Ham Radio Phased Vertical Arrays — Complete Guide
A phased vertical array uses two or more vertical antennas fed with specific phase and amplitude relationships to produce a directional radiation pattern from elements that are individually omnidirectional. The 4-square array — four quarter-wave verticals arranged in a square and fed with 90° phase differences — is the standard low-band DX system for serious 40m, 80m, and 160m operators. With switchable direction, a 4-square provides 3–6 dBd of gain toward any of four compass headings without a rotator. This guide covers the physics, design, construction, phasing networks, and practical operation of phased vertical arrays.
4-Square Array
Four quarter-wave verticals arranged in a square with side spacing of λ/4. Fed with 90° phase progression to produce a cardioid pattern switchable to four compass directions. The most popular and thoroughly documented phased array design in amateur radio.
2-Element End-Fire Array
Two verticals spaced λ/4 apart and fed 90° out of phase. Produces a cardioid pattern with approximately 3–4 dBd gain in the forward direction and a 15–20 dB front-to-back ratio. Simpler to build than a 4-square but covers only two directions (forward/reverse by switching phase).
Broadside Array
Two or more verticals spaced λ/2 apart and fed in phase. Produces a bidirectional pattern with gain broadside to the line of elements — similar to a high horizontal dipole but with omni azimuth characteristics. Useful for fixed-direction low-band paths.
In-Line End-Fire Array
Multiple verticals arranged in a line, fed with progressive phase delay to focus energy in the end-fire direction. Three or four elements in line can produce 5–7 dBd of gain in one direction with very good front-to-back ratio. Less common but highly effective for fixed DX paths.
Receiving Array (K9AY, EWE, Flags)
Small phased arrays designed exclusively for receive on 160m and 80m — K9AY loops, EWE antennas, and flag arrays. These compact designs provide directional noise rejection that dramatically improves weak signal copy on the low bands without any of the large footprint requirements of transmit phased arrays.
Large Arrays — 8-Circle and Beyond
Eight or more verticals arranged in a circle or grid, fed with precision phasing networks for steerable directional patterns and very high gain. Used at major contest and DXpedition stations where maximum low-band performance is the priority. W8JI and ON4UN are primary references.
Phasing — The Core Principle
When two antennas radiate at the same frequency, their signals combine in space. In some directions the signals add constructively — increasing the total field strength. In other directions they add destructively — reducing or canceling the field. By controlling the phase relationship between the two antennas, we control which directions receive constructive addition and which receive cancellation.
For a 2-element end-fire array with λ/4 spacing:
- Element 2 is fed 90° later in phase than Element 1
- In the forward direction (from Element 1 toward Element 2), the 90° phase delay of Element 2 exactly compensates for the 90° path-length difference between the elements — signals add constructively
- In the rearward direction, the phase delay adds to the path-length difference — signals partially cancel
- The result is a cardioid pattern with maximum gain forward and a null or near-null to the rear
- Reversing the phase relationship (feed Element 1 90° later than Element 2) reverses the pattern direction
The 4-square extends this to four elements arranged in a square, with 90° phase steps between adjacent elements in the firing direction. By selecting which element is the 0° reference and which are 90°, 180°, and 270°, the array can be pointed in any of four directions without physically moving the antennas.
Why Phased Arrays Excel on Low Bands
Phased vertical arrays are the dominant directional antenna choice for 40m, 80m, and 160m for specific practical reasons:
- On 160m, a full-size rotatable Yagi would be approximately 270 feet wide — completely impractical. A 4-square of 120-foot verticals fits on a 120-foot square of land and provides directional gain in four directions.
- Verticals already produce low-angle radiation ideal for DX. Phasing them adds gain to that already-favorable pattern without a tower.
- The phasing network is ground-mounted — no tower climbing required for direction changes or maintenance.
- The system is mechanically simple — no boom, no spreaders, no rotator. Just wire, pipe, and a switching network.
- The ground system (radials) for each element serves double duty as the RF ground for the full array.
The trade-off: phased vertical arrays require significant real estate. A 4-square for 80m has elements spaced approximately 65 feet apart — a square of 65 × 65 feet. For 160m, the spacing doubles to approximately 130 feet. This ground area requirement is the primary limitation for most residential installations.
The 4-Square Array — Design Details
The 4-square is named for its four elements arranged in a square, with adjacent elements spaced λ/4 apart. Each element is a quarter-wave vertical with its own ground system. The phasing network feeds each element with 0°, 90°, 180°, and 270° phase shifts relative to the first element — creating a progressive phase gradient that steers the main lobe in the desired direction.
Each vertical element is a standard quarter-wave vertical with a full radial system — the same as any ground-mounted vertical. The element quality and ground system quality directly determine the array's performance.
Phasing Networks — How to Feed the Array Correctly
Getting the correct phase and amplitude to each element is the most technically demanding aspect of phased array construction. Several approaches exist:
- Lahlum/Lewallen network — the most accurate and widely used homebrew phasing network. Uses L-networks at each element to provide the correct impedance transformation and phase shift simultaneously. Designed using the Lahlum/Lewallen spreadsheet (available free from W7EL). Requires measurement of each element's actual impedance with a VNA before designing the networks.
- Christman method — uses quarter-wave coax sections of specific characteristic impedances as phasing lines. Simpler to build than L-networks but less accurate and more frequency-specific.
- Commercial phasing controllers (DX Engineering, Array Solutions) — pre-engineered switchable phasing networks for standard array configurations. Expensive but reliable and well-documented. The Array Solutions ARS-4 and DX Engineering 4-square controller are the industry standards for amateur use.
- Comtek ACB-4 — a popular commercial hybrid combiner/phasing unit for 4-square arrays. Used by many serious low-band operators.
Current forcing — feeding each element with a constant current magnitude regardless of mutual coupling changes — is the key requirement for a phased array to perform as designed. A simple power splitter does not achieve current forcing; the Lahlum/Lewallen network does.
| Array Type | Elements | Typical Gain | F/B Ratio | Directions | 40m Footprint | 80m Footprint | Complexity |
|---|---|---|---|---|---|---|---|
| 2-El End-Fire | 2 | 3–4 dBd | 15–20 dB | 2 (switchable) | 34 ft line | 66 ft line | Intermediate |
| 2-El Broadside | 2 | 3–4 dBd | — | Bidirectional | 69 ft line | 131 ft line | Intermediate |
| 4-Square | 4 | 3–5 dBd | 20–25 dB | 4 (switchable) | 34×34 ft | 66×66 ft | Advanced |
| 3-El End-Fire | 3 | 5–6 dBd | 20–25 dB | 2 (switchable) | 68 ft line | 131 ft line | Advanced |
| 4-El In-Line | 4 | 6–7 dBd | 25–30 dB | 2 (switchable) | 103 ft line | 197 ft line | Expert |
| 8-Circle | 8 | 6–8 dBd | 25–35 dB | 8 (switchable) | Very large | Extremely large | Expert |
Building a 2-Element End-Fire Array
The 2-element end-fire array is the entry point into phased vertical array design — two quarter-wave verticals spaced λ/4 apart, fed with a 90° phase difference. It provides the directional advantage of phasing with the simplest possible phasing network and the smallest footprint.
The simplest phasing implementation uses a λ/4 coax section as a delay line. With both elements connected to the same feedline through a power splitter, adding a λ/4 section (accounting for velocity factor) to one element's feed introduces the 90° phase delay. However, this simple approach does not achieve current forcing — for precise pattern shaping, the Lahlum/Lewallen L-network approach is preferred even for a 2-element array.
To switch direction, swap which element receives the delayed feed and which receives the direct feed. This can be done manually or with a remote relay box at the phasing network.
Mutual Coupling — Why Simple Splitters Don't Work
The most common mistake in building a phased vertical array is assuming that feeding each element with the correct voltage phase is sufficient. It is not — because the elements are physically close to each other, they interact electromagnetically. Current flowing in one element induces current in its neighbors. This mutual coupling changes the effective feed impedance of each element away from the isolated element impedance.
If you simply split the power and add a phasing section without accounting for mutual coupling, the actual current magnitudes and phases delivered to each element will be wrong — and the resulting pattern will not match the design. The pattern will have less gain and poorer F/B than expected.
- The Lahlum/Lewallen network accounts for mutual coupling by measuring each element's actual impedance in the array environment and designing an L-network that forces the correct current regardless of coupling
- Current forcing is the key — controlling current (not voltage) at each element produces the designed pattern reliably
- Mutual coupling effects are stronger when elements are closer together and weaker with wider spacing
- For the standard λ/4 spacing in a 4-square, mutual coupling is significant and must be accounted for
Broadside Array Operation
A broadside array feeds two or more verticals in phase (0° phase difference) with λ/2 spacing. Unlike the end-fire array which produces a cardioid pattern, the broadside array produces a bidirectional pattern with maximum radiation perpendicular to the line of elements — similar in principle to a horizontal dipole.
The broadside pattern has two main lobes of equal strength pointing in opposite directions broadside to the element line, with deep nulls in the end-fire directions (along the element line). This makes it useful for fixed installations where two important DX regions lie on opposite bearings — Europe and Japan from the US central region, for example.
- Two elements in phase at λ/2 spacing: ~3.5 dBd gain broadside
- Four elements in phase (collinear): ~5–6 dBd gain broadside
- Pattern is bidirectional — equally good in both broadside directions
- Deep nulls along the element line — useful for interference rejection
- Simpler phasing than end-fire: all elements fed with equal power and equal phase
- Equal-length feedlines of any length to each element achieves in-phase feeding
Combining Broadside and End-Fire
The most powerful phased array configurations combine both broadside and end-fire phasing simultaneously. The 4-square is actually a combination of both — the four elements form both a broadside pair and an end-fire pair in the firing direction, with the two effects adding constructively.
More sophisticated designs use 2D arrays — elements arranged in a grid rather than a line — to achieve steerable beams with more gain than either pure broadside or pure end-fire designs. The 8-circle is the most common large amateur 2D phased array:
- Eight verticals arranged in a circle of λ/2 diameter
- Fed with progressive phase shifts to create a highly directional cardioid pattern
- Switchable to 8 compass directions — every 45°
- Typical gain: 6–8 dBd on 80m and 160m
- Used by major contest stations (W3LPL, K3LR, N2NT) and DXpeditions
- Requires precise phasing networks and element matching for optimum performance
Building a 4-Square Array for 40m
Four 33-foot quarter-wave verticals in a 34-foot square, fed with a commercial phasing controller — covers all of 40m with 3–5 dBd gain in four switchable directions.
Plan the Installation Site
Mark a 34.4 × 34.4 foot square on the property. Each corner is one element location. The center of the square is the natural location for the phasing controller box — equal cable runs to all four elements simplify the phasing network. Verify that all four element locations are accessible for radial installation and that the center is reachable for coax burial. The square can be rotated to any compass orientation — choose a rotation that aligns the four firing directions (N/S/E/W or NE/NW/SE/SW) with your most important target areas.
Install All Four Verticals
Install four identical quarter-wave vertical elements — for 40m at 7.15 MHz: 234 ÷ 7.15 = 32.7 feet each. Use the same materials and construction for all four elements to ensure identical element characteristics. Each element gets its own radial system — 16 to 32 radials of 32.7 feet each, buried 1–2 inches deep. All four radial systems should be as identical as possible — equal radial count, equal radial lengths. The center point of each element's radial bus connects to the element's feedpoint ground.
Measure Each Element's Impedance
With all four elements installed, measure the feedpoint impedance of each element individually while the other three are connected to their ground radial systems but not to any feedline. This gives the element impedance in the presence of mutual coupling — the actual operating impedance, not the isolated element impedance. Use the NanoVNA at the element base with a short reference cable. Record R + jX for each element at the operating frequency. These values are the input to the Lahlum/Lewallen phasing network spreadsheet.
Design or Select the Phasing Network
Enter the measured element impedances into the Lahlum/Lewallen spreadsheet (available from W7EL's website). The spreadsheet calculates the L-network component values needed to feed each element with the correct current magnitude and phase. Alternatively, use a commercial phasing controller (DX Engineering 4-Square Controller, Array Solutions ARS-4, or Comtek ACB-4) — these units are pre-engineered for standard quarter-wave vertical 4-square arrays and require only equal-length coax runs from the controller to each element.
Install Equal-Length Coax Runs
Run coax from the phasing controller position at the center of the array to each of the four elements. The coax lengths must be electrically equal — cut each run to the same electrical length (accounting for velocity factor). The physical length can vary slightly to reach elements at different distances from center, but the electrical length (physical length × VF) must be identical for all four runs. Bury the coax in conduit or direct-bury cable rated for underground use.
Install the Phasing Controller
Mount the phasing controller in a weatherproof enclosure at the center of the array. Connect the four element coax runs to the controller's element ports — maintaining consistent element numbering. Run the main feedline coax from the radio to the controller's input port. Install a direction-select cable or relay control cable from the controller to the operating position. Commercial controllers typically use a simple switch or relay board for direction selection.
Initial Verification and Pattern Testing
Connect the NanoVNA at the main feedline input. Sweep 7.0–7.3 MHz in each of the four direction settings. SWR should be below 1.5:1 in all four directions. If one direction shows significantly higher SWR than the others, suspect an element connection error or a failed element. Use the Reverse Beacon Network to verify pattern: transmit CW on 40m in each direction and confirm that spots from the forward hemisphere are 15+ dB stronger than spots from the rearward hemisphere.
K9AY Loop Array
The K9AY (Gary Breed) terminated loop is a small receiving antenna specifically designed for low-band noise rejection. It consists of a triangular loop of wire approximately 28 feet on each side, terminated with a resistor (typically 910Ω) at the bottom opposite the feedpoint. The termination makes the loop unidirectional — it has a cardioid pattern with a deep null in one direction.
Two K9AY loops at 90° to each other, with a phasing switch between them, allow steering the null to any compass direction. The combination provides directional noise rejection on 160m and 80m that dramatically improves weak signal copy in noise-rich environments.
- Loop size: approximately 28–32 feet per side (triangle)
- Termination: 910Ω non-inductive resistor at the apex opposite the feedpoint
- Two loops at 90°: cover all directions with switchable null steering
- Preamplifier required: 20–30 dB gain, low noise figure
- Footprint: approximately 30 × 30 feet for a two-loop system
- Used receive-only — a separate transmit antenna is required
EWE Antenna
The EWE (named for its inventor's call sign) is a terminated folded wire antenna for low-band receive. It consists of a horizontal top wire, a vertical front wire (the feedpoint end), a horizontal bottom wire, and a vertical rear wire (the termination end). The shape resembles a rectangular loop lying on its side with the far end terminated to ground through a resistor.
The EWE is even more compact than a K9AY loop — it fits in a space of approximately 30 feet long by 8 feet high. Two EWEs at 90° with phasing switching provide steerable directional receive coverage on 160m and 80m with excellent noise rejection.
- Length: 30–50 feet horizontal; Height: 6–10 feet vertical
- Termination: 800–1000Ω at the rear vertical-to-ground connection
- Pattern: cardioid, forward end is the feedpoint end
- Very compact footprint compared to a K9AY loop
- F/B ratio: 20–30 dB with proper termination resistor value
- Two EWEs at 90°: complete low-band directional receive system
How much real-world improvement does a 4-square provide?
A well-built 4-square with a properly designed phasing network provides approximately 3–5 dBd of gain over a single vertical in the forward direction, plus 20–25 dB of front-to-back rejection. In practice this means: signals in the forward direction are 3–5 dB stronger (about doubling effective power), while stations behind the antenna are attenuated by 20+ dB. On 40m during a contest, the directional advantage of a 4-square is immediately apparent — stations in the forward hemisphere are much more workable while QRM from the rear is dramatically reduced. The gain advantage is equivalent to switching from 100W to 200–300W, but the F/B improvement has no power equivalent — you simply cannot buy it with amplifier power.
Why is the radial system so important for a phased array?
In a phased array, the radial system quality of each element directly affects both the element's efficiency and the array's pattern symmetry. If one element has a significantly better radial system than the others, it radiates more efficiently — the elements are no longer equal contributors to the array pattern, and the pattern degrades from the design. For a 4-square to achieve its designed gain and F/B ratio, all four elements must have identical (or as close to identical as practical) ground systems. Install the same number of radials of the same length at all four elements — the extra effort of matching the ground systems pays off directly in pattern quality.
Can I build a 4-square for 160m in a typical residential lot?
A full 160m 4-square requires a 134 × 134 foot square — approximately half an acre. This is beyond what most residential lots provide. Options for 160m with limited space include: a 2-element end-fire array (needs only 134 feet of line rather than a 134-foot square), a single loaded vertical with a directional receive array (K9AY or EWE), or a 4-square built for 80m instead (66-foot square footprint, more realistic for suburban lots). On 80m a 4-square is achievable on a moderately large residential property and provides the most impact per square foot of any phased array design.
What is current forcing and why does it matter?
Current forcing is the technique of designing the phasing network so that each element receives the correct RF current magnitude and phase regardless of changes in element impedance due to mutual coupling and environmental effects. A simple power splitter controls voltage at each element — but because mutual coupling changes each element's impedance away from its isolated value, the resulting currents are wrong even if the voltages are correct. The Lahlum/Lewallen network uses L-networks specifically designed to force the correct current at each element, producing the designed pattern reliably. Phased arrays built without current forcing often show disappointing F/B ratios because the element currents are not what the design required.
Can I use a single set of radials shared between all four elements?
No — each element must have its own dedicated radial system. Shared radials between elements would create RF ground paths that couple the elements' ground currents together, degrading the array's pattern. The mutual coupling that already occurs through the air between elements is enough to manage — adding ground coupling through shared radials creates additional uncontrolled coupling that makes the array unpredictable. Install separate, independent radial systems for each element with the radial bus of each element connected only to that element's feedpoint ground and to the shield of that element's coax run.
How do I know if my 4-square phasing is correct?
The Reverse Beacon Network is the most practical verification tool. Transmit CW on the operating frequency in each of the four directions and compare spot strengths from stations in the forward versus rearward hemispheres. A correctly phased 4-square should show 15–25 dB difference between forward and rearward spots from stations at similar distances. If all directions show similar spot distributions (no clear directional preference), the phasing network is not working correctly. A NanoVNA can also verify the SWR is consistent and low (below 1.5:1) in all four direction settings — wildly different SWR between directions indicates a phasing or element problem.
What is the difference between a 4-square and a 4-element in-line array?
A 4-square arranges the elements in a square with end-fire phasing — the pattern is a cardioid in one direction switchable to four headings. A 4-element in-line array places all four elements in a straight line with progressive phase delay — the pattern fires off one end of the line with higher gain (6–7 dBd) and better F/B than a 4-square, but covers only two directions (forward and reversed). The 4-square trades some gain for the flexibility of four switchable directions. The in-line array trades direction flexibility for more gain in two fixed directions — preferred for fixed paths (e.g., always pointing toward Europe or Asia) where the higher gain is worth the loss of directional flexibility.
Does a phased array improve receive as well as transmit?
Yes — the gain and directional pattern of a phased array apply equally to receive and transmit. On receive, the forward gain means the array picks up signals from the target direction more strongly, and the F/B ratio means signals arriving from behind are attenuated. Both effects improve signal-to-noise ratio for stations in the forward direction. Additionally, the F/B rejection helps eliminate QRM from stations in the rear hemisphere — a 20 dB F/B ratio makes a station transmitting 100W from behind the antenna appear to have only 1W at your receiver. This combination of receive gain and interference rejection is often cited as more valuable than the transmit gain advantage.