3.3 Antenna Types, Charts, Cables and Lightning Protection

Pick the pattern for the job, then read the chart

Cedar Harbor now has three hanging decisions on the same work order: a ceiling AP in a four-bed ward, a wall AP at the end of a long corridor that should not blast the MRI waiting room behind it, and the roof-to-garage PTP hop. Those are three different patterns, not three copies of the same stick antenna. This OpenExamPrep section teaches omni, semi-directional, and highly directional types, how to read azimuth and elevation charts, how orientation and tilt steer energy, how cables and connectors steal EIRP, and how lightning arrestors and grounding keep a roof feed from becoming a fuse into the IDF.

Omni-directional: the doughnut, 360 degrees of azimuth

An omni-directional antenna is built to cover the horizon around it. In azimuth (the top-down view) the pattern is about 360 degrees. In elevation it is a doughnut (torus): energy goes out to the sides; nulls sit off the ends of a vertical dipole—more or less straight up and straight down.

Raise the dBi on an omni and the doughnut gets flatter. A 2 dBi rubber duck throws more energy upstairs and downstairs. A 8–10 dBi vertical omni throws energy farther along the floor and starves the floor above. That is why a high-gain omni on a ward ceiling can look strong in the corridor and weak in the room directly below the tile.

Indoor ceiling coverage is the classic omni job: clients sit all around the AP, and you want a horizon doughnut, not a spotlight. Do not hang a dish in that tile.

Semi-directional: patch, panel, and Yagi

Semi-directional antennas concentrate energy into a forward lobe that is wide enough for a room or a sector, not a needle.

• A patch is a flat, often square or rectangular element behind a radome. Typical azimuth beamwidths might be on the order of 60–90 degrees (catalogs vary). The back of the patch is much quieter: useful when the AP is on a wall and you do not want equal energy behind the wall.
• A panel is a larger, often multi-element patch-style aperture. Beamwidths can be similar or slightly narrower; gain is often higher than a small patch.
• A Yagi is an end-fire array: a driven element plus directors and a reflector along a boom. The boom points at the target. Yagis are common on short outdoor hops and on a warehouse wall that must reach one aisle.

Wall coverage is the classic patch job: fire a lobe down the corridor or into the clinic, keep a rear null toward the unused space. Cedar Harbor's corridor AP is a wall patch, not an omni that would equally light the MRI waiting room through the wall.

Highly directional: parabolic dish and grid

Highly directional antennas make a narrow main beam and high dBi.

• A parabolic dish uses a solid or perforated reflector with a feed at the focus. Beamwidths of a few degrees to a couple of tens of degrees are common as size and band change. Wind load on a solid dish is high.
• A grid (grid parabolic) uses a gridded reflector so wind can pass. Electrically it still behaves as a high-gain dish at WLAN wavelengths when the grid spacing is small compared with λ.

Outdoor PTP is the classic high-gain directional job: you know the far end's bearing, you want EIRP in that bearing, and you want to avoid lighting neighboring campuses. Cedar Harbor's garage hop uses a pair of dishes (or dual-pol panels with tight enough beams), not omnis.

If the work order says outdoor PTP and someone mounts a ceiling omni on a mast, the energy goes everywhere in azimuth, the far end is starved, and you pick up interferers you did not need. If the work order says indoor ceiling and someone mounts a 23 dBi grid in a tile, clients two meters off bore sight vanish.

Reading azimuth and elevation charts

Vendors publish polar plots (sometimes rectangular plots) for two cuts:

• Azimuth chart — the H-plane, top-down view. For a vertical omni it should look nearly circular. For a patch it should show a forward lobe and a smaller back lobe. Read the −3 dB points to estimate azimuth beamwidth.
• Elevation chart — the E-plane, side view. This is where you see whether an omni doughnut is fat or flat, and whether a patch looks down or straight out from the wall.

How to read a chart on an item:

1. Find the 0 degree mark. On azimuth that is usually the bore sight of a directional or an arbitrary reference on an omni.
2. Find the outer ring scale (often 0 dB at the peak, negative dB toward the center or labeled in dBi).
3. Walk to the −3 dB contour. The angle between the two −3 dB crossings is HPBW.
4. Look for sidelobes and nulls. A null toward a neighboring SSID can be a gift. A null toward a nurse station is a ticket.

Cedar Harbor's patch chart shows a 70-degree azimuth lobe and a 55-degree elevation lobe with the peak at the horizon when the patch is flat on a wall. If the installer hangs that patch on the ceiling like an omni, the peak now fires at the floor in a spotlight and the ward corners go dark. The catalog did not change. The mounting plane did.

Antenna orientation: tilt, polarization plane, mounting plane

Orientation is not decoration.

• Polarization plane: rotate a linear patch 90 degrees and you changed vertical versus horizontal. PTP both ends must match, as the previous section taught.
• Mechanical downtilt: physically tip a panel so the elevation lobe covers a lower parking lot instead of the horizon. Useful on a building face that must cover a plaza, harmful if you tilt a PTP dish toward the ground.
• Electronic tilt exists on some cellular panels; enterprise WLAN patches are usually mechanical. Do not invent a phased-array story the catalog does not print.
• Mounting plane: ceiling versus wall versus mast. An omni expects its doughnut parallel to the floor. A wall patch expects its face toward the clients. A Yagi expects the boom toward the far end, not parallel to the wall as if it were a shelf bracket.

A few degrees of dish pointing error on a 6-degree beam can drop the far end several dB. Use the chart, then a RSSI/SNR check at the far radio—not a guess from the parking lot.

RF cables and connectors

WLAN antenna feeders are almost always 50-ohm coaxial cable. Loss is a function of length, frequency, and construction (diameter, dielectric, braid/foil quality).

Rules of thumb, not a substitute for the cable's data sheet:

• Longer cable → more dB of loss, roughly in proportion to length.
• Higher frequency → more dB of loss on the same jumper. A run that is tolerable at 2.4 GHz can be ugly at 5 GHz or 6 GHz.
• Thinner cable → more loss than a short, thicker jumper of the same family.
• Every connector pair adds a little loss and a chance for water ingress outdoors.

Illustrative order of magnitude (check the actual sheet before you buy): a long thin jumper at 5 GHz can cost several dB per ten meters, which is enough to erase the extra dBi you just paid for on the antenna. The EIRP formula from the previous measurement section is where this number lands: minus cable and connector loss.

Keep outdoor runs short. Mount the radio near the antenna (integrated radio+antenna bridges exist for this reason) rather than dragging 30 meters of skinny jumper from an IDF to a dish.

Common connector families (no vendor advertisement—these are interface types you will see on pigtails and arrestors):

RP-SMA is not a better SMA. It is a different mating. Forcing SMA onto RP-SMA damages the center contact. Match the gender and the polarity the radio actually uses. Adapters add loss; a drawer full of adapters is not a design.

Lightning arrestors, grounding rods, and conductors

A roof coaxial run is a lightning and static path into the building. CWNA-depth practice:

• Install a lightning arrestor (often a gas-discharge device) on the coaxial at the building entry, as close to that entry as the layout allows.
• Bond the arrestor with grounding conductors into the building grounding electrode system—ground rods, building steel, or the electrode the electrical design already uses. Follow the electrical authority having jurisdiction; this study section teaches the WLAN intent, not a substitute electrical-code stamp.
• Do not dump lightning energy into the AP chassis as the only path, and do not leave the outdoor shield floating.
• Use outdoor-rated cable, drip loops so water does not follow the jacket into the connector, and weather boots on N-types.

An arrestor is not a miracle. A direct strike can still destroy hardware. The goal is to give surge current a preferred bonded path to earth before it prefers the radio's PCB. Indoor-only ceiling APs with no outdoor copper are a different risk picture; the roof PTP hop is not indoor-only.

Cedar Harbor lands the garage hop through a roof penetration, arrestor on a grounded bulkhead, short indoor jumper to the radio, copper bonding conductor to the building ground bus—not a random screw into painted steel.

Enclosures, mounting, and aesthetic concerns

Outdoor radios and junctions live in weather enclosures: UV, rain, and temperature. A sealed box that traps heat around a radio is a silent failure mode; ventilation and sun shields matter. Indoor APs use plenum-rated housings where the air-handling space requires it.

Mounting must hold wind and ice load for dishes and grids. A grid exists partly because wind load on a solid dish can twist a cheap mast and walk the beam off the far end.

Aesthetics are in the objective list because hospitals, campuses, and historic buildings reject gear that looks like a radar site. People hide APs above ceiling tile (watch the doughnut and the plenum rule), paint radomes, or use stealth enclosures. Paint, metal decorative cages, and foil-backed insulation can detune or attenuate an antenna. If the architect's cage is a Faraday hint, the RF design lost. Agree on RF-transparent covers before the install crew improvises.

Job-to-antenna matches worth memorizing

Accessory traps

1. Ceiling omni on a PTP mast, or a dish in a ward tile.
2. Reading the elevation chart as if it were the top-down azimuth cut.
3. Rotating a patch for looks and accidentally rotating polarization.
4. A 20-meter thin jumper that eats the extra dBi on the antenna.
5. SMA forced onto RP-SMA.
6. Outdoor copper with no arrestor and no bond to the grounding electrode system.
7. A metal decorative cage that becomes a shield.
8. Assuming aesthetics never change RF.