The city of Phoenix, Ariz. has pretty specific ideas about what it wants cellular antennas in residential areas to look like: anatomically correct palm trees of a maximum 65-feet with 55 fronds, a leaf cluster and a maximum trunk diameter of 26 inches.

If that doesn't suit, operators can also choose from cacti, pine trees or architectural elements – all with their own exacting specifications.

In 2009, the city did a wholesale rewrite of its wireless communications facility ordinance after years of grappling with cumbersome zoning laws that left carriers frustrated and residents disgruntled. The new ordinances laid out highly detailed rules for what new antennas in residential areas could look like if they couldn't be attached to an existing light pole or utility pole.

New cell sites would have to be disguised, and the city took great pains to provide specifics about exactly what the camouflage would look like. The regulations covered every inch of the so-called "stealth antennas," from their height and girth to number of branches.

The result: a faster, more predictable approval process that has made the placement of new antennas, often viewed as a blot on the urban landscape, more palatable to local residents.

"It's a win-win," says Randy Weaver, a Phoenix city planner. "There used to be a lot of fighting and neighborhood upheaval, but now people have become more accustomed to them and the hatred for them has declined. They're not always that visually appealing, but it's better than having an industrial-looking pole."

Sure, the "monopalms" might not look exactly like palm trees – they tend to be a lot taller and are covered in antennas – but many view them as an improvement over the industrial eyesore of an undisguised cell tower.

Carriers and local municipalities are finding out that camouflaging cell antennas can sometimes assuage residents' concerns about esthetics and property values, helping to expedite the permit process for new sites.

Ward WilsonWard Wilson, national director of site development for MetroPCS, says camouflaged sites are "becoming more and more common over the past four or five years." He includes distributed antenna systems and microcells – easily hidden or attached to existing structures – in his definition.

Many areas where carriers have to increase capacity are in heavily populated residential areas where municipalities can block new antennas over their impact on neighborhood esthetics and property values. Under the Telecommunications Act of 1996, local governments are prohibited from enacting all out bans on new cell towers, but allows them to regulate the placement and construction­­­­ of wireless facilities. The regulations also prohibit municipalities from blocking towers based on health concerns over radiation, but allow consideration for factors such as historic preservation and property values.

"If we go into those areas with a stealth design, we meet with a lot less resistance," Wilson says. "We've found that we can waste a lot of time trying to get a regular monopole zoned. If we had just gone with a stealth approach in the beginning we could have cut our time in half."

Stealth TowerStealth designs are especially common in markets on the West Coast like San Francisco and some East Coast cities like the Hamptons, where local governments have been notoriously reticent to approve new cell sites. Operators and their site contractors going with a stealth antenna could attach them to an existing structure, disguise them as part of a building or use a monopole design like the fake trees laid out in so much detail by the city of Phoenix.

Andrew Messing, president of Larson Camouflage, says carriers are more willing to take on the additional costs of disguising a site in cases where it could help smooth the permit approval process.

"At first, carriers weren't eager for our product unless they really needed it because they didn't want to add the additional cost," Messing says. "Now, the environment has changed. They realize that if they want to get a cell tower built in certain jurisdictions, or want to expedite the process, they'd design from the get go to have it disguised."

Sean McLernon, CEO of Stealth Concealment Solutions, has had a similar experience in his two decades in the stealth antenna market. McLernon's company has hidden cellular antennas in everything from mosques in the Middle East to Disney World in Florida.

"The usual motivation is to prevent additional visible pollution in a cityscape or in a private neighborhood – it's a good compromise on NIMBY," McLernon says, referring to Not In My Back Yard. Local residents often expect seamless cell service, but don't want to see unsightly towers in their neighborhoods. "After 20 years of doing this, I don't think it's an exaggeration to say that without concealments, some sites wouldn't have been built. People have become less and less tolerant of antennas going up."

Not everyone agrees that camouflage is a cure-all. John Harrison, vice president of engineering and operations at Sprint, says it's becoming increasingly rare to have to build new cell towers in the first place – Sprint is well past the greenfield stage and is focused primarily on infill coverage with distributed antenna systems and microcells – and even a stealth design doesn't guarantee a permit approval.

"Generally speaking, nobody wants to put a site in their backyard. Just coming in to say you'll camouflage a site doesn't necessarily make it easier to get it through a zoning board," Harrison says. "Can it help? Absolutely. But it's not a guaranteed fix."

An operator's best front line of defense for new antenna placements, whether it's a tower, colocation or DAS site, are local contractors who know the area's particular rules, requirements and regulations, Harrison says.

Both Wilson and Harrison agree that local governments have become increasingly sophisticated about the zoning process for new antennas. Most have specific ordinances for the placement of towers and antennas, and some even go into detail about their appearance. Knowing those ordinances is often the best way to get new equipment in place, regardless of the esthetic benefits of a stealth site.

Potential zoning benefits aside, there are some drawbacks to stealth antennas.

Designs have "changed dramatically"Camouflage designs also add thousands of dollars in additional costs to a site. Thor Holbeck with Environmental Integration estimates that a monopine can cost between $10,000 and $80,000 depending on its height and the intricacy of the design. More intricate installations can be even more expensive, such as exacting architectural concealments in historic landmarks.

Environmental Integration is currently working to install a series of hidden monopines in the Adirondacks State Park, where limited cell service had repeatedly left stranded motorists unable to call emergency services.

In addition, stealth sites like architectural concealments sometimes have space constrictions that make it harder to add new equipment. Wilson says it "can be a challenge" to engineer within the confines of some hidden sites, such as antennas hidden in a gap behind a false wall.

Adding new equipment to concealed sites can also necessitate some remodeling, adding additional costs to already expensive network upgrades. For instance, when AT&T went to upgrade its monopalm sites in Phoenix ahead of its LTE launch there, it had to bring Larson Camouflage back in to add additional foliage, since the addition of its new mobile broadband equipment brought the number of fronds on each tree under the city's requirement.

Stealth sites aren't anything new to the wireless industry. Many businesses formed in the early 1990s, when many operators were rushing to expand their networks into new areas of the country and demand was just starting to emerge for concealed sites.

Some companies in the antenna concealment space got their start making habitats for zoos and other clients who needed fabricated structures. Both Larsen Camouflage and Environmental Integration once made habitats before refining their focus on the wireless industry.

The booming wireless industry presented new opportunities for growth, and entrepreneurs began developing RF-friendly materials to hide antennas behind.

Holbeck admits that the early monopines weren't much to look at, bearing a closer resemblance to a wire brush instead of a conifer.

"The first generation were pretty bad," he says. Back when they first began to appear in the 1990s, many monopines were erected with broad disregard for realism, an attitude that changed as local governments began to demand more attractive designs.

Improvements have been made, and some of today's concealments look pretty close to the real deal.

"Our designs have changed dramatically," Messing says. "Today you get a much more esthetically pleasing product. We feel we're doing our job well when someone drives by our projects and they don't even k now they've passed a cell tower."

Technological advancements may eventually make stealth sites a thing of the past. As Harrison said, the need for new cell sites is already decreasing as established operators focus more on increasing capacity through small cell deployments and distributed antenna systems, which don't require elaborate concealments. Looking further ahead, infrastructure vendors Alcatel-Lucent, Ericsson and Nokia Siemens Networks have all come out with small cell architectures largely comprised of boxes so small they won't need to be concealed.

But until that happens, it's getting easier to blend wireless infrastructure into the landscape. So if you see a suspiciously tall tree or a newly constructed church steeple, look closely – it could be a cell tower.