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Why ends of trace are placed on square in dual band antenna?

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Junior Member level 1
Jul 27, 2001
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dual band antenna

Hi EM sim fans,

I don't why the both ends of trace is placed an suare pad to make it a 900/1800 antenna ? Anyone can come up with the anwer ?
Attached is the antenna photo. The other side of the board is left blank fir the antenna.

Thank you for your sharing.

Two antennas in parallel

These are two antennas in parallel. On the low frequency, the longer one is a quarter wave and the shorter one has a high reactance which shunts the drive port. The longer one is adjusted in length to have the opposite reactance. On the higher frequency, the short one is a quarter wave and the longer one is a half wave which makes its input impedance nearly infinite which has little effect on the drive port.
You may have seen scanner antennas with three parallel elements if different lengths. they use the same concept.

I saw PIFA with a resonator in a midle. the resonator was build by surface mounth capacitor and thin line thhat acts like an inductor. this resonator is resonance at low frequency. the overall length is at low frequency resonance. this configuration can give you any dual resonance.

common HF antenna

This is a common method in the HF range. A parallel LC network is placed in the center of each half of the dipole which is shorter than an ordinary, unoladed dipole at the lower frequency. On the low frequency the network is net inductance and makes the antenna appear longer than its physical length. At the higher frequency the nework looks capacitive and changes the phase of the currents. In this second case the antenna gain is slightly higher than a dipole.

The idea of having a physically longer antenna and changing the phase evry so far along the length by different means was invented back around 1910 and is called a Franklin antenna.

HF Antenna

Hi flautlent,

do you have any pdf articles on the fundamentals of such antennas i.e. with parallel LC loading etc?




The only article I know about is in the old Ham Radio Magazine sometime around 1990 or so. It did not give any details. You might try a NEC type program which allows LC networks to be placed in the wires.

Here are two utility programs that can get you started. First you select the overall length. Use the adaload program to get the inductance value for the lower frequency. Then use the Excel spread sheet. Calculate the antenna length compared to a half wave dipole at the higher frequency. Enter this in the length multiplication box. Select two sections and entr the higher freq. The capacitance will be calculated.

Then use some algebra on the impedance of a parallel LC network to find the values that give the right reactance (inductive and capacitive) at the two frequencies.

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