Build a Bisquare Loop Antenna
A Bisquare is a full-wave wire loop bent into a diamond shape and hung vertically between two supports, fed at one corner — a simple, single-wire way to get genuine gain and a low-angle pattern without a tower or beam. It's essentially the same full-wave loop perimeter used by a delta loop or a quad element, just reshaped into a diamond and typically supported by two masts rather than one, making it a practical option for stations with two trees or poles of suitable height but no room or budget for a rotatable beam. This guide covers the complete build from loop perimeter through feedpoint assembly and tuning.
Same Perimeter Formula as a Delta Loop or Quad
The Bisquare uses the same full-wave loop perimeter as this site's delta loop and cubical quad designs — the loop shape (diamond vs. triangle vs. square) changes the radiation pattern's exact details and the practical support arrangement, but the fundamental full-wave-loop electrical behavior and the gain-over-a-dipole benefit are shared across this whole family of antennas.
Corner-Fed for Vertical Polarization
Feeding the Bisquare at the bottom corner (with the top corner left as a simple insulated point) gives the antenna vertical polarization and a low-angle radiation pattern well suited to DX — the same "point-down diamond, fed at the bottom" configuration many delta loop builders use for the same reason.
Support Arrangement — Two Masts, No Tower Required
Unlike a rotatable quad or Yagi, the Bisquare is typically strung between two supports at the two side corners (left and right points of the diamond), with the top and bottom points held by guy ropes to nearby anchors or simply by the tension of the loop itself. This makes it a practical gain antenna for stations with two suitably spaced trees or poles but no tower.
- Side supports: two masts or trees at the loop's left and right corners, spaced to match the diamond's width.
- Top and bottom points: held by guy ropes running to additional anchor points, keeping the diamond shape taut and symmetric.
Feedpoint Impedance
A corner-fed full-wave loop typically presents a feedpoint impedance in the range of 90-120Ω — closer to 50Ω than an end-fed long wire, but still often benefiting from a simple 2:1 balun or a short quarter-wave matching section if you want a clean coax match rather than feeding directly with 50Ω coax and accepting a modest SWR.
| Band | Full perimeter (ft) | Each side (ft) | Notes |
|---|---|---|---|
| 40m (7.15 MHz) | 140.6 ft | 35.1 ft | Needs two well-separated supports |
| 20m (14.15 MHz) | 71.0 ft | 17.8 ft | A common, manageable size for this design |
| 17m (18.1 MHz) | 55.5 ft | 13.9 ft | |
| 15m (21.2 MHz) | 47.4 ft | 11.9 ft | |
| 10m (28.4 MHz) | 35.4 ft | 8.9 ft | Small enough for modest supports |
Bisquare Loop Calculator
Materials for a complete Bisquare loop build
Building the Bisquare Loop
This build creates a corner-fed diamond loop strung between two side supports.
Confirm Your Two Support Points
Verify you have two supports (masts or trees) spaced to match the diamond's width for your target band, with enough height for the top point and enough ground clearance at the bottom point.
Cut the Full Loop Wire
Cut a single length of wire equal to the full perimeter from the calculator, plus a small trim allowance.
Mark the Four Diamond Points
Mark the wire at quarter-perimeter intervals to locate the four corner points — top, bottom, left, and right — of the diamond shape.
Install the Bottom Feedpoint
Break the loop at the bottom point and install a feedpoint insulator here, with connections for both wire ends to your coax (through a balun or matching section, if used).
Attach Insulators at the Remaining Points
Attach an insulator at the top point and at each side point, with guy rope running to your side supports and to top/bottom anchor points.
Raise the Loop Into Its Diamond Shape
Raise both side points to your support masts, then tension the top and bottom guy ropes to pull the loop into a symmetric diamond shape.
Connect Coax and Verify SWR
Connect your feedline at the bottom feedpoint and sweep SWR with the NanoVNA. Trim the loop slightly (equally around the perimeter) if resonance needs adjustment toward your target frequency.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR high across the whole band | Feedpoint connection fault, or loop shape badly distorted | Check feedpoint continuity and overall diamond shape | Re-solder feedpoint connections; re-tension guy ropes to restore the diamond shape |
| Resonance off from the target frequency | Loop perimeter cut too long or too short | Measure the actual installed perimeter against the calculator | Trim (if too long) or splice in a short extension (if too short), adjusting equally around the loop |
| Pattern seems off-axis from expectations | Diamond not symmetric, one side longer than the others | Measure all four sides individually | Re-tension guy ropes to equalize all four side lengths |
| Gain seems underwhelming despite correct dimensions | Loop mounted too low, or nearby obstructions affecting the pattern | Check bottom-point height and clearance from nearby structures | Raise the loop if possible; relocate away from large nearby metal objects |
| SWR shifts noticeably with wind | Loop shape flexing under wind load, changing the effective geometry | Observe SWR during windy vs. calm conditions | Add additional guying to stabilize the diamond shape in wind |
How is a Bisquare different from a delta loop or a quad?
All three use the same full-wave loop perimeter formula and share the fundamental full-wave-loop gain benefit. The difference is shape and support arrangement — a delta loop is triangular (often one apex support plus two ground anchors), a quad is typically square and mounted on a rotatable boom, and a Bisquare is a diamond strung between two side supports without a boom or rotator.
Do I need a rotator for this antenna?
No — the Bisquare is a fixed-direction antenna, strung between two supports at a chosen orientation. If you want a rotatable version of a similar loop concept, this site's cubical quad guide covers that boom-mounted approach instead.
Can I feed it at the side instead of the bottom for horizontal polarization?
Yes — feeding at a side point instead of the bottom point changes the antenna to horizontal polarization with a somewhat different pattern, the same general tradeoff seen on delta loops fed at different points.
What gain should I actually expect?
Roughly 4 dBi over an isotropic radiator (about 2 dBd over a dipole) is a reasonable expectation for a well-built full-wave loop like this, consistent with other full-wave loop designs on this site.
Do I need a balun?
A 2:1 balun or a quarter-wave matching section improves the match at the roughly 90-120Ω feedpoint impedance, but many builders feed directly with 50Ω coax and accept the modest resulting SWR, especially if their tuner or radio handles it comfortably.
What supports work best for the side points?
Two trees, two masts, or one of each work equally well, as long as they're spaced correctly for your band and tall enough to keep the whole diamond well clear of the ground and any nearby obstructions.