Corner reflector antenna

 Do you need a high gain antenna? Have you suffered on picking up interference from unwanted direction? You need a directional antenna but a 12 element Yagi will be too attractive! Well, following might be the answer - a corner antenna. It can provide a forward gain of about 12dbi with a front to back ratio of well over 20dbi.

 This design is a periodic plane spaced behind a radiating dipole. The critical factors are the corner angle and the spacing between dipole/vertex ( fold point of reflector ). The curves in fig.A show that as angle is reduced, the gain becomes progressively greater.

 

 

At the same time the feed impedance of the antenna falls towards a lower value and starts creating difficulty in matching. In practice this angle is usually at 90 degree or 60 degree while 90 degree is easier to be matched although gain is lower.

Following are some key points when designing such antenna :

Impedance of these antennas will change upon operating frequency. Typical value will be around 50 ohm to 75 ohm. A slightly higher S.W.R (1.7:1) has to be expected on lower end of the band. Fig.A also shows relationship between resultant impedance and a change in wavelength (frequency). Following is a table that shows the general dimension of such antenna at UHF and VHF band (Fig.B). All value below are in inches (except Band in MHz). Final dimension might vary due to difference in materials employed. Try by error is the key for success.

 

Band

p

s

d

v

w

A

u

144

100

40.0

6

38

50

100

0.375

440

34

13.0

1.4

13

20

34

0.25

435

35

13.5

1.5

13

20

35

0.25

 

We can discuss it further on the air if you are interested.

 

 

By VE3RGW Sept 96.

 

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