{"id":203,"date":"2017-08-15T21:55:33","date_gmt":"2017-08-15T20:55:33","guid":{"rendered":"http:\/\/www.burningimage.net\/cattrack\/?p=203"},"modified":"2023-07-22T07:56:58","modified_gmt":"2023-07-22T06:56:58","slug":"gps-cat-tracker-antenna","status":"publish","type":"post","link":"https:\/\/www.burningimage.net\/cattrack\/gps-cat-tracker-antenna\/","title":{"rendered":"One last thing…. The Antenna!"},"content":{"rendered":"

I was a little premature with my previous post. \u00a0I can’t quite draw the schematic diagram yet – I need to work out the antenna!<\/strong><\/p>\n

Texas Instruments have produced an excellent guide<\/a>, examining a number of different types of antenna for embedded applications. \u00a0The table below summarises the pros and cons of a number of different antenna solutions and is taken from that guide.<\/p>\n

<\/p>\n

\"\"<\/p>\n

The antenna choice goes hand-in-hand with the frequency choice. \u00a0Technically, using the CC1125<\/a> I can transmit anywhere from around 160 MHz to 1 GHz. \u00a0However, in the UK I can only really choose from the 433 MHz or 868 MHz frequency bands as these are the bands I can transmit on without a licence.<\/p>\n

A critical parameter in antenna design is the wavelength (SI unit: \u03bb). \u00a0The wavelength at 433 MHz is around 69 cm. \u00a0At 868 MHz it is around 35 cm. \u00a0One of the simplest antennas you can make is a dipole<\/a>. \u00a0The full length of the dipole antenna \u03bb\/2, so for 433 MHz that’d be around 35 cm and for 868 MHz it’ll be 18 cm. \u00a0 Given that size I clearly won’t be using a dipole antenna in my design!<\/p>\n

As we’ve just shown, basic antennas at 868 MHz are around half the size of antennas at 433 MHz. \u00a0Therefore it makes sense to use an 868 MHz antenna in my design.<\/p>\n

After a good look at the TI guide, I’ve decided on a chip antenna – I reckon this will give me the best compromise between antenna size and performance. \u00a0It’s important to note that the ground plane is\u00a0really<\/em> important with chip antennas. \u00a0You can’t simply hook a chip antenna up to the RF output of your circuit on a tiny PCB with no ground and expect it to work. Looking at the Johanson 0868AT43A0020 datasheet<\/a>, they have conducted their tests using the following board:<\/p>\n

\"\"<\/p>\n

The entire board, including the ground plane, is important to the performance of the antenna – not just the chip antenna itself. \u00a0I reckon that my board will probably be of similar dimensions to the Johanson test board above, so I will try to fit my chip antenna in a similar position.<\/p>\n

It will be essential for me to ‘match’ the antenna into the output of my CC1125. \u00a0If I were to simply connect the antenna to the CC1125 output, even with the correct ground plane, it would barely work at all. \u00a0Antenna matching<\/a> is the process of adding components to a design between the antenna and the RF output (in my case the CC1125) to ensure maximum power transfer from the CC1125 into the antenna. \u00a0This is a fundamental job performed by an RF Engineer. \u00a0I’m a lucky enough to have a VNA<\/a>, so I’ll be able to match the antenna myself at home.<\/p>\n

Now… onto the schematic!<\/p>\n","protected":false},"excerpt":{"rendered":"

I was a little premature with my previous post. \u00a0I can’t quite draw the schematic diagram yet – I need to work out the antenna! Texas Instruments have produced an excellent guide, examining a number of different types of antenna for embedded applications. \u00a0The table below summarises the pros and cons of a number of […]<\/p>\n","protected":false},"author":1,"featured_media":204,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[4,67,39,7],"class_list":["post-203","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-posts","tag-cc1125","tag-chip-antenna","tag-transceiver","tag-transmitter"],"_links":{"self":[{"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/posts\/203","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/comments?post=203"}],"version-history":[{"count":5,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/posts\/203\/revisions"}],"predecessor-version":[{"id":216,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/posts\/203\/revisions\/216"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/media\/204"}],"wp:attachment":[{"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/media?parent=203"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/categories?post=203"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.burningimage.net\/cattrack\/wp-json\/wp\/v2\/tags?post=203"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}