Homebrew RF Circuit Design Ideas There is no such thing as a new idea. It is impossible. We simply take a lot of old ideas and put them into a sort of mental. Type or paste a DOI name into the text box. Click Go. Your browser will take you to a Web page URL associated with that DOI name. Send questions or comments to doi. TREVOR MARSHALL Slotted Waveguide 8. WLAN antennas. Slotted Waveguide Antennas. Unlike wideband antennas like the biquad, slotted waveguides are resonant antennas, and have a relatively narrow operating frequency range. The designs I am describing on this page have an adequate bandwidth for any WLAN, but they have been carefully designed and must be equally carefully constructed. The major attraction of a slotted waveguide design is its simplicity. Once you have built the first one it is very simple to build many more. The gain varies little across the 8. How I Produced These Designs and Charts. These slotted waveguide designs are the result of lengthy simulation using Zeland Softwares Fidelity and IE3. D electromagnetic simulators. Fidelity is much better at modelling waveguide structures than my favorite simulator, NEC2, but it is quite an expensive package, with a long learning curve. Rex Research established 1982 collects and disseminates reports about suppresseddormantemerging science, inventions, technologies, experiments, and. Simulation can give you much more information about the performance of a microwave antenna than you get from building it. This is because there are severe limitations in the accuracy of measurements at microwave frequencies. Simulation makes it easier to see subtle interdependencies that would be very difficult to measure. In this case, I used the simulation to tell me how the antennas should behave, and then verified the performance both in my lab and on my antenna test range. The results were surprisingly accurate and attest to the quality of the Zeland Fidelity software. How a Waveguide Antenna Works. A waveguide is a very low loss transmission line. MTScLQYlOOE/0.jpg' alt='Design Equations Patch Antenna' title='Design Equations Patch Antenna' />It allows us to propagate signals to a number of smaller antennas slots. The signal is coupled into the waveguide with a simple coaxial probe, and as it travels along the guide it traverses the slots. Each of these slots allows a little of the energy to radiate. The slots are in a linear array pattern, and the total of all the radiated signals adds up to a very significant power gain over a small range of angles close to the horizon. In other words, the waveguide antenna transmits almost all of its energy at the horizon, usually exactly where we want it to go. Its exceptional directivity in the elevation plane gives it quite high power gain. Additionally, unlike vertical colinear antennas, the slotted waveguide transmits its energy using HORIZONTAL polarization, the best type for distance transmission. At left we can see a graphical representation of the E field intensity shortly after starting excitation of an 8 slot waveguide. The slots are to the left of the image. The coaxial probe is at the lower end of the image, and the field can be seen to be clumped at maxima every half wavelength as they travel up the waveguide. The waveguide airspace takes up the middle 12 of the bluespace, the rest is air infront of to the left and behind to the right the antenna. If you click here you can bring up a Windows Media Format Movie version. Helix Antenna pop Here is the design of a 2. GHz antenna that is ideal for amateur satellite communications. This antenna is easy to assemble because the. An MPEG 1 version is at this link. You can see the wave travelling up the waveguide from the probe. The intensity of the E field is given by the color. Here we have primarily blue colors, about 4. B on the final red intensity which is achieved once the resonance is fully excited. Antenna-Design-Calculator_1.png]];var lpix_1=pix_1.length;var p1_0= [[638' alt='Design Equations Patch Antenna' title='Design Equations Patch Antenna' />When the signal first gets to the top and starts reflecting back down the air column it is still green, about 3. B from its ultimate intensity. Reflections are also occuring from the plug at the bottom of the airspace, and the sum effect of all these, including continual drive from the coaxial probe, allows the intensity to build up through yellow and red 0db signal levels. You can see the signal radiating out the slots at the left of the image. The radiation intensity is less at the top than at the bottom in an 8 slot design, it is hard to radiate perfectly with such a limited number of slots. The 1. 6 slot design has been made to radiate over a wider beamwidth by the addition of wings to each side of the guide, flush with the front slotted surface. It is, of necessity, higher Q, and the higher gain is obtained over a narrower bandwidth. They can be expanded aluminium or sheet, and should extend 9. They act as a ground plane for the slots. Do not change this dimension, it is two electrical wavelengths. Omnidirectional Slotted Waveguide Antennas. The slotted waveguide has achieved most of its success when used in an omnidirectional role. It is the simplest way to get a real 1. Bi gain over 3. 60 degrees of beamwidth. Horizontal Polarization in a wide area network can often double the number of users that can interconnect without interference. When using horizontally polarized Bi. Quads, or Patch antennas provided that they have been tested for good cross polarization performance at the client site, these omnis will be 2. B stronger than the signal from a similar vertical collinear. Camera Tracking Software For 3Ds Max Tutorial. Conversely, vertically polarized receiver antennas will prefer the vertically polarized colinear over the slotted waveguide by a similar amount. Transmission on an immediately adjacent channel, say, channels 5 or 7, normally not permissible because of interference, is now possible. So a judicious intermingling of horizontally polarized clients can talk with a horizontal central station on the same or adjacent channels that other clients are using with vertical polarization. To make the unidrectional antenna radiate over the entire 3. When looking stright at the face of the waveguide you will be able to see straight through both slots. Unfortunately, unless a lot of slots are used, the antenna becomes more like a bidirectional radiator, rather than an omnidirectional. This antenna was invented in the 4. The most common defect is a tilt in the radiation pattern at the extreme ends of the frequency range. This occurs when the wavelength of the signal travelling down the guide differs from the slot spacing. My current favorite uses 3. Bi of gain, radiated in a uniformly omnidirectional manner. The large number of slots makes it easier to dissipate the energy from the waveguide. Like with the 1. 6 slot unidirectional, two sets of wings one set at each slot surface are required to get equal radiation of energy over a full 3. Note that a higher Q is necessary to get all the slots illuminated evenly. Note that the gain vs frequency curve is peaked at 2. Highly Directional Slotted Waveguide Antennas. Sometimes it is useful to have a highly directional antenna. For example, when installing a point to point link between two buildings it is not desirable to have a wide angle of coverage. Any interference from other 8. The ideal antenna for such a situation is a dish, such such as the Primestar dish. When using my Biquad feed, it is possible to reject interference outside the dishs primary 5 degree cone by 3. B or more. But, if a 1. Its directivity in this plane is extremely good. As you can see from the diagram to the left, most of the spurious lobes are more than 2. B down from the main signal, and they are very narrow click to enlarge the image. This performance is comparable with my commercial HP2. G Parabolic Grid Antenna. So, if you dont have a dish handy, consider the possibility of using a pair of these slotted waveguides, parallel to the ground. They will work well. Very well. Constructional Details for the 8 Slot Unidirectional Antenna. The base extrusion for all my slotted waveguides is 4 inch by 2 inch O. D. rectangular aluminum tubing with approx 18 inch thick walls. Inside dimensions are 3. These inside dimensions are critical, and must be within 0.