Aircraft antennas

This category covers antennas for aircraft, uncrewed aircraft and spacecraft: blades, patches, phased arrays, radomes and the mounting hardware that holds them to the skin. The radio, receiver or terminal behind the antenna belongs in its own guide. The reason antennas earn a separate shelf is that they are bought by three different people in the same company, and each of them cares about something the others forget.

Three specifications, not one

The radio engineer wants pattern, gain, polarisation, bandwidth, voltage standing wave ratio and isolation from the other antennas on the aircraft. The stress engineer wants the doubler, the fastener pattern, the load path and what the cutout does to the surrounding structure. The certification engineer wants the environmental qualification and the lightning case, because the airplane must be protected against catastrophic effects from lightning, and the rule sets out how compliance is shown for metallic and nonmetallic components.² Ask for all three data sets at the request-for-quotation stage. A supplier who can produce the pattern data, the installation drawing and the qualification report without a delay is telling you something useful about how many times it has done this.

Approval, and where it stops

Antennas are commonly approved as articles under a technical standard order, which is a design and production approval for the article itself.¹ Putting one on a type certificated aircraft is a different approval, and a major change by a party that does not hold the type certificate requires a supplemental type certificate.³ Ask which approval each antenna in the quote carries, and ask who owns the installation approval for your model. For an uncrewed or experimental application the certification questions change, and the electrical and structural ones do not.

Installation is where the money goes

Ask what the installation needs beneath the skin: doublers, sealant, bonding, drainage, and access. Ask what the bonding resistance requirement is and how it is verified after installation. Ask about co-site interference with the antennas already fitted, and ask for the analysis rather than an assurance. Ask what the radome is made of, who repairs it, and what a repair does to its electrical performance. Ask about erosion, rain, ice and the paint scheme, because painting the wrong finish over a radome is a quiet way to lose performance you paid for.

Where the record can be checked

The FAA publishes its design approvals with searches for technical standard order authorisations, parts manufacturer approvals and supplemental type certificates, so the approval claims on a quote are checkable in minutes.⁴ Those registers prove what is approved and on what. They do not carry pattern data, qualification reports or the results of a co-site study, and none of those is a document you should accept as a summary.

Questions that sort suppliers

Ask for the qualification report and the environmental categories it was tested to. Ask for the installation drawing and the structural provisions it assumes. Ask what the lead time is on the mount and the doubler, not just the antenna. Ask which comparable aircraft already fly this part in this location.