.
- general antenna requirements determine the magnitude of the horn aperture diameter C, the angle 0 of section 15b, and the relative diameters A and B of guide sections 12 and 14.
- section 15a of the horn in accordance with the principles of this invention, is constructed to have a different half angle 0 than that of section 15b.
- the value of the half angle 6 is determined to be such that the relative phase between the TE and TM modes at the horn aperture is equal to an odd multiple of 11' radians.
- This relative phase can be calculated from the relationship ⁇ ULTIVF OTE) aperture (ITEM-(1T2?) disc.
- the quantities L and (a a can be expressed, respectively, in terms of 0 or 0 and the diameters B, C and D, from the well-known formulas describing the propagation of electromagnetic waves in conical waveguides. See, for example, F. Borgnis and C. H. Papas, Electromagnetic Waveguides and Resonators, Encyclopedia of Physics, vol. XVI, Springer, Berlin, 1958, page 356.
- a horn antenna for use at X-band frequencies was constructed in accordance with the principles of this invention having the following dimensrons:
- the antenna was provided with a variable trimming section 14, whose length could be adjusted in order to optimize the performance of the antenna. Phasing of the two propagating modes was achieved by monitoring the longitudinal wall currents and varying the length of section 14 until a minimum was observed. This condition occurs when the electric fields of the two modes perpendicular to the walls of the horn are the required 180 degrees out of phase.
- the length L of section 14 for this condition was approximately .26) ⁇ , where A is the signal wavelength at the center frequency of operating band, corresponding to approximately one-tenth the length required if prior art techniques had been utilized.
- A is the signal wavelength at the center frequency of operating band, corresponding to approximately one-tenth the length required if prior art techniques had been utilized.
- a dual-mode conical horn antenna comprising:
- a third truncated conical hollow waveguide section having a first predetermined half angle for reducing the phase differential between mode signals propagating in said third waveguide section conductively coupled to said second waveguide section, and
- a fourth truncated conical hollow waveguide section having a second predetermined half angle conductively coupled to said third waveguide section.
- a third hollow waveguide section comprising a frustrum of a cone having a first predetermined half angle for diminishing the aperture phase dispersion of propagating mode signals
- a fourth hollow waveguide section comprising a frustrur'n of a cone having a second predetermined half percentage of said mode signal into a second mode "signal,
- a dual-mode conical horn antenna comprising: at the aperture thereof.
- An antenna having a horn member responsive to section of first predetermined diameter having input and output means, said input means responsive to applied electromagnetic signals,
- horn member comprises:
- a third hollow conduetively bounded waveguide sec- References Cited UNITED STATES PATENTS tion comprising a frustrum of a cone having a first 3,373,431 3/1968 Webb 343 786 predetermined half angle coupled to said second FOREIGN PATENTS waveguide section output means for reducing the phase differential between propagating mode signal 9 05 5/1957 Germa y,
- a fourth hollow conduetively bounded waveguide section comprising a frustrum of a cone having a second predetermined half angle coupled to said third waveguide section.
Description
Dec. 2, 1969 E. R. NAGELBERG 3,482,252
DUAL-MODE CONICAL HORN ANTENNA Filed Nov. 29. 1966 FIG.
(PRlOR ART) SOURCE (C -C AS FUNCTION OF FREQUENCY 0 A.SMALL D|AMETER=2.| o B, LARGE DIAMETER=2.8 u no 1 I l 1 5.| 5.3 5.5 5.7 5.9 6.l 6.3 6.5 6.7 6.9
FREQUENCY IN KILOMEGACYCLES/ SEC.
m/ ws/v TOR E. R. NAGELBERG A TTORNE Y United States Patent O US. Cl. 343-786 5 Claims ABSTRACT OF THE DISCLOSURE A horn antenna wherein the horn member is excited by more than one electromagnetic mode signal. The use of a predetermined configuration for the horn member mitigates the effect of aperture phase dispersion.
BACKGROUND OF THE INVENTION Field of the invention This invention pertains to antennas and, more particularly, to dual-mode conical horn antennas.
Description of the prior art The dual-mode conical horn antenna, for example of the type described in an article by P. D. Potter, entitled A New Horn Antenna with Suppressed Sidelobes and Equal Beamwidths, in the June 1963 issue of the Microwave Journal, page 71, has proven to be a very useful primary feed element for low noise antennas, particularly those of the Cassegrain type. Its applicability to other general uses is now recognized as one of its more important features. By exciting the antenna horn aperture with an appropriate combination of spherical TE (dominant) and TM modes it is possible to produce a horn radiation pattern with approximately equal E-plane and H-plane beam widths, and sidelobe levels substantially lower than those for conventionally excited (TE only) horns with the same aperture dimensions. This improvement, obtained at a modest expenditure of gain, is achieved by equalizing the E-plane and H-plane illumination taper, thereby reducing the E-plane edge current and the corresponding sidelobe levels.
Generally, the most important phenomenon affecting dual-mode horn performance, over a band of frequencies, is aperture phase dispersion, a term used to describe the difference in relative phase between the TE and TM modes at the horn opening. For optimum performance it is required that the radial components of the electric field for the two modes be 180 degrees out of phase at the edge, i.e., at the boundary walls of the antenna.
Potter, in the above-mentioned article, teaches that mode conversion from the TE mode to the TM mode may be effected by a simple step transition between guide sections of a first and second predetermined diameter. The length of the guide section of said second predetermined diameter, identified by Potter as the phasing section, is selected to account for the relative phase lengths of the horn for the two propagating modes in the horn. Since overall antenna specifications usually determine the antenna aperture diameter, cone angle, and diameter of the phasing section, the length of the horn section is therefore determined, and, thus, so is the relative phase shift between the two propagating modes. Correction of this difierential phase shift at the horn aperture by varying the length of the phasing section, as per Potter, quite often results in a deterioration of overall antenna performance, rather than an improvement in performance. As the length of the phasing section is increased, its inherent phase dispersion with changes in operating fre- 3,482,252 Patented Dec. 2, 1969 ICC quency also increases, causing a degradation of the circular symmetry of the antenna radiation pattern, a decrease in overall antenna gain and an increase in unwanted sidelobe levels.
SUMMARY OF THE INVENTION It is, therefore, an object of this invention to mitigate the etfects of aperture phase dispersion in order to optimize the performance of dual-mode conical horn antennas.
It is another object of this invention to mitigate the elfect of aperture phase dispersion without resorting to lengthy and highly dispersive phasing sections.
In accordance with this invention, the effect of aperture phase dispersion is mitigated by the use of a horn antenna of a predetermined configuration. More particularly, a dual-mode conical horn is utilized which is characterized by a double flare. One section of the horn, i.e., the frustrum of a cone, has a predetermined half angle to give the correct aperture dimensions, and another section, i.e., a second frustrum of a cone, has a half angle selected to yield the correct relative phase. Thus, the dispersive phasing section, relied upon in the prior art, is relegated to a vernier or trimming function, required only to compensate for small errors in design and construction. The necessity for a lengthy and highly dispersive phasing section is therefore eliminated with a corresponding improvement in antenna performance.
These and further features and objects of this invention, its nature and various advantages may be more readily apprehended and understood upon consideration of the attached drawings and of the following detailed description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative diagram of a prior art dualmode conical horn antenna;
FIG. 2 is an illustrative diagram of a dual-mode conical horn antenna which embodies the principles of this lnvention; and
FIG. 3 is a graphical presentation of the difi'erential phase shift of a particular waveguide configuration.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION In order to appreciate the invention more fully, FIG. 1 is included to represent a typical prior art dual-mode conical horn antenna.
As discussed above, the principal difficulties in the design of dual-mode horn antennas are in properly phasing the two modes, TE and TM and maintaining the correct relative phase over the frequency range of interest. Generally, design specifications comprise the horn aperture diameter, indicated as C in FIG. 1, the half angle flare 0 of the conical horn, and the relative power in the two propagating modes, the specifications being determined on the basis of overall antenna requirements. Usually, there is a certain degree of freedom in selecting the diameter B of guide section 14; it should be made sufficiently large so that the TM mode is well above cutoff, but not so large that the required input waveguide 12, itself, becomes overmoded. A detailed discussion of antenna requirements and their relationship to antenna dimensions may be found in the article entitled The Open Cassegrain Antenna: Part I, Electromagnetic Design and Analysis, authored by J. S. Cook, E. M. Elam and H. Zucker, appearing in vol. 44 of the Bell System Technical Journal, at page 1255.
The most important phenomenon affecting dual-mode performance is aperture phase dispersion, a term used to describe the difference in relative phase between the TE and TM modes at the horn aperture 16. Proper phasing of these two modes at the horn aperture is therefore the dominant problem in constructing an efficient dual-mode conical horn antenna. Unfortunately, once the aperture diameter C, cone angle and guide diameter B are specified, the length of the horn section 15 is also determined and so, therefore, is the relative phase shift between the two modes. Quite often, the error in relative phase between the two modes at the aperture is so large that it becomes necessary to use a long and therefore highly dispersive phasing section 14. For example, in a particular horn antenna it was found that in order to substantially decrease the relative phase shift between the two modes, a phasing section 14 of length L was required which had phase dispersion by itself, over a ten percent frequency band, equal to approximately 25 degrees. Coupled with the intrinsic phase dispersion of the horn 15, which may, by itself, be of the same order of magnitude, the total aperture phase dispersion would be approximately 50 degrees. The effect of such a large phase dispersion, especially in a reflector feed system, is to decrease the circular symmetry of the radiation pattern and also to cause a decrease in the antenna gain with a concomitant increase in unwanted sidelobe levels.
This deleterious effect of prior art antennas may be eliminated in accordance with the principles of this invention by using a horn antenna of the type illustrated in FIG. 2. The antenna of FIG. 2 is characterized by a horn with a double flare, one section 1512, to yield the correct aperture dimensions (diameter and angle) and another section 15a, Whose angle is selected to yield the correct relative phase at the aperture 16. The phasing section 14, is thus relegated to a trimming function used only to compensate for small errors in design and construction.
More particularly, analogous to the operation of the antenna of FIG. 1, source 11 of FIG. 2, excites in waveguide section 12 a propagating wave in the TE mode. The step discontinuity 13, which forms a conductive boundary between guide sections 12 and 14, converts a portion of the incident propagating energy into the TM mode. The combined wave modes, TE and TM propagate in horn sections 15a and 15b and are radiated into the atmosphere at aperture 16.
The horn of the antenna, as illustrated in FIG. 2, comprises two frustrums, 15a and 15b, each having a predetermined half angle 6 and 0 respectively. As discussed above, general antenna requirements determine the magnitude of the horn aperture diameter C, the angle 0 of section 15b, and the relative diameters A and B of guide sections 12 and 14. In order to substantially reduce the eifect of phase aperture distortion, section 15a of the horn, in accordance with the principles of this invention, is constructed to have a different half angle 0 than that of section 15b. Generally, the value of the half angle 6 is determined to be such that the relative phase between the TE and TM modes at the horn aperture is equal to an odd multiple of 11' radians. This relative phase can be calculated from the relationship {ULTIVF OTE) aperture (ITEM-(1T2?) disc.
+(TMTE)U TM- Tn)e where n=integer, and (a u in each case denotes the relative phase shift between the two modes in the respectively identified sections. Thus, (a a denotes the relative phase at the horn aperture, (m a denotes the relative phase at the discontinuity between diameters A and B, (oL a denotes the ditferential phase shift in the frustrurn of half angle 0 and (oc a denotes the dilferential phase shift in the frustrum of half angle 0 The quantity h is calculated by solving the electromagnetic boundary value problem of the given discontinuity impinged upon by electromagnetic energy in the form of a TE mode. For example, FIG. 3 shows as a function of frequency for A=2.1 inches and B=2i8 inches.
The quantities L and (a a can be expressed, respectively, in terms of 0 or 0 and the diameters B, C and D, from the well-known formulas describing the propagation of electromagnetic waves in conical waveguides. See, for example, F. Borgnis and C. H. Papas, Electromagnetic Waveguides and Resonators, Encyclopedia of Physics, vol. XVI, Springer, Berlin, 1958, page 356.
In a specific application, a horn antenna for use at X-band frequencies was constructed in accordance with the principles of this invention having the following dimensrons:
A=7.2/k, B=9.6/k, C=18.8/k, D=16.8/k, 0 =5.5 and 0 :67, where k is equal to 21r divided by the signal wavelength at the center frequency of the operating band. The antenna was provided with a variable trimming section 14, whose length could be adjusted in order to optimize the performance of the antenna. Phasing of the two propagating modes was achieved by monitoring the longitudinal wall currents and varying the length of section 14 until a minimum was observed. This condition occurs when the electric fields of the two modes perpendicular to the walls of the horn are the required 180 degrees out of phase. The length L of section 14 for this condition was approximately .26)\, where A is the signal wavelength at the center frequency of operating band, corresponding to approximately one-tenth the length required if prior art techniques had been utilized. Thus, proper phasing of the two modes is accomplished without resorting to long phasing sections which are highly dispersive and degrade overall antenna performance.
It is to be understood that the embodiments shown and described are illustrative of the principles of this invention only, and that further modifications of this invention may be implemented by those skilled in the art without departing from the scope and spirit of the invention. For example, though the principles of this invention are particularly applicable to feed horn antennas, they are also applicable to any other situation Where horn antennas are used. In addition, diverse configurations may be implemented using mode signals other than the TE and TM I claim:
1. A dual-mode conical horn antenna comprising:
a first circular hollow waveguide section having a first predetermined diameter,
a second circular hollow waveguide section having a second predetermined diameter conductively coupled to said first waveguide section,
a third truncated conical hollow waveguide section having a first predetermined half angle for reducing the phase differential between mode signals propagating in said third waveguide section conductively coupled to said second waveguide section, and
a fourth truncated conical hollow waveguide section having a second predetermined half angle conductively coupled to said third waveguide section.
2. An improved dual-mode conical horn antenna,
4. An improved dual-mode conical horn antenna comwherein mode conversion is accomplished by a discontinuity between first and second hollow waveguide sections, having a horn member comprising:
a third hollow waveguide section comprising a frustrum of a cone having a first predetermined half angle for diminishing the aperture phase dispersion of propagating mode signals, and
a fourth hollow waveguide section comprising a frustrur'n of a cone having a second predetermined half percentage of said mode signal into a second mode "signal,
a horn member,
a first section of said horn member, responsive to said first and second mode signals, comprising a frustrum of a cone' having a first predetermined angle for diangle, 10 minishing'the aperture phase dispersion between said wherein said third and fourth waveguide sections are two inode signals, and a second section of said horn conduetively united and have a common axis of member comprising a frustrum of a cone having a propagation. second predetermined angle for radiating said signals 3. A dual-mode conical horn antenna comprising: at the aperture thereof.
a first circular hollow conduetively bounded waveguide 5. An antenna having a horn member responsive to section of first predetermined diameter having input and output means, said input means responsive to applied electromagnetic signals,
a second circular hollow conductively bounded wavemore than one microwave mode signal wherein said horn member comprises:
a first hollow conductive frustrum of a cone having a first preselected half angle for reducing the phase guide section of second predetermined diameter having input and output means,
conductive means uniting said first waveguide section output means and said second waveguide section indifferential of said mode signals, and
a second hollow conductive frustrum of a cone having a second preselected half angle for radiating said mode signals.
put means for converting a proportional part of incident electromagnetic energy into a different order mode signal,
a third hollow conduetively bounded waveguide sec- References Cited UNITED STATES PATENTS tion comprising a frustrum of a cone having a first 3,373,431 3/1968 Webb 343 786 predetermined half angle coupled to said second FOREIGN PATENTS waveguide section output means for reducing the phase differential between propagating mode signal 9 05 5/1957 Germa y,
and
a fourth hollow conduetively bounded waveguide section comprising a frustrum of a cone having a second predetermined half angle coupled to said third waveguide section.
H. K. SAALBACH, Primary Examiner T. VEZEAU, Assistant Examiner
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59760066A | 1966-11-29 | 1966-11-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US3482252A true US3482252A (en) | 1969-12-02 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US597600A Expired - Lifetime US3482252A (en) | 1966-11-29 | 1966-11-29 | Dual-mode conical horn antenna |
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3662393A (en) * | 1970-02-20 | 1972-05-09 | Emerson Electric Co | Multimode horn antenna |
| JPS5345844U (en) * | 1976-09-22 | 1978-04-19 | ||
| US4122446A (en) * | 1977-04-28 | 1978-10-24 | Andrew Corporation | Dual mode feed horn |
| US4442437A (en) * | 1982-01-25 | 1984-04-10 | Bell Telephone Laboratories, Incorporated | Small dual frequency band, dual-mode feedhorn |
| US4788553A (en) * | 1983-04-06 | 1988-11-29 | Trw Inc. | Doppler radar velocity measurement apparatus |
| US6411263B1 (en) | 2000-09-28 | 2002-06-25 | Calabazas Creek Research, Inc. | Multi-mode horn |
| US20120186747A1 (en) * | 2011-01-26 | 2012-07-26 | Obama Shinji | Plasma processing apparatus |
| US20170040709A1 (en) * | 2015-08-04 | 2017-02-09 | Nidec Elesys Corporation | Radar apparatus |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE963705C (en) * | 1955-03-23 | 1957-05-09 | Siemens Ag | Coupling system with a coupling funnel for surface waveguides |
| US3373431A (en) * | 1964-11-02 | 1968-03-12 | James E. Webb | Low-noise single aperture multimode monopulse antenna feed system |
-
1966
- 1966-11-29 US US597600A patent/US3482252A/en not_active Expired - Lifetime
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE963705C (en) * | 1955-03-23 | 1957-05-09 | Siemens Ag | Coupling system with a coupling funnel for surface waveguides |
| US3373431A (en) * | 1964-11-02 | 1968-03-12 | James E. Webb | Low-noise single aperture multimode monopulse antenna feed system |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3662393A (en) * | 1970-02-20 | 1972-05-09 | Emerson Electric Co | Multimode horn antenna |
| JPS5345844U (en) * | 1976-09-22 | 1978-04-19 | ||
| JPS6012328Y2 (en) * | 1976-09-22 | 1985-04-22 | 三菱電機株式会社 | horn antenna |
| US4122446A (en) * | 1977-04-28 | 1978-10-24 | Andrew Corporation | Dual mode feed horn |
| US4442437A (en) * | 1982-01-25 | 1984-04-10 | Bell Telephone Laboratories, Incorporated | Small dual frequency band, dual-mode feedhorn |
| US4788553A (en) * | 1983-04-06 | 1988-11-29 | Trw Inc. | Doppler radar velocity measurement apparatus |
| US6411263B1 (en) | 2000-09-28 | 2002-06-25 | Calabazas Creek Research, Inc. | Multi-mode horn |
| US20120186747A1 (en) * | 2011-01-26 | 2012-07-26 | Obama Shinji | Plasma processing apparatus |
| US20170040709A1 (en) * | 2015-08-04 | 2017-02-09 | Nidec Elesys Corporation | Radar apparatus |
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