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Modified 3D Corner Reflector Antenna
Dragoslav Dobricic, YU1AW
Note: This dish was later improved further optimized and improved. Final version with all the enhancements and improvements located in the file: Trimmed 3D Corner Reflector Antenna.
The original design of this exceptional aperturne antenna was first described in the literature:
IEEE Transactions on Antennas and Propagation, July, 1974. "Three-Dimensional Corner Reflector Array" by Naoki Inagaki (pp. 580-582). Accurate and comprehensive results of computer analysis and simulation announced LB Cebik W4RNL the article: "The 3-D Corner Reflector" which can be found on its website.
Antenna consists of three quadratic surfaces Reflector each placed at a right angle as half of the cube, and the radiant element in the form of monopoly in one of them. This structure focuses electromagnetic radiation in a relatively narrow beam whose direction of maximum radiation lies in the large diagonal that starts from the vertices (apex-a) cube which is part of the structure, ie. angle of 45 degrees in relation to all three Reflector plane. The size of the plane reflector is not critical. With its increasing increases gain antenna, initially and later significantly less. The optimal size is about 2-3 wavelengths. Further increase in size leads to increase in less gain antennas and at about 4-5 wavelengths reaches the maximum practical gain. Further increasing the size reflector surface does not make sense because it no longer leads to increased gain ..
The appearance of the original 3D Corner Reflector Antenna
Reflector surface can be made of solid materials such as aluminum, copper or brass plate, and at lower frequencies in the form of metal network whose density must be determined by the hole, measured by the largest dimension must be less than 0.1 wavelength.
What makes this antenna is its exceptional ease of excellent and very naive design, which guarantees high repeatability of results and practical possibility of its use, with the calculation of its dimensions, the frequencies of several tens of MHz up to several GHz.
Another nice feature of this antenna is that it has excellent suppressed side bundles of radiation, which makes it a very good choice when noise and interference of signals from other directions should be more suppressed.
The only drawback of this antenna is its source impedance. It changes with the position and length zračećeg element - the monopoly. At the same time these changes and change the gain antennas. The optimal position, about 0.6 x = iy = 0.6 wavelengths, measured from the apex-a, and the optimal length zračećeg element DR = 0.75 wavelength, measured from the Reflector plane, the value of the input impedance of approximately biggest gain antenna is about 72 ohms when the antenna in rezonansi, which gives the minimum SWR of about 1.5 to 50 ohm matching.
The value of the input impedance of the original antenna depending on the length zračećeg DR elements in wavelengths
Input matching of the original antenna depending on the length of the element zračećeg DR
Reinforcement of the original antenna and the suppression of secondary beams of radiation depending on the length zračećeg DR elements in wavelengths
Modification of the original 3D Corner Antenna
The SWR is acceptable at lower frequencies where the losses in the cables is small, but the UHF and SHF area it becomes problematic because the losses in the cables due neprilagođenja significant. The alternative is a power antenna cable of 75 ohms, which reduces losses but remains a problem of proper adjustments to equipment intended for work with impedance of 50 ohms.
At first glance it was clear that it would be good if this exceptional antenna in this direction refine. The first thing that came to mind is to add one element of which would impact on the radiant element was also calculated to reduce the impedance of 50 ohms. Of course, this surgery is meant to do his best to preserve the good features of existing antennas.
For that job Valjala use the best programs for the analysis that are currently available, since most programs for the analysis of the worst accuracy of the antenna shows exactly the results of calculation impedance. In addition here is the antenna that works primarily with the laws of optics and it was necessary and choose a program that is just the best in the field of simulation aperturnih antenna. The choice fell on the version of the famous professional program for simulation of antenna NEC-2.
After completion of analysis of different alternative solutions, finally we can find a solution with the additional element of a parasite that is in front zračećeg similar elements as the first director of the Yagi antenna.
Input matching the modified antenna depending on the length of the added element of DI tal. lengths
Of course it's only an analogy, it is the problem of the antenna impedance, just like with the solutions of Yagi antenna, because it is quite different principles of both antennas.
By placing an additional element and adjusting its length and distance from zračećeg element obtained almost perfect matching of 50 ohms.
Reinforcement of the modified antenna and suppression of secondary beams of radiation depending on the length of the added element of DI wavelengths at DR = 0.75 tal. length.
Investigation of other characteristics such as antenna gain, size of the side beams of radiation, efficiency and impedance changes with the change of frequency, ie. width of the working range for the SWR showed almost unchanged compared to the prior modification. The model was later developed in practice, tested and fully confirmed the predictions of computer simulations. In addition to laboratory measurements and adjusted the input gain, antenna is used in practical WLAN communication which showed an advantage compared to the classic corner reflector antenna with which he compares.
What was unusual when using this antenna is its direction. There are habits that antennas radiate in the direction of some of the geometric dimensions and the normal Reflector surface. However, with this antenna is not the case!
Its radiation diagram is at an angle of 45 degrees in relation to all three Reflector plane and it must be considered when directing! Therefore, it is required to be mounted on a pillar with carriers that will provide the first line that the antenna radiates toward the horizon, ie. with the elevation angle of 0 degrees. In order to achieve the required antenna mounted at an angle of 45 degrees (see picture). Only then we can easily direct the reporter turning the antenna around the axis of the supporting pillars.
Reinforcement of the modified antenna and suppression of secondary beams of radiation depending on the length of the added element of DR wavelengths when DI = 0.65 tal. length.
Making the test model
Simulation L.B. Cebika for the original antenna with a reflector of 2 wavelengths and 0.75 wavelengths monopoly position x = 0.6 iy = 0.6 wavelengths, gives a value of 16:19 dBi gain when the input impedance of 71 ohms + J7. Our simulation showed almost identical results of 16.2 dBi in the impedance of 69.2 + j8.5 ohms! This is compared and verified the accuracy of our models and simulations in relation to the professional version of NEC-4.
Simulation of the modified antenna with an added element to adjust impedance showed something a bit more gain, which is the logical consequence of decrease of resistance of antenna with 72 to 50 ohms. Gain amounted to 16.4 dBi with the input impedance of 51.2 + j0.2 ohms, with little change in the vertical radiation diagram. Horizontal radiation diagram has remained virtually unchanged.
In this modification, due to decrease radiation resistance of antennas and expected some small reduction in the width of the working frequency band antenna, which is also subject to examination. The obtained values adjusted with the change of frequency are given at the end of the article along to a modified (50 ohm) and unmodified (75 ohm) antenna.
Chart radiation and amplification of the original 3D Corner antenna 2 tal. length.
Chart radiation and gain Modified 3D Corner antenna 2 tal. length.
Tentative model is made of plastic boxes in the shape of a cube of dimensions 225 x 225 x 225 mm (for a little less than 2 wavelengths at 2.4 GHz) that is cut and the inside plastered with aluminum foil. On the surface, which was the bottom of the gamble plastic boxes were opened drilled for mounting a N female jack and a mesinganog screws M4 with two queens for fixing the length of a particular calculation. The N connector is zalemljena brass tube diameter of 4mm, so that its total length corresponds to the calculation of the length element zračećeg DR. Brass screw is extended by the end of his also zalemljena of 4mm brass tube whose length is chosen so that the half-length given calculated length of the bolt element for setting DI. Guided by the calculated mass of N connection to the motherland and mesinganog screws M4 have a good connection throughout the volume with aluminum foil to reflektorskoj surface. It is very important for the proper operation of the antenna!
Looking at the antenna front
Also, all Reflector surfaces in all three planes must behave as a continuous surface with good electrical contact throughout the length of the connections between the plane reflector. This is achieved flap, 30mm wide, individual layers of aluminum foil, which is a quarter wavelength at the working frequency. This ensures that, in the case of poor mutual contact, mirrored impedance "open" quarter-wave of water, which consists of two layers of foil, a "short circuit", which provides efficient operation of the antenna. Length of both elements and their mutual distance is set according to the calculation is very precise as to when placing the instruments see how the initial error in the calculation.
Technique zračećeg and added elements
It was a pleasure to see that the antenna on the instruments behave exactly as the computer simulations were provided. Input matching was over-30dB and the measured gain is 15.5 dB, with a possible error of + / - 1DB, since it was not able to set the measuring polygons that turned off some unwanted side effects and provide greater measurement accuracy.
When I take into account the test model, its accuracy, and method of manufacturing the reflector size, the results are well agree with the predictions of computer simulations, which largely confirmed the authenticity of the mathematical model used this antenna in the simulation.
Side View
Setting the impedance is a non-critical, wide and exactly as expected.
Practically it is possible to make the antenna precisely measure the necessary dimensions and distances and antenna elements will immediately be set without any further settings on the instruments that are most difficult to builders available. This is another great advantage of this antenna.
View and add to the radiant element
The appearance of the antenna in a position to work
Modified 3D Corner Antenna for 2.4 GHz
As the optimal size reflector was adopted value of 2.5 wavelength at 2.4 GHz which is 300 mm. Properly built in antenna provides 17 dBi gain over what is acceptable value for most needs.
Modified 3D Corner Gain Antenna
Horizontal and vertical diagram of the modified antenna
Input matching and wide working range of variation of the antenna to 50 ohms
Input matching and wide working range of the original antenna to 75 ohms
Input impedance of the modified antenna
The view from the front section of the main beam of antenna
View from above the horizontal pattern of the antenna
The view from the side of the vertical pattern of the antenna
Electric current in certain parts of the antenna input power of 100W
The view from above of a modified antenna elements with positions
Smith's diagram of the antenna impedance for a range of working frequencies
f = 2400 - 2450 MHz and the SWR circle on a 2430MHz
Mechanical construction of the modified 3D Corner Reflector Antenna
Reflector antenna area must be done almost as if cast in one piece!
Once a connection had to exist between the two planes, it is best to be on the two vertical planes. Then the line parallel to the circuit radiant element not to cut time currents that flow parallel to the element that radiates them.
If the circuit line at a right angle to the radiant element, then weak connection cut electricity that flow in the reflector antenna and the bad work! It is very important!
So should iskrojiti plate for the antenna exactly as it is given in the drawing and fold it at right angles by dashed lines!
Besides good naleganja surfaces that are mutually connected and the number of screws or pop rivets with which the connection should be made to be as large, and at least every 10-20mm! If the antenna made of copper or tin mesinganog best composition of sheet solder from the outside antenna.
Weight connectors and screw to adjust the length of the additional element must have a very good connection with the searchlight area!
Length elements are measured from the surface Reflector to their peak as given in the picture!
Details construction
Correct method of mounting the antenna on the pole
Calculating antennas for other frequencies
This antenna, due to its principle of operation, is easily adapted to work on any other frequency. At lower frequencies can be for the spotlight, instead of sheet metal, used a network with openings smaller than 0.1 wavelength. At very high frequencies requires precision design and zračećeg added element and good connections.
Dimensions Modified 3D Corner Reflector Antenna in wavelength (Lambda) are as follows:
Dimensions reflector (measured from the scalp to end): L = 2.5 x 2.5 x 2.5 Lambda
Zračećeg element length (measured from the reflector): DR = 0754 Lambda
Length of the added element (measured from the reflector): DI = 0650 Lambda
Diameter elements: FI = 0032 Lambda
Zračećeg element position (measured from the scalp): x = 0.6, y = 0.6 Lambda
Position added element (measured from the scalp): x = 0.7, y = 0.7 Lambda
Wavelength can be calculated by the formula:
Lambda = 299.8 / frekv.
Wavelength is given in meters, if the frequency is entered in MHz.
***
In Belgrade, March 2005. |
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