etched pcb biquad

Commercial patch antennas use PCB materials often. Perhaps it easier for DIYSers to bend and solder wire and etching a circuit board.

Yep. Etched PCB antennas work. However:

The dielectric constant of the PCB material will shrink the antenna by the square root of the dielectric constant. For example, G10/FR4 has a dielectric constant of about 5. One wavelength at 2.4GHz is about

12.5cm in free space and about: 12.5 / sqrt(5) = 5.6 cm The gain of the antenna is reduced very roughly by the same ratio. A common biquad with an air dielectric has a gain of about 10dBi. The PCB version on G10 will be about 2.5dB less.

Lots of other complications when you get away from wire antennas and go to a PCB dielectric version. Tolerance issues, reduced bandwidth on the smaller antennas, non-symmetrical cross sections make calcs a bit complex, problems with PCB feeds, coax to PCB interface issues, surface conductivity (oxidized copper sucks), ad nausium.

In my never humble opinion, if you're going to be building your own without adequate test equipment (i.e. network analyzer, antenna range, reference antennas, vswr bridge, etc), then do the wire antennas. They're much easier. However, if you have some control over tolerances, a good computer modeling program (4NEC2, EZNEC, etc), and a pile of test equipment, methinks you could try PCB antennas.

As for the original question: Has anyone tried a PCB biquad? I dunno. I haven't. PCB material is commonly used as the reflector, but not the driven elements as in:

Well, I lied. Here's a commercial antenna that's close. 's a 9dBi Maxrad 2.4GHz antenna. It's NOT a biquad but rather a mono-quad or just one loop. There's a 12dBi version that has two loops and I guess would be considered a biquad. The PCB material is polysulfone with a dielectric constant of 3.1 and quite low loss at

2.4Ghz. Note the weird looking lumps on the trace connecting the loop with the coax connection. All that is impedance matching which will need to be done on your do it thyself PCB antenna. This can't be done without a VSWR bridge or network analyzer.

I lied (again). See: |

on the green rectangle at the top center of the page. It's a PCB biquad for $10.

I'm trying to visualize how the pcb material interacts with the copper track. It's not like you are doing stripline, i.e. metal traces with the fr4 between the traces. The signal hits the copper from free air. But a reflector would have the dielectric of the pcb in the path.

snipped-for-privacy@sushi.com hath wroth:

Oh, that's easy. A non-radiating transmission line has at least one ground plane below the trace and is terminated at both ends. Sometimes, it's sandwitched between two ground planes but must always be terminated. A radiating trace antenna has no ground planes and is matched only at only one end by the output impedance of the transmitter or the input impedance of the receiver. The other end is matched to the impedance of free space or 377 ohms. Think of an antenna as an impedance transformer between 50 ohms (or whatever) and

377 ohms.

The easiest way to visualize this by having the dielectric between between the antenna elements and the reflector be composed of two different materials, air with e=1.0 and G10 with e=5.0 (approx) with corresponding variations in thickness. I don't know exactly how to model such an antenna. I'm also lazy and think it's time you dig out

4NEC2 or other modeling program and try it thyself first. me you model and I'll try to untangle it. Use this model: a starting point. You might also find it interesting to look at the web site where I stole the model: If you're going to dive into surface radiating patch or panel antennas, most of the NEC2 surface models are marginal approximations. Instead, use MSTRIP40: something more accurate. Incidentally, there's quite a bit on strip line and surface radiating calcs in the "lab manual" at: might explain how to visualize the antenna.

snipped-for-privacy@sushi.com hath wroth:

I just had a thought[1]. Many years ago, I designed (actually I threw together) an antenna using a PCB substrate. I didn't have the fancy modeling software available, so I did it by cut-n-try, with a pile of test equipment. I started with just 0.032 G10 PCB material and use copper tape (from the local stained glass supplier) to create the antenna elements. Exacto knife adjustments were quite easy. You could probably prototype something similar. I also made some using window glass as a substrate. That worked fairly well but was limited to designs were the coax was fed at the edge of the glass plate as it couldn't be easily drilled.

[1] It happens, but not very often.

I think you are thinking too much, or you didn't get my original statement. I understand stripline. [I made a high speed controlled impedance dut board for an ECL DAC I was evaluating.] In the case of the loop on a PCB, think of the antenna being used as a transmitter. Then the element radiates in one direction (i.e. forward) without a dielectric in the path. The reflector does have a dielectric in the path, but only for a short distance relative to the signal path. So I just don't see the pcb effecting the dimensions of the antenna.

I have copper tape, though hell if I know where. I think Excess Solutions in Milpitas sells it. I could make some fiberglass as a substrate if it is better than using pcb.

Back to the stripline board I designed, I had a HP TDR on loan at the time. It was a TDR plus oscilloscope. My traces were close to the target impedance. When I did the math, I came up with really wide traces based on the spacing between planes. I was glad went truth matched math. Then I was looking at a test board designed by HP for their high speed chip tester. The traces were quite small, so I figured the dielectric thickness was proportionally small. Still, you need the thickness to be well controlled. As it turns out, the HP traces were way off. I don't recall which direction (high or low), but I informed HP of this error. Needless to say, it didn't look good when I showed their board was no good based on their own instrumentation.