An HF/UHF compatible RFID transponder antenna is designed, simulated, and measured for dual band operation and HF range extension. A dual mode compatible RFID transponder antenna has the benefits of each mode and eliminates the disadvantages of single mode operation. One of the major drawbacks of UHF antennas is their poor performance when the tag is placed on or near metallic objects. To overcome this shortcoming, two-layer substrate with degenerate grounded is used and a 4-turn spiral antenna is placed on the top and bottom parts of the substrate for HF operation. The co-existence of both antennas affects standalone performances but desired specifications can be achieved with the proposed design. A prototype is built and measured to verify the target design criteria$.$ Measured inductance of the HF loop is 2.54 $\mu $H and the gain of the UHF antenna is 2.73 dBi when placed on a metallic can. The transponder antenna can be configured for HF mode, UHF mode, or HF with range extension through a wireless power transmission (WPT) using the UHF band. WPT at the UHF band provides additional DC voltage for HF tag operation. This relatively new idea of HF range extension is supported with simulations and basic measurements.