I want to build a Horn antenna to increase directivity of HB100 sensor and I studied principles on an Antenna's book. I started from a void rectangular waveguide.

Since the frequency is 10.525 GHz, the greater side of the waveguide is

$$L = \frac{c}{f_{cutoff}\cdot2\cdot20\,\text{mm}} = 14.28\,\text{mm}\text.$$

It's a very small waveguide, so I ask it's possible to use a smaller cutoff frequency to make a greater waveguide? Dimensions must be about of HB100 board, 40 mm × 46.5 mm.

Second question, to match intrinsic waveguide's impedance with charateristic impedance of air is necessary to increase gradually the dimensions of the waveguide, making it like a pyramid. But, how can I determmine the minimum length that of the horn?

HB100 mechanical drawing:

enter image description here

Dimensions: 40 mm × 46.5 mm

Given the distribution of the antenna patches, the opening of the waveguide needs to be approximately the size of the HB100.

What do you think about a guide of 28mm x 10mm? Fundamental mode is at 5.35 GHz and first higher mode is at 10.7 GHz, that permit a singlemode propagation. The problem is to connect at HB100 a so small waveguide. I thought to connect the guide centered on the arrays, is a good solution? Distance between two elements of array is exact 28mm.

Like this:

enter image description here

  • \$\begingroup\$ What documents have you found on the internet to help you? \$\endgroup\$ – Andy aka May 25 '18 at 18:12
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    \$\begingroup\$ It might be easier and possibly higher gain to use a parabolic reflector with the HB100 at the focus. Google "parabolic antenna booster". The solid ones for drones should work and are cheap. \$\endgroup\$ – crj11 May 25 '18 at 18:14
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    \$\begingroup\$ Horn antenna calculator \$\endgroup\$ – Andy aka May 25 '18 at 18:16
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    \$\begingroup\$ I wonder if you might be able use the wave guide from a Universal LNB as used in Europe as a base. They operate down to 10.7GHz, so at least close to the frequency of your radar. You'd remove all of the electronics, and use just the waveguide and the housing. As a bonus, you can mount it on a satellite dish and get some gain. And, probably a visit from your local equivalent of the American FCC. :) \$\endgroup\$ – JRE May 25 '18 at 18:18
  • \$\begingroup\$ I studied from "Antennas, typical applications" for the Horn antenna. About waveguides I used my notes of a electromagnetic fields course in my university, I study information engineering. This is part of a first level thesis, so I can't use a prebuild antenna, I have to build one from myself. I calculated the cutoff frequency from the formula that I posted at the initial post, this formula comes by the condition that propagation costant of e.m. wave must be real to have not attenuation of the wave. Sorry, but I'am new in electromagnetics and my knowledged comes only from this exam. \$\endgroup\$ – Fabio May 25 '18 at 18:49

I don't think this will work anywhere near as well as you expect it to.

As you already found out, no waveguide (can) exist that supports single-mode propagation at your frequency requirements and dimensions. Even the WR-112 (which in theory only goes to 10 GHz) is only 28 mm on the long side.

So lets say you use 4 waveguides, even then, I doubt you will gain anything with a horn. I suspect that the losses you will suffer because your entire system is not designed for a horn in the first place will result in your horns doing more harm than good. Keep in mind that this seems to already use a patch-antenna array, which means that it will already have a bit of directivity.

I suspect if you want to do with with a horn antenna, you should start with a transmissionline to waveguide transition.

  • \$\begingroup\$ I'am not using 4 waveguides, but one for each array. I'am working on a thesis in electromagnetic fields, and my professor assigned me this job. He has also built a horn antenna for HB100. It's possible to use two sectoral H-plane horns placed on the array? For example, something likes this: mega.nz/#!T0IlnRra!jSVsWKgSfFQ49hurxXinCfijZGDphUDcPFNmlt0pPHo I thought to place Supposed a TE10 mode, using two sectoral H-plane could work? Distance of two arrays is 28mm, so I thought to implement a (homemade) rectangular waveguide of 28mm x 10mm. \$\endgroup\$ – Fabio May 26 '18 at 15:34

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